# Zetex ZXSC300 single-cell LED driver



## **DONOTDELETE** (Oct 21, 2001)

I'm wondering if anyone has implemented the max-brightness single-cell LED driver circuit described at http://www.zetex.com/3.0/pdf/ZXSC300.pdf 

Although the circuit is designed for the white Nichia NSPW500BS, I wonder if it would drive an amber Luxeon Star with R1 set to 0.04 ohm, which should pulse the LED at 475 mA.


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## Mercator (Oct 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*Although the circuit is designed for the white Nichia NSPW500BS, I wonder if it would drive an amber Luxeon Star with R1 set to 0.04 ohm, which should pulse the LED at 475 mA. <HR></BLOCKQUOTE>*

Not sure myself. But, I think one might also have to change that one transistor as well. I beleive that National also has something in the same line. I went to the Zetex site to take a look and perhaps request a couple of samples. Not an easy thing to do. At least not as easy as getting samples from National.


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## Mercator (Oct 21, 2001)

I just went to National and found this information on their LED driver. Not sure of the max. output capabilities, but theirs doesn't require an inductor.
http://www.national.com/news/item/0,1735,610,00.html 

Mercator


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## MrAl (Oct 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I'm wondering if anyone has implemented the max-brightness single-cell LED driver circuit described at http://www.zetex.com/3.0/pdf/ZXSC300.pdf 

*<HR></BLOCKQUOTE>

That's the exact chip i was talking about in
other threads 
The minimum quantity for ordering around
here is 3000 pieces, which runs upwards of
about $1500.00 .
I inquired about getting smaller quantities,
but didnt get a response yet. It wont
help me that much to get samples if i cant
also buy in smaller quantities, because i 
wont want to shell out 1500 bucks for these
chips.

The National chip is a charge pump device,
thats why there is no inductor.
The drawbacks to the National chip are:
1. input min voltage is 3.0 volts.
2. drives a max of 2 LED's.

Maxim has charge pump ic's that can
drive 2 LED's at lower input voltages,
if thats all you want to do.

So far, the Zetex chip is the best i've seen
so far. It does exactly what you would want
in an LED driver. You can even expand it
to power any number of LED's just by using
a different NPN transistor with it.
This is certainly my choice, but getting
some is another problem 
Anyone have any luck with this company?

--Al


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## **DONOTDELETE** (Oct 21, 2001)

Yeah, I should have checked www.digikey.com before posting---they have a 3000-piece reel for sale for $1620 ($0.54 each), but if you buy just one ($1.05 each) you'll have to wait until January.

But, that may be okay---that's just in time for the release of the new white Lambertian Luxeon Stars, which promise to be awesome devices.

And, who knows---maybe DigiKey will cave in and peel off a few hundred chips from the reel for individual sale, if there's enough demand.

I like DigiKey: if you order $25 worth of stuff there's no handling charge, and if you send them a check with your order, there's no domestic shipping charge.

For $25 you can get the raw parts for both the Zetex solution AND the LM2621 solution, plus a bunch of other parts.


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## lightlover (Oct 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*...... wait until January.

But, that may be okay---that's just in time for the release of the new white Lambertian Luxeon Stars, which promise to be awesome devices.
............
*<HR></BLOCKQUOTE>

Duggg, what are these promising Lambertian Luxeon Star thingies ? Specs please !

lightlover

(And that's about the only thing I understood while reading through this topic ...... )


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## vcal (Oct 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by *something ridiculous:
*Duggg, what are these promising Lambertian Luxeon Star thingies ? Specs please !
lightlover
*<HR></BLOCKQUOTE>
Other people on this forum call 'em "high-dome or hi-top" -Stingmon has quite a bit on this 2nd gen. Luxeon module on his site.

Doug


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## Mercator (Oct 22, 2001)

*Dugg & MrAl*

I guess I should have read through the datasheet again on the National IC. 

The Zetex does sound ideal. Since I'm in the silicon valley area, I try asking around here at some of the parts houses and see if I can somehow get some samples out of Zetex.

I've got some National LM1117's coming now since I'm interested in a current limiting circuit.

Mercator


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## MrAl (Oct 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*
but if you buy just one ($1.05 each) you'll have to wait until January.

I like DigiKey: if you order $25 worth of stuff there's no handling charge, and if you send them a check with your order, there's no domestic shipping charge.

For $25 you can get the raw parts for both the Zetex solution AND the LM2621 solution, plus a bunch of other parts.
*<HR></BLOCKQUOTE>

Soundsss gooddd Duggg 
Thanks for that info.

But what is this about waiting until January?
Why January?

--Al


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## **DONOTDELETE** (Oct 22, 2001)

Digikey's web site says individual ZXSC300's (part #ZXSC300E5CT-ND) won't ship until January 3, 2002. The page tells you this if you enter "1" and press the Quantity Requested button. 

I read in another thread that LumiLeds will start producing the white Lambertian LS's at the end of the year. The batwing (aka "low dome") versions of the white LS are available now, but the batwing radiator doesn't produce as pure a beam as the Lambertian.


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## MrAl (Oct 22, 2001)

Oh ok i see. I guess i'll have to wait 

Thanks much,
--Al


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## Mercator (Oct 22, 2001)

*Dugg & MrAl*

I'm still interested in the Zetex IC, I looked through the Zetex site again. They also have an IC simular to the one in this thread. It's the *ZXCS100*. Digikey has them in stock now for $1.75 each. Perhaps one of you can take a look and see if this other IC specs out to something close enough to the ZXCS300 number. They (Zetex) has an Application Note that addresses using this IC for single cell LED flashlight apps. Search for An-33.
BTW - Digikey has the ZXCS100 both in SO8 and MSOP-8 packages. I think that the SO8 is bigger and therefore easier to work with. I'm not much into designing circuits, but certainly can build then from a schematic. 

This series of Zetex IC's could very well be what is being used in the Infinty and possibly the ARC AAA. Not sure about the ARC's "sun/moon" mode though.

Mercator


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## **DONOTDELETE** (Oct 22, 2001)

Yes, I saw the ZXSC100 too, but I rejected it mainly because of the efficiency difference of 82% versus 94%, and the 1-watt circuit (needed to drive the LS at full brightness) was considerably more complex than its 300 counterpart. (Note the 100 has twice the pins of the 300.)

But, you certainly have good points in that the 100 is available right now, and the SO8 is easier to work with than the SOT23-5, although the extra pins take away some of the advantage.

Still, I'm an efficiency freak so I'm holding out for the 300


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## MrAl (Oct 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Yes, I saw the ZXSC100 too, but I rejected it mainly because of the efficiency difference of 82% versus 94%, and the 1-watt circuit (needed to drive the LS at full brightness) was considerably more complex than its 300 counterpart. (Note the 100 has twice the pins of the 300.)

But, you certainly have good points in that the 100 is available right now, and the SO8 is easier to work with than the SOT23-5, although the extra pins take away some of the advantage.

Still, I'm an efficiency freak so I'm holding out for the 300



*<HR></BLOCKQUOTE>

Yeah i saw that 100 chip too. I guess im
just not in that much of a hurry anyway




Im looking at a ton of different circuit
configs right now. I found some interesting
stuff out there, but the myriad of possibilities takes a while to get through.
I think it will be hard to top the Zetex
300 chip though, except possibly with 
a combination chip plus on chip 
heavy duty Mosfet
and still keep all of the specs of the 300.

--Al


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## Mercator (Oct 23, 2001)

I asked afew of my parts sources around here this morning and it's looks like they don't buy directly from Zetex. So, that avenue didn't pan out for me.

I wrote Zetex directly and asked about purchasing samples. I received a reply this afternoon. Thay wanted my address so that a sales rep could send me information regarding samples. I wrote back, so we'll see what comes of that angle. I've got a feeling though that the sales rep is going to want to pay me a visit. Too bad Zetex isn't as easy to work with like National.

Both of your are right regarding the advantages of the 300 over the 100 chip. I sure would like to find something to build my LS around. I think the way to go is with a PWM circuit driving the LS at near max. I've been following the thread on the modified Brinkamn circuit and would like to see that simple circuit tweaked to LS specs. I would think it's possible once the right combination of componets are discovered. Perhaps the simple Sature design might work, but the drawback is the hand wound inductor. It's still a great design within it's limits.

I'll keep everyone posted if I have any luck getting samples out of Zetex. If I could buy a handful, I'd sell or trade them at cost.

Mercator


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## MrAl (Oct 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*
Too bad Zetex isn't as easy to work with like National.

I've been following the thread on the modified Brinkamn circuit and would like to see that simple circuit tweaked to LS specs
Mercator*<HR></BLOCKQUOTE>

Yeah Zetex seems to be a pain, too many 
sleeping employees 

What are the LS specs?

--Al


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## **DONOTDELETE** (Oct 23, 2001)

The spec sheet for the Luxeon Stars can be found at http://luxeon.com/pdfs/Luxeon_star_DS.PDF


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## MrAl (Oct 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*The spec sheet for the Luxeon Stars can be found at http://www.luxeon.com/pdfs/Luxeon_star_DS.PDF*<HR></BLOCKQUOTE>

Thanks for the link Duggg.
They are spec'ing the white LED light output
at 180 candela, while a 'regular' led is
about 5.6 candela. A little math says this
is over 32 times as bright as a regular white
LED. Is this correct? How can they get that
much brightness out of a single LED?
Wouldnt this make the brightest flashlight?
(even if it draws more current).

--Al


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## **DONOTDELETE** (Oct 24, 2001)

Comparing LEDs on the basis of candela output alone is like comparing how big homes are based on the size of their front yards.

Candelas measure the peak brightness, whereas lumens measure the total brightness.

A better way to do the comparison is to multiply the electrical efficiency (in lumens per watt) by the power dissipated.

According to http://www.misty.com/people/don/led.html the Nichia puts out 16 lumens per watt and the Luxeon puts out 18.

The Nichia can dissipate 120mW and thus produce 1.92 lumens.

The typical Luxeon draws 350mA at 3.42 volts for a total power of 1197mW and thus produce 21.546 lumens.

So the Luxeon should be equivalent to 11.22 Nichias in total output---assuming the 18 lumens/watt figure is correct.

Of course, the Luxeon is physically much larger than the Nichia. The Star/O collimator is 21.5 mm in diameter, for a total frontal area of 363 mm^2.

The Nichia comes in a typical 5mm package for an area of 19.6 mm^2.

You could theoretically cram 18.5 Nichias into the Luxeon's collimator, although in practicality, 12-14 is probably the best you can do.

So, keeping flashlight size the same, a 12-14 Nichia flashlight should be a tad brighter, but note that neither of these comparisons take heat into account. Both LEDs will produce much less lumens per watt if the heat is not properly dissipated, and I think heat would be more of a problem for the Nichias in such close proximity.

So I think the true winner would be the Luxeon, and that's why I'm excited about it.


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## Mercator (Oct 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*Yeah Zetex seems to be a pain, too many 
sleeping employees 

What are the LS specs?<HR></BLOCKQUOTE>*

I heard back from Zetex today. They provided me with my local rep's phone number. I'll try and call them in the morning. If I can get them to sell me several samples at a couple of bucks apiece. I'm going to go for it. If anyone wnats some for themselves, let me know and we'll work the details out later.

MrAl... for some reason I thought you already owns an Luxeon Star. Dugg's explaination is correct regarding the equivalent light output. There are several advantages in favor of the LS compared to the equivalent number of single LED's. Top on the list are overall cost and packaging. I've bench tested my two LS modules using different batteries, voltage and currents. The more I play with the LS the more impressed I am. The one thing I have yet to try is a circuit that will drive the LS with PWM at or near the spec'd max of 500mA. With non-oscillating voltage/current the LS does get quit warm at max input. I suspect that with a plused input the heat problem would not be as severe.

Although I/m interested in the Zetex IC, I'm not sure if it will be the right choice for the lithium 3.6v batteries I want to run the LS on. Without any regulation one of these batteries could drive the LS at over 800mA.
I've limited this high current with a resistor, but of course that has major drawbacks regarding efficiency throughout the battery discharge cycle. I figure that with a PWM circuit running at about 450mA would deliver a flatter level of light output for a longer time verses just opperating off the battery and a dropping resistor.

I've mentioned this before... I'm not all that knowledgable to design my own circuits, so I guess I'm pretty much waiting for something to come along like the Zetex chip.
So far from what I seen and read, it looks like it might fit the bill.

Mercator


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## MrAl (Oct 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Comparing LEDs on the basis of candela output alone is like comparing how big homes are based on the size of their front yards.

*<HR></BLOCKQUOTE>

You cant drive a 'regular' LED to 350ma
now can you?

--Al


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## **DONOTDELETE** (Oct 24, 2001)

I don't see your point; combined, 12-14 Nichias can certainly draw over 350mA.

If you're asking how the LS can draw that much current without burning up, its junction has a much larger surface area than a typical 5mm LED, and it comes mounted on its own heat sink.

I hope that answers your question...


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## MrAl (Oct 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I don't see your point; combined, 12-14 Nichias can certainly draw over 350mA.
*<HR></BLOCKQUOTE>

You cant always expect to see the point in
some casual questions. You cant always be
that critical in the wording either. I 
noticed there are a few people who do this,
but, in any case, if i want to compare
apples to oranges, then so be it. I may 
have a use for the results of this comparison
that someone else doesnt see or even care
about.
Case in point:
when comparing a single LED to multiple
LED's, and saying they both put out the
same amount of light. That's fine, but
in the case of external optics, one LED
has an advantage over several mounted
very close to each other.
But this is only one case for example.

All i meant to do was to compare the 
light outputs and find out how they
are doing that. If its a larger chip,
then fine, why not just say that?

I was also going to compare the 10mm, 7000
candela white LED to the smaller ones, but
geeze, maybe i better not or i might end up
buying another house 

--Al


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## **DONOTDELETE** (Oct 25, 2001)

Peak luminosity (measured in candela) is a function of the package.

There's a 10mm amber LED that's been out for a while that can produce 23 candelas. It does so by focusing the beam into an extremely tight viewing angle, something like 4 degrees.

That's too small an area to be practical for flashlight applications. If a lens is used to spread out the beam, then the brightness falls way off, making it no brighter than other LEDs consuming the same power.


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## Mercator (Oct 25, 2001)

Well.... Wasn't easy but, I've got 10 of the Zetex ZXSC300's coming my way. I called the sales rep this morning and inquired on sample prices on 10 to 20 peices. Also, inquired about pricing on their little evaluation board. The gal I spoke with didn't have prices for the 300 on her machine and had to find out and call me back. I heard from her this afternoon and was told that they will send me 10 samples of the IC and if I needed more I'd have to go through distruibtion. I asked for the cost and she told me they would be free. I reminded her that I was also interested in the evaluation board and she told me that the person she spoke with sugested that we try the individual chips first. That didn't make a bit of sense to me. I explained to her that the eval. board was an ideal pre-assembled test platform to evaluate the new IC's on. Especially since these are SMD components. She agreed and promised to get more information and call me back in the morning.

So... As it stands, I've got 10 of the little guys coming and will share with anyone in exchange for developing a circuit that will drive an LS. I guess I should have inquired about obtaining several of the transistors they recomended using with the 300. I suppose those can be obtained from Digikey or locally. Without the eval. board one would still have to come up with the inductor and diode elsewhere. 

If you haven't noticed it yet, Zetex shows the layout of the eval board. I printed it out and it looks like it's to scale. Also, you'll notice that it looks like it is designed with some through holes for use with leaded components. Sure would make it easy to test the 300 that way. If I can't get the eval boards, I'm thinking that I could use the template along with some photo-sensitive PCB matererial and come up with my own little board. I have and use an older PCB layout program, but it doesn't directly address most of the newer (ie smaller) SMD footprints. Nor does it have a grid smaller that 1/10 inch. Which would be necessary with the SOT23-5 package.

Anyways, let me know if you're interested and
capable of working with this IC and we'll take it from there.

Mercator


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## **DONOTDELETE** (Oct 25, 2001)

Hi Mercator,

Along the same lines, I mailed my order to DigiKey last weekend, and asked them why they show a distant ship date for individual pieces while at the same time they have 3000-piece reel just sitting there.

Anyway, let me see if they agree and include the chip with my order, because otherwise it sounds like you got a great deal there, and I don't want to have to wait months to get the chip.

As far as driving an LS with the ZXSC300, I have a cyan LS already in hand, I ordered a slew of test components, and plan to use a breadboard to develop the circuit. 

How can a breadboard work with a SOT-23-5?
DigiKey sells a little board with standard DIP pins on which the SOT-23-5 can be soldered---great for experimenting!


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## Mercator (Oct 26, 2001)

> Originally posted by Duggg:
> *Hi Mercator,
> 
> Along the same lines, I mailed my order to DigiKey last weekend, and asked them why they show a distant ship date for individual pieces while at the same time they have 3000-piece reel just sitting there.*
> ...


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## **DONOTDELETE** (Oct 26, 2001)

Digi-Key does have the ZXSC100 evaluation board (note 100 not 300) in stock for $50.

Its price might be a good indicator of the cost of the 300 eval board, but your rep's willingness to part with 10 free chips may also mean a free board is headed your way.

Thanks for the shipping info re Digi-Key. I'll give them until Thanksgiving to ship, otherwise I'll take you up on your offer.

As far as the components I ordered, I didn't buy any duplicates, just variants. For example, a 0.04-ohm and a 0.05-ohm resistor; a 68uH and a 100uH choke.

I also ordered the stuff to make the LM2621 eval circuit. I'm hoping the ZXSC300 circuit works out so I don't have to deal with hand-soldering the microscopic LM2621


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## Mercator (Oct 26, 2001)

Dugg

*Digi-Key does have the ZXSC100 evaluation board (note 100 not 300) in stock for $50.*

Wow!!! $50 That's not good news. I called the rep twice today and never did get a return call with pricing. I suspect you're that the cost will be about the same. Way to much to play with. Still I will presue getting a quote from Zetex.

*Thanks for the shipping info re Digi-Key. I'll give them until Thanksgiving to ship, otherwise I'll take you up on your offer.*

Other than waiting, if you want, I'll send you two or three to get started on. You'll be ahead of me since you already have the supporting components ordered. 

*As far as the components I ordered, didn't buy any duplicates, just variants. For example, a 0.04-ohm and a 0.05-ohm resistor; a 68uH and a 100uH choke.*

I assume you ordered SMD components? Did you order the Zetex transistor? How did you figure the values to order on the inductor and resistor. Was it based on driving an LS and if so at what voltage? For me determining the values will be the hard part.
I would like to do as you did and order a selection of various components from Digikey.

*I also ordered the stuff to make the LM2621 eval circuit. I'm hoping the ZXSC300 circuit works out so I don't have to deal with hand-soldering the microscopic LM2621*

Well the 300 ain't gonna be that much easier to solder. Less pins will help. Both IC's are ridiculously small. That little SOT23-5 board you mentioned will certainly help. Also, a home brewed PCB will make the task easier. I've replaced several SMD parts in the past and while it's not easy it is possible. Never have built anything from scratch with SMD's but can amagine that on a clean, new PCB it would be easier than replacing parts. So... I'm up-to and looking forward to the challenge. 

Mercator


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## MrAl (Oct 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*Well.... Wasn't easy but, I've got 10 of the Zetex ZXSC300's coming my way.

Mercator*<HR></BLOCKQUOTE>

I would be interested in trying one of 
those chips myself, but i dont have 
a high powered Luxeon to try it with.
Also, i think i would try one of the 
transistors Zetex recommends just to 
see how close the actual circuit comes
out too compared with the spec's they
gave. That would be very interesting.
If you want to sell me one or two
chips when you get them ill do the
initial testing. I have the test
equipment to check these out with.

--Al


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## **DONOTDELETE** (Oct 26, 2001)

Since I'll be breadboarding, I didn't want to use the suggested SMD components (other than the ZXSC300 and LM2621 themselves), so I tried to order "regular" equivalents of the transistor, resistors, rectifiers, and chokes.

I have virtually no experience with SMD at all, and since physical size isn't critical to my project, I'm happy to work with bigger components, even though they're becoming harder to find and are a tad more expensive.

The Digi-Key order should arrive any day now, so I'll let you know if they included the ZXSC300. I'm not in a terrible rush, but on the other hand, I don't want to have to wait several months for a $1.05 component if I don't have to.


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## Mercator (Oct 27, 2001)

*MrAl & Dugg*

I was hoping you'd jump aboard for this project.
Email me your address and I'll send a couple of 300's when they get here. First.... If you'd would please put together a shopping list (Digikey part numbers) and I'll place an order thru Digikey. I agree we should first try the Zetex transistor. Not sure of what values of other components we might want to stock up on. Ie: a selection of inductors, resistors, caps. and resistors.

Dugg, you mentioned that you were going to use leaded components. I assume you found a transistor that closely matches the specs of the Zetex FMMT617. If so what did you come up with? 

Dugg came up with a SOT23-5 adaptor board that would make prototyping easier. I beleive it is Digikey Number 33205CA-NB. The price was something like $1.80 each Or, if someone has a PCB program that could be used to create a simple eval board with that might be another option. Of course it would have to have the ability to design for the SOT23 footprint. My program won't, but I can expose and etch boards here, providing I have a 1 to 1 template.

Another possibility comes to mind and I'll have to take another look at the SMD Surfboard. One might be able to modify the board traces and mount the few additional components directly on the board. 

Personally, I like the idea of testing by using all the same family of parts and doing so while those parts are in close proximity to one another as they would be in a finalized circuit design.

Open to any thoughts and suggestions,

Mercator


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## MrAl (Oct 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*MrAl & Dugg

Email me your address and I'll send a couple of 300's when they get here. First.... If you'd would please put together a shopping list (Digikey part numbers) and I'll place an order thru Digikey. I agree we should first try the Zetex transistor. Not sure of what values of other components we might want to stock up on. Ie: a selection of inductors, resistors, caps. and resistors.

Mercator*<HR></BLOCKQUOTE>

Hi there again Mercator,

I'm glad your interested in this project too.
I tryed to email you, but the email feature
on this server is blocked by admins for some 
reason, giving one of those FYI pages 
You can email me with your email address if
you would rather do that:

[email protected]

please put "Zetex Chip" or something like
that in the subject and i wont miss it 

I think we will finally be able to come up 
with a very widely applicable circuit.

As far as other parts go, i'll try to get
spice model info on the Schottky they
spec, and if it looks significantly different
then your average 1N5817 then maybe we should
try to get one of these to go with the chip
as well as the special Zetex transistor.
If not, then a common 1N5817 or equiv would
work just as well.
I'll take another look at the coils they are
recommending as well and the current sense 
resistor.
The main parts of concern though are the
chip itself and the transistor, if we
really want to shoot for maximum efficiency
too (which i would like to see with this
circuit).

After that, all we have to do is hope this
company never goes out of business 

--Al


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## MrAl (Oct 27, 2001)

I found out the Zetex Schottky
ZHCS1000 may be a 
little better then a standard 1N5817.
Unfortunately, its not so much better
that it deserves prime consideration
like Zetex's data sheet would have us
believe.
For example, when driving LED's in 
parallel it will raise the overall effciency
by about 2% over the standard Schottky diode.
If this sounds good enough to you, then
maybe you should try and get these diodes
also. If they arnt more then about 50 cents
each it might be worth it.

They have a new diode that is rated at
twice the current also: part number ZHCS2000
which looks even better then the 1000 diode
because the forward voltage drop is even
lower still.
Since you might want to drive several LED's 
in parallel or one of those Lux's at 350ma
the extra current rating of that new diode
will come in very handy. I just hope its
not too much higher priced then a regular 
Schottky. For higher current outputs,
this part might actually be necessary.

Also, since the reference design given by
Zetex shows that they are setting the 
peak current through the inductor to about
10 times that of one LED (190ma) that might
mean if we want to drive 10 leds at 40ma
each or one Lux at 400ma we would have to
set the max current peak to 4 amps!
Since this sounds unrealistically high,
perhaps the current peak tapers off at
higher load currents. If not, problems
might come up that prevent us from driving
a load of 400ma with the recommended design.
This means more transistors might have to 
enter the picture for increased drive, but
at least they can be run-of-the-mill types
(to drive the final low sat type).
If we end up needing a 4 or 5 amp transistor
to drive these heavy loads, we will have to
get that later. I think we should start with
one LED and go from there.
As far as the low resistance value for the
sense resistor: if they spec a 0.1 ohm
resistor for a 20ma LED, then i would guess
a 0.05 ohm for 40ma, .025 for 80ma, etc.
I havent looked into the coil yet, but i'm
thinking that maybe a hand wound coil to
start(that way we can create any current 
rating we need on demand) and then go with
a comercially available one once we know
exactly what we are dealing with. I have
a multitude of toroid cores of various sizes
i can use. For only one led Zetex spec's
a few different coils. For a couple in 
series, they spec coils in the data sheet
for the ZXSC310 part number.

The unusual thing about this circuit is that
they are regulating the peak current through
the inductor, not the average current
through the LED(s). This bothers me a little
because i would prefer to regulate the
current through the led's since that's
what keeps the brightness constant over
battery life. The good point is that their
data indicates that doing this regulates
the current through the LED(s) to a much
better degree then having no regulation at
all. I agree with this, but would still 
prefer to control the LED current directly.
I guess some testing is certainly in order

In the mean time, im going to try to develop
a spice model for the Zetex ZXSC300 chip
and do some theoretical testing to see
what happens at higher current outputs.
The chip itself isnt that complex, so it 
shouldnt take too long. I'll post the
results to this thread. Unfortunately, they
dont have one posted at the site yet
although they do have the models for the 
transistors and diodes.

Good luck with your LED circuits 

--Al


----------



## Mercator (Oct 27, 2001)

MrAl,

Reading through your last post and looking through the Zetex Datasheets I've put together a list of components. I'm about to head out to a local surplus house to see what I can come up with. They have a small selection of partial rolls of SMD devices. Not cataloged, so will have to dig through stacks. If I can get away tomorrow I'll head down to Santa Clara. There's another store down there that has a larger and better organized supply of surplus SMD components.
At both places I should be able to walk away with a couple of handfulls of stuff for a couple of dollars. I plan on trying to find the common items; caps, resistors and maybe coils. Not to likely I'll find the Zetex diodes or transistors. But... you never know. If you want, put togeteher a small list of things, and if I can get there tomorrow I'll try and locate them as well.

Here's what I have on the shopping list so far:

diode........ ZHSC100 and/or IN5817
resistors.... 0.1 and 0.05 and 0.025 and 0.33
capacitors... 2.2uf
inductors.... 68uh and 100uh
transistor... FMMT617 and/or FMMT618


I'm still working on options for building a simple eval baord. The more I draw the circuit out the simplier it looks. Would help to have the actual components though. The footprint of the IC and the trans have the lead spacing identical which helps in laying out a simple block solder pad type of PCB design. In fact, the ckt is so simple that one could almost solder the parts to one another.

I've sent you my email address so that you can forward your mailing address to me.

Mercator


----------



## **DONOTDELETE** (Oct 27, 2001)

The actual components I ordered from Digi-Key:

IC ZXSC300E5CT $1.05
68uH choke M5816 $1.88
100uH choke M5818 $1.88
2 Schottky diodes 1N5818DICT $0.39 ea.
Surfboard for SOT23-5 33205CA $1.80
Resistor 0.04 ohm 2 watt 12FR040 $1.54
Resistor 0.05 ohm 2 watt 12FR050 $1.45
Transistor ZTX1049A $1.14

Also included in the order were some heatsinks and the components for the LM2621 circuit.

From what Al says, I wish I had ordered beefier Schottkys, although even at 190mA the LS is pretty impressive, and I'm very apprehensive about even thinking about sending 3500mA through a $15 LS, even in a pulsed circuit, when the specs say 500mA is the pulsed max.


----------



## MrAl (Oct 28, 2001)

Thanks Mercator, i sent you the info.

Duggg, sounds like you have quite a few
good parts comming. Also, when i said
the current might have to be as high
as 4 amps, i meant the transistor and
possibly the Schottky, not the LED's or 
other load. The LED's should have a
slight pulsing, but not too high at all
above their average current value.

Hope we get to try these out soon, and 
i hope i hear from anyone who gets too it
before i do  As soon as i get the
part, ill test it.

--Al


----------



## Mercator (Oct 28, 2001)

*Dugg*

_*The actual components I ordered from Digi-Key:*_

That's sounds like a good start. I'm about to place an onlline order through Digikey myself. Can't wait for the printed catalog.
I went to a surplus electronics house and picked up several SMD components. Actully ran out ot time before they closed. I wanted to get a supply of leaded components as well. Digikey's prices are one hell of alot more. If you want I'll send you some of the SMD's I picked up. Not sure if you said that you'd build a working driver if this circuit works out. But. I you might want to go with SMD's all the way. Let me know.

MrAl wrote and sounds like he has a pretty good handle on putting this IC through it's paces. Just hope it lives up to Zetex's claims. My main interest is driving the LS, but wouldn't mind having a single cell ckt. for smaller lights.

I've been working on a PCB design that will aid in testing the circuit. Won't etch any boards until I have the actual 300 IC and the
transistor on hand. I'm trying to design the
board so that it will accommodate many different components. I normaly use a regular breadbaord, but with these SMD's I feel it might be easier to use a PCB that will hold the SOT23 Ic's and then add the needed test oomponents to it rather than running jumper wires all over the place.

Anyways, Hope to get the 300's this coming week. I'm sending MrAl a couple and if you need a couple let me know.

Mercator.


----------



## **DONOTDELETE** (Oct 29, 2001)

I've been doing more general research on boost converters.

With more attention toward efficient components, I think I would have ordered an inductor with higher load current and lower DC resistance, namely Digi-Key DN4512 (100uH, 0.084ohms, 2.81amps, $2.08).

But that leads me to an important question... is 100uH the ideal inductance for a 500mA current pulse? (I'm afraid I haven't dealt with AC circuits since college and I'm a bit rusty with the math.)

I would also consider a better Schottky rectifier, one with a higher current rating and a lower forward voltage, such as the Digi-Key 95SQ015 (9amps, 0.31volts, $2.88). Darn expensive though!


----------



## **DONOTDELETE** (Oct 29, 2001)

Hi Mercator,

Thanks for the info regarding the SMD components.

Although SMD isn't ideal for testing purposes, it does have a cost and size advantage, the selection is greater, and the components tend to be more efficient.

So once we get a good efficient circuit going, I think SMD would be ideal for the working circuit, especially if someone like you can provide the PC boards (for a price, of course!)

Regarding Digi-Key, I know their prices are pretty expensive, but they have a good selection, and for the most part, you get what you pay for. My experience with surplus places is that you get a lot of "mystery components" that are lacking in the spec department.

Oh, and don't place an online order with Digi-Key, otherwise you have to pay shipping, which just adds to the cost. Unless time's a big factor, just mail them a check and save a few bucks with free shipping.


----------



## MrAl (Oct 29, 2001)

10/2001

Results of Circuit Simulations using Zetex ZXSC300 chip
idealized model and one white LED.

The entries below are arranged in order of application:
One cell, two cells, etc., and show circuit component
values and battery voltages and LED currents in this order:

1. the inductance L (varied over a few decades)
2. the output filter capacitance C
3. the value of the sense resistor Rs, set for an output of 32ma at
the battery's top voltage when it's new (or fully charged).
4. the three lines following the above show the battery voltage as
it drains down, and the resulting change in the white LED current.

Following the entries for the chip 
simulations is a comparison to the
simple series resistor LED solution
driven from three cells in series.

-------------------------------------------------------------

ONE CELL NiCd

L= 10uH C=8uf Rs=0.065 ohms
1.20v 32ma
1.10v 30ma
1.00v 27ma

L= 20uH C=8uf Rs=0.078 ohms
1.20v 32ma
1.10v 29ma
1.00v 26ma

L= 50uH C=8uf Rs=0.110 ohms
1.20v 32ma
1.10v 29ma
1.00v 26ma

L=100uH C=8uf Rs=0.131 ohms
1.20v 32ma
1.10v 29ma
1.00v 26ma

L=200uH C=8uf Rs=0.144 ohms
1.20v 32ma
1.10v 29ma
1.00v 27ma

L=500uH C=8uf Rs=0.153 ohms
1.20v 32ma
1.10v 29ma
1.00v 27ma

L=1000uH C=8uf Rs=0.156 ohms
1.20v 32ma
1.10v 29ma
1.00v 27ma

-------------------------------------------------------------

ONE CELL ALKALINE

L= 10uH C=8uf Rs=0.076 ohms
1.50v 32ma
1.25v 27ma
1.00v 22ma

L= 20uH C=8uf Rs=0.094 ohms
1.50v 32ma
1.25v 27ma
1.00v 21ma

L= 50uH C=8uf Rs=0.133 ohms
1.50v 32ma
1.25v 26ma
1.00v 20ma

L=100uH C=8uf Rs=0.161 ohms
1.50v 32ma
1.25v 26ma
1.00v 21ma

L=200uH C=8uf Rs=0.179 ohms
1.50v 32ma
1.25v 27ma
1.00v 21ma

L=500uH C=8uf Rs=0.192 ohms
1.50v 32ma
1.25v 27ma
1.00v 21ma

L=1000uH C=8uf Rs=0.197 ohms
1.50v 32ma
1.25v 27ma
1.00v 21ma

-------------------------------------------------------------

TWO CELL NiCd

L= 10uH C=8uf Rs=0.109 ohms
2.40v 32ma
2.20v 29ma
2.00v 26ma

L= 20uH C=8uf Rs=0.144 ohms
2.40v 32ma
2.20v 28ma
2.00v 25ma

L= 50uH C=8uf Rs=0.209 ohms
2.40v 32ma
2.20v 28ma
2.00v 24ma

L=100uH C=8uf Rs=0.255 ohms
2.40v 32ma
2.20v 29ma
2.00v 26ma

L=200uH C=8uf Rs=0.286 ohms
2.40v 32ma
2.20v 29ma
2.00v 26ma

L=500uH C=8uf Rs=0.309 ohms
2.40v 32ma
2.20v 29ma
2.00v 27ma

L=1000uH C=8uf Rs=0.318 ohms
2.40v 32ma
2.20v 29ma
2.00v 27ma

-------------------------------------------------------------

TWO CELL ALKALINE

L= 10uH C=8uf Rs=0.140 ohms
3.00v 32ma
2.50v 23ma
2.00v 18ma

L= 20uH C=8uf Rs=0.189 ohms
3.00v 32ma
2.50v 23ma
2.00v 17ma

L= 50uH C=8uf Rs=0.276 ohms
3.00v 32ma
2.50v 23ma
2.00v 16ma

L=100uH C=8uf Rs=0.330 ohms
3.00v 32ma
2.50v 25ma
2.00v 18ma

L=200uH C=8uf Rs=0.366 ohms
3.00v 32ma
2.50v 26ma
2.00v 20ma

L=500uH C=8uf Rs=0.391 ohms
3.00v 32ma
2.50v 26ma
2.00v 21ma

L=1000uH C=8uf Rs=0.400 ohms
3.00v 32ma
2.50v 27ma
2.00v 21ma

-------------------------------------------------------------

THREE CELL NiCd
Inductance values less then 20uH didnt work at these higher
input voltages.

L= 20uH C=8uf Rs=0.275 ohms
3.60v 32ma
3.30v 24ma
3.00v 19ma

L= 50uH C=8uf Rs=0.374 ohms
3.60v 32ma
3.30v 26ma
3.00v 21ma

L=100uH C=8uf Rs=0.426 ohms
3.60v 32ma
3.30v 28ma
3.00v 24ma

L=200uH C=8uf Rs=0.457 ohms
3.60v 32ma
3.30v 29ma
3.00v 25ma

L=500uH C=8uf Rs=0.478 ohms
3.60v 32ma
3.30v 29ma
3.00v 26ma

L=1000uH C=8uf Rs=0.486 ohms
3.60v 32ma
3.30v 29ma
3.00v 27ma

-------------------------------------------------------------

THREE CELL ALKALINE (not recommended)
The highest voltage the circuit configuration
would handle was 4.3 volts. Above that, the circuit
doesnt appear to function properly, probably because
the input voltage is already above the LED voltage.

L= 20uH C=8uf Rs=0.582 ohms
4.30v 32ma
3.75v 15ma
3.00v 6ma

L= 50uH C=8uf Rs=0.587 ohms
4.30v 32ma
3.75v 22ma
3.00v 11ma

L=100uH C=8uf Rs=0.588 ohms
4.30v 32ma
3.75v 25ma
3.00v 16ma

L=200uH C=8uf Rs=0.590 ohms
4.30v 32ma
3.75v 26ma
3.00v 19ma

L=500uH C=8uf Rs=0.590 ohms
4.30v 32ma
3.75v 27ma
3.00v 21ma

L=1000uH C=8uf Rs=0.590 ohms
4.30v 32ma
3.75v 28ma
3.00v 22ma

----------------------------------------------

For comparison, here is the result of running a 
single white LED from three cells in series with
only a single series resistance of 11.9 ohms:

3 alkaline cells with 11.9 ohm series 
resistor using the same theoretical model 
for the LED as was used in the chip 
simulations:

4.5v 43ma
4.3 32ma
3.75v 10ma
3.0v 0.77ma

note how fast the current drops off as the
battery discharges. Compare to one of
the entries above using the chip for
regulation.


SUMMARY:

This chip doesnt regulate perfectly as
pure current feedback would, but it
does a much better job then not having
any regulation at all.


Have fun 

--Al


----------



## **DONOTDELETE** (Oct 29, 2001)

MrAl,

At first I was very discouraged by your test results, because at first glance it appeared the output current was simply tracking the input voltage.

But when you included the results of the simple resistor-in-series test, it was eye opening.

Scaling the currents by 11 to simulate a Luxeon Star, one could start out at 350mA and still be driving the thing at 286mA when a simple resistor circuit would only provide 6mA.

I know from experience that an LS even at 286mA is pretty nice






Thanks for the simulation work!


----------



## Mercator (Oct 29, 2001)

Thanks Al for your modeling. Like Dugg, I was disapointed to see the results. Until Dugg wrote....

*
At first I was very discouraged by your test results, because at first glance it appeared the output current was simply tracking the input voltage.

But when you included the results of the simple resistor-in-series test, it was eye opening.

Scaling the currents by 11 to simulate a Luxeon Star, one could start out at 350mA and still be driving the thing at 286mA when a simple resistor circuit would only provide 6mA.*

I don't fully understand the part about "scalling the currents by 11" and "one could start out at 350mA and get 286mA"

If it's not to much trouble alittle explaination please. From what I read it deos look possible to utilize the 300 to drive an LS. 

I received a call from Zetex today. I wasn't home but the message was regarding the eval board. Seems that Zetex wanted more info regarding the intended application for the 300. I called back and got the reps voice mail. I left a message stating that unless the eval board was very reasonably priced we wouldn't be interested. I did asked though if we could get the SPICE Model and perhaps a sample of the 310 chip. Do you still want the SPICE Model if I can get them to part with it? I plan on calling them again in the morning. I think I might ask for the spec'd transistor and maybe for the beefer one as well. I hope it's not pushing my luck to far. They seem very hard to work with. Had to tell some little white ones and I hate doing that. I guess I realy don't mind because comparing their sample program to National's is like night and day. From National... No questions Asked and they have shipped stuff FedEx from the East Coast and from Asia for me.

Mercator


----------



## Mercator (Oct 29, 2001)

*Looking at he simple schematic of the ZXSC300 is one thing. But... seeing the actual components in relationship to one another just shows how simple this circuit can be. The image is the basic "Maximum Battery Life" design. With the addition of a single diode and a capacitor one gets the "Maximum Brightness" version. *

Just thought I'd offer this for those who might be reading this topic and not have any idea what we're talking about. This chip does have possibilities.

Mercator


----------



## **DONOTDELETE** (Oct 29, 2001)

Hi Mercator,

Very nice board diagram! One of the things that really attracted me to the ZXSC300 was the simplicity of the circuit.

Regarding "scaling by 11", MrAl had done his simulations using a typical white LED drawing 32mA, which is about 1/11th of the 350mA needed by the LS. At the end of his one-cell NiCd simulation using the 100uH inductor, the currrent had dropped to 26mA, and 26 times 11 is 286mA.

Of course, we're only inferring about the expected LS performance without its SPICE model, but still, the results look promising, IMHO.

I was out biking this evening with my cyan and amber LS's hooked in series with six NiMH AA's and a 3.9-ohm resistor. Starting current was 350mA, and 1.5 hours later it had dropped to 260mA, but it was still lighting up everything in sight.

If I can get the same performance out of a single AA, or even two AA's, I would be ecstatic!


----------



## MrAl (Oct 30, 2001)

Hi there again Duggg and Mercator,

Yeah i was a little disappointed too, lets
hope they have something built into that
chip that they arent advertising 
In any case, its not that bad after all.

Thanks for going after the parts Mercator,
and yes, i could still use the spice model
to possibly learn to model the circuit
even closer to the real thing.

As for running at 350ma, i've included 
simulations below. It looks like for
that current level a higher rated
schottky diode will be needed too.
The max current went up to 1.2 amps
at 1.2 volts input. A 1 amp diode might
live, but i wouldnt want to depend on that.

Thanks again for the ideas and inputs,
--AL

Here are some simulations of running the Zetex 300 chip
with a theoretical LS led. The LS is modeled as
10 white led's in parallel, so this applies for
10 white led's in parallel also, provided they are
somewhat matched in vi characteristics.

-----------------------------------------------------
Some notes about the results:

1. The max inductor current in all these runs was always
above 1 amp, typically 1.00 to 1.20 amps. This indicates
a 1 amp diode probably wont work. There is a chance
that the actual LED(s) used will have a lower forward
voltage, and therefore the max inductor current may
be slighly under 1amp. In any case, it will run
very close to or above its limit unless the output
current is reduced or a higher rated diode is used.

2. The higher the output capacitance, the lower the 
max LED current. In all cases 16uf isnt a bad choice
if 420ma current peaks through the LED(s) can be tolerated.

-----------------------------------------------------

The following entries are arranged by application of
either 1.2v (NiCd) or 1.5v (alkaline).
For each app the inductance is varied with output filter
capacitance equal to 16uf, then the cap is changed
to 64uf and the whole routine is repeated.
In each case, Rs is set to provide about 350ma average
output with the battery voltage at it's top
level, then the voltage is decreased as the
cell discharges and the resulting decrease in
average LED current recorded.


-----------------------------------------------------

ONE NiCd CELL using C=16uf:

top Batt=1.2v
iLED peak=420ma

L= 20uH C=16uf Rs=0.013 ohms
1.20v 351ma
1.10v 322ma
1.00v 293ma

L= 50uH C=16uf Rs=0.014 ohms
1.20v 351ma
1.10v 323ma
1.00v 294ma

L= 68uH C=16uf Rs=0.014 ohms
1.20v 350ma
1.10v 322ma
1.00v 293ma

L=100uH C=16uf Rs=0.014 ohms
1.20v 351ma
1.10v 323ma
1.00v 294ma

L=200uH C=16uf Rs=0.015 ohms
1.20v 350ma
1.10v 322ma
1.00v 293ma

L=500uH C=16uf Rs=0.015 ohms
1.20v 350ma
1.10v 322ma
1.00v 293ma

L=1000uH C=16uf Rs=0.015 ohms
1.20v 351ma
1.10v 323ma
1.00v 294ma

-------------------------------------------

ONE ALKALINE CELL using C=16uf

top Batt=1.5v
iLed peak=400ma

L= 20uH C=16uf Rs=0.017 ohms
1.50v 349ma
1.25v 290ma
1.00v 232ma

L= 50uH C=16uf Rs=0.018 ohms
1.50v 350ma
1.25v 292ma
1.00v 234ma

L= 68uH C=16uf Rs=0.018 ohms
1.50v 350ma
1.25v 293ma
1.00v 235ma

L=100uH C=16uf Rs=0.018 ohms
1.50v 350ma
1.25v 293ma
1.00v 235ma

L=200uH C=16uf Rs=0.018 ohms
1.50v 350ma
1.25v 293ma
1.00v 236ma

L=500uH C=16uf Rs=0.018 ohms
1.50v 351ma
1.25v 294ma
1.00v 237ma

L=1000uH C=16uf Rs=0.018 ohms
1.50v 350ma
1.25v 293ma
1.00v 236ma

-----------------

ONE NiCd CELL using C=64uf

top Batt=1.2v
iLED peak=370ma

L= 20uH C=64uf Rs=0.0132 ohms
1.20v 350ma
1.10v 321ma
1.00v 291ma

L= 50uH C=64uf Rs=0.0140 ohms
1.20v 350ma
1.10v 321ma
1.00v 292ma

L= 68uH C=64uf Rs=0.0141 ohms
1.20v 351ma
1.10v 322ma
1.00v 293ma

L=100uH C=64uf Rs=0.0143 ohms
1.20v 349ma
1.10v 320ma
1.00v 291ma

L=200uH C=64uf Rs=0.0144 ohms
1.20v 350ma
1.10v 322ma
1.00v 292ma

L=500uH C=64uf Rs=0.0145 ohms
1.20v 350ma
1.10v 321ma
1.00v 292ma

L=1000uH C=64uf Rs=0.0145 ohms
1.20v 351ma
1.10v 322ma
1.00v 293ma


---------------------------------------

ONE ALKALINE CELL using C=64uf

top Batt=1.5v
iLED peak=365ma

L= 20uH C=64uf Rs=0.0164 ohms
1.50v 351ma
1.25v 291ma
1.00v 232ma

L= 50uH C=64uf Rs=0.0175 ohms
1.50v 351ma
1.25v 292ma
1.00v 234ma

L= 68uH C=64uf Rs=0.0177 ohms
1.50v 351ma
1.25v 293ma
1.00v 234ma

L=100uH C=64uf Rs=0.0179 ohms
1.50v 351ma
1.25v 293ma
1.00v 235ma

L=200uH C=64uf Rs=0.0181 ohms
1.50v 351ma
1.25v 293ma
1.00v 235ma

L=500uH C=64uf Rs=0.0183 ohms
1.50v 349ma
1.25v 292ma
1.00v 234ma

L=1000uH C=64uf Rs=0.0183 ohms
1.50v 350ma
1.25v 293ma
1.00v 235ma


----------



## Mercator (Oct 30, 2001)

*Dugg*... Thanks for the expanation on the "scaling by 11" factor, Makes sense to me. I guess I thought it was something more difficult to figure out. Thanks for the kind word on the circuit design drawing. Just something I ended up with while trying to design the PCB for this project.

_ Off Topic A Bit_
You mention having both a cyan and an amber LS. As far as overall preceived light output, which do you feel does a better job?
My applications would normally require a light source closer to white since the true color of viewed items is important. Although the aility to "light-up" large cavernous rooms is equally important. I know that the light output of the blue/green Photon is amazing, but the color of viewed items is considerably off. I can amagine that the amber LS would be more like an incandescent bulb.

*MrAl*... Thanks again for the modeling.
Looks like we should consider utilizing the ZHCS200 Zetex Diode rather that the ZHCS1000
Unless you think another chioce will provide better results. From what you see so far, does it look like the spec'd transistor (FMMT617) will handle our requirements. Or, should we try, say the FMMT618 or better.
Maybe it's to early to tell, I don't know. I'm just trying to put together a shopping list of some of the harder to obtain components. I can and will order from Digkey, But if possible, I'd like to source the surlpus house since the prices are much better. Their supply and selection of SMD's is actually pretty good. Shelf after, shelf of partial reels of various components. All have the manufactures name and part numbers. It's mostly a matter of looking up the actual specs on each item, although they are all sorted out in general catagories and values.

I'll let you know if I have any luck today on getting the SPICE Model and maybe other samples. If the SPICE model is something they can email (or snailmail) I'll have them send it directly to you.

Mercator


----------



## **DONOTDELETE** (Oct 30, 2001)

Guys,

I got good news and I got bad news.

The good news is that Digi-Key finally shipped my order today. The bad news is that I mailed the order to them eight days ago.

The good news is that I checked www.digikey.com and I looks like they took my chip off their 3000-piece reel, and they now have 2999 ZXSC300's available to everyone at $1.05 each!

The bad news is that my order includes not only two 1-amp Schottky diodes, but a 632mA and 804mA choke as well, all inadequate for the one-cell estimated current around 1.2 amps.

The good news is that there's no way my circuit would work with that kind of draw anyway. An AA cell providing 1.2 amps would have so much heat building up inside it, the true efficiency of the circuit would be dismal, and it would be lucky to last an hour.

The bad news is that they shipped my order via UPS ground, which means it will be another week until it gets here.

The good news is that with 2 AA cells, the current demand should be much less.

MrAl, could you please re-run your simulation using two NiMH AA cells and let us know what the peak inductor current would be then?


----------



## **DONOTDELETE** (Oct 30, 2001)

Mercator,

Regarding which has more light output, the cyan appears much brighter than the amber, even though the amber supposedly has a higher flux. The amber

As I mentioned, I attribute this to the fact that the eye is most sensitive to blue light.

As far as which one would render color better, the problem with any non-white LED is the monochrome light it produces, making everything appear in weird colors.

You can easily see the color effect of an amber LED by going to some parking lit up with those sodium vapor lamps. Try to make out actual car colors---it's hard!

Incandescent lights, though dominantly red/orange, do produce light that's much more polychromatic than non-white LEDs.


----------



## MrAl (Oct 30, 2001)

Duggg:

I think i made a mistake when
i tried to convey the info about the diode.
That diode actually has two current ratings:
The average rating is 1 amp, while the
peak rating is 12 amps; more then enough
to withstand 1.2amp peak for 25% duty cycle.
In other words, i think it will work ok,
but the eff will be better with the ZHCS2000
diode, thats all. The current obviously
(now that im a little more awake today )
cant be continuous through the diode, or
the transistor wouldnt be turning on.
When the transistor conducts, the diode doesnt, and vice versa. This causes current
pulses though the diode, not a continuous 
current. Also, the current from the battery
wont be continuous, but sawtoothing up
and down. I guess the average is still 
going to be high though, like 1 amp or so.
After all, .350 amps times 4 volts comes
out to 1.4 watts any way you look at it,
and 1.4 watts divided by the battery voltage
of 1.2 volts (NiCd) comes out to 1.17 amps.
That is quite a drain on a single cell,
and it's worse when you consider less then
100& eff.
If we look at two cells in series, we get
2.4 volts tops. If we divide that same 
1.4 watts by 2.4 volts we get about 
0.58 amps, a little better. Considering
efficiency, about 0.67 amps drawn from 
the two batteries.

I'll run a simulation for 2.4 volts tonight.
Should be interesting.


Duggg & Mercator:

I found a very nice transistor for
high current outputs like 350ma.
The part is FCX688B (Zetex again).
Its got very high gain with low
base currents, handles 3amps, the
drawback is its only got a 12v rating so
it will only work in apps that use
only one LED or two LED's in series,
so we cant try like 3 or 4 in series with 
that transistor or it will blow out fur 
shure  The voltage rating is one rating
you cant play with (he he). Other then that,
if it matches the specs, it looks real good.
I wouldnt mind testing one of these 
transistors with the chip too.
If the price is low enough, it could be 
a solution for any app. If not, perhaps 
just in higher current apps like the LS
or many parallel LED's.

Again, thanks for all the input and ideas,
and part searches and such. We will be able 
to come up with something for most LED apps
soon. I like Mercator's drawing too, it
shows how simple this arrangement really is.
I wouldnt mind using this chip for a 2 LED
flashlight either running from one cell.

I think eventually i will want to come up
with a pure current regulating solution also,
even if it means adding a pre-boost regulator. I think it will be acceptable
in high current apps, unless we can find
something simpler. I dont think it would
be worth it for one led apps though, unless
your a real constant light output freak 

I'll get to the simulations tonight.

Bye for now,
--Al


----------



## MrAl (Oct 30, 2001)

Hi there again,
Here are the simulations for
2.4 volt input (two NiCd's)
with one LS type LED with an
output current of 350ma.

Following the simulation results
are a number of simplifications
that can be used to calculate the
general results with different
capacitors, inductors, output 
currents, input voltages, etc., as
well as calculate a starting value
for Rs.

Simulations for 2.4v battery input
with 350ma output current:
(C is varied over two different values
and L is varied over 3 different values)

(C=64uf)
[max peak iL=.67 amps]
[max peak iLed=356ma]

L= 68uH C=64uf Rs=0.0286 ohms
2.40v 350ma
2.20v 321ma
2.00v 292ma

L=100uH C=64uf Rs=0.0290 ohms
2.40v 350ma
2.20v 321ma
2.00v 292ma

L=500uH C=64uf Rs=0.0296 ohms
2.40v 350ma
2.20v 321ma
2.00v 293ma


(C=16uf)
[max peak iL=.67 amps]
[max peak iLed=372ma]

L= 68uH C=16uf Rs=0.0286 ohms
2.40v 350ma
2.20v 321ma
2.00v 292ma

L=100uH C=16uf Rs=0.0290 ohms
2.40v 350ma
2.20v 321ma
2.00v 292ma

L=500uH C=16uf Rs=0.0296 ohms
2.40v 350ma
2.20v 322ma
2.00v 293ma
--------------------------------------------

Here are the simplifying formulas:


Zetex ZXSC300 LED current regulating chip simplification
of estimation of operating levels.


The examples that follow the general estimation formulas use:
1. C=16uf
2. Iout=350ma
3. Vout=4volts (when LS conducts 350ma)
4. Vin=2.4volts(two NiCd's)
5. Zetex's nominal Toff spec of 1.7us
6. L=100uH
7. the function "power(x,y)" is taking x up to the power of y.
 This can be found on "Calculator" that comes with Windows95+,
and is the key labled " x^y ". Of course you have to click on
"View" and then "Scientific" to get this function.
8. Zetex's nominal Isense spec of .019 volts

estimate Toff:
Toff=1.7us

estimate Ton:
Ton=Toff(Vout-Vin)/Vin
=1.7us*(Vout-Vin)/Vin
=1.7*(4-2.4)/2.4 = 1.133us

estimate absolute value of di (transistor off):
di= (Vout-Vin)*Toff/L = 0.0272

estimate average input current(eff=85%):
iavg=(1/0.85)*Vout*Iout/Vin
=4*.35/2.4=0.686 amps

estimate peak inductor current:
iLpk=iavg+di/2 =.6996

estimate Rs:
(This might provide a trial starting value for Rs. In practice,
i would start 1.5 times higher and work it down if necessary.)
Rs=Vsense/iLpk
=.019/.6996
=.0272 ohms (this comes close to the simulation optimized value of .029 ohms)

estimate C voltage discharge:
dv(on)=Iout*Ton/C
=0.024792, (C=16uf)

estimate dILed current:
(This uses approx LS LED model around 4 volts at 350ma. Should work for
10 LED's in parallel also, operating around 35ma each.)
iLed(Vc)=10*K*power(55,Vc), with K=3.825e-9, and Vc is cap voltage
dILed=Iout-iLed(Vc=Vout-dv)
=0.350-[10*3.825e-9*power(55,4-dv(on))] 
=0.350-0.317=.033 amps

estimate peak Led current:
iLedpk=Iout+dILed/2
=0.350+0.033/2=0.367 amps


estimate min Led current:
iLedmin=Iout-dILed/2
=0.350-0.033/2=0.334 amps


in case you want to estimate the running frequency:
F=1/(Ton+Toff)


---------------------

Good luck with your LED circuits,
--Al


----------



## MrAl (Oct 31, 2001)

In addition to above, i posted a new circuit
to my web page earlier today.
The address is
http://members.aol.com/xaxo/page1.html 

and the circuit is a current regulating 
four white led driver. The circuit
accepts voltages from 1.5 volts to
4 volts or so, and provides a constant
current to four white led's. The current
is regulated to about 2% from voltages from
2 to 3 volts input, and about 10% from
1.5 to 4 volts. The circuit uses 4 common
transistors and other common parts.
The current regulation method is similar
to other designs, but uses an integration
error stage to achieve very close regulation.
I finished up this circuit a couple weeks 
back, but couldnt get it to regulate down to
1 volt or so, so i almost abandoned it, but
then i realized that it could still be useful
for two cell NiCd or Alkaline apps. For
these applications, the circuit would act
like an almost perfect regulator, and regulate the light output untill both batteries are deader then dead 
I'll have to build this circuit up soon, but
if anyone else wishes to do so, please do, and
let us know how you made out.

Good luck with it,
Al


----------



## **DONOTDELETE** (Oct 31, 2001)

Hi MrAl,

Thanks a lot for the simulations! They are awesome, and I'm glad to see all the components I ordered are now in range.

I do have a concern about the operating frequency though.

With Ton=1.133us, F is 353kHz, which is above the recommended 200kHz.

Should that be a concern?


----------



## MrAl (Oct 31, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Hi MrAl,

I do have a concern about the operating frequency though.

With Ton=1.133us, F is 353kHz, which is above the recommended 200kHz.

Should that be a concern?*<HR></BLOCKQUOTE>


I dont think the operating frequency is
that significant, unless the delays on
the chip turn out to be relatively
long. I almost left out the estimation
of operating frequency just so it wouldnt
draw too much attention  but then figured
maybe someone out there might be interested
in thinking about that too.
In any case, there isnt a real lot you can
do about that. It's not a set point or
anything, just perhaps a general check
on what the circuit is doing. It's also
not a drawback to have a freq higher then
200kHz, since if Zetex can regulate
the minimum off time down to about 1.7us 
they have to be using high speed circuitry
anyway. If there are any differences, they
will just add to the initial error possibilities, which by the way abound with
this chip  and will be compensated for
by adjustment of Rs.
For example, the initial Isense voltage can 
vary by some 25%, so this alone means that
the resistor value chosen for Rs will have
to be hand selected, or else chosen for
worst case which would mean decreased
output current for some production runs.
This means 350ma becomes 262ma.
If you dont mind hand selecting Rs and you
can find an easy way to do this with
very low value resistors like this, then
you wont have a problem.
The only other thing i should mention is
that for those very high output currents
you may have to go with their special 
transistor that i mentioned somewhere else
on here. The part number ended in 688B
and its spec'd at low base currents of
1ma and 10ma, and has min gain of 400.
You may actually need this transistor
or one like it. I'm hoping not, but
the output current spec on the chip is
only like 2ma or something, and a lot
of the other Zetex transistors are spec'd
at 10ma or higher. If you end up with 
a problem getting to higher current outputs,
i would suggest trying this transistor.

Also, the data sheet might be a little
misleading with regard to the calculation
of Imin. I wouldnt use their recommendation
to calculate Imin or Ipeak. In fact, is
it even possible to calculate Ipeak with
their equations? Unless i missed something?

The layout will be somewhat critical im 
sure, short current paths are a necessity.

Good luck with all your LED circuits,
and thanks for your input also 
--Al


----------



## **DONOTDELETE** (Oct 31, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
In fact, is it even possible to calculate Ipeak with their equations? Unless i missed something?
*<HR></BLOCKQUOTE>

Yes, using their Pout equation on page 9, if you assume Pout=1200mA, you can solve for Ipeak and get 797mA with the circuit operating at 200kHz.


----------



## MrAl (Oct 31, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*
using their Pout equation on page 9, 
*<HR></BLOCKQUOTE>

Yeah, thats what i mean, that equation
just isnt accurate, or even useful 

The output power is very easily calc'd
by:
P(out)=V(out)*Iavg(out)

Also, if you notice the other two
equations they give with Imin in them,
you cant calculate Imin because you dont
know what Ipeak is yet, and you cant
calculate Ipeak because you dont know what
Imin is yet 

Kind of strange 

Take care for now,
--Al


----------



## MrAl (Nov 1, 2001)

Here's some new simplified equations for
the calculation of Rs and the peak
transistor and Schottky currents:

Rs=.038/[2*iAvgOut*((Vout+0.4)/Vin)+(Vout+0.4-Vin)*Toff/L]
and
Ipeak=0.019/Rs

where

Rs is the current sense resistor value in ohms
L is the inductor value in *microhenries*
iAvgOut is the actual output current in amps
Vout is the actual output voltage in volts
Vin is the battery voltage in volts
Toff=1.7

Example:
Drive an LS to 350ma, at 4 volts output
with a 2.4 volt battery:

Rs=.038/[2*iAvgOut*((Vout+0.4)/Vin)+(Vout+0.4-Vin)*Toff/L]
=.038/[2*0.350*(4.4/2.4)+(4.4-2.4)*1.7/100]
=.038/1.317333
=.0288
and
Ipeak=0.019/Rs
=0.019/.0288
=0.6597 amps

Also, in order to keep the peak LED
current from becomming too high,
try to keep the change in output
voltage during the off time down to
less then about 40mv by calculating:

dv=iAvgOut*Toff/C {C in uf, Toff=1.7}

So for 350ma output and C=16uf,
dv=0.350*1.7/16
=.037
which is just under 40mv so it should 
be ok. As an extra precaution when dealing
with the tolerance of the cap and ageing,
you could double this value. Here, 32uf 
would be even better.

Good luck with it,
--Al


----------



## php_44 (Nov 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
The only other thing i should mention is that for those very high output currents you may have to go with their special transistor that i mentioned somewhere else on here. The part number ended in 688B and its spec'd at low base currents of 1ma and 10ma, and has min gain of 400. You may actually need this transistor or one like it. I'm hoping not, but the output current spec on the chip is only like 2ma or something, and a lot of the other Zetex transistors are spec'd at 10ma or higher. If you end up with a problem getting to higher current outputs, i would suggest trying this transistor.

The layout will be somewhat critical im sure, short current paths are a necessity.
--Al*<HR></BLOCKQUOTE>

The ZXSC300 maximum base drive current is 3.6mA with a specified minimum of 1.6mA, which probably limits the output power available unless you can find a very special transistor. If you did find one with a gain of 400 *at the switching frequency - not DC* that could pass an amp or so then you could get 320mA worst case. It would be a nice solution. Although less efficient than the ZXSC300, the ZXSC100 has a special output for driving a PNP transistor that would provide extra drive for the NPN transistor doing the hard work. In this way they specify the zxsc100 will produce up to 2W of power. At 4V output this would be 0.5A - plenty to drive an LS. The suggested circuit is in the data sheet. I'd take the suggested circuit, leave the fb pin disconnected, and use Rsense to set the maximum current. You'd probably want a two cell battery for this unless you're using a single "C" or "D" cell. A single AA would whither up and die in short order!

As far as layout - I'm with you that it would be critical. I think a carefully thought out PCB - like the one in the data sheet, but modified to add PNP driver for high power - would be mandatory. I don't think you could hand wire it anyway. It's still a simple enough circuit to draw on a clean PCB blank with a sharpie marker and etch (you can still get the stuff at Radio Shack for under $8) - and the beauty of SMT is you don't have to drill holes :^). I do all my flashlight PCB's this way and have made boards for Maxim boost convertor ICs with great success.


----------



## Mercator (Nov 1, 2001)

*Dugg,*

Thanks for you input on the amber Vs. the cyan LS.
I still haven't gotten my supply of the 300's. So you might end up being the first to actually get this IC in your hands and on a bradboard.

*MrAl,*
Not intending to trash your design efforts on the 4 transistor ckt. 
I looked at the schematic on your site for the 4 transistor regulator. Admittedly, I don't know enough about electronics to be able to ascertain anything about the circuit. I did note though that it is comprised of many components, thus making it a rather difficult circuit to build. Not to mention overall size factor of the board. Back to just how small the 300 IC ckt. is and for that matter the MrAl/Brinkman and Satcure ckts. It seems to me that many folks like a circuit that they can use to retrofit into an existing flashlight design. Therefore size and component count might be a consideration.

I can fully understand your interest in developing a regulating ckt. That's why I
was interested in what the EU38 Constant Current Laser Driver would do. Makes most sense for larger battery sources. But, I still do think that the 300 deserves a close look. I'm impressed on how simple and small the actual ckt. can be. Thus making it ideal for may applications. The only draw back is the small size of the SMD components and working with them.

*You wrote in a seperat correspondence:*
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>The thing I'm now wondering though is would it just be simpler to sit down and come up with a regulating circuit that handles 2 to maybe 10 LED's and regulates very very well? Well, i guess the Zetex chip can't be beat for a single LED though, i don't think anyone wants to through 10 parts at a single LED app. Possibly even a two LED app.<HR></BLOCKQUOTE>

I sorta get the impression that you don't feel that the 300 is as well suited for
driving the LS as it is for single or multiple LED's. Looking through your
theoretical data on driving the LS at near max specs. it looked adequate to me. But then, maybe I'm missing something.

I've been following the recent posts my you and Dugg and I have to say that this is getting over my head when it comes to calculating and tweaking this circuit design. I guess for me, I'll have to wait and see what you EE types come up with and then build from the finalized results. I'm still waiting to get my components for this project
and will start breadboarding using the results posted thus far.

Mercator


----------



## MrAl (Nov 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by php_44:
*The ZXSC300 maximum base drive current is 3.6mA with a specified minimum of 1.6mA, which probably limits the output power available unless you can find a very special transistor. 
Although less efficient than the ZXSC300, the ZXSC100 has a special output for driving a PNP transistor that would provide extra drive for the NPN transistor doing the hard work.
*<HR></BLOCKQUOTE>

The transistor is the FCX688B made by Zetex.
It's got an FT of 150MHz, even higher then 
the other recommended transistors.
This is the transistor i was talking about.

I'll take another look at the Zetex 100 chip
also, driving a pnp/npn combo sounds like
a good idea. Perhaps they spec'd that
eff number because of certain circuit
restictions not mentioned in the 300 chip
data sheet.

Mercator:
As far as the 4 transistor circuit goes,
i had mentioned sometime earlier that
not everyone will be willing to build 
a circuit that requires 4 transistors,
but it does work very well as i tested it
this morning (posted results in the 
other thread). These numbers are from 
an actual real life circuit built up
for testing with one white led.
The strong points are very low cost,
very good current regulation, parts 
available everywhere and at several
manufacturers. The drawback is
component count. If your after very
small size, one of the ic chips is 
probably the best way to go. I'll be
looking at other chips too, but see i
started that circuit before we found
distributers for the 300 chip and all.
The circuit operation is fairly straight
forward also, and i was thinking of 
perhaps replacing three of the transistors
with a multi transistor ic for a lower parts 
count. There are a few ic's that house
4 transistors on one chip. Some of them
have 2 pnp and 2 npn. That would bring us
back to one ic and one transistor, but still
more resistors The advantage now starts
to show up in extreme versatility also.
Also, replacing two to three transistors 
with a commonly available comparator ic
chip ( probably my next step ) and 
special voltage reference diode will bring
the current regulation in better than
1% over the entire operating voltage range
of about 2 volts to 4 volts.
I guess it amazes me how many possiblities 
there really are out there 
Dont get me wrong though, i still like the
300 chip, im just hoping we dont have
any problem getting to 350ma or so with it.
That's my last worry with that chip as
i was mentioning elsewhere 
The theoretical data, unfortunately, is just
that. It's not only theoretical, it's also
idealized, except for Vsat and the Schottky
diode drop. Although most of it is probably 
fairly accurate (comes up the same with
totally different calculation schemes)
there is one major parameter left out:
that is the base drive current available
at any given time from the chip. If it turns
out that this drive current is not adequate
for 350ma using the best transistor we can 
find, then we either have to modify the 
design by throwing more parts at it
(if that is even possible) or we have to
move to a different chip for higher currents.
This is something that is harder to model
in a simulation, but real life testing
will give us the answer. We can measure
the base current while running at a high
current and decide if all the production run
chips from Zetex will always provide
enough drive for that app. 

Also, although a long way around the problem,
it might be possible to simply parallel TWO
chips for twice the current output.
Of course it wont be a direct parallel, but
connecting the two Schottky output diodes
from two identical circuits to the same
output capacitor might easily achieve
double the current output. After all, these
chips are pretty cheap right? Two cheap chips, two cheap chokes, two cheap Schottky's, two cheap resistors, one cheap
capacitor. In fact, building the circuits
up separately will modularize the whole
high current solution if we just simply
parallel the two finished boards at the
inputs and outputs.
600ma here we come 

Good luck with your LED circuits,
--Al
ps. We'll get there one way or another


----------



## **DONOTDELETE** (Nov 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*The transistor is the FCX688B made by Zetex. It's got an FT of 150MHz, even higher than the other recommended transistors. This is the transistor I was talking about.
*<HR></BLOCKQUOTE>

I still stand behind my original transistor choice, the 4-amp Zetex ZTX1049A. At an expected collector current of 800mA, it has a good gain of 450, and the lowest saturation voltage.

Its SPICE parameters are available at http://www.zetex.com/3.0/pdf/ZTX1049A.pdf 

With minimum FT's around 100-150 MHz, I don't think any of the transistors we've looked at will have any adverse performance issues around 200-400 kHz.


----------



## MrAl (Nov 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I still stand behind my original transistor choice, the 4-amp Zetex ZTX1049A. At an expected collector current of 800mA, it has a good gain of 450, and the lowest saturation voltage.

With minimum FT's around 100-150 MHz, I don't think any of the transistors we've looked at will have any adverse performance issues around 200-400 kHz.*<HR></BLOCKQUOTE>

Oh ok, i like that transistor too 
The only reason i was recommending the
FCX688B transistor was because it was
spec'd with very low base currents as
well as everything else. If you notice
the base current specs on the other 
transistors, they are at least 10ma.
According to the 300 chip data sheet,
you cant get 10ma base drive out of the chip.
The only thing i dont like about the 
688 transistor is the turn off time
of 500ns, which is longer then any other
transistors we have looked at so far for
this app.
This might be all nit picking anyway
though, because if the transistor still has
enough gain down to low base currents then
we wont have a problem anyway  This was
just a precaution in case the transistor
doesnt have enough gain down there.

Good luck with it,
--Al


----------



## MrAl (Nov 1, 2001)

I just took another look at the data sheet
of the ZXSC100 chip, and noticed that
the spec they claim of 80% efficiency
(compared to the ZXSC300 claim of 90%)
isnt that bad, because they are spec'ing
that with an output Schottky and filter
cap like we are using with the 300 chip
anyway 
The 300 chip with Schottky wont be 90%
either, more like 80% also, so now
this means that the 100 chip would be more 
suited for higher current outputs then 
the 300 chip would. The base drive spec
on the 100 chip is higher too.
There is one major drawback to the 100 chip
for the general user though, and that is
that the biggest chip available is S08
package outline, which means it has
4 leads on each side spaced 0.05 inches
apart. This would be harder to deal with
then the 300 chip.

One nice thing about a lot of the Maxim chips
is that they are available in mini dip
packages.

Good luck with your LED circuits,
--Al


----------



## **DONOTDELETE** (Nov 1, 2001)

I really like the elegance of the simple circuit design of the ZXSC300.

By comparison, as you noted, the ZXSC100 would be a pain to work with and the circuit requires a lot more support components, all of which would require careful selection in order to achieve an efficiency comparable to the 300.

Of course, a couple of years from now, the new Zetex ZXSC500 will drive a Luxeon Star directly at 99% efficiency, and all our collective design work will have been for nought






However, I'll have no regrets---I'm having loads of fun working on this circuit with you guys. And I don't even have the parts yet!


----------



## MrAl (Nov 2, 2001)

Yeah i like it too, and it will end up being very compact.

On the other hand, when i was working with the
4 transistor circuit (again) i found a way to 
simplify it greatly. Now it uses two transistors,
one very cheap and very common 8 pin ic, and one
voltage reference diode.
It regulates the output current to almost no
perceptable change with 1.4 to 3.6 volts inputs,
and a wide range of temperatures, and isnt
sensitive to the gain of the transistors.
I should be able to post details in a few days.
It's not as simple as the 300 chip of course,
but its not too complex either.

Here's the simulation results driving
four white LED's:

Vin Iout
1.4v 20ma
2.0v 20ma
3.0v 20ma
3.6v 20ma

at 4 volts i think it was up to 25ma.

I'm glad you like working on this kind of stuff, Jeff
(also on here) has been working with the two transistor
circuit quite a bit.

Well take care and good luck with your LED circuits,
--Al


----------



## Mike (Nov 2, 2001)

MrAl, I'll be curious to find out what happens with this simplified circuit under 1.4 volts.

Good work!


----------



## php_44 (Nov 2, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I really like the elegance of the simple circuit design of the ZXSC300.

By comparison, as you noted, the ZXSC100 would be a pain to work with and the circuit requires a lot more support components, all of which would require careful selection in order to achieve an efficiency comparable to the 300.
*<HR></BLOCKQUOTE>

Actually, although I have some ZXSC300's on the way for 1-5LED circuits, if I had an LS LED I wanted to drive at 300mA+ -- I'd get some ZXSC100's. 



To drive the LS I'd want the schottky diode and capacitor with either the '300 or the '100. That is recommended by Zetex for maximum brightness. If that's a given, using the '100 for a guaranteed 500mA requires only an additional PNP transistor and one resistor. I'd leave fb unconnected and set the current to the LS via the current sense resistor (just like on the '300). As MrAL pointed out, by the time you put the schottky diode and cap on either part for an LS, the efficiency of the '100 and '300 are probably equivalent. With either solution, driving an LS, you'd have to use similar inductors - Ipeak over an amp, low DC resistance, inductance around 22-100uH.



All that said - if the '300 can be made to efficiently drive at 300mA+ - awesome! Just make sure the '300 can keep your switching transistor saturated or you'll waste energy heating up the NPN transistor, rather than lighting your LS.



Can't wait to get my ZXSC300 stuff - looks like Monday...


----------



## **DONOTDELETE** (Nov 2, 2001)

MrAl,

Would your 4-transistor (now 2-transistor) circuit be able to drive an LS at 350mA using 2 AA's?

How much battery current would it require?What kind of efficiency do you think it would get?

Doug


----------



## MrAl (Nov 3, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*MrAl,

Would your 4-transistor (now 2-transistor) circuit be able to drive an LS at 350mA using 2 AA's?

How much battery current would it require?What kind of efficiency do you think it would get?

Doug*<HR></BLOCKQUOTE>

Hi again Doug,

I didnt think at first to do a simulation
with a large output current like that,
but because the circuit is so versatile,
replacing one 2N4401 transistor with
a heavier duty transistor (like Jeff did
with the original 2 transistor Brinkmann
circuit) would get you up to well over
350ma. I'll do that simulation next, i
think that should be interesting, especially
since i hope to purchase an LS and try that
out with it too. Any ideas on a reliable 
source for the LS where you have actually
gotten one from too?
That's one thing nice about using discreets:
if you need more output, beef up the circuit
a little  You dont have to depend on 
a company to produce a certain part with a
certain rating. Of course you have to
put up with a little bigger pc board size :-(
Thats the nature of the beast(s).

As far as efficiency, i'd say about 75% the
way it stands now. I hope to improve that
too though, and i think i can get about
85% with the addition of one more
resistor and one more low value capacitor.

All the parts in this kind of circuit
will be low cost. Also, you can choose
what kind of reference diode you wish to
use: if you want super well regulated
current output with temperature, use a 
LM329DZ, if you dont mind a little change
with temperature, use a run of the mill
2.5 volt zener (like NTE5001). It's up to you and what you want out of the circuit.
I might test it with both just for the 
heck of it to see how well it performs.
As far as input voltage is concerned 
however, it will always be almost exactly
20ma per LED (or whatever you set the 
output too) because part of the circuit
is constructed just for the sole purpose
of measuring the output and correcting it if 
it's not right. It's like haveing a meter
in the circuit all the time, measuring the
output and making corrections as needed.

I found a really nice chip with two op
amps and an included 2.5 volt reference 
diode, but the dang thing is about 
one tenth of an inch wide !! Who the heck
(or how the heck) does a guy solder this
thing????? Any ideas??? 
I think the leads are 1/20 of an inch apart!

--Al


----------



## MrAl (Nov 3, 2001)

Oh your talking about NiCd AA's right?
Im not sure if AA alkalines can handle
that much current.

--Al


----------



## **DONOTDELETE** (Nov 3, 2001)

I'm actually talking two 1600-mAh NiMH AA's.

Yeah, these chips are getting smaller and smaller every minute, which makes experimenting with them more and more difficult.

As far as where to get the Luxeon Stars, there are three places I know of:
http://www.future-active.com --- Complete selection, but some models require large quantity order. Single LS prices as low as $9.45, even cheaper in large quantities. Shipping $7.00 up.
http://shop.store.yahoo.com/flashlight/luxeonstarled.html --- Run by Forum member Gransee. Only Star/O's available in white, green, and amber for $14.00 each. Shipping $5.00 up.
http://www.nwlink.com/~mhannah1 --- Large variety available for $15.00 each. Shipping from $3.50.


----------



## MrAl (Nov 4, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I'm actually talking two 1600-mAh NiMH AA's.
*<HR></BLOCKQUOTE>

Oh ok yes, but i wouldnt bet on alkalines
working very well with an LS with any of
these circuits, although i havent tried any
myself i have read the recommended current
max for an AA alkaline is 250ma, although
you could probably push it. The e squared
line is supposed to handle more pulse current
but i dont have any specific data on that.
For two cells and LS at 350ma i guess i
would have to go with NiCd or NiMH anyway.

Now these LS's put out a fairly nice beam of
light too, with no strange patterns
(like the 'target' pattern that that 
blue-green 10,000 mc LED puts out) ?
I would hope for that price you get a nice
flashlight type, uniform beam?

Thanks for the source info,
--Al


----------



## Mercator (Nov 4, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*
As far as where to get the Luxeon Stars, there are three places I know of:
--------------
http://www.future-active.com --- Complete selection, but some models require large quantity order. Single LS prices as low as $9.45, even cheaper in large quantities. Shipping $7.00 up.
*<HR></BLOCKQUOTE>

*Dugg,*

Where on the "Future-Active.com" site do you find the LS's ?? I've been to that site several times and could never find them. I know several people have mentioned them as a source, but once again, I can't seem to locate a listing. I looked everywhere and even searched using some part numbers.

Also, would you please send me a "PM" (private message) with your regular email address. I'm still waiting for the Z300's to arrive that I mentioned awhile back and my offers still stand.

Mercator


----------



## **DONOTDELETE** (Nov 4, 2001)

Mercator,

Future Active's site search engine works only with part numbers. Enter something like "LXHL-NW98" and you should get a hit. The spec sheet at http://www.luxeon.com/pdfs/Luxeon_star_DS.PDF contains all the various part numbers.

I sent you the Private Message.


----------



## MrAl (Nov 5, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mike:
*MrAl, I'll be curious to find out what happens with this simplified circuit under 1.4 volts.

Good work!



*<HR></BLOCKQUOTE>

Mike sorry i missed you reply earlier,
and thanks for the vote of confidence

As you may know, the 4 transistor circuit i 
presented last month now became the circuit
with 2 transistors and one opamp and one
reference diode(or zener), but there are a 
few standard resistors and a couple standard 
low cost caps also, meaning the parts count
will be a little higher then the Z300
circuit anyway.

On the plus side:

1. it will regulate over a wide temperature range.
2. it uses very common parts(see note below).
3. transistor gains not too important.
4. eventually will have selectable one-cell
or two-cell operation by changing one or
two commonly available resistors.
5. will operate with one LED to 10 LED's
(and possibly more).
6. no SM parts required
7. Still works under 1.2 volts at
somewhat reduced output.

Parts count could be reduced by using 
a special opamp/reference diode combo
ic available from National, although
this is an SM part.

If you build any of these circuits up,
please let us know how you make out.

Good luck with your LED circuits,
--Al


----------



## **DONOTDELETE** (Nov 5, 2001)

Woohoo! My ZXSC300 has arrived from Digi-Key!

Later this evening, I will try soldering it to its SIP board, then the fun can really begin!

Update: The thing is WAY too tiny for an ordinary soldering iron. I guess I just wasn't prepared for how small it actually is! I'm going to drop by Radio Shack tomorrow and look for a needle point iron and some really thin solder.

I found some good tips about soldering SMD's at this web site: http://203.199.69.53:8080/examples/jsp/smd/workingwithsmd.html


----------



## php_44 (Nov 5, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Woohoo! My ZXSC300 has arrived from Digi-Key! Later this evening, I will try soldering it to its SIP board, then the fun can really begin! Update: The thing is WAY too tiny for an ordinary soldering iron. I guess I just wasn't prepared for how small it actually is! I'm going to drop by Radio Shack tomorrow and look for a needle point iron and some really thin solder.
*<HR></BLOCKQUOTE>

I got some ZXSC310's today, along with the transistors and diodes. I also got a demo board (on loan) which I will use to take some measurements and post the results here. The demo board is powering two strings of two LEDs each from 1.5V. I'll have to check the component values used, estimate the current through the LED's, and measure the current from the battery so that we can get a real world efficiency estimate. 

Yes the parts are tiny. Before I got a good soldering iron from the dumpster at work, I made my own. I used to coil 5-6 turns of #12-14 solid copper wire (the stuff they wire your house with) around the rather blunt tip of my 40 Watt iron, and let it extend past the blunt tip a little. I'd then file the tip of the wire to a nice fine point and tin it well. It doesn't work well unless the wire's tip is within 1/4-1/2 inch of the irons tip. In other words if you have five or six turns of wire on the iron's tip, but the wire extends too far - it's gets too cool to solder with. This arrangement makes a really nice SMT arrangement - and it's cheap to make a new tip when the tip gets eaten away after an hour or so. I also put a diode in series with the iron and a switch in parallel with the diode. This made my iron a 20/40 watt unit. I generally warmed it up at 40watts (diode shorted / switch closed), and ran it at 20 watts (diode in series / switch open) I used a 1N4007 (2/$0.99 @RS). Ideally, you could put a lamp dimmer on it. 

Also - get yourself some good fine tipped tweezers. I really can't work well on this SMT stuff without them. Solder wick is handy for those inevitable times when you blob too much solder on the joint and you want to remove some in the least disruptive way.


----------



## **DONOTDELETE** (Nov 5, 2001)

Wow php_44,

Your homemade SMD soldering iron idea really worked!

You can even file the solder itself, saving you from having to buy the really thin stuff, because SMD pads don't hold much solder!

So now I have the 5-pin SIP version of the ZXSC300. I'll wire the rest of the circuit later this evening.


----------



## **DONOTDELETE** (Nov 5, 2001)

Hey, it actually works!

I am driving a cyan Luxeon Star off a single NiMH AA cell.

Unfortunately, it seems I can't be too much help in the quantitative measurement department. I only have an analog multimeter.

If I try to measure the DC current flowing from the battery, the meter's impedance has a very noticeably dimming effect on the LED, so I have no way of accurately measuring it, but I can measure voltages and output current:

Input voltage: 1.30v 1.17v 
Output voltage: 2.80v 2.79v
Output current: 75mA 63mA

The 75mA current appears to be correct, unfortunately---the LED is just as bright with 75mA of pure DC through it.

The circuit is the maximum brightness one, with Rsense = 0.04 ohm. If I try 0.022 ohm
(0.04 ohm & 0.05 ohm in parallel) for Rsense, the circuit shuts off.

I am going to let it run for a few hours and see how it behaves as the battery voltage falls below 1 volt.

We obviously have some work ahead of us if we want to see 350mA through the LED, but I'm still pleased to see the circuit at least operating on a single AA.


----------



## Mercator (Nov 5, 2001)

Wow Guys.... I'm jealous.

Still waiting on my order. From Dugg's first
stab at powering up the Z300 looks like he's on his way to driving his LS on a single cell. Will be interesting to see just how much current you can get out of the IC.

Dugg, What transistor, diode and inductor are you using?

The link to the SMD soldering site will help to releave any apprehensions some folks might have with working with these little components. It's not really as hard as most people think. I started out working with my first SMD's while replacing a bad transistor. Now, that's alittle bit harder than working with a new unpopulated board. 

I've used the technique of wrapping the iron with copper wire. Works alright, but I eventualy broke down and bought the proper iron. I do like the idea of the diode or better yet a lamp dimmer. Actually, I have a dimmer already set up that I use with my dremel and larger die grinder. Will have to try it out on a soldering iron. Maybe I'll ask santa for a soldering station this year.

Good luck to both you guys and keep us posted on the results.

Mercator


----------



## **DONOTDELETE** (Nov 5, 2001)

I'm using a Zetex 1049A transistor (TO-92), a cheap 1N5818 Schottky diode, a 68uH choke, a 68uF electrolytic capacitor, and a 0.04 ohm resistor.

The above combination of components seem to produce the best results:

Vin=1.27v Iin=260mA Pin=326mW
Vout=2.95v Iout=75mA Pout=221mW

Of course, my component selection is quite limited, and we already know of a better diode and inductor.

I was able to get around the meter impedance problem and determine Iin using a 0.05 ohm resistor in series with the battery, and measuring the voltage drop across it.

The above results show an efficiency of only 68%. I hoping the two-cell tests tomorrow will be more optimal.


----------



## MrAl (Nov 5, 2001)

Hi Duggg im happy to hear you got your
parts in. I cant understand just yet
why the circuit might not function
when you decrease Rs to a value
close to what i thought would provide
about 350ma output, unless...
the base drive problem is cropping up
on us. With a smaller resistor,
the output current MUST reach that
upper level peak in order for the 
circuit to switch off at least once
to start the circuit 'oscillating'.
If the base drive can't supply enough 
current to drive that transistor,
the transistor will never be able to turn
on enough to draw that peak I through it
and the coil, and the resistor.
One way to check for this condition is
to measure the input current with the
decreased Rs value (.022) and see what
current it draws even though the circuit 
isnt really oscillating yet.

Of course it could be that the battery cant
supply enough current either.

In any case, thanks for the info.
We havent gotten our parts yet :-( 
so we cant test it yet, but ill be
looking forward to seeing more of your
results on here.

Take care for now,
--Al


----------



## php_44 (Nov 6, 2001)

Here's an initial result from the demo board. It's wired as the high brightness mode with a diode and a cap at the output. Here are the component values:

Inductor: 68uH 0.8ohms
Current sense resistor: 0.27ohms
Transistor: ZTX618
Diode: ZHCS1000

The circuit runs at 190kHz. I made the following table to show the circuit's characteristics as built. It's interesting to see the flat current draw for 2,3,&4 LEDs in series and the effect of having a higher efficiency at two LEDs than any other config. These power levels are not yet interesting to me. I'm sure y'all would agree







*We need MORE POWER!!* 



```

```

I'm embarassed to admit - I blew one LED on the board already. This is the first LED I've ever blown!! The output has a capacitor and I accidently hooked up the LED string to it while it was charged - *PING* one LED blown. Arrggh.


----------



## MrAl (Nov 6, 2001)

Hey thats some very good data there.

We now can be sure we can run a
few LED's from this chip, even if we never
get it up to 350ma. Plus, we have some
low base current transistors on the way.

php_44:
did you try halving the resistor
to try for double the current output?
Then halving it again, etc, to possibly
determine the max current output using
your chosen transistor?

Also, what value output capacitor were
you using with this data set?

Duggg:
can you measure the current input with
the 0.022 ohm resistor even though the
circuit doesnt appear to run normally?

Thanks for posting this interesting data.
--Al


----------



## **DONOTDELETE** (Nov 6, 2001)

php_44, what was your power source for your 1-4 LED experiment?

MrAl, I can't measure the input current with my analog ammeter, because of the dramatic impedance effect. And I can't use the voltage drop across the 0.05-ohm resistor to estimate the current, because I need that resistor in parallel with the 0.04-ohm one in order to make Rsense=0.022 ohm. Any ideas? 

More data points for 1-cell AA test:

Vin=0.86v Iin=50mA Pin=43mW
Vout=2.58v Iout=7mA Pout=18mW eff=42%

Vin=0.82v Iin=32mA Pin=26mW
Vout=2.49v Iout=3.3mA Pout=8mW eff=31%

Once Vin hit 0.8v, output current was nil.

Now, on to the two-cell tests!


----------



## php_44 (Nov 6, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>posted by MrAl & Duggg:
*

php_44:
did you try halving the resistor
to try for double the current output?
Then halving it again, etc, to possibly
determine the max current output using
your chosen transistor?

Also, what value output capacitor were
you using with this data set?

php_44, what was your power source for your 1-4 LED experiment?
*<HR></BLOCKQUOTE>

As I had mentioned - I'll be modifying the demo board to get more current out of it. I'll substitute a simulated LS LED for the small nichias on the board. See 
Simulating Luxeon Voltage and current specs I'll try experiments at 1.5V and 3V input.

I think ultimately, though, the inductor on the demo board is too feeble. I may construct my own circuit with one of my Dale 68uH / 0.1 ohm / 3A+ saturation inductors. The demo board has an inductor with 0.8 ohm resistance. At an amp peak current (to get 300-400mA LED output) this thing is dissipating a watt of heat, wasting a volt, and probably very saturated. The Dale unit I have will be much happier. 

The transistor is rated for 2A peak, but I don't know if the ZXSC300 can drive it hard enough to get there. My calculations say the ZXSC300 will only drive hard enough to get 500-700mA through the coil with this transistor at 3V input - less with 1.5V. If the '300 can push this hard, I might be able to squeeze [email protected] or [email protected] 


As far as my last post--

My power source for my last posting was a brand new alkaline "D" cell - that remained at 1.504V through all the runs. Sorry that detail got dropped from the post!

MrAL-
The output cap on the demo board is not labelled, but according to the documentation it is 2.2uF.


----------



## **DONOTDELETE** (Nov 6, 2001)

Here are some two-cell results.

Power source: 2 NiMH AA cells, 1600mAh each
Rsense: 0.022 ohms
Inductor: 68uH rated at 804mA with 0.145 ohms DCR
Capacitor: 68uF, 16v


Vin=2.70v Iin=320mA Pin=864mW
Vout=3.18v Iout=210mA Pout=668mW eff=77%

Vin=2.53v Iin=320mA Pin=810mW
Vout=3.00v Iout=175mA Pout=525mW eff=65%

Vin=2.42v Iin=330mA Pin=799mW
Vout=2.99v Iout=173mA Pout=517mW eff=65%

Vin=2.28v Iin=330mA Pin=725mW
Vout=2.97v Iout=163mA Pout=484mW eff=64%

Vin=2.10v Iin=335mA Pin=704mW
Vout=2.95v Iout=163mA Pout=481mW eff=68%

Vin=2.00v Iin=320mA Pin=640mW
Vout=2.92v Iout=130mA Pout=378mW eff=59%

Vin=1.90v Iin=305mA Pin=580mW
Vout=2.90v Iout=120mA Pout=348mW eff=60%

Vin then began to fall off very rapidly, and the circuit shut off completely upon reaching 0.7 volts. I was unable to measure the other parameters, it occurred so fast.

Note: As in the one-cell case, using the analog ammeter to measure Iin results in a noticeable output reduction, so its value, and the related efficiency figures, may be in doubt. I truly wish I had a third ultra-low-ohm resistor, with which I could more accurately estimate Iin by measuring the voltage drop across it.


----------



## **DONOTDELETE** (Nov 6, 2001)

Although the ~150mA current figures are less than half of what we are ultimately looking for, I feel the circuit is still doing an amazing job.

Think of what would be the result of simply hooking a cyan LS to two NiMH cells: it would draw less than 25mA!





So I'm pretty happy



that the ZXSC300 is providing 6-8 times the current, and 6-8 times the brightness.

Now, let's see if we can get 14, 12, or even 10


----------



## MrAl (Nov 6, 2001)

Duggg & php:

Thanks for posting the data, it looks
pretty interesting. Now we have some
idea how this thing is working.

Duggg:
when you use one cell and
Rs=.022 ohms, if you cant measure the
input current then can you measure
two voltages across the transistor:
1. base to emitter voltage
2. collector to emitter voltage
These two measurements will tell us
what is going on when the circuit
doesnt appear to start normally.
Also, when you said "Vin began to
fall off rapidly" so you were not
able to make more measurements,
how charged up where the NiMH cells
before you started the test?

Thanks again for the data, and good
luck to you two and anyone else 
working with these circuits!
--Al


----------



## **DONOTDELETE** (Nov 7, 2001)

I've been getting flaky behavior, and I've come to the conclusion that my old breadboard is introducing contact resistance on the order of Rsense, 0.01-0.05 ohm.

I also went out and got two 0.01-ohm resistors this morning, so not only will I be able to refine Rsense more closely, I'll be able to more accurately measure Iin.

Tonight I'll solder most of the components together using a perfboard, find the brightest value for Rsense, and repeat the tests.


----------



## MrAl (Nov 7, 2001)

Oh that sounds great Duggg. Cant wait
to find out how you make out with it.
If you remember, could you measure
the two transistor voltages if at any
time the circuit doesnt start up 
normally?

Thanks for the feedback.

--Al


----------



## **DONOTDELETE** (Nov 7, 2001)

MrAl,

The problem occurs if Rsense is too low.

In that situation, Iin begins to rise sharply, then the transistor apparently stops turning off, and quickly starts to heat up and smell!

So I can't really take those voltage measurements, as I only have one transistor, and I don't want it to melt


----------



## MrAl (Nov 8, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*MrAl,

The problem occurs if Rsense is too low.

In that situation, Iin begins to rise sharply, then the transistor apparently stops turning off, and quickly starts to heat up and smell!

So I can't really take those voltage measurements, as I only have one transistor, and I don't want it to melt



*<HR></BLOCKQUOTE>

Oh ok thats fine Duggg, that's really
all i needed to know to confirm my
suspicions about the transistor not
being able to turn fully on for some
higher iL attemps, unless something more
basic is wrong like the connections or 
something. These circuits need to be
soldered because of the higher currents
running through the connections and
parts mounted in close to each other too
for best results. Using these low value 
resistors, the leads between the chip and
the resistor have to be very short too.
You might want to keep in mind that a one 
inch piece of #32 gauge wire has a resistance
of about 0.014 ohms. This means with
1/2 inch on both sides of the resistor,
a 0.022 resistor looks more like a 0.036 ohm 
resistor. The same lenght of #22 gauge wire
will have one tenth of that resistance,
which would only add about 0.0014 ohms to
the chosen resistor, making it look more
like 0.0234 ohms. It is best to run the lead from the emitter directly to the 
resistor, keeping it very short, then
running a separate lead from that same
terminal on the resistor to the chip,
keeping that very short also.
The other terminal of the resistor (that
connects to ground) should run directly
to the chip ground terminal, with a separate 
lead running from the chip ground terminal
to the power supply minus terminal.
All the leads connected to the resistor 
should be short.
This special attention to wiring detail
in the area of the sense resistor will
aid in getting the circuit to function
optimally.

I'm happy to hear about the data you did
post too, even though we couldnt measure
those voltages.

Thanks to anyone else who posts their results
with these circuits on here too, this stuff
is very informative and very interesting too.

Bye for now,
--Al


----------



## ElektroLumens (Nov 8, 2001)

Hello all,

I haven't been to this forum in quite a while. It is interesting to see all you are doing with power supplies. I have not tried the Zetex IC, but I have had success with a couple of other chips. One is the MAX756 step up ship. It is set at 3.3 volts, and drives the Luxeon just fine at 3.3 volts, even with one AA Alkaline. Another chip I have tested sucessfully on a bread board is the LT1302, which is a variable chip. It also works fine, but I have not put it on a PCB yet, as I have with the MAX756. This are both 8 pin DIP chips, and easy to work with. I make my own inductors. I use the Schottsky diodes recomended, and the capacitors recomended in the schematics. 


I also tested successfully the LT1070 chip, which is a T0220-5 type. It will drive up to 5 amps! Well, It worked until I crossed a few wires on the bread board and french fried the chip.

Walk in the light.


----------



## **DONOTDELETE** (Nov 8, 2001)

Thanks Wayne,

I looked at the MAX756 before ordering the ZXSC300 and rejected it for four reasons:

<UL TYPE=SQUARE><LI>I thought it could only handle 200mA, and we wanted at least 300mA.
<LI>The fixed 3.3-volt output was a concern due to LS forward voltage variances, especially if I wanted to drive an amber LS. And although the similar MAX757 has adjustable output, Digi-Key doesn't carry it.
<LI>The $4.80 cost, compared with $1.05 for the ZXSC300.<LI>The lower efficiencies associated with five-year-old technology.
[/list]

Now that I see it can put out 300mA and my LS can safely handle 3.3 volts, and the efficiency of the ZXSC300 isn't anywhere near 85% in any of my test cases, I may well look into a MAX756 for one of my future LS projects.

I have to admit, I really hate the microscopic size of the ZXSC300


----------



## **DONOTDELETE** (Nov 9, 2001)

All right, with the circuit mostly soldered together, it's much more stable.

I no longer have the weird problem where I couldn't measure Iin using the ammeter without causing a noticeably dimming effect.

However, now I have a problem measuring Rsense. I'm using a 0.01-ohm resistor with a 1% tolerance, hooked to about 8 inches of #24 tinned copper wire for ease of experimentation. Add to that a Surfboard and a DIP socket, and Rsense may well be on the order of 0.03 ohms.

Still, with this setup, I got 185-205mA for over 3.5 hours off of two 1600mAh AA's, and after 4 hours it was still providing over 165mA, although the batteries quickly gave up the ghost after about 4.5 hours.

Efficiency was around 65%, so I'm looking forward to testing out a superior diode and inductor, and seeing how your experiments go using SMD components, especially with the other transistors.

But I'm very encouraged with the results so far.

P.S. As php_44 pointed out, beware the capacitor! If you disconnect the LED for any reason while the circuit is going, the capacitor quickly charges to over 30 volts. Although a 16- or even a 10-volt cap may work in the final circuit, for experimentation you might consider one rated at 35 volts or even 50. And whatever you do, discharge it before hooking up the LED! I forgot to do this once. The cyan LS briefly flashed purple and I thought for sure it got fried. Fortunately, it seemed to survive, but I doubt it could keep doing so.


----------



## **DONOTDELETE** (Nov 9, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by php_44:
*Here's an initial result from the demo board. It's wired as the high brightness mode with a diode and a cap at the output. Here are the component values:

Inductor: 68uH 0.8ohms
Current sense resistor: 0.27ohms
Transistor: ZTX618
Diode: ZHCS1000

The circuit runs at 190kHz. I made the following table to show the circuit's characteristics as built. It's interesting to see the flat current draw for 2,3,&4 LEDs in series and the effect of having a higher efficiency at two LEDs than any other config. These power levels are not yet interesting to me. I'm sure y'all would agree






We need MORE POWER!! 




Code:





I'm embarassed to admit - I blew one LED on the board already. This is the first LED I've ever blown!! The output has a capacitor and I accidently hooked up the LED string to it while it was charged - PING one LED blown. Arrggh.*<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Nov 9, 2001)

Well, just on a whim I decided to solder the 0.01-ohm resistor directly to the perfboard.

I hooked up the milliammeter and was shocked to see over 420mA going through the LS!



I had to hook a 2-ohm resistor in series to get the current down to a safe level. That just goes to prove how sensitive the circuit is to long connections. Hard to believe that eliminating just a few inches of hookup wire would have such dramatic results.

So that's the good news---we can get our 350mA out of the ZXSC300, probably with Rsense around 0.015 ohm, just as MrAl calculated it.

The bad news is that the battery is pulling 840mA, and that means only 60% efficiency.





But, my diode and inductor choices weren't optimal. Hopefully the new ones will perform much better.

P.S. At these higher currents, the circuit seems happier with a 100uF or even a 220uF capacitor.


----------



## MrAl (Nov 9, 2001)

Duggg:

Thanks for the info.
Hopefully i'll be able to add to the
info pool soon too
We havent heard anything else from php
for a while now, wonder what he's up too?

We should be able to get about 80% out of this circuit.

Try putting a large cap in parallel with the input (200uf), then
measuring the current with the meter between the battery +
terminal and the cap, and measure the input voltage 
across the cap.
You have to realize that putting a 2 ohm resistor in series
with anything in this circuit will cut eff by as much as 20%.
A 1 ohm resistor will cut eff by about 10%.
If your inductor has 0.8 ohms dc resistance, count on losing
about 8% there. The Schottky loses about 11%.
The transistor loses between about 6 and 10%.
This means considering only transistor and Schottky
losses, we would have 79% eff.
Adding your inductor dc resistance brings it down to
71%, so you should see at least 70% with your setup.

Since your Rs resistor is too low, try trimming it in
with a short piece of copper wire in series instead of adding
a 2 ohm series resistor. Then check eff again.

Also, what battery voltage were you useing,
1 cell or two cells?

--Al


----------



## **DONOTDELETE** (Nov 9, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>

*Try putting a large cap in parallel with the input (200uf), then measuring the current with the meter between the battery + terminal and the cap, and measure the input voltage across the cap.*

The voltage across the capacitor was 2.3 volts. The battery current with the capacitor in place was 700mA. Without it, it was 650mA.

*You have to realize that putting a 2 ohm resistor in series with anything in this circuit will cut eff by as much as 20%.

Since your Rs resistor is too low, try trimming it in with a short piece of copper wire in series instead of adding a 2 ohm series resistor. Then check eff again.*

I was already ahead of you on that. I adjusted the length of wire so that the starting current (with completely fresh NiMH's) was 360mA. The current fell to 350mA within a few minutes, and by 30 minutes, it was at 340mA.

Efficiency is now around 65%.

* Also, what battery voltage were you useing, 1 cell or two cells?*

Two cells.

<HR></BLOCKQUOTE>

I'll do some more experiments this evening and report my results.


----------



## ElektroLumens (Nov 9, 2001)

Duggg,

The MAX756 does work, but I do not like the fixed voltage. I wanted the MAX757, but as you say, I could not get ahold of one, unless I bought a huge quantity.

This chip does work fine, however, and the light from the Luxeon is nice and bright. (Seems to be about the same as the 12 LED flashlight I made.) I found that what seems to be a good voltage for the Luxeon is 3.4 volts. Any higher and the heat produced seems to be too much. I am using a very large CPU heatsink, and it barely gets warm, at 3.4 volts, and is very bright. So I am looking at Linear Technologies LT1302. It has a 2 amp rating. It has a drop out at 2 volts though, so I am not too sure. However, it is adjustable, and is a 8 pin DIP IC, so it is easy to work with and design the PCB board, which I have done, and am ready to mount the components. The circuitry worked fine on the bread board. The board I am making is 1" X 2".

I have also designed and tested a LT1070 chip. It might be usefull for multiple Lux's. It can handle up to 5 amps. It's droppout is 3 volts, and can drive up to 50 volts or somewhere areound there. It also seems promising. It is very easy to work with as it is a TO220-5 chip, but it is expensive, going for $7.00 each (and I burned the last one up.)

later, Wayne
I think the LT1302 will work fine, if 'D' cells are used, to get more use of the batteries before reaching 2 volts. The maximum voltage of this chip is 5 volts.

I like the MAX756 because it has such a low droppout, down to .8 volts, which gives a good use of batteries. The Max 757 would be great, if I could get one.

I might conjoin the MAX756 and the LT1302, thus getting the low drop out, and getting the variable output of the LT1302. Not sure of the efficiency of doing this, but it probably would work okay.


----------



## **DONOTDELETE** (Nov 9, 2001)

Well, I'm pretty happy.

I was able to get above 300mA for two hours off of two NiMH AA's, which is good enough for my purposes, although the higher the efficiency, the longer the run time, which is always a good thing. At 65%, there's a lot of room for improvement!

One thing I noticed is that the no single component got particularly hot during the 350mA test. At an ambient temperature of 80F, the Schottky diode heated to 95F, the inductor was at 96F, and the transistor was at 97F. With more efficient components, it should operate even cooler.


----------



## **DONOTDELETE** (Nov 10, 2001)

Capacitor selection seems to be quite important.

Should we choose a WVDC based on what I measured as the voltage without the LED (about 30 volts), or one based on the voltage across the LED (no more than 4 volts)?

Should we choose one with a low ESR, like an expensive tantalum or solid aluminum, or go with a cheap electrolytic?

Testing with electrolytics, I got the best result with a 220uF rated at 35 WVDC, although a 100/25 and even a 68/16 gave good performances.

So the question is, would a much smaller tantalum produce the same result? Any suggestions on good value(s) to buy and test? I was just allocated a $3 tantalum test budget


----------



## MrAl (Nov 10, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Capacitor selection seems to be quite important.

Should we choose a WVDC based on what I measured as the voltage without the LED (about 30 volts), or one based on the voltage across the LED (no more than 4 volts)?

Should we choose one with a low ESR, like an expensive tantalum or solid aluminum, or go with a cheap electrolytic?

Testing with electrolytics, I got the best result with a 220uF rated at 35 WVDC, although a 100/25 and even a 68/16 gave good performances.

So the question is, would a much smaller tantalum produce the same result? Any suggestions on good value(s) to buy and test? I was just allocated a $3 tantalum test budget



*<HR></BLOCKQUOTE>

The output voltage will never be higher then
5vdc, so a 10v rating should be fine.
It's very important that the parts be
soldered to insure the connections
stay together while the circuit is running.

The choice between tant or electrolytic
usually only means a difference in ripple
output, which we dont have to worry about
directly in this app. I have seen
some electro's with ESR up as high as
3 ohms though, so it really depends on
the exact cap you are using. Low ESR
(like 0.1 ohms) electrolytic caps should
be just fine for what we are doing here.
The effect of the series resistance is to
allow small pulses to appear riding on
the dc output signal.
The lower the ESR the better, but 0.1 ohm is 
going to be fine.
If you only have a few caps available, it
would be worth it to try them all. If you
see an efficiency change, note the result
here if possible. One thing to be aware of
though: if the ESR is really high, the max
pulse current throught the LED could be
much higher then the average current.

To test for this, connect a 10k resistor in
series with a 0.1uf disc cap to the output
with the other side of the cap to ground,
and measure the dc voltage across the 0.1uf
cap with a 10 megohm input digital voltmeter
and multiply this reading by 1.01, and
then record the result. This will show
the average output voltage.
Then turn off and take another 1 amp Schottky
in series with another 0.1uf cap with the
cathode connected to the cap and the other
side of the cap to ground and the Schottky
anode connected to the output,
then turn the circuit back on.
Now measure the dc voltage across the 2nd
0.1uf cap with a 10 megohm input digital
meter and add exactly 0.150 volts,
then record the result.
This will approximate the peak voltage
appearing at the output.
Now compare the peak reading
obtained with the extra Schottky and cap to
the reading obtained with the 10k resistor
and cap and note the increase in voltage.
Subtract the peak from the average output
(obtained with 10k and cap) and record the
results obtained with different size and
types of capacitors. The one that gives
the lowest peak minus average will be the one
that works the best overall.

If you have both series networks discribed 
above hooked up at the same time, you can simply
measure the voltage difference between the
two caps to get the peak minus average
difference voltage. Hook the minus lead to
the average network cap (10k+cap) and the
positive lead to the Schottky network cap.
This will allow you to measure the 
difference without doing any calculations
for comparative purposes, but if you wish
to know the real difference you still have
to add 0.150 volts for the Schottky 
network reading and subtract about 1% more.
You can then substitute various caps and
note the results on the meter. You really
need a high input impedance 10M input 
meter though, cant use an analog one.

If you dont have a 10M ohm meter let me know.
In case you dont have any extra Schottky's 
lying around, you might use a 1N4148 diode,
but then you have to add 0.350 volts
instead of 0.150 volts. For comparative
purposes, always use the same diode and
then you dont really have to subtract anything
because the cap that gives the lowest 
reading will work the best. If you use
jumper leads keep them short and make sure
they clamp on making good contact, and
use the same leads for all the tests.
As far as comparing the different types of
caps, you should compare units with the
same capacitances.

As far as ordering new caps, a cap with 
an ESR around 0.1 ohms should work fine.
There are plenty of them for low cost 
at DigiKey.

Note that the above quantitative results 
will vary at output voltages other then
about 3.0 to 4.5 volts, but the comparative
results should work at voltages down
to maybe 1 volt, as long as you dont
compare results of circuits with different 
output voltages.

Good luck with it,
Al


----------



## **DONOTDELETE** (Nov 10, 2001)

Hi MrAl,

I don't have a digital meter, so I wasn't able to conduct the experiment you recommended.


However, here are my electrolytic capacitor results:


```

```

It's unclear which the circuit seems to like more: a low ESR, or a high capacitance.

The original circuit spec calls for a 2.2uF ceramic. Scaling it by 5 in proportion to the extra current needs of our circuit, a 10uF, 10v ceramic has an ESR of 0.01 ohm. By comparison, a 10uf, 10v tantalum has a typical ESR of 1.7 ohms, much higher than I would have expected.

Is the ceramic worth looking into, or are we happy using large electrolytics?


----------



## MrAl (Nov 11, 2001)

It looks to me like 100uf with max ESR=0.1 ohms should work fine.
I wouldnt go lower then 47uf under any 
circumstances.
Since the ESR and the capacitance play a
part in the output ripple, and we do need
to be mildly concerned with the ripple,
these values seem good enough.
If the output ripple goes too high,
so does the peak current, which could easily
exceed 500ma for a short time period.
Of course we arnt designing a super
low ripple power supply here though

Since i was told that the max spec on
and LS was 500ma, i wouldnt think anyone
would want to go higher than that for any
amount of time.
With the new model i made for the LS, i have
found that when operating at about 3.5 volts
and 350ma, if the voltage rises 0.2 volts
for any reason the LS current exceeds 500ma.
With too much ESR or too little capacitance
this can occur, thats why im saying 100uf
and 0.1 ohms or less.

Right now the only data i have to go by
is what you guys related to me on the LS,
because i dont have one yet.

If you want to take some current measurements at
3.3v, 3.4v, 3.5v, 3.6v, and 3.7 volts across
the LS that would help too. You have to
do the 3.7v measurment fast though, as the 
predicted current could be 520ma or so.
If you want to limit the test to 500ma,
then measure the current and stop at
the highest value of 500ma, then measure
the voltage across the LS at that point.
Dont take too long with that measurement though either

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 11, 2001)

With an analog meter I have no way of measuring peak values, only average values.

The LS spec says the average current cannot exceed 350mA. So I adjusted Rsense so that with freshly charged NiMH's, the meter reports 350mA.

At that current, the voltage across the LED is 3.18 volts.

If I supercharge the NiMH's, I can get get 370mA at 3.21 volts before it falls to 350mA after six minutes or so.

Regarding capacitor choice, would you still select a 10-volt version, given that the data suggests the higher the WVDC, the less the ESR and the higher the output current?


----------



## MrAl (Nov 11, 2001)

Hi there again Duggg,

Thanks much for the new data.

How many ohms per volt is your voltmeter?
Do you have any FET's laying around?

When i said 10v, i meant 10v min, but you 
might get away with even a six volt unit.
When selecting a cap, it should meet all
three of these requirements:
1. 50uf or better, prefer 100uf
2. 0.1 ohm esr or less
3. 6v or more, prefer 10v or more

If any of these requirements are not met,
there could be a problem. If you cant 
find the required esr in a 10v unit, then
look at 15v, 20v, or whatever it takes.

This capacitor selection turns out to be
much more critical then with the single
white LED. By comparison, the single
white LED circuit can handle a wider
range of cap and esr values.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 11, 2001)

My meter's sensitivity is 25,000 ohms/volt, double that measuring certain ranges.

No FETs laying around.

The Panasonic FC series of electrolytics have especially low impedance. The following all have an ESR around 0.1 ohm and are all the same physical size:

16 volt: 220uF, 270uF, 330uF
25 volt: 180uF, 220uF
35 volt: 100uF, 120uF, 150uF

My personal pick would be 150uF/35v.


----------



## MrAl (Nov 12, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*My meter's sensitivity is 25,000 ohms/volt, double that measuring certain ranges.

No FETs laying around.

The Panasonic FC series of electrolytics have especially low impedance. The following all have an ESR around 0.1 ohm and are all the same physical size:

16 volt: 220uF, 270uF, 330uF
25 volt: 180uF, 220uF
35 volt: 100uF, 120uF, 150uF

My personal pick would be 150uF/35v.*<HR></BLOCKQUOTE>


Duggg:
It looks like you can still measure the
peak if you want too with the Schottky
and 0.1uf cap, but you have to add
0.15 volts to the reading you get on the
meter. This means if you get a reading
of 2.85 volts, add 0.15 and you get 3.00v peak.
If you use a 1N4148 the accuracy probably
isnt as good, but you add 0.575v to the 
meter reading. So if you read 2.425v on 
the meter, adding 0.575 brings it up
to 3.00v. 
Note this is for a diode temperature of
around 25 degrees C only.

Note also in my original post(which i have now
edited, that i stated incorrectly that you
should SUBTRACT 0.15 volts, but you really
have to ADD that voltage to correct for
the diode drop (as shown above). The 
Schottky drops about 0.15 volts while the
1N4148 drops about 0.575 with a load of
about 75k and a triangle wave input.
These corrections apply with a 25k ohms/volt
meter.

To get a decent average reading, you can
use a 1k resistor in series with a 1uf cap
(instead of 10k and 0.1uf) and measure the
voltage across the cap, then multiply that
reading by 1.0133 to get the average 
voltage. This makes up for the drop caused
by the meter internal resistance at about
3 volts. For other voltages, multiply by
(v*25+1)/(v*25) using this 1k series resistor.

Good luck with it, and let us know if you
do any peak/average measurements ok? 

Take care for now,
Al


----------



## MrAl (Nov 14, 2001)

Is anyone else still working with this
circuit? I wont have any parts for a 
little while yet to test this circuit
out myself.

--Al


----------



## **DONOTDELETE** (Nov 15, 2001)

Sorry I have been out of the loop for a little while. I've been training for a bike race coming up this weekend, and I too am awaiting some new parts to test.

In the mean time, how about let's discuss individual components, and how to choose them to provide the greatest circuit efficiency.

In the past we've just said "this part's better" without really explaining why, so let's start explaining why.

1. Capacitor. My experimentation revealed that the bigger the capacitor, the higher the Iled. We attempted to justify this through the fact that a 220uF, 25v electrolytic has an ESR around 0.1 ohm, and MrAl declared that an ESR of 0.1 ohm and anything above 100uF should do fine.

However, the original circuit spec calls for a 2.2uF ceramic capacitor with an ESR of 0.001 ohm, and I'm not yet convinced that the Zetex circuit designer is an idiot.

Scaling the value for the increased current of our application, I would think a 10uF ceramic would be worth looking into as well, especially since they're comparable in cost.

Is a 220uF electrolytic the same as a 10uF ceramic? Why or why not?

We talked about ESR, but what about impedance? Isn't the capacitor behaving like a resistor at 200kHz, wasting energy that could be going to the LED?

2. Schottky Diode. We want a diode that can handle Ipeak. With Rsense=0.015 ohm, Ipeak is 1267mA. Diodes have voltage drops, making them act as resistors, with the power wasted being V*I. Moreover, V rises as I does. So the big question is, what current do you use, Ipeak or Iled (340mA)? Personally, I would average them, getting 804mA.

At that current, the Zetex ZHCS2000 has a typical voltage drop of 0.32 volts, implying the power wasted is 257mW. That sounds huge to me, considering the battery is only putting out 1625mW (2.5 volts at 650mA).

Thus the argument for a diode with a lower forward voltage drop. The International Rectifier 95SQ015's drop at 804mA is 0.23 volts, for a power of 185mW, saving 72mW. Using it would increase efficiency by 4.4% (72/1625).

However, the 95SQ016 costs $1.59 more than the Zetex diode, it's not SMD, and it's a lot bigger than the ZHCS2000. Is it worth it?

3. Inductor. Inductors have DC resistance and a specified maximum current. The question is, do we use Ipeak for the max current, or Iavg? The answer makes a huge difference with regard to physical size, and also to DC resistance, since big inductors tend to have lower resistance.

Let's compare the gigantic 68uF API Delevan DN4510, which is rated at 3.35 amps and 0.059 ohms, to the SMD JW Miller M9711, rated at 1.4 amps and 0.200 ohms.

At 804mA, the DN4510 is wasting 38mW. The M9711 is wasting 129mW. The DN4510 saves 91mW and would increase efficiency by 5.6%, but is its large size worth it?

4. The ZXSC300. Zetex says it draws 2-4 mA. At 2.5 volts, that's about 8mW.

5. Rsense. It turns off at 19mV, implying its average voltage is 9.5mV. Power is therefore a negligible 6mW.

6. Transistor. I'm sorry to admit that my experience with transistors is very limited, so I really have no idea about its efficiency considerations, especially at 200 kHz. However, Zetex recommends one with high gain and low VCE(sat).

Rather than just trying every transistor that seems to fit these requirements, it might be nice to come with some formulas to zero in on which one(s) would be especially good for our application.


Please feel free to praise or criticize any of the efficiency considerations I have noted!


My Power Loss Summary:

1. 220uF Capacitor: impedance of 0.15 ohm with current of 464mA (804-340) = 32mW.

2. Cheap 1N5818 Diode: drop of 0.45 volts



at 804mA = 362mW. Way looking forward to testing better diode!

3. Inductor: 0.145 ohm at 804mA = 94mW.

4. ZXSC300: 8mW.

5. Rsense: 6mW.

6. Transistor: who knows, but it can be deduced by taking input power of 1625mW, subtracting output power of 1003mW, and subtracting 1-5 above, leaving 120mW.


----------



## MrAl (Nov 16, 2001)

We find that most of the efficiencies can be estimated by
taking the ratio of the voltage drop of the device to either
the input voltage or the output voltage.
The eff loss we get by doing some simple calculations is the 
major influence on our choice of components.

In other words either:
1. Vd/(Vd+Vin) or
2. Vd/(Vd+Vout)
where
Vd is the device voltage drop we are looking at, such as the diode or transistor.
This is a simple way to estimate the efficiency loss from the individual
circuit elements.

1. Capacitor
Not sure where you got the factor of '5' from. It looks to me
that if you were going to scale it, you would scale it by a
factor of 350/20, or 17.5, because the original design was for
20ma, and the new design is for 350ma. If we multiply 2.2uf
times 17.5 we get 38.5uf for the new design, but we also have
to take into account the fact that the LS is more sensitive to
output ripple then the single white 20ma LED is, so in order 
to adjust for that, we take the ratio of the max current of the
single white LED to its nominal current, and then take the ratio
of the max current of the LS to its nominal current, then take
the ratio of the two ratios, and we get 3.5 . Multiplying
38uf times 3.5 we then get about 135uf. This i would think would
be a more reasonable scaling from the reference design.
You might want to keep in mind that they might also have
been going for an optimum eff design, regardless of any other
factors.

2. Schottky Diode
The best Schottky is the one with the lowest voltage drop at the
peak inductor current.
Estimate the efficiency loss using equ(2) above:
EffLoss=(Vd)/(Vd+Vout).
Example:
Vd=0.4 volts
Vout=3.5 volts
so,
0.4/(0.4+3.5)=0.103, or 10.3 percent loss.

3. Inductor
Here, the one with the lowest series resistance will be the most efficient,
as long as it doesnt saturate with the peak current.
You can examine the efficiency losses with min current and max current, or
just assume 1 amp to compare inductors.
Example:
Inductor #1 has 0.1 ohms series resistance, what is the eff loss
at 1 amp? How does it compare to an inductor with 0.2 ohms series resistance?
Again, we calculate the voltage drop first, then use either equ(1) or
equ(2) above:
1 amp times 0.1 ohms = 0.1 volts = Vd for the inductor, so now 
we use equ(1) for the transistor on time:
Vd/(Vd+Vin)=0.1/(0.1+2.5)=0.0385, or 3.85 percent eff loss for this inductor
during the on time.
then we use equ(2) for the transistor off time:
Vd/(Vd+Vout)=0.1/(0.1+3.5)=0.0278, or 2.78 percent eff loss for this inductor
during the off time.
Now we add the losses during on and off times and divide by 2:
(3.85+2.78)/2=3.31 percent loss assuming 50% duty cycle.

Now lets do the 0.2 ohm inductor:
1 amp times 0.2 ohms = 0.2 volts = Vd for this inductor, so now
Vd/(Vd+Vin)=0.2/(0.2+2.5)= 0.0741, or 7.41 percent eff loss during on time.
Now for the off time:
Vd/(Vd+Vout)=0.2/(0.2+3.5)=0.0541, or 5.41 percent eff loss for this inductor
during the off time.
(7.41+5.41)/2=6.41 percent loss assuming 50% duty cycle.

Comparing the two inductors, we can see that the one with half the 
series resistance has about half the loss of the higher resistance
inductor. This should be true regardless of the duty cycle or
the peak current.

4. The chip 
Since this doesnt consume much power, and there isnt much we can do
about it anyway, we live with whatever we get here 

5. Rsense
Dito as with the chip  The sense resistor has to be set according
to output current, so we have no choice here.

6. Transistor
You first have to estimate the saturation voltage, then compare it
to the input voltage using equ(1). You can get the value of Vsat
from the Zetex site data sheet for your prospective transistor.
The one problem is that you have to be sure you have enough
base drive to get the transistor into Vsat in the first place.
At low input volts, this may be impossible with some transistors.
Lets assume the transistor goes into Vsat, and Vsat=0.2 volts,
then it's simply a matter of using equ(1):
Vd/(Vd+Vin)=0.2/(0.2+2.5)=0.2/(0.2+2.5)= 0.0741, or 7.41 percent eff loss during on time.
Since the transistor is off during the off time, its not consuming energy, and
we also assume the rise and fall times are very fast, so that during the transition
periods between on and off we dont use much power.

SUMMARY

Looking at the above estimations for eff of the individual devices, we 
notice that we can always use one of two equations of the form:
EffLoss=a/(a+b)
where a is almost always less then one tenth of b.
This fact leads to another simplification in order to quickly 
approximate the efficiencies of the various devices, and that is:
EffLoss=a/(a+b) =~a/b (=~ means approx equal to)
In other words, 
equ(1) can be simplified with a good enough accuracy by:
1a. vd/Vin
and equ(2) can also be simplifed:
2a. vd/Vout
So to get a feel for the loss in eff due to a certain device in our
circuit, we can just take the ratio of the voltage drop of the device
to either the input or output voltage, and get a good idea of what
we are dealing with. Of course which equ you use depends on the element
in the circuit and whether the transistor is on or off.
To make a table of which equations to use:

```

```

Note that when you use both equations,
divide the result by 2 to find the
total loss. When the device calls for
using only one equation, dont divide by 2.


COMPONENT SELECTION

In order to decide what component would be better then another, you have
to weigh the cost and size into the decision. For any given component, 
you almost always go for the lowest voltage drop, but if the component
you end up with is too costly or too big to fit into your flashlight
case (or whatever) then you have to go to a more lossy device and
consider how it will effect battery life.


Duggg:
By the way, perhaps some praise is in order, because for someone
who hasnt worked much with transistors you did a pretty good job
of testing out the Zetex 300 chip already.

Hope this aides somehow to your LED circuit understanding.

Good luck with it,
Al


----------



## **DONOTDELETE** (Nov 18, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Not sure where you got the factor of '5' from.*

I simply divided the original value of Rsense by the value we'll likely be using.

Last week it was 0.015 ohm, but this week it's looking closer to 0.02 ohm, especially when we go SMD with its lower intercomponent resistance.

Ipeak is inversely proportional to Rsense, so I still feel a factor of five is reasonable, and a 10uF ceramic capacitor is worth the small cost to investigate, especially considering it would have virtually zero ESR & impedance loss in comparison with a 100uF electrolytic.

*2. Schottky Diode 10.3 percent loss.

3. Inductor 6.63 percent loss.

6. Transistor 7.41 percent loss.*

Yipes, we're already down to only 76% max efficiency, no matter what components we select.

This irritates me, since the manufacturer claims 87% efficiency for the maximum brightness circuit.

I attribute the lower efficiency to the higher currents we want, since most losses are proportional to the square of the current (I^2R).

Thanks for explaining how to determine the transistor loss. 

*Duggg: By the way, perhaps some praise is in order, because for someone who hasnt worked much with transistors you did a pretty good job of testing out the Zetex 300 chip already.*

Thanks very much. I really appreciate all the effort you and Mercator and others have taken in getting a good circuit going here.
<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Nov 18, 2001)

Well, some new non-SMD components arrived on Friday and I built Board Number Two using a DN4510 inductor and that expensive 95SQ diode with the super-low voltage drop.

These components would be superior to any SMD component, but the superiority comes at a cost: they are GIGANTIC! The diode is the size of a 3-watt resistor and the inductor is four times its size. Add the 220uF, 25v electrolytic capacitor, and forget about putting the circuit into any reasonably sized flashlight.

The good news is that MrAl was right on in his prediction: 76% efficiency. The bad news is that I seriously doubt we'll do as well using SMD.

The good news is that we may be able to build a circuit board half the size of the popular LM2621 board, which still might be worthwhile, especially if the LM2621 board has a comparable efficiency driving an LS.


----------



## papasan (Nov 18, 2001)

just wanted to drop you guys a line and give you some moral support...

i just ordered a lambertian amber ls with the optics and i plan on putting it into my 2aa-mag if it will fit...i was also hoping to put a small cv-cc (constant volatage, constant current) in there to keep it bright to the bitter end...i appreciate what you guys are trying to do, but i'm not sure how to help you out.

also, i wonder how effecient peter's arc-ls curcuit is...perhaps 80% is setting a new bar...

anyways, if there's anything you can think of that i could do to help...i do have a small bread/test board, a fluke, and a couple local surplus stores; i would just need some direction as far as components and a 300 (or whatever looks best at the time, the LM2621 looks okay, but a higher minV and alot bigger)...

keep up the good work...


----------



## MrAl (Nov 19, 2001)

Duggg:

Doesnt using a lower R inductor raise your efficiency? You should
see better results with a very low R inductor like 0.01 ohms.
What is the series R of the inductor you are using in board #2?
Also, you might want to consider winding your own inductor. This
is something i will be trying myself too, so i can make a very
very low R inductor for very low cost, and size shouldnt be too
much bigger then about a stack of 5 US pennies.

The diode will always consume power, there's no way around that
other then going to syncronous rectification, which would require
too many extra components for our purposes here.
If the bigger diode drops 0.1 volt less then the smaller one,
it only saves about 2.8 percent on efficiency (0.1/3.5 as per equ #2).
You will have to judge whether or not your circuit needs that
extra eff or not as well as the size factor.

I do have to caution you on lowering the capacitance too low,
the simulations showed very low values of output capacitance
would give rise to higher peak currents then the LS is rated for.
I think the lowest i found to be about 32uf, but the higher values
offer more of a safety margin for the LS.
You may wish to try that peak measurement i
was talking about in an earlier post too.


One thing i dont have is efficiency ratings for the LS. That is,
a graph of current vs relative efficiency for the LS. Anyone have
this info or know where to get it?


Hi there papasan:

We are using the Zetex 300 chip because it looked like it could
function with a very low parts count. There are some drawbacks,
such as what transistor you can use with it, and selection
of the current sense resistor isnt that easy because the 
variation of parameters of the chip itself may make one
value work in one circuit while another value works in
the next circuit. Since there are ways around these
problems, we are still trying it, and getting some
decent results. I'm still waiting for my parts though :-(
There was someone else working on this circuit also, "php_" something,
but we havent heard from him in a while.
If you want to build a circuit up let us know. We are all building up different
versions and posting results pretty much

Good luck with all your LED circuits,
--Al


----------



## **DONOTDELETE** (Nov 19, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Duggg: Doesnt using a lower R inductor raise your efficiency? You should see better results with a very low R inductor like 0.01 ohms. What is the series R of the inductor you are using in board #2?*

Its rated DCR is 0.059 ohm, which is much lower than any SMD 68uH inductor.

However, I happened to put a 100uH inductor in parallel with it, and noticed no output change whatsoever, which may imply that a lower inductance may work as well.

However, you would have to go down to something like 1.5uH to get a DCR of 0.01 ohm in an SMD version.

*Also, you might want to consider winding your own inductor. This is something i will be trying myself too, so i can make a very
very low R inductor for very low cost, and size shouldnt be too much bigger then about a stack of 5 US pennies.*

Sounds like a plan! Let us know how that goes. Will it be an air core, or ferrite?

*I do have to caution you on lowering the capacitance too low, the simulations showed very low values of output capacitance would give rise to higher peak currents then the LS is rated for. I think the lowest i found to be about 32uf, but the higher values
offer more of a safety margin for the LS.*

Ahh yes, I forgot about the simulations you ran. However, you keep dodging my concern about electrolytic capacitor impedance---do you feel it's not a factor at 200kHz?

*You may wish to try that peak measurement i was talking about in an earlier post too.*

Sorry I haven't done that yet. It's hard to do when the circuit isn't on a breadboard. And I'm a bit leery about its accuracy, since not all Schottky diodes share the same voltage drop, and the actual voltage drop is dependent on the current, so we have kind of a Heisenberg thing going on.

<HR></BLOCKQUOTE>

_It is with profound sadness



that I must report the untimely death of Cyan Luxeon Star #1, who succumbed suddenly to a 220uF capacitor discharge while I was distracted during one of measurements today.

Although we will miss CLS1, his successor is on the way and hopefully should arrive later this week.



_


----------



## **DONOTDELETE** (Nov 19, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*just wanted to drop you guys a line and give you some moral support...*

Thanks, it's good to hear more than 3 or 4 people are reading this thread =)

*i just ordered a lambertian amber ls with the optics and i plan on putting it into my 2aa-mag if it will fit...i was also hoping to put a small cv-cc (constant volatage, constant current) in there to keep it bright to the bitter end...i appreciate what you guys are trying to do, but i'm not sure how to help you out.*

I also have an amber Lambertian and a 2AA MagLite. The LS's optics are larger than the head of the mag, and I'm not sure where you'd put the CVCC circuit. It would have to be AWFULLY small.

The good news is that the amber LS is more efficient than the cyan/white, and Circuit Board #2 is currently driving the amber one at 375mA with 83% efficiency.

Our ZXSC300 experiments have been geared toward white LS's, which typically require more than 3 volts.

*also, i wonder how effecient peter's arc-ls curcuit is...perhaps 80% is setting a new bar...*

I would love to hear some actual measured efficiency results of various solutions---esp. battery current measurements. In another thread, someone was reporting 85%, but I doubt that was driving an LS at 350mA, as efficiency generally drops at high currents, due to I^2R losses.

*anyways, if there's anything you can think of that i could do to help...i do have a small bread/test board, a fluke, and a couple local surplus stores; i would just need some direction as far as components and a 300 (or whatever looks best at the time, the LM2621 looks okay, but a higher minV and alot bigger)... keep up the good work...*

Thanks Papasan, your comments are help enough for me!
<HR></BLOCKQUOTE>


----------



## ElektroLumens (Nov 19, 2001)

Duggg,

I have a question as to how you measure the efficiency? 

Regarding winding inductors. I have done this with ferrite toroids, and this has worked for me. I also have just wound some wire around a 1/4" rod, and removed the rod, and this air inductor also is working for me. I have not as yet measured the inductance, as I have not assembled the inductance tester kit I have. I found a website explaining how to wind inductors and compute the inductance. However, it's not extremely accurate I'm sure. But the proof is in the pudding, it works, and saved me the expense of buying inductors.

I requested a few sample MAX757 chips from MAXXIM, and to my suprise, they arrived in the mail today. So, I'll be making a board with this chip real soon. It is adjustable, and that's cool. The MAX756 is only 3.3 or 5 volts. I have designed a PCB board for this chip that is 1" diameter, to fit inside a flashlight head easier.


----------



## papasan (Nov 19, 2001)

glad you guys are still going strong =)...

peter has said a couple times that the ls in arc-ls is _under_driven, so perhaps that will give him 85% (if the ls follows traditional leds so far as current vs. efficiency)...

from the arc-ls pictures (keep using this as an example, one of the few ls flashlights i know anything about) it actually smaller than the 2aa-mag so i was hoping there would be room in the head for some electronics...perhaps for a single chip, but not much more...maybe a decent 2c light...

btw, the spec sheets for the lambertian dies spec a forward voltage of 2.95v, but still a 350mA draw...so a 2 cell housing should be perfect, just to build a regulator into it...basically if you want to run it from a single cell you need 700mA plus overhead...so say 1A...my digital camera draws up to an amp of juice and with 2 batteries alkalines last only about 6-7 pics...nimhs last longer, and lithium the best...alkalines are much easier to find and store for need tho...


----------



## **DONOTDELETE** (Nov 19, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
*Duggg,

I have a question as to how you measure the efficiency?*

Hi Wayne,

Measure the battery current and multiply it by the battery voltage under load. That will give you the "power in" figure.

Next, measure the LED current and multiply it by the voltage across the LED. That's the "power out".

Efficiency is then simply "power out" divided by "power in", expressed as a percentage.

*Regarding winding inductors. I have done this with ferrite toroids, and this has worked for me.*

I just can't imagine a homemade inductor being smaller in size than an SMD one, although the cost savings is significant---why pay $2 or more for a tiny coil of wire?

*I requested a few sample MAX757 chips from MAXXIM, and to my suprise, they arrived in the mail today. So, I'll be making a board with this chip real soon. It is adjustable, and that's cool.*

Wow, let us know how it goes. The MAX757 is a standard 8-DIP so it's a lot easier to work with, and if it shows superior efficiency, it may be useful in circuits where size isn't as critical.

<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Nov 19, 2001)

By the way, I mentioned earlier this afternoon that it appeared that an inductance smaller than 68uH may work.

Unfortunately, while it was true that the LS light output appeared constant, in reality, there was a 5-10mA reduction in LED current when I placed a 100uH inductor in parallel with a 68uH one (making an effective 40uH inductor, since 68*100/(68+100) = 40).

So forget what I said about using anything less than 68uH...


----------



## MrAl (Nov 20, 2001)

Duggg:
I didnt mean the home made inductors would
be smaller then the SMD parts, but they
would be smaller then some of the other 
inductors we have found so far.
The drawback is that you have to wind them
yourself.
The following is just a test of UBB code
<UL TYPE=SQUARE><LI>Item 1
<LI>item 2
[/list]

Good luck with it,
Al


----------



## ElektroLumens (Nov 20, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
[QB]


> Originally posted by Wayne Johnson:
> [qb]Duggg,
> 
> 
> ...


----------



## MrAl (Nov 20, 2001)

Hi there Wayne,

Nice to hear about your experiences with
other regulator ic's and hope to see some
of your results and comments soon on any
of these too.

I had done some testing on the Max756, and
i must say the low dropout feature isnt
all as good as they say it is, but at 
voltages above 1.5 or so you can get pretty
good results, up to about 200ma i think, and
thats without an external transistor too.
The main reason we are trying the Zetex 300
chip is to try to get to 350ma at least with
two cells, and also a single circuit that
will support between 1 and maybe 10 or so LED's, without having to change too much.
So far it looks like the only difference
between 1 led and 15 led's will be the
choice of inductor, output capacitor,
and R sense, but the circuit itself will 
always be wired exactly the same
no matter how many led's are being driven
(up to maybe 15 or so). For 30 led's you
would use two circuits driving 15 led banks
each, etc. Using separate circuits adds to
reliability also: if one circuit craps out
you still have 15 leds running full steam 
If you have enough room for 30 leds, then you
have enough room for two circuits.
In the end, we might try to miniaturize this
circuit too, to get the minimum size possible
using this chip. Like i was saying elsewhere,
the inductors i had made in the past where 
about very nearly equal in size to about
5 US pennies stacked one on top of the other.
The only thing about them is that the inductance
was typically higher then what we are really 
trying to use here, so i'll have to wait to
see how it all works out. The other circuits
had worked fine with these inductors though.

Ok, well take care for now,
Al


----------



## ElektroLumens (Nov 20, 2001)

Hello Al,

The Zetex chip sounds really good. I did look into it at one time. One reason I didn't try it is it is hard to get ahold of. I did have one of their salesperson give me a call, but I never did get back with them. 

It looked simple enough to work with, if I remember correctly.

Getting the maximum amperage, yes, that's what I want. That is why I have been trying different chips. The MAX756 works okay for me down to 1 volt or so. With a larger inductor. This is what I got: with input of .876 in, driving the lux I got 2.84 volts out. With 1.9 volts in, I got 3.1 volts out. I do not have a VDM which can measure amps, and that is what I need to do.

Anyway, I'll post my results on these other boards else where. The Zetex chip looks pretty good.


----------



## MrAl (Nov 20, 2001)

Hi there again Wayne,

Yeah for a while there the Zetex 300 chip was impossible to get ahold of.
Since then, DigiKey has been selling them in single quantities.
I'm eventually going to try the 100 chip as well, regardless of the outcome
of the 300 chip circuit.

It seems simple enough, but of course it's only available in the
SM package, not a dip package.

BTW, how much current can you get out of the MAX756 with say
about 2 volts input? You can use a small series resistor of
1 ohm or less and measure the voltage drop across it.
If you use 1 ohm, the voltage measured equals the current
though it. If you use 0.1 ohm, multiply the voltage by ten
to get the current. A lot of meters dont measure current
in these circuits too well anyway, as sometimes their internal
resistance is too high.

I'd be interested to hear what you get out of the MAX and other chips.

Bye for now,
Al


----------



## ElektroLumens (Nov 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
[QB]Hi there again Wayne,



> Yeah for a while there the Zetex 300 chip was impossible to get ahold of.
> <HR></BLOCKQUOTE>
> 
> 
> ...


----------



## ElektroLumens (Nov 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
[QB]Hi there again Wayne,




> Yeah for a while there the Zetex 300 chip was impossible to get ahold of.
> <HR></BLOCKQUOTE>
> 
> 
> ...


----------



## Mercator (Nov 21, 2001)

*Wayne*

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
*
The smaller SO chips seem pretty hard to work with. I am impressed you have been able to work with them. How are you making your boards? With the photo sensitive copper boards? I am looking into that, as I can produce real nice circuit printouts with the software I have. I would like to be able to print out the design on a transparency, and transfer it to the boards, as opposed to drawing the design on.*<HR></BLOCKQUOTE>

Regarding the process of making PCB's I've recently been working with the "Laser Toner Transfer" method. You print out your design onto a specially coated paper and then using an ordinary clothes iron you iron the image onto the copper clad board. Peel off the paper and etch as usual. I even tried this technique using regular inkjet photo paper that was ran through my laser printer. Then proceeded as mentinoned above. Works pretty good. I decided to try the commerical product and the results are very good. Other methods of producing boards are either crude, time consuming or expensive.

Check out this link for more info:

PCB Fabrication Methods

Looking forward to you jumping in on this project. So far the Zetex 300 looks pretty promising.

Mercator


----------



## ElektroLumens (Nov 21, 2001)

Mercator,

I have heard of the Laser toner method. My wife informs me our iron is burned up (ha ha). Well, anyway, it doesn't work. I don't like the idea of buying an iron to do this work, so I'll keep my eye out for one at a garage sale.

I like the idea you have of making the PCB boards. The crude way I do it now would not work for a project like the Zetex chip.

I am planning on getting a few of the chips, and trying my hand with this chip.

I am also planning on testing my present circuit designs, for amperage and efficiency.

The best ink I have found for drawing my circuits, you might not believe this, is Liquid Paper (white out). The etchant solution doesn't begin to touch it, so the copper come out perfect. 

I hope to try the photo sensitive method, although I have heard excellent concerning the method you describe for PCB creation.

I now have my MAX757 board completed and functioning perfectly. I will run tests on it when I've the chance.


----------



## **DONOTDELETE** (Nov 22, 2001)

One thing I happened to notice while visiting the DigiKey web site is that while the ZXSC300 cost $1.05 each, the ZXSC310 costs only $0.81 each---23% cheaper!

The 310 seems to be identical to the 300, except the 310 also has the additional (though questionably useful) shutdown feature.

Did I misread something? Why is the 310 so much cheaper than the 300?


----------



## Mercator (Nov 22, 2001)

Hello Again Wayne...


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
*Mercator,

I have heard of the Laser toner method. My wife informs me our iron is burned up (ha ha). Well, anyway, it doesn't work. I don't like the idea of buying an iron to do this work, so I'll keep my eye out for one at a garage sale.

The best ink I have found for drawing my circuits, you might not believe this, is Liquid Paper (white out)

I hope to try the photo sensitive method, although I have heard excellent concerning the method you describe for PCB creation.
*<HR></BLOCKQUOTE>

With the Toner Transfer Method, heat and time are a critical factor in producing good results. Expermentation is needed to get the feel for what it takes. If you do buy a used iron, make sure the surface is perfectly level, smooth and that the heat output is constant. I ended up buying another iron because the old one I had was warped and it was hard to get even presure on the board.
If you decide to try this method, design a simple ckt. design and print out several copies. Start with the iron set at about 275 degrees (f) and then vary the times like from 2 minutes to 5 minutes in 30 second intervals. After ironing peal off the media right away. Most likely all transfer will look about the same. You might have to make a few minor repairs before etching. Your "White Out" should work, I use Sharpie marker or clear nail polish. After you have ironed on the samples they may look alright, but I've found that you have to actually etch the test samples to see the results. It appears that with to little heat/time the resist factor of the toner is not as good and the etchant slightly seeps through the resist and leaves a stained effect on the copper. I noticed this most often on larger areas of copper. Fine lines and solder pads seem to come out alright.

The commercial product I decided to go with was the "Press N Peel Blue" Not only does it transfer the toner, it also leaves a coating on top of the toner. The other type of transfer method only transfers the toner. In fact the other paper is nothing but a paper coated with a water soluable starch (Dextrin). that was what gave me the idea ti try the glossy inkjet photo paper. Which by the way did produce pretty good results. The commercial product is much better and worth your time and money.

In the past, I've used the photo sensitive methods. Both the spray-on and the pre-sensiized boards. Both methods have problems in getting good results without alot of trial and error. Biggest issue is the cost factor. If you don't get it right the first time you wasted a costly board. With the toner transfer method, if it doesn't look right after ironing you can start over.

Give it a try, I think you'll be impressed.

Mercator


----------



## MrAl (Nov 22, 2001)

Wayne:

Part of the decision to start with the 300 chip came from the following:
The ZXSC300 has 5 pins but one doesnt connect to anything, so
in effect it only has 4 leads making it the easiest to use.
The ZXSC310 has 5 pins all of which must be connected to something.
The ZXSC100 has 8 pins, so its the most complex to connect.


I'll have to look up that To220 chip also on
the Zetex site. Thing is, im getting hooked on
these little parts. They sure do save board space.
As i was noting earlier, the other app i was working on
uses an op amp package with 8 pins. The 8 pin SM part
takes up only one-eighth the volume of the same 8 pin dip
package. Maybe even a little less than that. That's 
a lot of difference. You can make a fairly complex circuit
in the space it takes to mount one 8 pin dip package.
Talk about motivation 
The To220 chip would be a heck of a lot easier to work with
though.
Wow that Max chip sure is expensive! I didnt realize the 
price difference was so great. I guess it has to do with
having the output transistor right on the chip, and its
a MOSFET too, and the sense resistor is also on the chip.
If you add the price of the chip, transistor, and sense
resistor we have found so far for the Z300 chip you get
about $4.00 (for single quantity pricing of each part).
But i dont think you can get the Max chip to perform up
to 350ma under any conditions, because the output current is
preset with the parts selected on the chip already.

Also, i havent worked yet with small SM parts that much. I just
made a small adapter board the other night and soldered a part onto
the board and had good test results so far. Mercator (also on here)
seems to have a pretty good method of making transfers and ironing
them onto the copper board. I'm going to have to try that sooner
or later because making the smaller outlines by hand is way too 
tedious and tiring and time consuming. The methods i had used
for dip layouts just dont work as good for SM parts, as the
dimensions are much more critical.

It's also interesting that you used white out as an acid resist,
i have been using lacquer type pens so i'll have to try the white out
too.

Duggg:
Thats a good question, since the 310 has more funtionality then
the 300. Perhaps it's because of the way the market worked
and reflects the history of buying for the industries in general.
More chips sold probably brings the price down. I forgot to
check the price of the 100 chip, did anyone check this out yet?
This chip is actually spec'd for higher currents, and doesnt
need to be pushed as hard as we are pushing the 300 chip right now
to get to 350ma 

Mercator:
If you could supply me with a list of stuff to bring to the
local copy office, and a list of things to tell them to use
while making the copies, i'd like very much to try your toner
transfer method. It sounds very promising especially since you
can make very accurate drawings on the computer of any circuit
you wish.
The important thing is, i'll have to be able to tell them
exactly what paper to use (or bring my own, or try both!)
and what toner would be best, right?
This sounds very exciting...i cant wait to try it now.


Thanks to all of you for all of your inputs and ideas!
--Al


----------



## ElektroLumens (Nov 22, 2001)

Mercator,

Thanks for the tips on this process, when I have a chance, I'll try it.

I heard someone mention they use the paper that labels are stuck on. When you iron the circuit design on the board, it easily transfers. They said they had used the photo sensitive method, but prefer it this way.


----------



## ElektroLumens (Nov 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Wayne:

Part of the decision to start with the 300 chip came from the following:
The ZXSC300 has 5 pins but one doesnt connect to anything, so
in effect it only has 4 leads making it the easiest to use.
The ZXSC310 has 5 pins all of which must be connected to something.
The ZXSC100 has 8 pins, so its the most complex to connect.


I'll have to look up that To220 chip also on
the Zetex site. Thing is, im getting hooked on
these little parts. They sure do save board space.
As i was noting earlier, the other app i was working on
uses an op amp package with 8 pins. The 8 pin SM part
takes up only one-eighth the volume of the same 8 pin dip
package. Maybe even a little less than that. That's 
a lot of difference. You can make a fairly complex circuit
in the space it takes to mount one 8 pin dip package.
Talk about motivation 
The To220 chip would be a heck of a lot easier to work with
though.
Wow that Max chip sure is expensive! I didnt realize the 
price difference was so great. I guess it has to do with
having the output transistor right on the chip, and its
a MOSFET too, and the sense resistor is also on the chip.
If you add the price of the chip, transistor, and sense
resistor we have found so far for the Z300 chip you get
about $4.00 (for single quantity pricing of each part).
But i dont think you can get the Max chip to perform up
to 350ma under any conditions, because the output current is
preset with the parts selected on the chip already.

Also, i havent worked yet with small SM parts that much. I just
made a small adapter board the other night and soldered a part onto
the board and had good test results so far. Mercator (also on here)
seems to have a pretty good method of making transfers and ironing
them onto the copper board. I'm going to have to try that sooner
or later because making the smaller outlines by hand is way too 
tedious and tiring and time consuming. The methods i had used
for dip layouts just dont work as good for SM parts, as the
dimensions are much more critical.

It's also interesting that you used white out as an acid resist,
i have been using lacquer type pens so i'll have to try the white out
too.

Duggg:
Thats a good question, since the 310 has more funtionality then
the 300. Perhaps it's because of the way the market worked
and reflects the history of buying for the industries in general.
More chips sold probably brings the price down. I forgot to
check the price of the 100 chip, did anyone check this out yet?
This chip is actually spec'd for higher currents, and doesnt
need to be pushed as hard as we are pushing the 300 chip right now
to get to 350ma 

Mercator:
If you could supply me with a list of stuff to bring to the
local copy office, and a list of things to tell them to use
while making the copies, i'd like very much to try your toner
transfer method. It sounds very promising especially since you
can make very accurate drawings on the computer of any circuit
you wish.
The important thing is, i'll have to be able to tell them
exactly what paper to use (or bring my own, or try both!)
and what toner would be best, right?
This sounds very exciting...i cant wait to try it now.


Thanks to all of you for all of your inputs and ideas!
--Al*<HR></BLOCKQUOTE>


Al,

The Zetex chip seems like a good choice. Size is a major consideration. I am also looking into a MAX1709, which is a very small chip, 16 pins. Really a hard one to work with. It is rated at up to 9 amps! Probably impossible to get ahold of?

I have had good results with white out, probably because I can put a thick coat on. The copper gets stained a bit, and needs to be scrubbed after etching, but no problem. It takes a while to get used to using the brush, but I suppose it is like painting a fine photo with a brush?

I plan on purchasing the parts to build a regulator with the Zetex chip. Not sure which one I'll go for?

I got one of the MAX757 chips to work great, but I french fried the other! Gaaaaaaah! (Not sure what I did, but I think the inductor did it.) I have not tested the amperage as of yet with this chip, but there is a limit of what it can do, I know. It seems fine for the one luxeon though. I have several MAX756 chips, and I plan to make a number of boards with them. This chip has a cutoff of .8 volts, so it seems like a nice choice. I am using at the moment a board made with the LT1302, but it has a cutoff of 2 volts. I plan to use it with a larger setup, perhaps the 2 Luxeon setup I had criticized someone else about doing. Perhaps I will drive a 6 volt halogen with 4 'AA' batteries? It can drive more amperage than the MAX756 or the Zetex chips.

Maybe if you consider the additional parts to purchase in order to use the Zetex chip, maybe the MAX756/MAX757 chip is not that much more??

I put the boards I make in a container about the size of a 'D' cell battery, and put it in place of one of the batteries, and follow up with the other 2 batteries. Nice setup. The Zetex chip would allow a smaller board which should fit it the head of the flashlights I make. I like to use the 'D' cell flashlights. Super long life. 

I hope to make a smaller flashlight using 2 'AA' batteries, so I can carry it around easier.


----------



## LED-FX (Nov 22, 2001)

Hi Im following this thread with great interest,the Zetex chip looks avery good idea,hope your enjoying Thanksgiving on your side of the pond.

PCB making,

I`m with the photoetch side of things,my trusty old Epson 600 inkjet printing on to inkjet transparecies,made for using on overhead projectors for presentations,make sure its inkjet and not laser transparencies and your printing on the slightly matte side.

Use highest resolution and heaviset ink setting, like tell the printer its photo glossy film, allow it to dry on printer out tray and put it printed side down on the photo board.

For exposure I use a couple of old blacklight blue tubes,keep meaning to get one of these double 12" fluro fittings for caravans and pair of 12" Blacklight Blue tubes and make a neater exposure unit.If you live in sunny climes simply place in direct sunlight for a bit,probably >=15 mins.Experiment on a couple of test strips of baord.

Develop with proper developer or mild solution of caustic soda,etch as usual with ferric chloride.

I get very good results with this method, certainly fine enough to run tracks between pins on normal DIL ICs so guess it should go fine enough for SMD...soon find out I think..

For board design try the evaluation version of Eagle,integrated schematic and pcb design with autorouter.Fully functinal board size is limited but hey smaller the better.
http://www.cadsoft.de/ 

HTH

Adam


----------



## papasan (Nov 22, 2001)

heay...doing some searches for a simple 3v power regulator, the usual stuff...anyhow, came across this chip and it looked good to my unknowing eye...anyhow, check it out and let me know if it's feasable and/or better/worse than the 300 and maxim chips...

http://www.seiko-usa-ecd.com/intcir/products/power/s8323-27.html

hmm...nevermind, just noticed that the really low voltage one (0.9v) on;y puts out 1mA...


----------



## ElektroLumens (Nov 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by LED-FX:
*Hi Im following this thread with great interest,the Zetex chip looks avery good idea,hope your enjoying Thanksgiving on your side of the pond.

PCB making,

I`m with the photoetch side of things,my trusty old Epson 600 inkjet printing on to inkjet transparecies,made for using on overhead projectors for presentations,make sure its inkjet and not laser transparencies and your printing on the slightly matte side.

Use highest resolution and heaviset ink setting, like tell the printer its photo glossy film, allow it to dry on printer out tray and put it printed side down on the photo board.

For exposure I use a couple of old blacklight blue tubes,keep meaning to get one of these double 12" fluro fittings for caravans and pair of 12" Blacklight Blue tubes and make a neater exposure unit.If you live in sunny climes simply place in direct sunlight for a bit,probably >=15 mins.Experiment on a couple of test strips of baord.

Develop with proper developer or mild solution of caustic soda,etch as usual with ferric chloride.

I get very good results with this method, certainly fine enough to run tracks between pins on normal DIL ICs so guess it should go fine enough for SMD...soon find out I think..

For board design try the evaluation version of Eagle,integrated schematic and pcb design with autorouter.Fully functinal board size is limited but hey smaller the better.
http://www.cadsoft.de/ 

HTH

Adam*<HR></BLOCKQUOTE>

Hello Adam,

Your comments on this photo processing of PCB boards is helpful. I plan on trying this way. I also heard someone say that you can run the sheet through several times to get a thicker ink pattern?

I presently use the Eagle PCB board software, version 4.08 I think it is. This is a nice program. I bought the materials, and I purchased what I thought was photo sensitive PCB board, but I ordered the wrong stuff, and got the ordinary copper plated PCB board (1oz copper board). When I use this stuff up I will purchase some of the correct board. 

I could spray the photo sensitive stuff on I've heard. Any luck with doing this. I heard it is a real pain and doesn't work to well?


----------



## **DONOTDELETE** (Nov 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*The ZXSC310 has 5 pins all of which must be connected to something.*<HR></BLOCKQUOTE>

Actually that's not true. According to the 310 spec sheet, if the STDN pin is left unconnected, it never goes into shutdown mode---in other words, it behaves exactly like the 300.

If I got a 310 instead of a 300, I would just snip the STDN pin off, because the 0.15-volt threshold is too low IMHO.


----------



## **DONOTDELETE** (Nov 23, 2001)

I'm going to be putting another order to Digi-Key in Saturday's mail, in preparation for testing some SMD boards.

Here's what I'll be ordering:

M9711CT-ND	68uH SMD inductor $ 9.30 for 3
PCE3400CT-ND	220uF 16v SMD electrolytic $ 7.37 for 10
RW1S0BAR010JBK-ND 0.010-ohm SMD resistor $ 4.10 for 2
RW1S0BAR015JBK-ND 0.015-ohm SMD resistor $ 4.10 for 2
ZXT11N15DFCT-ND	Zetex NPN SMD transistor	$ 0.72

Feel free to comment on any of the above items, or suggest other items be added for testing, but please do so by 9am MST Saturday.

I'm ordering the SMD inductors because I have no practical way of measuring inductance if I were to make my own inductors, and even if I could, I want something reasonably small in size.

Regarding 220uF versus 100uF capacitors, 220uF clearly produces more output current. I was going to order a 10uF ceramic, but I think MrAl is right in that the lower the capacitance, the higher the value of Iledpk, and I certainly don't want to fry another LS!

Regarding the resistors, although we were moving toward 0.02 ohm being the ideal value for Rsense, the circuit will likely be less efficient with SMD components, so the correct value may be closer to 0.01 ohm. And I think it's better to underestimate Rsense anyway, as it's a lot easier to add resistance (with a #32 AWG jumper, for example) than subtract it.

Regarding the SMD transistor, it seems to have the lowest Vce(sat) (and price) of all the transistors we've looked at, and according to Zetex, it's a new exciting 4th generation product


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## LED-FX (Nov 23, 2001)

Hi Wayne,

"I also heard someone say that you can run the sheet through several times to get a thicker ink pattern?"

Never found this to be needed, just set it as a paper type in the printer driver that delivers a lot of ink, on my old Epson, glossy film works a treat.Just let it dry off before moving the sheet.

The spray on or sponge on photoresists are a royal pain to use,they tend to be softer than factory applied stuff and come off easily in the developer and it is really hard to get an even coating.

For the cost of a tin of spray you can probably get a decent sized panel of photoresist board.Much more likely to yield useable results.

Adam


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## ElektroLumens (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
BTW, how much current can you get out of the MAX756 with say
about 2 volts input? You can use a small series resistor of
1 ohm or less and measure the voltage drop across it.
If you use 1 ohm, the voltage measured equals the current
though it. If you use 0.1 ohm, multiply the voltage by ten
to get the current. A lot of meters dont measure current
in these circuits too well anyway, as sometimes their internal
resistance is too high.

I'd be interested to hear what you get out of the MAX and other chips.

Bye for now,
Al*<HR></BLOCKQUOTE>


Al,

Maybe I'm dince or something. I tried to do as you suggested to test the amperage of my circuit designs. I don't think I clearly understood you in this testing process. Sorry, perhaps you can hold my hand and lead me through this amperage testing process again. I myself am still learning a lot regarding electronics. I am learning by doing these things. I have no education in electronics. 


Thanks for your helpful comments. 


To me, I am amazed that I am actually able to get the circuits I designed and built to actually work. Now, I would like to concentrate on getting the size of the boards and components down, and to increase efficiencies, etc. In other words, improve the quality of the regulators I'm making, including constructing a board with the Zetex chip.


----------



## MrAl (Nov 23, 2001)

Duggg:
Yes your right, if the shut down pin on the Zetex 310 chip is open
circuit the device is enabled, so cutting off the pin would reduce
pin count to 4 like the 300 chip.
The inductor you selected looks a little lossy though.
I thought i would let you know so perhaps you might find
another one.


I have updated my eff loss calculation for the inductor.
We use equ(1) plus equ(2) and then divide by 2, because
the inductor is in series with the input voltage for half
the time and in series with the output voltage for the
other half of the time, assuming 50% duty cycle,
so we average the two equations. I left out the
divide by 2 factor in the previous post.

equ(1)=Vd/(Vin+Vd)
equ(2)=Vd/(Vout+Vd)

INDUCTOR (series resistance R):
(2.5 volt input, 350ma output @ 3.5 volt, 1 amp through inductor)

eff loss=[equ(1) + equ(2)]/2

```

```
From this it can be seen that an inductor with 0.3 ohms series
resistance will cause a loss of 9.3 percent in efficiency, while
an inductor with 0.01 ohms will only cause a loss of about 
one third of one percent in efficiency.
You may wish to check out the Delevan 
inductor line at DigiKey.


LED-FX:
Have you used the presensitized boards very much? How well do they work out?
Can you see the photo resist ink after exposing them to light?
Do you have to work in the dark all the time with these boards?
How does the price compare to regular boards?


Good luck with all your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*From this it can be seen that an inductor with 0.3 ohms series resistance will cause a loss of 9.3 percent in efficiency, while an inductor with 0.01 ohms will only cause a loss of about one third of one percent in efficiency. You may wish to check out the Delevan inductor line at DigiKey.*
<HR></BLOCKQUOTE>

Before I made my list, I thought I checked out all the one-amp 68uH SMD inductors available from Digi-Key, and rated each according to DCR, physical size, and price. Here were my findings:

1st place: JW Miller M9711, 0.200 ohm, 13x10x5mm, $3.10
2nd place: Delevan DN3223, 0.145 ohm, 21x9x7mm, $3.36
3rd place: TOKO TKS5500, 0.170 ohm, 12x12x5mm, $6.24

While the Delevan was 1-2% more efficient, it didn't win because it was more than twice the size of the JW Miller.

I found no suitable inductor anywhere near 0.01 ohm DCR... did you see one?


----------



## Mercator (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*

Mercator:
If you could supply me with a list of stuff to bring to the
local copy office, and a list of things to tell them to use
while making the copies, i'd like very much to try your toner
transfer method. It sounds very promising especially since you
can make very accurate drawings on the computer of any circuit
you wish.
The important thing is, i'll have to be able to tell them
exactly what paper to use (or bring my own, or try both!)
and what toner would be best, right?
This sounds very exciting...i cant wait to try it now.*<HR></BLOCKQUOTE>

MrAL,

While I haven't tried using the "Transfer" paper with a photocopier, all I can say is that the supplier states that it does work.
I stopped by a local Stinko's Copy place today, which was next to my favorite Starbucks. I asked them if it wouold be possible to have them run a special paper through their behind the counter copier. They said that they would have to see the paper first. They also mentioned that it is possible to bring in a disk with an image in a standard format and they could run copies from that. I was originally thinking that you could bring in your artwork and use one of their self-serve copy machines. IF you ahd the transfer sheets already cut and taped to a regular 8.5 x 11 sheet of paper you could then manually feed that paper through the copier. I wouldn't try to just feed a full sheet of transfer paper into the copier. Since the paper I started using is actually a plastic film. it might get jammed on it's way through. Besides, since most of the boards we want to work with are small, there is no need to waste alot of the transfer paper. I've been cutting the transfer paper into thirds and taping that onto a full sheet of paper as a backer. Even if you were to fill the page with images, I'd still suggest that you trim the transfer paper a bit smaller than a regular sheet of paper and still tape in on top. Two things I'd check for.... is the copier producing an exact size repo and when you make a copy can you increase the darknes with out causing the background to show traces of black. If you make the copy darker it lays more toner on the paper which is good. I've found that with my laser printer, I get better results with a darker print setting. This is adjustable through my laser printer driver in windows.

If you plan on trying a local copy house it might be a good idea to talk with them and see what services they offer. If they don't like the idea of using your paper, then I just head over tho the self-service machines and try it out. You should be able to get a pretty good idea how the copier will work by looking at a copy made on regular paper. If it looks good enough them most likely it will work on the transfer sheets. The only thing I can't comment on is the toner that is used in the copiers. It has to be a plastic based toner since that is what makes this method work. In essence... while ironing the image on the copper, the plastic toner is remelted and deposited on the copper. The special sheet of transfer paper just allows the melted plastic toner to release from the sheet. I might add that with the Press 'n Peel Blue paper I've been using the blue coating comes off the clear plastic sheet and seem to add to the toner makeing a stronger more dureable resist coating.

Hope that helps some.

Mercator


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## Mercator (Nov 23, 2001)

*Regarding the photo sensitive methods*

I've tried both the spray on and the pre-sensitized products. The spray on stuff is junk. I suppose you could get it to work, but you have to make sure that the coating is ever evenly applied. The results I've had with the pre-sensitized boards was good once you figure out the exposure time and light source distance and the actual light source (color temp)

I keep harping about how good the "Toner Transfer" method is. That's because, I very pleased with the process. It's alot simpler than any other method, has less steps to go through in order to get the board into the etch bath. One great advantage is that you can cut the board to any size you want before you transfer the image. With pre-coated boards you have to wait until the board is etched before you can either cut out seperate boards or trim the one board down to size. For the coast of just one small pre-coated board you can purchase a pack of five 8.5 x 11 sheets of the transfer paper. Uncoated copper clad board is not very expensive. With the toner transfer method, if the image has problems after being ironed, you can make repairs and then etch the board. This isn't always possible to do or to tell if needed with pre-coated boards. If with the transfer process, the image is realy messed up (beyond repair), then the tramsfered toner can be removed from the copper and re-applied.

Mercator


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## Mercator (Nov 23, 2001)

*The Mighty Zetex Claims The Life of Another Star*

Well, I finally made time to piece together my Z300 board. I started out using the 68uH coil, the 688 trans, a .015 and a .025 (in series) to get close to the Rs I thought I needed. I used the IN5821 diode and a 220uf cap. I used 2 AA cells for input.

I wasn't able to get the circuit to work with the 688 trans. It checked out alright on the board. So I removed it and replaced it with the FMMT618 trans. This produced results. Before the LS died, I was getting something like 280mA output. Not great but I suspected that I would have to adjust my crude Rsense set-up in order to get better output. Somehow in the process of powering up after reconfiguring my meter to take other readings the LS up and died. I was careful to discharge the cap, knowing that this is what was responsible for the death ot at least two other LS's. Not sure what happened, At least I have another LS on hand. I really do need to make a subsitute for the LS before I go much further. Php_44 provided me with a ckt. but Like a dummy I didn't build it before hand. If anyone has any ideas how to simulate the LS please post it here. I guess my main concern is that I couldn't get the Zetex 688 trans to work. Perhaps it went bad or my combination of supporting components wasn't right. Any Ideas??? I know Duggg and MrAl also have the 688, so I'll be looking for their test results. 

I'm still mourning the loss of my LS and feeling responsible for it's demise. So, after a bit of grieving and a couple of left-over turkey sandwhiches, I'll get back to the project.

Mercator


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## MrAl (Nov 23, 2001)

Duggg:

Did you check out the DN4512-ND at DigiKey?
It's about 20mm long by 10mm round, about the
size of a 2 watt resistor. This is the one
i had picked because of it's low
dc resistance (0.084 ohms).
It might be a little bigger then you want though.


Mercator:

I just got a warehouse of small parts in today 
I've been busy cataloging all these tiny parts 
and looking up data on the web.

I'd like to try that transfer method, and i'll even get some
transfer sheets. First off, i need to know where to
get the transfer sheets. Secondly, i need to know
what kind of toner i should ask them to use at
the copy shop, or, i need some way to be able to tell
what kind of toner they usually use in their copy 
machines. I mean, what if i go one time and they
have the right kind of toner, and next time they
use a different kind? Perhaps there is some writing
on the toner package you use to refill your printer?

It sounds like one way or another this would work out
very well. I now was able to examine the board you made
and it looks like a reasonable outcome. Did you have to
touch that up much before etching? If so, how much 
touch up?

I'll be able to post some results now that i have some
parts to work with. I think i might check some spec's
on the individual parts before i hook them all up.
The 100uf cap we got looks very small for only 0.1 ohms ESR.
I'm going to check that out before i use it.
I'm going to have to order an LS too now
For my initial tests, i'll use a load that will drop
3.5 volts at 350ma. Does that sound close enough to an LS?


Take care for now,
Al


----------



## Mercator (Nov 23, 2001)

Hello, MrAl,

Looks like we both posted a message at he same time. I went back to look at the post I just placed and there was your questions.


*Mercator:
I'd like to try that transfer method, and i'll even get some transfer sheets. First off, i need to know where to get the transfer sheets. * 

I tried to find some locally, but no one carried it. I ended up ordering from:

All Electronics

Look for there part number TEK-5

*Secondly, i need to know what kind of toner i should ask them to use at the copy shop, or, i need some way to be able to tell
what kind of toner they usually use in their copy machines. I mean, what if i go one time and they have the right kind of toner, and next time they use a different kind? Perhaps there is some writing on the toner package you use to refill your printer?*

Again.... Not sure what to tell you. I would suspect that the toner used in a particular copier would be the same from time to time. The toner cartgidge I use is for a HP or Canon laser printer. I guess the only thing you can do is to try a copier and test the results. I know that when I have refilled the cartridges for my printer and used just any toner powder I didn't alwasy get good results with regular printing tasks. I think it has to do with the printer's fuser temp and speed. This most likely wouldn't be a concern (different types of toner) when you print on a transfer sheet. All laser printers and I assume newer copiers use a powdered plastic based toner. I doubt that the kid behind the counter at a Stinko's will have much knowledge about the toners used in any one machine. I think you mentioned having a inkjet printer. If so and you happen to have some glossy photo paper, you might try running that through a copier first and then try ironing it onto something. The results might not be very good since I've found that different inkjet papers give differing results. But... You should be able to tell if the toner will at least re-melt and transfer to the copper.

*It sounds like one way or another this would work out very well. I now was able to examine the board you made and it looks like a reasonable outcome. Did you have to touch that up much before etching? If so, how much 
touch up?*

Keep in mind that these first boards I sent out were made using the inkjet photo paper, not the commercial product. As far as touch ups needed.... Mostly had to paint over the large copper areas since with the inkjet paper,(for what ever reasons)the toner didn't lay on fully and left pin-holes. This might have been due to not using enough heat or time under the iron. For the most part the trace edges and the traces and pads came out alright. With the commercial paper, I've made several more of the same boards and had much better success. Although I should have adjusted my ironing time alittle bit longer. even though, the results were near perfect. No touch needed except for a few minor flaws, again in the large copper fill areas. These flaws are very evident after the transfer backing is removed.

*I'll be able to post some results now that i have some parts to work with. I think i might check some spec's on the individual parts before i hook them all up. *

Good, I'd like to see if and how you do with the Zetex 688 trans.

*The 100uf cap we got looks very small for only 0.1 ohms ESR.
I'm going to check that out before i use it.*

I used the 100uf cap as the input filter cap. I used a 220uf at 25 volts (I had here) as a output cap. This is from Duggg's results.

*I'm going to have to order an LS too now*

I knew it would be a matter of time before the LS bug bit.

*For my initial tests, i'll use a load that will drop 3.5 volts at 350ma. Does that sound close enough to an LS?*

I think that's about right. Duggg might have a better idea than I do for sure. Please post your ckt for a simulated load. I don't want to loose another LS. Especially so early in the game.

Mercator


----------



## **DONOTDELETE** (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
*I tried to do as you suggested to test the amperage of my circuit designs. I don't think I clearly understood you in this testing process. Sorry, perhaps you can hold my hand and lead me through this amperage testing process again.*<HR></BLOCKQUOTE>

Wayne, using Ohm's Law, voltage equals resistance times current. Put another way, current equals voltage divided by resistance.

That means if you have a resistor of known value (for example, 1.2 ohm) and you measure the voltage across it (for example, 0.6 volts), then the current flowing through the resistor is 0.6/1.2 = 0.5 amperes.

If you insert a 1-ohm precision resistor somewhere in a circuit, you can calculate the current through it by simply measuring the voltage across it, while the circuit is running. 

If you put the resistor in series with a battery, you can then figure out the battery current without using an ammeter.

Now, in practicality, you really would want to use a resistor even smaller than 1 ohm, because any resistor in a circuit wastes power, and the higher the resistance, the more power it wastes. If you're trying to calculate circuit efficiency, you don't want this test resistor wasting a good portion of the power.

That's why there are "current sense" resistors available with values like 0.01 ohm. While these ultra low value resistors steal very little power from a circuit, the voltage across them may be very small and hard to measure.

Hope this helps!


----------



## **DONOTDELETE** (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Duggg:

Did you check out the DN4512 at DigiKey?
It's about 20mm long by 10mm round, about the
size of a 2 watt resistor. This is the one
i had picked because of it's low
dc resistance (0.084 ohms).
It might be a little bigger then you want though.*<HR></BLOCKQUOTE>

Actually my Circuit #2 is using the DN4510, which has an DCR of only 0.059 ohm. But at 23x12x12mm, it's way too big for most flashlights.


----------



## **DONOTDELETE** (Nov 23, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*I guess my main concern is that I couldn't get the Zetex 688 trans to work. Perhaps it went bad or my combination of supporting components wasn't right. Any Ideas???*

I haven't tested any of the SMD transistors yet. You said it "tested alright on the board". What does that mean?

The 688 is in a SOT-89 package, which is different than the 618's SOT-23. The 688 has a collector pin on both sides of the chip. Is it possible there was a short? 

*I'm still mourning the loss of my LS and feeling responsible for it's demise. So, after a bit of grieving and a couple of left-over turkey sandwhiches, I'll get back to the project.*

You get kinda attached to that little square aluminized board and that round plastic collimator. I know how it is! But you quickly get over the loss, especially if you got new ones in the mail today, like I did




<HR></BLOCKQUOTE>


----------



## Mercator (Nov 24, 2001)

Duggg...

*
I haven't tested any of the SMD transistors yet. You said it "tested alright on the board". What does that mean?*

The only way I have to test a transistor is with my ohm meter. Checking for a slight difference in resistance between the base, collector and emmiter leads. It checked out to the extent that it wasn't shorted or open.

*
The 688 is in a SOT-89 package, which is different than the 618's SOT-23. The 688 has a collector pin on both sides of the chip. Is it possible there was a short? *

Actually, in order to have the 688 fit better on the board I filed back the center lead about half way so that there wasn't any possibility of it shorting out. I didn't think it would be a good idea to bend it upward and left as is, it would bridge the base and emmiter solder pads. I'm going to wait for the second supply of Z300's and build another board where I will try the 688 again. Maybe you or MrAl will try the 688 before I can and let me know how it works out.

*
You get kinda attached to that little square aluminized board and that round plastic collimator. I know how it is! But you quickly get over the loss, especially if you got new ones in the mail today, like I did



*

So far I'm lucky to have had a spare. The first one had been around for awhile acting as a test pilot for various drivers. I guess it lived up to its intended purpose. It had been driven hard and long with very little concern for it's safety. Streached to it's limits several times in it's lifetime, it held up pretty well. It was a silly error on my behalf that caused it to finaly crash and burn.

Mercator


----------



## MrAl (Nov 24, 2001)

Hi there again Duggg, Mercator, Wayne,

Wayne: when you insert a small resistance
in a circuit you can measure the current
through the resistor by measuring the 
voltage across the resistor. As Duggg was
saying, to obtain the current (that would
be the same as measured with an ammeter)
you divide the voltage measurement by
the value of the resistor in ohms. This 
means that by measuring a voltage you
actually get the current value without
using an ammeter. This is a good trick to
use because you can insert resistors into
the circuit and make measurements without
constantly disturbing the circuit.
Of course you have to also compensate 
for the drop when you determine efficiency,
and 0.1 ohm resistors are better to use then
1 ohm because they drop less voltage.
I use 1 ohm a lot during a circuit start up
to see how things look. This way i get 
current limit action as well protecting
the parts untill i can see how it looks.
Then i switch to 0.1 ohm resistors.
Hopefully i'll be able to use 0.010 ohm
resistors also, although i havent tried
these yet. These insert very little loss 
into the circuit, but dont offer any
protection to the circuit during intial trials.

Mercator:
One thing i would be very very careful about
is using a random capacitor in the output
circuit of this circuit. If you dont know
what the ESR is and you happen to end up
with something like 3 ohms, the peak current
could take out the LS. I would only use 
a cap with known ESR to be less then about
0.1 ohms for any lenght of time. The ESR 
contributes to the output ripple voltage
which contributes to the output peak current.
If you dont know what your cap is, send me
a sample and i'll measure it for you.
I've seen extremely high ESR in some caps
that would surprise anybody, thats why i 
say this. I'm going to measure all mine
before i use them.
As far as efficiency goes, in a simulation,
raising the ESR to 0.1 ohms caused a decrease
in eff by 0.8 percent(thats almost one percent) so i didnt think that was too
significant, but going above this could do
the LS harm even though the eff might not 
go down too much more.
The 688 transistor: i hope to be able to 
test this today sometime. I should have
my first Z300 chip circuit up and running
by later tonight. Another thing i dont like
about Zetex is their inability to spec
max values with the switching times
of the transistors. They only spec 'typical'
values. I hope this doesnt crop up and
bite us later, because looking at their
data sheet, how can we tell if one of their
transistors that worked today, when we buy
an identical part number tomorrow, will work
the same in a second circuit? What if they
have a spread in values of 2 to 1, that means
the switching time increases to twice the
'typical' value, and our circuit suddenly
no longer works. One of us is going to 
have to confront Zetex about this sooner or
later if we wish to be sure we have a long
term solution using this (and other similar)
Zetex chips. We have to be able to say something like:
"ok, this min time is 1us an that max time
is 0.5us, so our circuit will always work".
Right now, it's impossible to say this
because Zetex doesnt spec the Max times on
their data sheets. We HAVE to know what
THEY guarantee or WE cant guarantee anything
either, right? Like, what if i say:
"i'll typically give people very thirsty
crossing the desert a full glass of water",
he he. See the point?

The toner/transfer method:
This still sounds good to me, so im going to
try it out, but i think i'll wait untill
i do a little testing with some
of the Zetex parts i got now first.
Once i get to know what we are dealing with
here, i'll turn some attention back to 
the processes of board making. I think
im getting the idea of what you have been
saying now. I have seen some printouts that
appear almost "shiny" on the surface, while
other printouts appear very 'flat'. I 
think the shiny ones are plastic toners,
while the flat ones are plain inks. I'll
eventually be looking into this more too.
The reason for the pin holes you were talking
about were probably from the uneveness of
the paper itself; the paper has a rough
surface when you look at it close up, and
any high points get coated well, while the
valleys dont get any toner at all. The valleys 
therefore dont contribute to the transferred
pattern, so a pit occurs there. The photo
paper has a much more even surface, meaning
it gets coated with toner very evenly and
in all areas. I would bet that some copy 
shops have photo paper already. It is 
probably a matter of talking to them like
you said 

Well i guess i got some more tiny tiny soldering
to do 
Catch you all a bit later, hopefully with some
positive results.

Good luck with your LED circuits,
Al


----------



## MrAl (Nov 24, 2001)

WELL, i finally got some results for the
Zetex 300 circuit
Dang, thats the tiniest transistor i ever saw! It's about 1/16 inch wide and 1/8 inch long.(FMMT618)

Ok here's the data:

11/2001

Z 300 chip circuit measurements:

output cap: 100uf, 0.2 ohms ESR (was suppose to be 0.1 ohms)

transistor: FMMT618, measured max Vsat=0.2 volts at 280ma average output

inductor: 220uH, hand wound toroidal core, measured peak 1.5 amps, series R=0.026 ohms,
with added 0.1 ohm series resistor for current measurements.
(to calculate actual eff this loss is added to the final eff calc.)
Note: the store bought inductor didnt function normally (see below).

1N5821 diode: (3A Schottky) measured 0.37v at 280ma average output

Rsense=0.015 ohms 

LS equivalent: 3 x 1N4006 diodes in series, also in series with a 3 ohm resistor
(note i havent checked to see how well this simulates the LS, but it 
does draw about the same current at 3.5 volts. 2.5 ohms would come closer.

Output: measured 280ma avg out at 3.5 volts, 200mvpp ripple
Input: measured 517ma avg in with 2.4 volts input

from the above input/output, calculated 
80.8% eff. by adding 
0.0517/2.4+.0517)/2+.0517/3.5+.0517)/2=0.01782
to 79%:
79.0%+1.8%=80.8% eff.

Final analysis:

81 percent efficiency overall.

Output current can be increased by decreasing Rsense. Apparently,
a number of factors cause this R value to have to be much lower
then expected. I suspect the 19mv level is actually lower then that.
One thing though: if the resistor is too low such that not
enough current can be drawn through the inductor's series R, the circuit
will hold the transistor in saturation, forever waiting for a high
enough current level to trip the 19mv sense level so the circuit can
start up. This situation can easily be detected by measuring the
collector to emitter voltage of the transistor if the output doesnt light
the LS. If it reads about 0.2 volts dc, then the circuit isnt starting.
Either increase the input voltage or get an inductor with a lesser
series R value.

An output cap with less then 0.1 ohms ESR has to be found and used
to keep the output ripple down to an acceptable level for the LS.
The cap used was suppose to have 0.1 ohms, but appears to have twice
that ESR. Perhaps double the capacitance may help the situation
(also as reported by Duggg), but in this case it would be to
keep the ripple down, not to increase brightness.

The Delevan inductor tried caused some instabilities making the
circuit operate at a sub harmonic of what it should be operating at.
This causes several problems, including requiring the output cap
to have to be increased several fold. It looks like the eff drops
as well, but its hard to tell because of the instability of the circuit.
In general, this is the most electronically incorrect part i've seen to date
I'm not sure why this happened just yet. The rating of the inductor is high
enough. I'll have to do more testing with it i guess. Untill i can find
out what doesnt work about it, i cant recommend buying these inductors.

Since the FMMT618 transistor seems to saturate to 0.2 volts, it seems like
a good enough part to use for 2 cell operation. Since we already determined 
that using one 1.5v cell for the LS isnt that good of an idea, the point of
using the 688B transistor may be now moot. I might still try this though.
The FMMT617 part should work exactly the same as the 618.

I have contacted Zetex about their transistor min/max specs and am waiting
to hear back from them.


----------



## **DONOTDELETE** (Nov 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*An output cap with less then 0.1 ohms ESR has to be found and used to keep the output ripple down to an acceptable level for the LS.*<HR></BLOCKQUOTE>

Some good things to remember about ESR---it falls as frequency increases. The caps I ordered are 0.26 ohm at 100kHz, but only 0.19 ohm at 400kHz, which is where our circuit is operating.

And although I looked at caps with ESRs around 0.1 ohm, just like the low-DCR inductors, they were both gigantic and expensive. TANSTAAFL.

Keeping the LS peak current under 500mA isn't nearly as vital as keeping the average current at 350mA, and keeping it cool with a good heat sink.

And the LS doesn't have to absorb excess energy alone---the diode and capacitor do it too, and the higher the ESR, the more energy it absorbs.


----------



## MrAl (Nov 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Some good things to remember about ESR---it falls as frequency increases. The caps I ordered are 0.26 ohm at 100kHz, but only 0.19 ohm at 400kHz, which is where our circuit is operating.

And although I looked at caps with ESRs around 0.1 ohm, just like the low-DCR inductors, they were both gigantic and expensive. TANSTAAFL.

Keeping the LS peak current under 500mA isn't nearly as vital as keeping the average current at 350mA, and keeping it cool with a good heat sink.

And the LS doesn't have to absorb excess energy alone---the diode and capacitor do it too, and the higher the ESR, the more energy it absorbs.*<HR></BLOCKQUOTE>

ESR change with frequency:
I dont see that much difference between .26 and .19 though Duggg. My test circuit 
runs close to 300kHz.

The 0.1 ESR cap i got was about 15 cents.
It looks more like 0.2 though. I'll test it
better also. The cap measures about 10mm 
long x 5mm diameter.
Were you looking to use all surface mount
parts? I'm thinking any inductor that
can handle 1.5 amps peak will have to 
be at least so big. What is the smallest
you have found so far?

The inductor i'm using only has 0.026 ohms
series R. I'm about to cut that down to
.006 ohms. It measures 10mm diameter by
5mm high.

I thought i saw on here somewhere that it
wouldnt be good to allow the LS to go above
500ma? If we dont have to worry about that,
we have it made  but are you sure it's ok?

--Al


----------



## ElektroLumens (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
[QB]Wayne, using Ohm's Law, voltage equals resistance times current. Put another way, current equals voltage divided by resistance.

<HR></BLOCKQUOTE>

Thanks Duggg, that's an excellent explanation. I will try this and see if I can now measure the amperage. I think I may need to first get a low ohm resistor, and then try it. I'll let you know if I, er, uh, what my results are.


----------



## ElektroLumens (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi there again Duggg, Mercator, Wayne,

Wayne: when you insert a small resistance
in a circuit you can measure the current
through the resistor by measuring the 
voltage across the resistor. As Duggg was
saying, to obtain the current (that would
be the same as measured with an ammeter)
you divide the voltage measurement by
the value of the resistor in ohms. This 
means that by measuring a voltage you
actually get the current value without
using an ammeter. This is a good trick to
use because you can insert resistors into
the circuit and make measurements without
constantly disturbing the circuit.
Of course you have to also compensate 
for the drop when you determine efficiency,
and 0.1 ohm resistors are better to use then
1 ohm because they drop less voltage.
I use 1 ohm a lot during a circuit start up
to see how things look. This way i get 
current limit action as well protecting
the parts untill i can see how it looks.
Then i switch to 0.1 ohm resistors.
Hopefully i'll be able to use 0.010 ohm
resistors also, although i havent tried
these yet. These insert very little loss 
into the circuit, but dont offer any
protection to the circuit during intial trials.

Good luck with your LED circuits,
Al*<HR></BLOCKQUOTE>

Thanks Al, this is also a big help. Perhaps I can get some kind of results for you guys to see what this MAX756 chip and other chips I am working with are doing are doing. ??


----------



## **DONOTDELETE** (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*The 0.1 ESR cap i got was about 15 cents.
It looks more like 0.2 though. I'll test it
better also. The cap measures about 10mm 
long x 5mm diameter.*

The special ultra low-impedance 0.19 ohm cap I'm looking at (220uF, 16v) measures 6.2mm long x 8mm diameter. Yours is not only half the size, but half the ESR, and one fifth the price... please provide more details.

*I'm thinking any inductor that can handle 1.5 amps peak will have to be at least so big. What is the smallest
you have found so far?*

No doubt, the inductor is the largest component on the board at 13x10x5mm.

*The inductor i'm using only has 0.026 ohms series R. I'm about to cut that down to
.006 ohms. It measures 10mm diameter by
5mm high.*

Again, that's quite an accomplishment for a 68uH inductor. I'm very curious as to how yours has 1/30th the DCR of a typical manufactured unit of the same physical size.

*I thought i saw on here somewhere that it
wouldnt be good to allow the LS to go above
500ma? If we dont have to worry about that,
we have it made  but are you sure it's ok?
*

It's true that the spec sheet says 500mA max pulsed current, but I wouldn't exactly take the spec sheet as gospel considering the wide variance from piece to piece. I think at this point, Luxeon is being conservative with their max specs.
<HR></BLOCKQUOTE>


----------



## Mercator (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*



It's true that the spec sheet says 500mA max pulsed current, but I wouldn't exactly take the spec sheet as gospel considering the wide variance from piece to piece. I think at this point, Luxeon is being conservative with their max specs.
<HR></BLOCKQUOTE>

Click to expand...

*


> First off I'm very pleased to see such promising results in the Z300 testing. It looks like from here on it mostly a matter of parts selection.
> 
> Regarding the max current specs. Luxeon recommendes....
> 
> ...


----------



## Mercator (Nov 25, 2001)

One of the problems in working with SMD's and using hand soldering techniques is to hold the part in posistion while soldering. In the past while replacing a bad component a very small dab of glue would do the trick. Working with a new board and soldering on the components with a conventional soldering iron, the glue trick isn't the ideal solution. I designed this platform using simple materials I had on hand. I used some scrap pieces of 3/8" ABS plastic sheeting, a short section of 1/8" drill rod (coat hanger), a rubber band and some ABS pipe cement. Assembley took less than a half hour. If you deside to build a jig like this take into consideration the size of the PCB you'll be working with and give yourself plenty of working room to easily get your iron into and to be able to see what you're doing. Several holes can be drilled on the top rail so that the pin can be posistioned to either side. Tension on the part can be adjusted by either the length of the rod or the tension of the rubberbands. I secured a section of non-skid material under the PCB to keep it from sliding around. In actual use, all that you normally need to do is to solder one lead to the pad and then from there you don't need the jig any further for that one component.

Mercator


----------



## MrAl (Nov 25, 2001)

Mercator:
That's an interesting idea, i might use that too.
One of the problems i had was soldering the first lead
to the board. After that, it went smooth.

But thats not my main concern anymore. Something must
have happened with the output caps we ordered. These 
are not low ESR caps after all, just some standard
filter caps. I'm not sure what happened, but we have to
look for some new 100uf caps. I thought these things
look suspicious when i first saw one. I might have
gotten the part number wrong or something, but all we have
to do is look up some new caps. It's possible i was reading
the online catalog late at night and after sorting through
the millions of caps they have ended up choosing the wrong
number or something. It looks like putting a 1uf ceramic
disc capacitor in parallel with the 100uf we already bought
will work ok, maybe even a regular 0.1 uf disc,
but perhaps we are better off just getting the
right cap to begin with. Appologies for the mix up.
This could be the reason the circuit was oscillating at
a lower frequency harmonic. It might have been resonating
with the crappy cap. I'll try to pick up a decent cap locally
and run the test with the store bough inductor again. Funny
it does run ok with the hand wound one, just with higher
then expected output ripple. Perhaps the mistake will pay off
in the long run. The only drawback is that the caps i see at
digikey are over 2 dollars each for low ESR. I was hoping to
get away with 32 cents 

Duggg:
From the above you can see what happened regarding the output cap
selection. I'm going to look for another cap. I'll post anything i 
find that looks good. The original cap was 32 cents also, not 15 cents.
I'm glad you brought this up  Maybe i'll check out the cap
you had selected, what was the part number?

The inductor is hand wound, so you have lots of freedom
over how you can make it. The drawback here is your stuck
with whatever kind of core you end up with. If you end up
with a "high u" core you might not be able to get enough
turns on it in order to sustain the kind of voltage or
current that satisfies the core area. If you can get
away with 10 turns of #24 gauge wire, you end up using
about one foot of wire, which measures about 0.026 ohms
for a one foot length. That's how the resistance comes out
so low. Also, i suspect that using a toroidal core is the
best possible shape of core due to the fact that the 
eff of this kind of core is higher then a bobbin type.
The drawback is that a toroid is harder to wind then a
bobbin type, although 10 turns isnt that difficult either.
Since this core worked out the best, i'll probably use that
in my final circuit, although i will be testing the store
bought inductors again too once i get a decent output cap.
I would think they sell these kind of inductors also, but
the price probably isnt that great. I'll check that out too.
Also, the inductor measures 220uH, not 68uH.

Wayne:
I'd be interested to see what kind of results
you got with the Max chips and compare it to
mine.

Good luck with your LED circuits,
Al


----------



## Mercator (Nov 25, 2001)

*Toner Transfer Paper And PhotoCopy Machines*

I went down to my local Stinko's Copy house today. Actually, I went to my favorite Starbuck's which is next door to Stinko's.

I took with me a sheet of transfer paper that was cut down to 7.5 x 10 with the leading edge taped onto a regular sheet of bond paper. After getting aquainted with the copy machine, that required at least a BA in Stinko-olgy, but that's another story. I ran the transfer paper through the manual feed tray and copied onto it a series of sample PCB images. I set tnhe copier to the darkest setting. I just now finished ironing the image onto a small piece of clad board. Worked just as it does with my laser printer.
The copy machine I ended up using was a Canon ImageRunner Model 550. Not the one I was first steered to by the green haired weirdo with the Stinko's logo printed on his apron.

Bottom line is.... It worked!!! That's not saying that every make and model of photo copier will yeild the same results. I would suspect that they will, providing they use a conventional powdered toner. Anyone wishing to try this out is simply going to have to do just that.... Try it out for yourself. I would suggest that on your first try, you print out several test images and then work out the iron temp setting and times. Start out with 3 minutes at 275 degree 9(f). Further details on the technique, upon request.

Mercator


----------



## ElektroLumens (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*

The inductor is hand wound, so you have lots of freedom
over how you can make it. The drawback here is your stuck
with whatever kind of core you end up with. If you end up
with a "high u" core you might not be able to get enough
turns on it in order to sustain the kind of voltage or
current that satisfies the core area. If you can get
away with 10 turns of #24 gauge wire, you end up using
about one foot of wire, which measures about 0.026 ohms
for a one foot length. That's how the resistance comes out
so low. Also, i suspect that using a toroidal core is the
best possible shape of core due to the fact that the 
eff of this kind of core is higher then a bobbin type.
The drawback is that a toroid is harder to wind then a
bobbin type, although 10 turns isnt that difficult either.
Since this core worked out the best, i'll probably use that
in my final circuit, although i will be testing the store
bought inductors again too once i get a decent output cap.
I would think they sell these kind of inductors also, but
the price probably isnt that great. I'll check that out too.
Also, the inductor measures 220uH, not 68uH.

Wayne:
I'd be interested to see what kind of results
you got with the Max chips and compare it to
mine.

Good luck with your LED circuits,
Al*<HR></BLOCKQUOTE>

Al,

I've had a small amount of time to do some testing this weekend. I came up with some results, but I don't have the confidence that my mearsurements are accurate. I will post some details when I have more time. I don't have the time at this moment. However, if my measurements are correct, the Luxeon is drawing 400mA. I don't see how that is possible. So, I think the efficiencies I came up with are incorrect as well. I hope I have more time next week. I am always so busy, I hardly have time for these things. Sorry.

I also am hand winding the torroid core inductors. Seem to work okay. I have not as yet tested the inductance. The problem with this method is the large size of the inductor. I have purchased some surface mount inductors and capacitors to get the size down of my boards.

When I can, I'll post some of the voltage readings, and perhaps you can help me calculate the amperage and efficiencies. I don't think it is as efficient as it could be. The MAX756 is working, but probably could use better efficiency. Perhaps better selection of capacitors, and maybe a better matched inductor.

I am seeking to develope a 1" or less disc regulator, to fit inside the head of a flashlight, like the double barrel or similar small flashlights. This would make the mod to the Luxeon or even multiple LED's easier, to have a step up regulator. I am using the MAX756, and am also developing a board with the LT1073 chip, which is also a 8 pin dip chip.

Later


----------



## Mercator (Nov 25, 2001)

*It's Always Nice To Get Something For Nothing*

Here lately, we've been doing and learning alot about working with Surface Mount Devices. I have personally done afew replacements in the past and just thought I'd share with you a product that I've found to work extreamly well. 

Of course it would be an ideal world if all we ever had to do was to solder new parts onto a circuit board. What do you do if the part is bad or you end up discovering that that part you thought was the proper choice nolonger lives up to you expecations. Somehow, you need to remove that part and start over. Sure you could just heat that little guy up and slide him off the pads, but you run the risk of over heating the copper pads and worse yet distroying that expensive little IC. 

If you need to remove an SMD from a project there isn't an easy and safe way of doing so without very specialized equipment. Sure that's fine if you have unmlimited resources or work for a big company. Not the case with most of us I'm sure.

There is a product that I've used several times and have had excellent results with. It's called *The ChipQuik SMD Removal System*

Here's what it is.... You get a special solder and solder paste. This solder melts a vary low temp. You apply this special solder to the part to be removed and it mixes with the regular solder. What you end up with is a solder connection that looks like a mess of solder, but and here's the magic... the part is nolonger adhered to the solder pads. In fact the stuff that looks like solder simply flakes off the SMD and the board. After alittle clean-up with alcohol you're ready to solder on a new part.

So, what this *"Something For Nothing" deal??*

If you go to the following website you can read about this product and request a free sample.

ChipQuik Web Site

I got my free sample about a year ago and what I got was enough material to do quit afew removals. It's free, it works and if you ever have a need to use it you'll be glad you picked some up. I can hardly beleive this company is giving away such a generous sample. But they are. With no string attached.

Mercator


----------



## MrAl (Nov 25, 2001)

Mercator:
Hey that image transfer info sounds great, i'll have to try that next.
Did you noticed if the printing appears "raised up" from the surface a little?

That SM part removal system sounds interesting too, and hey
its only *$82.50* for 16 foot length 

The 100uf cap i have now calculated to have about 2.5 ohms 
ESR, so i guess we go after another one with low ESR. It's
going to cost more though.

Wayne: 
As soon as you get the circuit running, post some results.
Should be interesting. I was working with the Max chip too
a few weeks back. It sure is easy to use that ic.

Good luck with your LED circuits,
Al


----------



## Mercator (Nov 25, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Mercator:
Hey that image transfer info sounds great, i'll have to try that next.
Did you noticed if the printing appears "raised up" from the surface a little?

That SM part removal system sounds interesting too, and hey
its only $82.50 for 16 foot length 
*<HR></BLOCKQUOTE>

MrAl....

*Toner Transfer....*
No, didn't notice that the printed area was "raised up" any more than normal. It does appear to be kinda shiny though. The output from the photo copier looked just as it does out of my laser printer. The transfer paper, which is actually a sheet of clear plastic material is coated with a dull, matt, blue coating which is the release agent. When it's printed on the black toner from the copier/printer looks shiny.

*ChipQuik......*
$82.50 for 16 feet of the stuff. Man, you could remove all the SMD's on this side of the planet with that much of this stuff. If you ask for the free sample you'll get enough to last a very long time. That is, unless you're a Klutz like me (and I know you're not) who finds a need to replace SMD's (a certain 688 trans) for no good reason. Hey it's free and when I come across a good product and a good deal, I like to pass it on.

Mercator


----------



## papasan (Nov 26, 2001)

do you guys have some site links for searching for components?...for instance, if your looking for a low-resistance inductor do you go through every data-sheet on digikey or do a search somewhere?...

also, has anyone tried the max-battery life?...only 3 components: ic, resistor, inductor...how much juice can you get out of it?...i'm no ee so i wonder how a diode and a cap can give more amperage, i would assume that they were there to smooth out the current...


----------



## MrAl (Nov 26, 2001)

Hi there again,

Here's a cap i found at digikey:
P11289CT-ND, 150uf, 10v, .1 ESR, over 1.2 amp ripple current, 3.13 each in quantities of 10
Check it out. It's SM also.

Mercator:
I was just wondering about that toner, if the printing
appeared to be raised up a little, because i think it
would make a good quick test to see if the printer or
copier someone might use to make the transfers has the
right kind of toner to begin with. That would make the
test for the right copier or printer easier. If i can
get this method to work as well as you have already,
that would be great!
The ChipQuik stuff sounds very good too -- i was just kidding
around about the price, but i would like to be able to buy
a smaller quantity myself.
I should be able to check out that surface mount diode too 
today. Since i already measured the drop of the 1N5821
diode (at 1.5 amps it measured 0.37 volts while switching
in the circuit), i'll be able to compare the Zetex part with
this common part. Since it's SM, it's a real lot smaller too,
taking up very little board space by itself.
I guess in the final design we can use all SM parts, but
even with an SM inductor i think that will always be
somewhat large because it does have to handle 1.5 amps peak.
The smallest inductor i have used is the hand wound one,
which measures about 10mm in diameter by about 5mm high.
That's not too bad i guess.
I'm going to try to get an order in for and LS today too
so i can test this circuit with the real thing next.
The 3 x 1N4006 diodes in series with a 3 ohm resistor does
make a good simulator for the LS, but i would like more
exact data on the LS now.

papasan:
digikey does have a search mechanism for looking up parts with
specific ratings, but once you do the search and find a part, you
click on it and it brings you to a partial page which only lists
the parts, and doesnt tell you the specs sometimes.
You end up looking up the specs separately  by opening a new
window. Its a little bit of a pain but i guess it works.


Good luck with all your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Here's a cap i found at digikey:
P11289CT-ND, 150uf, 10v, .1 ESR, over 1.2 amp ripple current, 3.13 each in quantities of 10. Check it out. It's SM also.
*<HR></BLOCKQUOTE>

I looked at that tantalum capacitor before placing my order, but rejected it for three reasons:

1. It's out of stock until Mid-January.
2. I'm not comfortable with the 10-volt working voltage. Tantalums are especially sensitive to overvoltage damage.
3. I didn't like the high price.

The Panasonic FK-series low-ESR electrolytics were a good compromise. Although physically much larger than the tantalums, they're also much cheaper.


----------



## MrAl (Nov 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*
also, has anyone tried the max-battery life?...only 3 components: ic, resistor, inductor...how much juice can you get out of it?...i'm no ee so i wonder how a diode and a cap can give more amperage, i would assume that they were there to smooth out the current...*<HR></BLOCKQUOTE>

One way of looking at the energy stored in an inductor is
in the form of "volt seconds". If you had a perfect inductor
and charged it up by placing a constant voltage v across it's 
terminals for a known time t and then disconnect the voltage
at the end of that time t, you would have stored
v*t volt seconds in its core, and the current waveform would
look triangular.
This means you could then get v*t volt seconds out of this
inductor when you discharged it thought an LED, and the current 
waveform though the LED would also be triangular. The thing is,
since in a boost config the input voltage is lower then the
output voltage (ie the LED voltage is higher then the input 
voltage) the time to discharge the inductor is shorter then
the time to charge it. This means we get a duty cycle less 
then 50%, or D=Vin/(Vin+Vout), where D stands for 'duty cycle'.
With 2.4v in and 3.5 volts out this leads to:
2.4/(2.4+3.5)=.407, or 40.7% duty cycle.
Now to get 350ma average through the LS at 40.7% duty cycle
using a flat topped current wave we need to drive it at 
Ipk=Iavg/D 
amps peak current, which works out to:
Ipk=0.86 amps, which equals 860ma.
This is already too high for the LS max of 500ma.
Plus, we havent considered the effect of only having
a triangular wave shape to deal with. As it turns out,
using a triangular waveshape deteriates the ability
to put out average current (using a flat top wave as reference)
by exactly another 50%, meaning we have to multiply our
flat top wave peak current by 2 to get the peak for a triangular
wave needed to drive the LS to 350ma average.
Multiplying 860ma times 2 brings us to 1.72 amps, which is WAY too
high for the LS.
Since we can't drive the LS to max with a pulsing source, lets see
what we can do...

if we had a flat topped wave we could drive the LS to 203ma safely
(500ma * 0.406).
With a triangular wave, we could drive the LS to half of that safely,
or about 101ma.

On the other hand, with a triangular wave and diode and filter cap
we can drive the LS to 350ma while keeping the peak current though
the LS down to less then 500ma.

Now about the efficiency:
The overall efficiency while driving a standard LED at a high peak
triangular current while pulsing it drops more then when using a
Schottky diode and filter cap to provide a near constant output
current though the LED. That's why we have abandoned not using
a diode and filter cap. The funny thing is, although the light
output drops without the diode and cap, the battery lasts longer
because the ELECTRICAL efficiency is still higher then with the
diode and cap. With the LS however, it seems we dont have a choice
like with the regular white LED's, because the ratio of the 
max peak current to the normal operating current isnt as high
as with a regular white LED.

Good luck with all your LED circuits,
Al

Added later:
Right now im making up a small 'adapter'
board for the small Zetex 2000 diode.
I hope to make adapters for the 
transistors also so i can freely interchange
all the parts without having to heat them
up again. The adapter boards will be almost
as small as the devices themselves, with
#24 leads about 1/2 inch long coming off
the boards that can be soldered at the ends.
This will allow me to get the data on the
other parts for comparisons. I should have
done this to start with. For testing it 
doesnt matter that much. For your final 
circuits of course you wont want to do this.
--Al


----------



## papasan (Nov 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Wayne Johnson:
*When I remove the output capacitor, the light will flash in fast pulses.*<HR></BLOCKQUOTE>

wow, you could actually see the LED pulse?...i would have thought it to be way too fast for the human eye to pick out...


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*2.4/(2.4+3.5)=.407, or 40.7% duty cycle.
Now to get 350ma average through the LS at 40.7% duty cycle
using a flat topped current wave we need to drive it at 
Ipk=Iavg/D 
amps peak current, which works out to:
Ipk=0.86 amps, which equals 860ma.
*<HR></BLOCKQUOTE>

ahh...thanks for the math...so without the cap you run a greater risk of frying the LS as up the voltage/amperage from discharging batteries...makes sense...

found some pretty low-R inductors at Coil Craft, hopefully i'll get the samples i asked for soon and i'll report back...


----------



## ElektroLumens (Nov 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>wow, you could actually see the LED pulse?...i would have thought it to be way too fast for the human eye to pick out...
[/QB]<HR></BLOCKQUOTE>


papasan,

I mentioned the wrong chip I was testing, it was actually a LM2595. And yes, I could see it flashing. It did seem fast, but I could see it flashing. Perhaps it was pulsing slow?? Maybe I was doing something else wrong? Anyway, when I removed the output capacitor, it was flashing. This particular chip is a step down. The input was 12 volts, and the output was 3.1 or 3.2, something like that.


----------



## Mercator (Nov 26, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
Mercator:
I was just wondering about that toner, if the printing appeared to be raised up a little, because i think it would make a good quick test to see if the printer or copier someone might use to make the transfers has the right kind of toner to begin with. That would make the test for the right copier or printer easier. If i can get this method to work as well as you have already, that would be great!*<HR></BLOCKQUOTE>


Today at one of my work sites I saw a Canon
Copier Repair Techn. I asked him if he knew much about toners used in modern copiers. In particular, if they were plasic based. After having to explain to him why I was so curious, he became curious about the toner transfer method of making PCB's. He proclaimed that he hadn't heard of such a thing and then admitted, "Sure that would certainly work". I then asked him if all toners were about the same and he told me that he could only speak for Canon copiers for certain, but they are all basically the same. So, I would think it a pretty safe bet that the transfer system would work using a photo copier.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> *
The ChipQuik stuff sounds very good too -- i was just kidding around about the price, but i would like to be able to buy a smaller quantity myself.
*<HR></BLOCKQUOTE>

I was only kidding about being able to un-solder ever SMD on this side of the planet with 16 feet of the stuff 

The sample I received was about six or seven inches long, judging from how much I have left and how little it takes to do the job. I also received a small bottle of flux. So, lets see here... If you got 32 of yor friends to request a free sample you'd end up with the $82.00 worth of the stuff for nothing. Now, that's a damn good deal. 
Actually, I have seen this product sold at Fry's Electronics. Do you have those on your side of the country? They also carry the complete SMD rework kits. Don't remember the prices though, since I've got a good supply left.

* <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The smallest inductor i have used is the hand wound one, which measures about 10mm in diameter by about 5mm high. That's not too bad i guess. *<HR></BLOCKQUOTE>

10mm x 5mm isn't bad at all compared to some of the dimensions of the ones we looked at through Digi-Key. If it works out in future testing, perhaps this is the way to go. Please post the core specs and the winding info.

* <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The 3 x 1N4006 diodes in series with a 3 ohm resistor does make a good simulator for the LS, but i would like more exact data on the LS now.
*<HR></BLOCKQUOTE>

I just finished putting together and testing my LS simulator. The best I could scrounge up around here were two resistors that yielded 3.3ohm. I'll try and measure an actual white LS running at 350mA and adjust the simulator closer to the real thing. Right now, my Z300 circuit without having been tweeked, using the Delevan 68uH inductor is delivering 220mA measured through the resistor in the simulator. Haven't done any other testing as I'm waiting on the final word on the output cap and the coil.

Your little surf boards are a good idea. Are you making these on a clad board or just soldering the SM leads to a short section of wire?

Thanks for all your help and all the help and assistance that Duggg has porvided. I'm learning alot about this type of circuit. I never thought this little project would end up being so involved. In a way it's a good thing that it is, since we are all learning alittle bit more about the different methods, techniques, theory and elements of circuit design. Not only with just the Z300, but more so with working with surface mount devices. 

Mercator


----------



## MrAl (Nov 26, 2001)

Hi there again,

papasan:
I was interested in what Coilcraft had to offer also.
Did you check to see where you could get these coils
in single quantities at all? Can you even get these
in single quantities? If so, please let us know.
I'd like to try a couple of theirs also.
I'm only a little interested in samples unless
i can get the parts in quantities of 1 to maybe 10.
I dont want to have to order 100 though 

wayne:
If you could actually see the LED flashing, something
is very wrong with the circuit. These circuits should run
absolute min of about 1kHz or something, and even that is
really too low. I wouldnt want anything under 20kHz, prefer
50kHz and above. The output ripple would be disastrous.

Mercator/Z300 project:
hopefully this or next week i'll try out the toner thing
using various store copiers. I'll post whatever i find out.
Right now, im doing some more electrical work on our circuit.

Tonight i etched a small adapter board for the ZHCS2000 schottky
diode made by Zetex. I didnt do this before because i was thinking
parts placement had to be very close, but i think we have a little
more room for error in the actual physical layout then i had thought
before. I etched a small board (3/8 inch wide by 1 inch long) to
fit the diode on, and then soldered short leads to the board.
The etched copper really only has one thin line (about 0.03 inch wide)
etched out of it across the 3/8 inch width. The rest is still copper 
clad, so it looks like a pure copper clad board with one very thin 
line of copper missing about in the center of the lenght of the board.
This forms two lands of copper clad.
The diode, being in a 6 pin package, gets four pins soldered to
one land of the copper clad, and two pins soldered to the other land.
The land with the four pins is the cathode, the land with the two pins
soldered is the anode.
Then, two short leads of #24 wire are soldered to the very ends of the 
board, one to each land. This forms two wire leads, which can then be
soldered to the circuit board and unsoldered at will without harming
the diode itself. Since i only have one, this is important right now 

I wont solder leads directly to the package though. This could work,
but the small leads probably cant support the larger leads flexing
and probably will break off. The boards are small and not too hard
to make i guess. In fact, with a dremel tool you could probably
just cut a groove in the copper and solder the device across the
groove, without doing any etching.

I've been learning a lot too on this project. These small parts 
are a bit harder to deal with, but the advantages really outweigh 
the other problems. Once you come up with a few ways to deal with
the smaller sizes, the advantages really start to kick in. I can
envision this circuit eventually on a very small board, maybe 1/2 wide
and 1 inch long. The equivalent 'regular' parts version would probably
take up 4 times that area or more, plus be higher up off the board too.

Next, the diode was soldered in place of the previous diode, which was
a 1N5821 Schottky.
The test results really surprised me. In fact, i put off this test because
when i looked the diode up in the data sheet supplied by Zetex, i found
that this diode wasnt suppose to be much better then a standard 1N5821.
In fact, the current rating was LOWER.
What i found out was that the diode only drops a hair over 0.2 volts
at 1.5 amps! If you read previous posts, i had found that the 1N5821
diode drops 0.37 volts at 1.5 amps. Of course this is quite a bit
less voltage drop when using voltages as low as this, so it effects
efficiency by as much as 3%. The efficiency went up to about 84% after
replacing the 1N5821 with the ZHCS2000 diode.

Ok now here's the kicker:
The drawback here is
that Zetex doesnt actually spec this voltage drop, so i'm wondering now
if some diodes wont actually have this lower drop. I might write them
about that, but i still havent heard anything about the transistor specs.
Specs are something that have always worried me about Zetex. I hope the
situation changes with them or it's going to be hard to say whether or not
we can build a circuit that will always run the same with every part we
buy from Zetex. If the diode only performs as well as a standard diode,
then the extra cash isnt worth it at all. It's a nice small package though,
only about 1/8 inch wide and 1/16 inch long.

More Z300 circuit data:
The next test i did was to determine if the original caps selected would
ever work out in this circuit. I measured the output ripple with the
new diode and it turned out to be almost 0.5 volts peak to peak. This is
really unacceptable for driving an LS, except maybe at lower current average.
Since we dont want that, we need a new cap for sure. Also, i tried a
3.3uf, 10v tant cap in parallel with the electrolytic and the ripple peak 
to peak came down to 0.3 volts. This is a little better, but im shooting
for 0.15 volts peak to peak with the LS running at 350ma average. This will
be a safe level to run the LS. Right now im using the LS simulator,
so the peak to peak data might not be as accurate as with a real LS, but
i would trust the simulator once the ripple is down to 0.15 or so.
In any case, with the original cap i wouldnt run the LS. Using a cap
with 0.1 ohms ESR or less should solve the problem. If i cant find one
locally, i'll have to order it mail order, which will take a little while
to get :-(

I am hoping to build boards for the other transistors tomorrow sometime.
Once mounted, they can be soldered and unsoldered without running into
problems. I'll see if the other transistors will allow this circuit to
be used at voltages lower then 2 volts (like with a single cell), or
if the transistor is even the real problem with getting down to lower
voltages and still maintaining 350ma output. It could be that we just
need to make the sense resistor smaller in value while using an inductor
with very very low series resistance. If the transistor still saturates,
it should work. Of course it's going to draw a lot of current from
the batteries, so battery life is going to go down quite a bit when using
only one cell. Most people probably wont want to do this anyway 

I'll post more results tomorrow also.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*i'm no ee so i wonder how a diode and a cap can give more amperage, i would assume that they were there to smooth out the current...*<HR></BLOCKQUOTE>

Without the capacitor and diode, the LS absorbs all the inductor energy when it discharges. For that reason, it's important to trigger the discharge before the inductor exceeds the maximum pulse current of the LS, which is spec'd at 500mA.

As the inductor discharges, its current falls from, say, 500mA to 400mA. Let's pick 450mA as a good intermediate value.

Then the inductor charges again, and since the transistor is effectively short circuiting the LS, the LS sees little current during the charge cycle.

If the duty cycle is 67%, the LS sees 450mA 67% of the time, and 0mA the other 33%, for an average of only 300mA of current. Thus, it's not as bright as with 350mA.

Because the capacitor can absorb a lot of peak energy, the peak current can be increased, increasing the average current a bit.

However, the capacitor's main job is to supply current to the LS while the inductor is charging (when it would otherwise see zero current). The diode's sole function is to prevent the capacitor from being short circuited by the transistor during this time.


----------



## ElektroLumens (Nov 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
* also, has anyone tried the max-battery life?...only 3 components: ic, resistor, inductor...how much juice can you get out of it?...i'm no ee so i wonder how a diode and a cap can give more amperage, i would assume that they were there to smooth out the current...*<HR></BLOCKQUOTE>

papasan,

I have done a bit of experimenting as you are asking. I was testing the MAX756 IC on a bread board. When I remove the output capacitor, the light will flash in fast pulses. As Duggg pointed out, the capacitor will store energy, and release it when the swith in the IC is off. This as I have observed smooths out the output to a steady flow, kind of like a water gate in a dam.

If I power the IC without the inductor, there is no increase in voltage. This is because the inductor stores the electrical energy as magnetic flux. This flux can be released as higher voltage, lower voltage, or opposite in polarity, depending on the switching topology. The inductor is actually where we can get the increase or decrease in voltage. 

I have noticed that on boost type regulators that the inductor is on the 'IN' voltage side, and that on the step down topology, the inductor is on the 'OUT' side.

The following is an explanation I clipped from somewhere:


A DC/DC converter operates by storing energy as magnetic flux, in an inductor core and then switching this energy into the load. Since it is flux, not charge, that is stored, the output voltage can be higher, lower, or opposite in polarity to the input voltage by choosing an appropriate switching topology. To operate as an efficient energy transfer element, the inductor must fulfill three requirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst-case condition of minimum input voltage and switch ON time. The inductance must also be high enough so that maximum current ratings of the LT1073 and inductor are not exceeded at the other worst-case condition of maximum input voltage and ON time. Additionally, the inductor core must be able to store the required flux, i.e., it must not
saturate. 

The best way to learn these things is hands on, using a bread board. Unfortunately, sometimes things get fried. This can be the school of hard knocks (french fried circuits) sometimes. One time I was removing a diode while the circuit was under load. BAADDDD thing to do. I must have touched the diode lead to the inductor, and, zzzzzzzzt, the chip shorted and became extremely hot! I stupidly used my finger to touch the IC to see if it was hot. Man, that was dumb, I got a blister on the tip of my finger. It is truly amazing how hot these things can get when something goes wrong!


Hope this helps.


----------



## papasan (Nov 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I was interested in what Coilcraft had to offer also.
Did you check to see where you could get these coils
in single quantities at all? Can you even get these
in single quantities? If so, please let us know.
I'd like to try a couple of theirs also.
I'm only a little interested in samples unless
i can get the parts in quantities of 1 to maybe 10.
I dont want to have to order 100 though *<HR></BLOCKQUOTE>

i didn't look into actually ordering any of them, i was waiting to see if they were close to what we wanted first...but you can get samples of 1 or 5 at the smallest depending on which coil it is, and i think it was 10 & 20 max...i got minimums at 5 and 2 when 1 was the min...all 100uH...


----------



## MrAl (Nov 27, 2001)

Hi there again papasan,

The reason i asked was because if i get
1 or 2 samples and i like the samples,
then when i want to buy more if i have to
buy 100 or 1000 pieces, i wont want to
do that 
If you get around to it, maybe you could
check?

--Al


----------



## ElektroLumens (Nov 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> wayne:
If you could actually see the LED flashing, something
is very wrong with the circuit. These circuits should run
absolute min of about 1kHz or something, and even that is
really too low. I wouldnt want anything under 20kHz, prefer
50kHz and above. The output ripple would be disastrous.

<HR></BLOCKQUOTE>

Al,

Your right. Something must have been very wrong, in order to see the pulses. In testing on the bread board, I tried a lot of different combinations. Different inductors, different capacitors. Who knows at this point how I actually had it set up at that particular moment. I wish I had taken meticulous notes of what I had been doing. Also, all the leads would have been really long, with wires going here and there. I'm sure that had something to do with it as well. I have read documentation where the placement of components was critical, and I'm sure on a bread board, I for sure had the parts spread out too much, with too long wires connecting parts. ??


----------



## ElektroLumens (Nov 27, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> Wayne: 
As soon as you get the circuit running, post some results.
Should be interesting. I was working with the Max chip too
a few weeks back. It sure is easy to use that ic.

<HR></BLOCKQUOTE>

Al,

Sorry not to get the results back to you on this MAX756 chip. I wrote all the info on a piece of paper, and I don't have it with me at the moment. I wrote down the different voltage measurements, and computations. I will try to do this tonight. Your feedback to me will be helpful, and also, I really want to learn how to do this testing. Otherwise, how can I know how my circuit designs are doing? I want to improve them to be very efficient, and I would also like to make them small enough to fit inside a small flashlight head. This is all extremely interesting to me.

Also, I placed an order for the Zetex ZXSC300 and components from DIGIKEY. Should be arriving any day now. This should be interesting.


----------



## MrAl (Nov 28, 2001)

Hi there again,

I got to do next to nothing yesterday on
the circuit, as i had some unrelated things
to take care of. Today sometime i hope
to do some more testing. I did however
think over the output ripple problem, and
came up with the following simplification
to understanding the significance of the
output ripple voltage when running an LS:
The LS can be approximately modeled by
three diodes in series, also in series with
a 2.5 ohm resistor. But i think a better 
model could possibly be three standard silicon
diodes in series, also in series with a
Schottky diode, also in series with a 
2 ohm resistor. Once i get an actual LS
i'll be able to nail this down better, but
for now i'll use the 2 + 3 diodes + 1 Schottky
model to explain the significance of the 
output ripple. Believe it or not, this
helps to simplify and clarify what happens
when the output ripple becomes too high, as
well as help to establish a safe operating 
point for running the LS.
Ok, having said that  because we are looking
at changes in output voltage of relatively
small values (0.1, 0.2, 0.3) when the
output changes the resistance sees most of
the voltage change, because even if the
current changes by half the value of the
change in voltage (0.05, 0.1, 0.15) the
voltage across the diodes doesnt change that 
much. This means for a basic idea of what
is happening to the current, we can apply 
the total change to the resistor, and come
up with the resulting increase in output
current though the LS simulator circuit.
We can then ADD this resulting change in
output current to the nominal value
(usually 350ma) to get the peak value
through the LS.
Lets look at a few values of output
ripple and resulting current using this idea:

ripple volts: 0.10 0.20 0.30
ripple amps.: 0.05 0.10 0.15

because we are assuming a 2 ohm resistance
that makes up the LS, we can simply divide
the ripple volts by 2 to come up with
the ripple current.

Now lets take these ripple current calculations and add them to the nominal current of 0.35 to get the peak LS current:

ripple volts: 0.10 0.20 0.30
ripple amps : 0.05 0.10 0.15
peak amps.. : 0.40 0.45 0.50

From this it's easy to see that an average
of 350ma output requires less then 0.15
amps ripple, which requires less then
0.30 amps ripple voltage. This is the
most important reason for needing a low ESR cap. The efficiency has to be secondary
(recall that having a output cap with
10000 ohms ESR would be extremely efficient,
but the output ripple would be astronomical).
Therefore the cap ESR is chosen based solely
on the output ripple requirement.

Now lets see how much we can vary from this.
If we reduce the average current, we can
tolerate an increased ripple voltage.
Adjusting the output current to obtain
0.300 amps output instead of 0.350
and adding the ripple amps to the
average current:

ripple volts: 0.10 0.20 0.30 0.40
ripple amps : 0.05 0.10 0.15 0.20
peak amps.. : 0.35 0.40 0.45 0.50

Now we are able to withstand 0.40 volts
of output ripple. Lets equate this to
ESR to see how much savings this would lead
to in the output cap.
We increased the ripple volts max from
0.30 to 0.40 volts, which would have
come about by a change in ESR of about
+33.33 percent. This means that if we had
chosen a cap with an ESR of 0.10 ohm
originally, we could now get away with
a cap with an ESR of 0.1333 ohms;
not a heck of a lot. Since a cap with
an ESR of about 0.1333 ohms is in the
same price class as one with 0.1 ohms ESR,
we havent accomplished anything at all.
This means we might as well set the average
output current to 0.350 and get the right 
cap to begin with 

wayne:
Welcome to the Zetex 300 project 
What kind of output cap did you order?

Good luck with your LED circuits,
Al


----------



## papasan (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi there again papasan,

The reason i asked was because if i get
1 or 2 samples and i like the samples,
then when i want to buy more if i have to
buy 100 or 1000 pieces, i wont want to
do that 
If you get around to it, maybe you could
check?

--Al*<HR></BLOCKQUOTE>

there are a dozen reps in north america and half a dozen direct sources, i'm sure that with enough begging and pleading that one of them could be conviced to ship a small volume...even if it was just a 'tip' or something for a larger than normal sample shipment...again, let's look into what they actually have before worrying about how to order some...


----------



## ElektroLumens (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*

Wayne: 
As soon as you get the circuit running, post some results.
Should be interesting. I was working with the Max chip too
a few weeks back. It sure is easy to use that ic.

Good luck with your LED circuits,
Al*<HR></BLOCKQUOTE>
Al, Duggg, et. al. . . .

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
MEASURE.BATTERY.EFFICIENCY

Measure the battery current and multiply it by the battery voltage under load. That will give you the "power in" figure. Next, measure the LED current and multiply it by the voltage across the LED. That's the "power out". Efficiency is then simply "power out" divided by "power in", expressed as a percentage.


MEASURING AMPERAGE

BTW, how much current can you get out of the MAX756 with say about 2 volts input? You can use a small series resistor of 1 ohm or less and measure the voltage drop across it. If you use 1 ohm, the voltage measured equals the current though it. If you use 0.1 ohm, multiply the voltage by ten to get the current. A lot of meters dont measure current in these circuits too well anyway, as sometimes their internal resistance is too high.
<HR></BLOCKQUOTE>


Well, I did a little more testing with the MAX756 last night, and here are my results. I hope I did this correct.

Input voltage to the MAX756:	2.078 volts
Voltage across LUXEON: 3.310 volts

On 40/400mV setting on my DVM:

Voltage across 1 ohm resistor on input:	.408
Voltage across 1 ohm resistor on LUX:	.257

If I understood how to use these numbers, and if I did this correctly:

Power IN:
.408 * 2.078 = .847824 

Power Out:
.257 * 3.310 = .85067

.85067 / .847824 = 1.0033568

Or is it? .847824 / .85067 = .996

I think I'm lost here? Anyway, I'm trying.


----------



## ElektroLumens (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
wayne:
Welcome to the Zetex 300 project 
What kind of output cap did you order?

Good luck with your LED circuits,
Al*<HR></BLOCKQUOTE>

Hi Al,

I basically used a list from one of the posts on this thread. Here is what I ordered:

PCE3400CT-ND 220uF 16v SMD electrolytic 

I am hoping that I can find small capacitors and inductors for a few of the other chips I'm playing with. The hand wound inductors, for one thing, are too big. Another thing is I am not exactly sure what the inductance is, at least until I construct the inductance test kit I have. (Too many projects, too little time.)


Perhaps I should have waited until I saw what you were using?


----------



## **DONOTDELETE** (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>MrAl says,
*This means we might as well set the average output current to 0.350 and get the right cap to begin with *<HR></BLOCKQUOTE>

MrAl, check out Digi-Key #P10295. It's a 150uF, 35v non-SMD electrolytic with a 100kHz impedance of 117 millohm. ESR is always less than impedance, and the ESR is even less at 300kHz, so it is electrically very similar to that tantalum you recommended.

Of course, it's much larger physically. But at $0.63 it's way cheaper, and you don't have to buy them in lots of 10.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Wayne says,
*
I basically used a list from one of the posts on this thread. Here is what I ordered:

PCE3400CT-ND 220uF 16v SMD electrolytic*<HR></BLOCKQUOTE>

Wayne, sorry you ordered those same 220uf/16v caps I ordered. The problem, pointed out by later posts, is that they have an ESR at 400kHz of 190 millohm, which is well above MrAl's 100 millohm guideline, and using them may subject the LS to too much peak current. The good news is that you can get the ESR to less than 100 millohm by putting two of them in parallel---using a much larger board, unfortunately.


----------



## **DONOTDELETE** (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Wayne says,
*.85067 / .847824 = 1.0033568

Or is it? .847824 / .85067 = .996

I think I'm lost here? Anyway, I'm trying.*<HR></BLOCKQUOTE>

Wayne, with the test resistors in place, is there any visible reduction in output? You can safely short the test resistors to see.

If so, you need to use smaller value resistors, because the resistors are eating too much power. If you have several one-ohm resistors, you can put them in parallel to cut the resistance in half.

Also, you need to take all four voltage measurements with the test resistors in place, otherwise the comparisons isn't valid.

Obviously, output power must be less than input power, because every circuit has losses. There's something amiss here.


----------



## jeff1500 (Nov 28, 2001)

This topic sure is one for the record books. 

I just got a couple MAX757 adjustable output 8 pin dip chips in the mail. They're huge in comparison to the QSOP MAX1700s. I just keep those in a little box for some future attempt to hook them up to something. 

I'm going to try to get the MAX757 circuit going one of these days. The chip plugs directly into my breadboard. The data sheet says 87% efficiency at 200 mA and operates down to 0.7 volts input for a output range from 2.7 to 5.5 volts.

Maybe someone has posted the answer to this, but, If I hook up an led directly to the chip with the voltage adjusted to 3.6 or so, will the led by itself draw too much current or will I need a resistor in front of the led to limit the current?

How critical is the inductor size? The circuit calls for 22 uH. Can I use a hand wound ferrite bead inductor of relatively unknow inductance?


----------



## MrAl (Nov 28, 2001)

Hi there everyone interested in this project,
I responded to the various posts in the order i read them.

papasan:
Ok papasan, i just like to know ahead of time 

wayne:
>>
Or is it? .847824 / .85067 = .996
<<
It's Pout/Pin, so you will always get a number less then 1.
If you get a number greater then 1, its not right.
If you get a number too close to 1 (like 0.996 above), something
is wrong with the measurements. Since this is the case, you might
try making the measurements more carefully. You should get an efficiency
between about 70% and 90%. This is generally where converters operate.

Perhaps you might
need to use a 10k ohm resistor in series with a 0.1 uf ceramic disc
cap, and measure the voltage across the 0.1uf cap rather then directly
with the meter directly. If you are using an analog meter, you might have to use
a 1k resistor rather then a 10k, and a 1uf cap instead of a 0.1uf cap.
Using the resistor/cap combination will average the measurement
better then some meters will.
Also, as Duggg was saying, you will have to get some 0.1 ohm resistors
instead of 1 ohm resistors, because the 1 ohm resistors drop too
much voltage for measuring electrical quantities associated with an LS.
Then, to calculate the real approximate efficiency, you can simply add
the voltage drop you read to the input voltage if you are measureing
input current or to the output voltage for the resistor
on the output and use this voltage in the calculation instead of the
input or output voltage.
For example, you have 2 volts input and 3 volts output, with 0.5 amps in
and 0.3 amps out, and you have a 0.1 ohm resistor in series with the input and
another 0.1 ohm resistor in series with the output:
normally you would take the Vout*Iout/(Vin*Iin) to the get efficiency.
Instead, use:
eff=[(Vout+(0.3*0.1))*Iout]/[(Vin+(0.5*0.1))*Iin]
and this will give you a better idea of the eff without removing
the resistors.
Note the only difference was we added the resistor's voltage drops
to either input or output voltage to get the efficiency.
Whether we add to the input voltage or output voltage simply depends on
where the resistor is located

Here's the new cap i chose:
150uf, 10v, ESR=0.1 ohms, Irms=1225ma, P11289CT-ND $3.13 (panasonic EEJ-L1AD157R)

After checking out Duggg's post, i went and looked at those caps also,
and it's possible the
470uf, 35v, ESR=0.052, Irms=1220ma, Hours life=3000, part# P10301-ND $0.99 (Panasonic EEU-FC1V471)
might work also.

The reason i chose the first cap is because of the low 0.1 ESR and that value doesnt
change over time because of the type of capacitor (also its a SM device), and
because it's pretty certain this cap should work very well.

The reason i chose the second cap is because of the low 0.052 impedance, which is
about half of the 0.1 ESR because after 3000 hours the ESR doubles to about 0.10 ohms,
meaning the cap will still function pretty good after 3000 hours of operation,
and it's cheaper then the first cap  The first cap doesnt age like this.

>>
I have a question regarding switching frequency, and how it relates to the capacitor selection and the diode selection. For example I am looking at 2 chips, one is the MAX756, which has a maximum switching frequency of 500kHz. Another is the LT1073, which has a frequency of 15-23 kHz. Now, I am assuming because of the slower frequency of the LT1073, it is a noisy chip, producing a lot of EMI? Ripple?
<<
In general, the higher the frequency of operation the lower output capacitance
required to attain a certain upper limit on the peak current. At 12kHz, you
would require 10 times the capacitance as at 120Khz to attain the same limit
on peak output current and ripple voltage. On the other side of the coin,
the transistor has to switch 10 times more then at 12kHz, so this requires 
a modern fast switching transistor with fast rise and fall times.
With today's transistors this isnt too hard to achieve, meaning the higher
operating frequency is to be preferred over the lower.

As far as the diodes go, the standard silicon diodes drop too much voltage
at about 1 amp or more and are also pretty slow because of lots of
parallel capacitance, so we go with a Schottky diode that normally has
half the voltage drop, and this solves the speed problem simultaneously.
Thanks to Dr. Schottky 

Jeff:
Hi there again !
I had worked with the Max756, and i had found this circuit to be VERY easy
to work with. For one thing, i used inductor sizes of 100uH to about 1000Uh
and they all worked.
The only exception to this is that the low voltage input spec didnt seem quite
as good as the spec said.
The higher inductance works better at low input voltage,
probably because there are more turns with the same core size that i used.
I tried 10 turns to 20 turns, and they all worked well. With a big inductance,
the circuit operates by ratcheting the current up and then finally 
letting the inductor discharge. The only drawback is that this would 
create higher ripple voltage, but with the normal 20ma LED's this
isnt a problem.

About the voltage with no resistor:
This is one thing you can get away with with the Max757 chip that i couldnt
do with the Max756 because you can adjust a resistor to set the output
voltage. With the Max756 you can't do this, so you have to use a series
resistor which cuts eff. If you want too, you can use a pot to set the
output current. Start with the lowest current of course and adjust up.
I used the output Schottky and about 10uf capacitor. You can probably get
away with 2.2uf for one 20ma LED.
You can probably get eff up to about 85% with that circuit at nominal
input voltage, as that ic chip uses a MOSFET for the switching transistor.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Meaning the P10301 will still function pretty good after 3000 hours of operation, and it's cheaper then the first cap  The first cap doesnt age like this.*<HR></BLOCKQUOTE>

The 3000-hour figure is quoted when the capacitor is operated at 105° Celsius.

Correct me if I'm wrong, but I doubt many of us will be using our Luxeons as oven lights.

The general guideline is that lifetime is doubled for each 10° drop from the rated temperature. That means a capacitor with a 3000 hour rating at 105°C will last 256 times longer at 25°C. 3000x256 = 768,000 hours. That's over 87 years.

In other words, age-related changes are a non-issue, and there's no reason to pick a larger and more expensive capacitor. The P10295 should do just fine. It's actually smaller than its nearest SMD electrolytic counterpart.

When the P11289 SMD tantalum finally becomes available in a couple of months, its much smaller size may appeal to those willing to spend the extra $2.50, assuming a smaller board is also made available.


----------



## ElektroLumens (Nov 28, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jeff1500:
*This topic sure is one for the record books. 

I just got a couple MAX757 adjustable output 8 pin dip chips in the mail. They're huge in comparison to the QSOP MAX1700s. I just keep those in a little box for some future attempt to hook them up to something. 

I'm going to try to get the MAX757 circuit going one of these days. The chip plugs directly into my breadboard. The data sheet says 87% efficiency at 200 mA and operates down to 0.7 volts input for a output range from 2.7 to 5.5 volts.

Maybe someone has posted the answer to this, but, If I hook up an led directly to the chip with the voltage adjusted to 3.6 or so, will the led by itself draw too much current or will I need a resistor in front of the led to limit the current?

How critical is the inductor size? The circuit calls for 22 uH. Can I use a hand wound ferrite bead inductor of relatively unknow inductance?*<HR></BLOCKQUOTE>


Jeff,

I also receive a couple of MAX757 chips, and I also have put together a number of boards with the MAX756. Drives the LUXEON real nice, even down to 1 volt in. The board I made measures about 1" X 2". Kind of big, but it works.

I have driven just one Nichia just fine.


----------



## ElektroLumens (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Wayne, with the test resistors in place, is there any visible reduction in output? You can safely short the test resistors to see.

If so, you need to use smaller value resistors, because the resistors are eating too much power. If you have several one-ohm resistors, you can put them in parallel to cut the resistance in half.

Also, you need to take all four voltage measurements with the test resistors in place, otherwise the comparisons isn't valid.

Obviously, output power must be less than input power, because every circuit has losses. There's something amiss here.*<HR></BLOCKQUOTE>


Duggg,

Okay, I thought something was off. I thought I'd post what I had anyway, so I could actually figure this thing out. Probably very simple to do, but anyway, I'm just a learner.

There was a very slight reduction in brightness when I powered the Luxeon with the resistor. I figured it was probably too much resistance, and I guess it is. I am using a 2 watt 1 ohm resistor, which actually had a 1.1 ohm reading.

I will run the test with a lower resistor, or a few in series, and do it at all 4 points as mentioned. I'll post results later.

I have a question regarding switching frequency, and how it relates to the capacitor selection and the diode selection. For example I am looking at 2 chips, one is the MAX756, which has a maximum switching frequency of 500kHz. Another is the LT1073, which has a frequency of 15-23 kHz. Now, I am assuming because of the slower frequency of the LT1073, it is a noisy chip, producing a lot of EMI? Ripple?

Anyway, in selecting capacitors, what is the criteria for this. If you've posted this elsewhere, you might just point me to that post, or re-answer?

Also, in selectin Diodes, the speed, forward drop, and leakage are mentioned in documentation as selection criteria. I'm not sure I adequately understand how this relates to oscillation speed of the IC.

You are testing different caps for the ZETEX chip, and I ordered the incorrect one, and I can correct this and order the correct ones. I probably made some bad choices for the other chips I am working with, and perhaps I can learn something here related to capacitors and the diodes. Of course, things might work, but maximum efficiency should be very high up there on the list of importance, and then the size of the board comes behind that.


Thanks for your help and input.


----------



## MrAl (Nov 29, 2001)

Duggg:
You're right about the lesser extent of the ageing then i made it
sound like, but this time i wanted to cover all the bases with
one cap that would certainly do the job. The SM cap will
do everything we want it too do, as well as be small in
size to make the most compact circuit possible. If we have to
wait a couple months then thats the way it goes. In the mean time
we can test with other caps like the other one i posted.

The second cap i chose wasnt just for the ESR either. It also
has a very high ripple current rating. In the circuit i have here,
im seeing 1.5 amps peak inductor/diode current. With 500ma peak flowing
through the LS, that leaves 1.0 amps flowing through the cap.
The second cap i chose has a ripple current rating of 1.2 amps, as
well as the first cap i chose. I'm just not sure if your P10295 cap
will be able to handle this, as the ripple current rating at 100kHz is
555ma. I couldnt find any re-rating notes on frequencies HIGHER
then 100kHz, or temperatures lower then 105 deg C for the ripple current
rating, did you? It's possible it still might work if there isnt
too much internal heating. If you find anything else out about this
please let me know.

I'm sorry to hear that the SM cap wont be in for a couple months too,
i was looking forward to trying that cap out.

Well, good luck with your circuit, and 
thanks for looking up that information.

Al


----------



## papasan (Nov 29, 2001)

there's been soem coil talk and alot of cap talk...did a transistor ever get settled on?...perhaps i missed it, but 14 pages is alot to go back through =P...so is there one that stands out as being ideal for this z300/z310 circuit?...


----------



## MrAl (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*there's been soem coil talk and alot of cap talk...did a transistor ever get settled on?...perhaps i missed it, but 14 pages is alot to go back through =P...so is there one that stands out as being ideal for this z300/z310 circuit?...*<HR></BLOCKQUOTE>


papasan:
It looks like the FMMT617 or FMMT618 
transistor will work ok for 2 cell apps.
The 688B transistor will be a little less
efficient, so we are trying to stay with
one of these two for now. These transistors
are pretty good. It's too bad Zetex doesnt
guarantee any max switching limits for their
transistors, but so far they are working
pretty darn good. Also, when i talked
to the Principle Device Engineer, he
told me he would forward my request for
guaranteed specs and see what happens, but for
the moment they dont spec this.
Whatever we get, we get i guess 

--Al


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## papasan (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*It looks like the FMMT617 or FMMT618 
transistor will work ok for 2 cell apps.*<HR></BLOCKQUOTE>

looking over the data sheet it seems that the only difference between these two is the max power...the 617=3A, the 618=2.5A...since they are both the same price, is there any reason to get the lower rated one?...smaller package?...also, rates the R of 617 50mO @ 3A, the 618 50mO @ 2A...so does it follow that the 617 would have a lower R at 2A?...

** edit **

going over the stuff again i see this is the exact one recomended frem zetex...so there recomended components remain the same?...just changing to cap to better control the power ripples?...i'll have to go back and see why we're looking at ~150uF caps instead of the recomended 2.2uF one...

as you can see i'm still learning =)...


----------



## **DONOTDELETE** (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*In the circuit i have here, im seeing 1.5 amps peak inductor/diode current. With 500ma peak flowing through the LS, that leaves 1.0 amps flowing through the cap.*

I think your value of Ipeak is a tad high. I'm getting the full 350mA output current with Rsense=0.017 ohm in my non-SMD circuit, which implies Ipeak=0.019/0.017 < 1200mA, of which no more than 700mA should be flowing through the cap.

*I'm just not sure if your P10295 cap will be able to handle this, as the ripple current rating at 100kHz is 555ma. I couldnt find any re-rating notes on frequencies HIGHER then 100kHz, or temperatures lower then 105 deg C for the ripple current rating, did you?*

No, but I did research the general behavior of electrolytic capacitors at higher frequencies and lower temperatures. 

Max ripple current can be 5% or so higher at 400kHz, and at least 100% higher at 45°C. 205% of 555mA is 1137mA, so I think we're safe.

And I haven't noticed any substantial capacitor heating, even with the high-ESR capacitor I'm currently using.

No noticeable heating of any component for that matter, except of course the LS itself.
<HR></BLOCKQUOTE>


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## **DONOTDELETE** (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*Looking over the data sheet it seems that the only difference between the 617 and 618 transistor is the max power*

Actually, the 617 is much faster at switching:

617: Ton=120ns, Toff=160ns
618: Ton=170ns, Toff=400ns

With Ic only around 1 amp, max power is not as much a concern as switching speed, especially at 400kHz operating frequency.

*rates the R of 617 50mO @ 3A, the 618 50mO @ 2A...so does it follow that the 617 would have a lower R at 2A?*

Possibly, but the spec sheet Vce(sat) reveals the following for Rsat when Ic=1A:

617: 0.07 ohm typical, 0.10 ohm max
618: 0.07 ohm typical, 0.15 ohm max

So the 617 is not only faster, but has the same or less resistance as the 618. So the 617 is definitely the better choice.

*so there recomended components remain the same?...just changing to cap to better control the power ripples?...i'll have to go back and see why we're looking at ~150uF caps instead of the recomended 2.2uF one...*

Well obviously Rsense is much smaller in order to get the 350mA current demanded by the LS.

Keeping in mind that the original circuit was designed around the popular Nichia NSPW500BS white LED, there are two reasons why the Luxeon Star circuit requires a larger capacitor:

1. The Nichia LED draws 30mA at 4 volts, for an effective resistance of 4/0.03=133 ohms. The LS draws 350mA at 3.5 volts, for an effective resistance of 10 ohms. In order to maintain the same RC time constant during the capacitor discharge phase, we have to multiply C by at least a factor of 133/10 or 13.3, making Cmin=29uF.

2. The Nichia LED operates at 30mA max, but can accept pulses of 100mA. So it can tolerate a huge degree of ripple (100/30 = 3.3!). The LS operates at 350mA max, but can only accept pulses of 500mA. Its ripple tolerance is much less (500/350=1.4) so the capacitor value has to be larger in order to keep the ripple acceptable. MrAl's SPICE simulations show that Cmin has to be at least 47uF with an ESR of no more than 0.1 ohm.

However, only very exotic 47uF caps have an ESR that low. The best we could find was an expensive yet tiny 150uF tantalum, followed closely by a cheaper yet "gigantic" 150uF electrolytic.

<HR></BLOCKQUOTE>


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## **DONOTDELETE** (Nov 29, 2001)

Digi-Key part numbers. All components are SMD unless listed otherwise.

IC ZXSC300E5CT-ND $1.05
Transistor FMMT617CT-ND $0.99
Diode ZHCS2000CT-ND $1.29
Capacitor 150uF P10295-ND (non-SMD) $0.63

For 0.015 ohm resistor, either
P15TCT-ND $11.08 for 10 or
RW1S0BAR015JBK-ND $2.05 or 
12FR015-ND $1.56 (non-SMD)

For 68uH inductor, either 
DN4510-ND 0.059 ohm DCR $2.08 (non-SMD) or
DN3223CT-ND 0.145 ohm DCR $3.36 or
TKS5500CT-ND 0.170 ohm DCR $6.24 or 
M9711CT-ND 0.200 ohm DCR $3.10


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## ElektroLumens (Nov 29, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Digi-Key part numbers. All components are SMD unless listed otherwise.

IC ZXSC300E5CT-ND $1.05
Transistor FMMT617CT-ND $0.99
Diode ZHCS2000CT-ND $1.29
Capacitor 150uF P10295-ND (non-SMD) $0.63

For 0.015 ohm resistor, either
P15TCT-ND $11.08 for 10 or
RW1S0BAR015JBK-ND $2.05 or 
12FR015-ND $1.56 (non-SMD)

For 68uH inductor, either 
DN4510-ND 0.059 ohm DCR $2.08 (non-SMD) or
DN3223CT-ND 0.145 ohm DCR $3.36 or
TKS5500CT-ND 0.170 ohm DCR $6.24 or 
M9711CT-ND 0.200 ohm DCR $3.10*<HR></BLOCKQUOTE>

Duggg,

Awesome! Thanks for the parts list. When I get something going, I'll be sure to let you know.


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
*A FLASHAHOLIC WITHOUT A FLASHLIGHT IS LIKE A SAMARAI WITHOUT A SWORD!* <HR></BLOCKQUOTE>


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## MrAl (Nov 29, 2001)

Duggg:
>>Max ripple current can be 5% or so higher at 400kHz, and at least 100% higher at 45°C.
205% of 555mA is 1137mA, so I think we're safe.
<<
Ok then Duggg, i'll include one for my next digikey order for testing.

papasan:
I agree with Duggg, in that the 617 transistor is to be preferred over
the 618, but it's very hard to compare transistors when you dont have
the max turn off time or the rise and fall times of the transistors. 
The rise and fall times of the transistors determine the effect
of efficiency loss with frequency, something we cant compare because
Zetex doest spec this. We can guess, going by the typical specs,
so thats what we are doing.
This is what i was writing about in one of my previous posts. It's
very hard to say that one transistor will always be faster then another
when they dont spec the max times.
I started with the 618 because i thought it was the lesser
of the three transistors i received, so that if i had any initial problems
that took out the 618 transistor i would still have the 'good' ones left
It looks to me that the only way you can destroy the transistor in this
circuit is to use a resistance for Rsense that is too low, causing too 
much current to flow in the transistor.
In general though im pretty impressed with
Zetex's parts, especially the 2000 diode which drops almost
half as much voltage as a typical 1N5821 diode.

Everyone working on this circuit:
Lets not forget though that the variations in the chip may require
one circuit that operates at 350ma to be different then an exact 
looking circuit that also operates at 350ma because of the variation
in the Isense voltage. One circuit may require 0.010 ohms while another
circuit requires 0.015 ohms while still yet another circuit requires
0.020 ohms. This means the sense resistor will have to be hand selected.
Already i have seen some variation in the sense resistance, as Duggg has
reported using 0.017 ohms while at 0.015 im only getting 280ma output.
It might also vary according to the voltage drop you happen to get
with your particular LS.

One thing about this project looks good now, that is, we are getting
ever so much closer to the preferred components. The only down side
looks like this circuit sure wont be the cheapest solution. I'd
say about $8 to $10 (US) for one circuit just for the parts.
On the other hand, it may be the smallest solution obtainable for
driving up at 350ma.

I hope to get the adapter boards done very soon for the other transistors
so i can test my circuit with them also.
I've had some other things to do this week
so ive been a little slow getting to test 
the others.

Good luck with your LED circuits,
Al


----------



## papasan (Nov 29, 2001)

the thread that never dies...

so i got some coils from CoilCraft...not the smallest ones they have, but they're not *too* bad and they have decently low resistance...the shielded DS5022P and the unshielded DO5022P...i'm not used to dealign with metric units so i couldn't really visualize them before i saw them...about the height of 5 pennies stacked, but thinner than a dime...

i'm trying to get some caps samples from the illinois cap company, but from their site they seem very uptight about who they give samples to, so i'm not holding my breath...

so here's my shopping list...

<UL TYPE=SQUARE>02 x ZXSC310CT-ND = Zetex IC @ $0.81
01 x 33205CA-ND = Surfboard SOT23-5 SMD-SIP adapter @ $1.86

02 x ZHCS2000CT-ND = Zetex Schottky diode @ $1.29
01 x 33206CA-ND = Surfboard SOT23-6 SMD-SIP adapter @ $2.07

02 x FMMT617CT-ND = Zetex NPN transistor @ $0.99
01 x 33003CA-ND = Surfboard SOT-323 SMD-SIP adapter @ $1.01

02 x (if no illcaps come in) P10295-ND = Panasonic 150uF low DSR capacitor @ $0.63

01 x (got a few) = CoilCraft 100uH SMD inductor

various ?watt resistors from 10 to 20 mO
[/list]

the surfboards i'm still considering...be nice to breadboard, but seems like alot has been settled on already so i don't know if it's worth the effort...

a question about resistors...how much heat do they need to disapate?...are 1/4 watts okay or are they going to be taking full load (1.5~2 watt)?...i would think that Isense wouldn't be able to take but so much juice so 1/4 or 1/8th would be okay, but i thought i would ask...

any thoughts/comments/suggestions?...


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## ElektroLumens (Nov 30, 2001)

Duggg, Al,

I ordered some parts for the Zetex project I am about to start. I guess I didn't order the right stuff. I would like to place another order, and perhaps get my regulator to work. I realize you're still in the process of determining the best components, but I wonder if you could summarize for me a parts list, so at least I can put something together anyway, and perhaps later I can improve upon it with better components. I am having trouble determining from your previous posts what would be best to order. I don't want to order stuff I cannot use. Sounds like this will be a real nice regulator for the Luxeon, when all the testing is done.

Thanks for all your help and advice.


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
*A FLASHOHOLIC WITHOUT A FLASHLIGHT IS LIKE A SAMURAI WITHOUT A SWORD!* <HR></BLOCKQUOTE>


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## MrAl (Nov 30, 2001)

>>>
the thread that never dies...
<<<
he he he he he...
This turned out to be an interesting circuit/project as more people
are going in for the LS now and multiple LED's too.

Pmax=0.0004/R<=0.08 watts
so this resistor could be 1/8 watt or up.

You can save some money on the diode surf board by taking a strip of
copper clad board about 1.4 inch wide and cutting a groove across the
width about in the center of the board, making it about 0.025 inches 
wide creating two lands of copper. Then, simply solder the diode
across the gap, 4 leads to one side and 2 to the other.
1,2,5,6 are the cathode, and 3,4 are the anode (look that up anyway).

I'm also working on a new electrical model of the LS as i have obtained
some more accurate data now. It appears that the LS has a flatter curve
then the Nichia LED, which means it is more sensitive to output ripple then
originally thought. I'm now thinking that it would be best for anyone
building this circuit (for the LS) to measure the output peak current,
or at least measure average output voltage and peak output voltage just
to make sure they are operating their LS at a safe level. If it becomes
necessary we will incorporate a simple output filter to help with the
ripple output current making absolutely sure the LS runs under safe
operating conditions as per the manufacturers recommendations.
I dont want my LS (when i get one that is) failing prematurely, i dont
think anyone else does either.

About the parts:
We now know the ZHCS2000CT-ND drops the least amount of voltage, so
thats probably going to be the best for currents up to 2 amps. Since
we are running around 1.5 amps peak, it should work great. I will be
getting more of these diodes in soon too, and i will test every one of
them and report results here.

Good luck with your LED circuits,
Al


----------



## Mercator (Nov 30, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*

the surfboards i'm still considering...be nice to breadboard, but seems like alot has been settled on already so i don't know if it's worth the effort...

thoughts/comments/suggestions?...*<HR></BLOCKQUOTE>

*papasan....*

Hello and welcome to the Z300 project.

You can build the surf board for the 2000 diode as MrAl suggested or purchase the surfboards from Digi-Key for both the trans and diode. Or.... if you like to do alittle trading I can supply you with one of the proto-boards I've designed for the project. It will accept both the IC and transistor. It is designed to make mounting just about any other supporting component possible. I designed it in such a way that the soldering on the SMD's is easy. You can take a look at this board at the following link:
Z300 ProtoBoard

I'm mot looking for much in trade value. Perhaps a few Zetex Z300's, transistors or diodes.

If you're interested, send me a personal email with your addresses.

Mercator


----------



## MrAl (Nov 30, 2001)

Hello again everybody interested in the Zetex 300 circuit (or just driving
the LS at 350ma average current),

I found a pretty decent method of measuring the output ripple
voltage. This means you can measure the approximate output
ripple in order to determine if the output is suitably safe
for driving the LS. Assuming you are driving it at 350ma,
you wont want more then about 150mv of ripple voltage, because
the dynamic impedance of the device is about 1 ohm around this
voltage. This means for every increase in voltage of 0.15 volts
there will be a corresponding increase in current through the
device of about 0.15 amps. Since at 350ma the device can only 
tolerate another 150ma, we can allow only another 0.15 volts
on top of whatever it happens to be running with 350ma average
current through it.
The only requirement is that you need a voltmeter with a 10 megohm
input in order to measure this fairly important quantity. Since
most digital meters have this feature, it shouldnt be hard to do.
If you dont have a digital meter yet, maybe you should look into it.
Even the cheap ones around 15 to 20 dollars (US) have 10 megohm inputs.
Of course you want to check the specs before you buy, and while you are
doing that make sure the dc scale measures down at least into the 100's
of microvolts. This means you can measure a voltage such as
167.3mv on the 200mv scale. Beware some very very cheap meters wont
let you do that; they will only read out 167mv on the 200mv scale,
or else doesnt have a 200mv scale!
That extra digit comes in handy for measuring voltages across small
value resistors such as when measuring dc currents.

Ok here is the method, it requires a small network as shown below.

Parts:
C1 0.1uf 50v ceramic disc cap
C2 0.001uf, 50v ceramic disc cap
C3 0.01uf 50v ceramic disc cap
R1 22 ohm, 1/4 watt carbon resistor
R2 10k, 1/4 watt carbon resistor
D1 1N5817 Schottky diode (a=anode, c=cathode)


Network:

```

```
Connect as shown and set the meter on 2 volts dc.
Fire up the circuit and read the dc volts on the meter.
Anything over 0.100 volts is no good. Anything under 0.100 volts is good.
Thats the general idea, to have a go/no-go test for output ripple.

I tried various types of caps i had laying around. 
The results obtained reading the network output dc voltage correlated well
with the actual ripple max output around 0.100 volts. 
I found that using high capacitance worked almost as well as
low ESR capacitance. Using a low ESR tant cap 100uf, 20v, worked
the best, but a combined total of 100uf and 300uf cheap electrolytics in
parallel wasnt too bad either. Both came in under 0.100 volts dc with the
network while the actual ripple was just under 0.150 volts for the electrolytics
and under 0.030 volts with the low ESR cap, looking at the major harmonics.

If you assemble your circuit and measure the output ripple to be over
0.100 volts (with the network) and you dont feel like adding another
cap in parallel, you can also lower the average current somewhat if you
change the current sense resistor or add a little resistance in series
with it. If you read 0.120 volts for example, you can always lower the
average current to 300ma and still drive the LS safely.
The limit here though should be about 0.120 volts. Anything over 0.120 volts
should be avoided in any case. Either get a better cap or add another one
in parallel untill it comes in under 0.120 volts. I would prefer a limit
of 0.100 volts. With a limit of 0.100 volts you can be sure the circuit
will run the LS safely.

If you dont want to get a digital meter,
you might be able to get away with using
a JFET input op amp. They are very cheap too
and have high input impedance. Set the
gain for 1 and use the op amp as a buffer
for the voltmeter. Since the output to the
meter from the network is dc, it wont require
a high speed op amp, just a general purpose
JFET input like the LF353 or TL082 for 
example.
Good luck with it,
Al


----------



## Klaus (Nov 30, 2001)

MrAl, Wayne, Mercator, Duggg, php, papasan, jeff, - did I forgot someone ?

You were the guys I tried to adress in my thread CPF project light "Ultimate Nighthunter Dominator Killer" at 1000+ lumens/1hour when I wrote about the "technical guys around here who are doing their circuit stuff for variuos applications" - pls just have a fast click and look over there and see if this would be of any interest for you.

TIA

Klaus


----------



## MrAl (Nov 30, 2001)

Hi there Klaus,

Sounds interesting. What type of LED's
do you plan to use?

Everyone working on the Zetex 300 circuit:

Some slightly bad news:

The Delevan inductor has proven to be a bad 
choice. Apparently, both inductors i tested
show signs that they have an extremely large
air gap. This time i tested BOTH inductors
under conditions apart from the circuit and
found out that they both have such large
air gaps that they wont be suitable for
our application. We need inductors with
closed magnetic paths or very small air gaps.
The delevan inductor is apparently an
open bobbin construction. I proved this by
wrapping 10 turns around the outside diameter
of the inductor, and sure enough, it acts as
a lossy transformer, coupling the signal 
from the primary to the secondary. From 
the level of the output, i would say it
has about 40 turns on it, but it doesnt matter.
We may wish to stick with toroid core 
inductors for this circuit or other types that
have completely closed mag paths.

The problem with an air gap that is too large
is that the inductor saturates with much less
current then the max spec shown on the data sheet. This explains the sub harmonic 
oscillation: the inductor 'swings' between
two extremes in inductance, like the so-
called 'swinging choke'. The difference
here is that we DONT want that 

To see the difference, the Delevan doesnt show
desirable properties untill up around 1MHz,
and even then its not really that good.
Driving other cores with a square wave,
the current ramps up slowly. Driving
the Delevan, it ramps up too quick and,
way before it ramps down the silly thing is
in complete saturation eating eff by the tons.
Testing the value of the inductance with a
sine wave says the inductance value is within
tolerance for both inductors. It's just
the huge air gap that kills its use for us
here.

I would like to get some stock cores from
Magnetics, Inc., that way we know exactly what
we are dealing with. The only problem is
i think their distributors have a minimum
order of $150 US.

I'm ordering 100 cores. Anybody else
want one or two?

If you want to look for a ready made
coil, look for a toroid design with
1.5 amps capability or better and
0.05 ohms dc resistance or less.
BTW, the dc resistance using a hand wound
type comes down to about 0.026 ohms
without even trying to maximize the
wire size to completely fill the core 
I was thinking of trying an even smaller
core size, like 0.2 inches diameter.
I'll try to get a hold of some.

Good luck with your LED circuits,
Al


----------



## jeff1500 (Nov 30, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Klaus:
*MrAl, Wayne, Mercator, Duggg, php, papasan, jeff, - did I forgot someone ?

You were the guys I tried to adress in my thread CPF project light "Ultimate Nighthunter Dominator Killer" at 1000+ lumens/1hour when I wrote about the "technical guys around here who are doing their circuit stuff for variuos applications" - pls just have a fast click and look over there and see if this would be of any interest for you.

TIA

Klaus*<HR></BLOCKQUOTE>

That's quite a project. See if you can formulate some questions for people to think about. Maybe a heavy duty version of something like this that I'm studying now. http://edusite10.tripod.com/led3/max757.html


----------



## MrAl (Nov 30, 2001)

Jeff that file wont display, wonder why?

--Al


----------



## jeff1500 (Nov 30, 2001)

Try it again. I think I fixed it. gif or jpg images have to be in an html file so Tripod ads show up. It used to work with direct image links but people were using it for free ebay hosting and none of the ads were showing up.
http://edusite10.tripod.com/led3/max757.html 

The IC data sheet calls for a 22 uH inductor. That'll make it go at 500 kHz. I wonder if just about any old hand wound inductor would work and make it run at a lower frequency. Something tells me that 500 kHz is way more than I need.


----------



## Mercator (Dec 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*

Network:


Code:




*<HR></BLOCKQUOTE>

MrAl,

Scrounged up the parts for the "Ripple Test Network" Then noticed that for some reason, the way the diagram came out in the post it wasn't clear on just where R2, C2 and C3 connect into the series string of C1, R1 and D1.

Could you please either re-draw this ckt or otherwise advise. Such as... R2 is left of C1, etc., etc..

Thanks,
Mercator


----------



## MrAl (Dec 1, 2001)

Here it is, the "o" indicate a connection point.

```

```
If the post comes out a little strange, here is a verbal description of the network:
Do these in this exact order:
Connect C1 to R2.
Connect loose end of R2 to ground.
Connect loose end of C1 to " cir out + " .
Connect R1 to C2.
Connect loose end of R1 to juntion of C1 and R2.
Connect loose end of C2 to ground.
Connect D1 cathode to C3.
Connect D1 anode to juntion of R1 and C2.
Connect loose end of C3 to ground.
Connect " + dc meter " to D1 cathode (junction of D1 and C3)
Connect " - dc meter " to ground.
Connect " cir out - " to ground.

I suggest you solder all the components in place, and solder the
appropriate connection to the circuit outputs also, making tack solder
connections exactly where you intend to connect the LS in the final circuit.


To help understand the circuit a little:

C1 & R2 make up a high pass filter, so that we only measure
the non-dc component of the output of our circuit (ripple voltage).
R1 & C2 make up a low pass filter, so that we dont measure frequencies too
high that wont bother the LS.
D1 and C3 make up a high speed rectifier/filter to take the ac we do
want to measure and turn it into a dc voltage so that we can measure
it on a regular dc scale, because most ac meters dont respond well to the
kind of ac we want to measure. Also, since we have a dc output,
we can connect an FET input op amp to the output of the network
to use as a buffer without needing an amplifier that would have
to respond to high frequencies. This would allow any kind of meter
to be used. Without the op amp, a digital meter should be used because
of its high 10 megohm input. The op amp of course should have its own
power supply, which could consist of two 9v alkaline batteries, one
for the + supply, and another for the - supply.
The op amp circuit could be made by simply connecting
the inverting terminal of one op amp to it's output, and connecting the
non-inverting input to "+ dc meter" and using the output of the op amp as
the regular meter + dc input. This makes up a unity gain amplifier
sometimes called a "voltage follower" connection. The type of op amp
should be a JFET type, such as LF353 or similar.

Example:

```

```
 Note 1: the LF353 power supply connections are: 8=positive, 4=negative, (there is no ground).
Note 2: power supply common is the common of the two 9v batteries.
Note 3: R3= 10 megohm, 1/4 watt resistor.


Good luck with it,
Al


----------



## papasan (Dec 1, 2001)

mention of the next chip in this line, the 320, that i read about here, mentions that it will have a dimmer control as well...very excellent...just thought i'd pass the word around =)...

anyone know anything about this?...logic control or variable resistor one wonders...no mention of the chip on zetex...


----------



## Mercator (Dec 1, 2001)

*MrAl....*Thanks for the clarification on the "Ripple Test Network". I'm glad I thought to ask. The proper way to build the circuit wasn't what I saw. Too bad displaying the ASCII text that way doesn't always come out right. I had a feeling that the middle rungs of the ladder were shifted over some. Which way I wasn't sure.

I also appreciate the explanation of how this circuit works. You made it clear to understand.

*papasan....* That link to the Zetex 320 is interesting. Wish we had more info. It would be nice if the IC was also an SOT23-5 and not some little 6 or 8 legged solder monster.

Mercator

PS... I stand corrected, The artical did state that they were 5 pin IC's


----------



## MrAl (Dec 1, 2001)

papasan:
thats an interesting link, but i cant
find the part on the Zetex site or at
Digikey. I guess they are planning to
release that chip next.

Mercator:
No problem  It might help to play with
the font settings in your internet options 
too.
The way i see it, if anyone uses the network
and gets a high reading (like 1 volt or more)
it probably means the circuit is oscillating
at a sub harmonic like mine did with the
Delevan inductors and so they really need 
another inductor. If they get a reading 
of about 0.15 to 1 volt it means they 
need a better cap.

While we are waiting for new caps to come in,
i think i'll put the new op amp i got into
the two transistor/one op amp circuit.
Maybe i can get it up to 350ma also.

If that Zetex diode continues to show
such low voltage drop (like 0.2 volts
at 1.5 amps) i think i'll use that diode
in all my circuits. That will increase
the efficiency of the Nichia white led 
circuits also.

You know what else is interesting,
since this circuit functions as a boost
regulator, i dont see why we cant use it
in a dc power supply circuit also.
Possibly using an adjustable linear regulator on the output, we should be able 
to get a variety of output voltages for 
testing other devices that require dc power.
All we have to do is beef up the output 
capacitance a little.

Good luck with it,
Al


----------



## **DONOTDELETE** (Dec 1, 2001)

MrAl,

What Delevan inductor are you using? I've been using the Delevan DN4510 all along and I noticed nothing out of the ordinary.

Of course, the only test tool I have is my analog multimeter, and the Delevan coil may be why I'm only seeing efficiencies in the 70s.

As far as toroid inductors go, it looks like the best bet is the JW Miller PM3604 SMD, 68uH, 1190mA, 0.14 ohm DCR, 14x11.5x6.8mm, Digi-Key M1231-ND, $1.81 each.

I really like its price, although its large size and low current rating aren't as good as the other ferrite bobbin types.

The only toroid meeting the stringent 0.05 ohm DCR requirement is the JW Miller 2211-V, 68uH, 4900mA, 0.046 ohm DCR, Digi-Key M9798-ND, $3.92 each. However, at 24x24x14mm, it's way too big for any flashlight application.


----------



## **DONOTDELETE** (Dec 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*That link to the Zetex 320 is interesting. Wish we had more info. It would be nice if the IC was also an SOT23-5 and not some little 6 or 6 legged solder monster.*<HR></BLOCKQUOTE>

The article says "the IC range includes three SOT23-5 packaged devices", which implies the ZXSC320 should also be a SOT23-5.

How they'll do all that with just five pins remains to be seen!


----------



## **DONOTDELETE** (Dec 1, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I would like to get some stock cores from Magnetics, Inc., that way we know exactly what we are dealing with. The only problem is i think their distributors have a minimum order of $150 US.

I'm ordering 100 cores. Anybody else want one or two?

I was thinking of trying an even smaller core size, like 0.2 inches diameter. I'll try to get a hold of some.
*<HR></BLOCKQUOTE>

MrAl, 0.2 inches (5mm) is a good diameter for our purposes, but are you describing a toroidal or cylindrical core? What height are we talking about? What core material are you thinking of using?

How much would one or two cores cost?

That should give us an idea as to whether a homebrew coil would truly be more practical than a manufactured one, as there are lot of factors to consider when designing an inductor.


----------



## MrAl (Dec 2, 2001)

Hi there again Duggg,

I tested the DN4510 and the DN4512. The inductance checks out ok,
about 10% lower then the marked value for both inductors. That 
doesnt bother me at all. The thing that bothers me is that 
both inductors are wound on a magnetic material bobbin with no
magnetic cover sleeve. This means about half the magnetic path
is through the air. Since air is a poor 'conductor' of magnetic
flux, we loose lots of efficiency. If, on the other hand, the
device had a magnetic material sleeve that covered it and connected
from the bottom of the bobbin to the top of the bobbin it could
form a magnetic path composed entirely of magnetic material, which
means the flux would always be traveling though a high mu medium.
A pot core would be a good example, where the flux could travel up the
center bobbin (in the center of the coil) and down the sides (on the
outside of the coil) all the while though magnetic high mu material.
Another good example is the toriod core, where the flux travels around
the circle of the toriod almost all of which remains inside the core
material. If efficiency was the only issue we might get by, however
the inductor doesnt function properly in this kind of circuit.
It might work in a circuit operating up in the MHz, but im not really sure
about that. I think the efficiency would still suffer anyway.
In our lower frequency application, the inductor 'looks' like
a normal inductor for a very very short period of time, but then 
saturates WAY before the normal charge cycle is completed.
To make a toriod into an inductor that might act like these Delevans, we
could cut a toriod in half so that we have two "C" shapes. Then, wind
turns of wire around one of these halves. Now the flux travels partly
in the magnetic core material and partly in air, as the return flux path
is now outside of the construction. This would cut efficiency down badly.
On the other hand, if we could cut just a very thin slice out of the
toroid so that we still had mostly a donut shape with a thin slice 
removed so that there was a small 'gap' in the donut, then most of the
flux would still remain in the core, with only a little 'leaking' out
as fringe flux. This would still effect efficiency, but not as much.
The best though is no gap at all, and that works fine anyway. We just
need a core that we can get with known characteristics so that we can
repeatedly get the same core, thats why i suggested Magnetics, Inc.
Some typical cores to be tried could be:
A-40402-TC, which is about 0.2 inches in diameter,
and A-40705-TC, which is about 0.3 inches in diameter.
I guess it would be worth it to try the "F" material versions of 
each of these cores also, if we could get samples. If you feel like
contacting Magnetics, ask about those parts. Let me know what happens.
Last time i contacted them was about 3 years ago, but it was for
100 to 500 watt apps that were using pot cores. They referred me to
a distributor who generously provided 2 samples of about 4 different cores.
The only problem is, if your going to build 10 circuits to start with
that only require 1 core each, you may have to buy 150 cores at $1 each to make the
minimum. On the other hand, that was then. Perhaps things have changed since
then at that company. Maybe i'll give them a call and see what surfaces.
I dont know what the actual price would be either yet, but i dont imagine
it could be very high with such small cores.
Untill then, i can get cores that work, but they are 3/8 inch diameter.
Im in the process of trying to find out who makes them, otherwise we may have
to test our circuit at elevated temperatures to make sure the core mu
doesnt change too much. I have a feeling it wont matter all that much though,
because the mode in which we are using this chip allows a very wide
range of inductance values, so probably the only change we would see
at higher temperatures is a bit lower efficiency.
Also, if we design our own inductor, we know exactly what we have. In case
some company goes out of business, we can look elsewhere for a similar core
and get the same results. I dont really like using a core i dont know
where to get more of.

It doesnt surprise me now that you are getting less then 70% efficiency
after seeing first hand how this inductor works in our circuit.
If you want to see 80%, try winding your own core. Perhaps you have
a core laying around you can try? If not, i'll send you one to try.
If i can get more, i'll send more too.

Is there any way possible for you to get a hold of a digital meter
so you could test the output ripple voltage? See, when the circuit
oscillates at the sub harmonic i was talking about, the output ripple
goes WAY up. I didnt measure it under that condition (perhaps i should)
but typically it would go up to something like 1.5 volts with the LS simulator
connected to the output of the circuit (dont use the real LS yet). 1.5 volts
is a REALLY lot of ripple to see im sure you will agree. When this happens,
it may not hurt the LS because the peak is still under 500ma, but i wouldnt
want to take a chance. With the right inductor, you will see a nice
smooth output (of course with the right cap too). Is there any way you could
borrow a digital meter with 10 megohm input, or build the LF353 buffer circuit?

Oh, another idea that might work is to perform an impedance transformation
on the network:
raise the value of all the caps
in the network (without op amp) to 100 times their values now. This means
change the 0.1uf to 10uf, and the 0.001uf to 0.1uf, and the 0.01uf to 1.0 uf.
Also, change the 22 ohm resistor to 0.2 ohms (or 0.25 ohms if you have one),
and the 10k resistor to 100 ohms. This divides all the resistors by 100.
Then try taking a reading with your analog meter on the 10v dc scale.
This might tell us how the ripple is doing also. You will want to
put the + side of the 10uf toward the circuit + output, and
the + side of the 1uf toward the cathode of the diode.
All this circuit does anyway is remove the dc part of the output
and turn the ac part (ripple voltage) into dc so we can read it on
a dc scale.

Knowing the ripple output is a very important aspect of this circuit.
Anyone using this circuit should somehow measure the ripple and try to 
get it under 0.15 volts max. Using any of the networks, 0.12 volts dc max.

The inductor's dc resistance isnt really all 'that' strict:
for every 0.1 ohm resistance, the efficiency will drop about 3.5%.
So, for 0.2 ohms, it will drop about 7%, etc.
I figured if we had 0.05 max, we would lose only about 1.5% or something.
If we use our own core and 3/8 inch diameter is an acceptable size,
then we can bring it down even lower, like maybe 0.01 ohms, which would
lose less then 0.5 percent eff. (2.4 volt input and 3.3 volt output).

Maybe i'll contact Magnetics sometime this week and see what happens.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Dec 2, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*The inductor's dc resistance isnt really all 'that' strict: for every 0.1 ohm resistance, the efficiency will drop about 3.5%.*<HR></BLOCKQUOTE>

I think that figure's a bit exaggerated. At 2.4 volts, average input current is about 600mA. I submit this is also the average inductor current.

At 0.1 ohm DCR, the inductor is dissipating 0.6*0.6*0.1 = 36mW. With input power at 2.4*0.6 = 1500mW, 36mW is 2.4%, so each 0.1 ohm of DCR represents an efficiency loss of 2.4%, not 3.5%.

Regarding inductor air gaps, their purpose is to increase the saturation current, not lower it. Eliminating the air gap will cause the inductor to saturate even sooner, which is exactly what we don't want.

However, air gaps do cause inductance leakage, which lowers the effective inductance and results in lower efficiencies, so I agree with you that ungapped is probably preferable for power applications like ours.

What I suspect is happening, though, is skin effect, which is very significant at 400kHz, and especially in high-current inductors which use larger diameter wire. The skin effect forces most of the current to the surface of the conductor wire, increasing its AC resistance, and thus lowering the circuit efficiency.

This is one of the reasons why high-quality inductors not only use small diameter wire, but expensive stranded wire with insulation around each strand. This in turn is why the commercially available inductors seem so expensive and seem to have such relatively high DCR.

Therefore, I'm quite skeptical about whether we can successfully design a 12x12x6mm 68uH coil with a DCR less than 0.1 ohm that won't saturate under 1000mA, or exhibit these skin effect losses.

The good news is that the smaller inductors I spec'd should not saturate until well above Ipeak. Indeed, the M9711 shows a saturation current of 1400mA.

The bad news is that trying to get inductor loss much below 2.5% will likely be a fruitless endeavor. That's the main reason why Zetex doesn't claim an efficiency higher than 87%.

However, I'm not at all discouraged! Even with a 3% inductor loss, circuit efficiency should still be in the 85% range, which is quite acceptable, to me at least.


----------



## **DONOTDELETE** (Dec 2, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*What i found out was that the Zetex diode only drops a hair over 0.2 volts at 1.5 amps! If you read previous posts, i had found that the 1N5821 diode drops 0.37 volts at 1.5 amps.*

That's great news about the Zetex diode. The diode is the main power waster in the circuit. If you're getting 200mV at 1500mA, it should be even less at 1000mA. Very exciting news!

*Ok now here's the kicker: Zetex doesnt actually spec this voltage drop, so i'm wondering now if some diodes wont actually have this lower drop.*<HR></BLOCKQUOTE>

Zetex does in fact spec the 1500mA drop at 445mV max, with a typical drop of 380mV, so the fact that you're seeing only 200mV appears quite atypical. Either there's a large variance in component quality at Zetex (not good), or they have improved their production runs and just haven't updated the spec sheets yet (also not good, but better).

I have one of those diodes myself, but am eagerly awaiting the arrival of an SMD soldering iron in the mail this week to put it to the test.

By the way, I just took some efficiency measurements again. The new LS must be more efficient, because instead of 3.1 volts, it's now dropping 3.35 volts at 350mA. That boosts my efficiency to just above 81%.


----------



## MrAl (Dec 3, 2001)

Hi again Duggg,

My only point with the inductor DCR was that 
if you can put up with a few percent of eff loss, then
you can use a 0.1 ohm inductor.

Inductor air gaps are used to increase the level of current
that the construction saturates at, but they are always very small.
When you get an air gap that is just as long as the magnetic metal,
you get another situation altogether. With the Delevan inductor,
i am seeing saturation way too soon in the cycle. Without even 
considering the air gap, it is sufficient to know that the
overall permeability is much less then the initial permeability.
This makes the inductor look 'ok' untill some significant
current starts to flow, and then it looks like a dead short. It could be that
the core diameter is too small. I may
take one of mine apart and examine the
construction completely.

Skin effect plays a part in the ac resistance. The more skin effect the 
higher the ac resistance. The only problem with larger diameter wire is
that the copper utilization goes down. Since the larger diameter wire has
a larger surface area, the ac resistance goes down. The reason for using
Lutz wire sometimes is to decrease the impedance of the wire, but the small
conductors are used just to get maximum copper utilization out of the materials,
not because thinner wire conducts better at higher frequencies.

You shouldnt be skeptical about getting an inductor with dc R less then 0.1 ohms,
i already posted that i had a small construction that has about 0.026 ohms.
The current waveform through the device looks like a normal inductor, ramping
up and down with only a slight tendency to peak a little faster (a small amount
of nonlinear permeability).
Perhaps the other inductors you chose will work better. If you want one tested,
send it to me and i'll return it after the testing.

When i said "Zetex doesnt actually spec this voltage drop"
i was talking about 0.2 volts at 1.5 amps, because they spec more then
twice that as you noticed.

An LS that drops 3.5 volts at 350ma cant be more electrically efficient then
one that drops 3.1 volts at 350ma, now can it?

Are you going to make that output ripple voltage measurement?

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Dec 3, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*This makes the inductor look 'ok' untill some significant current starts to flow, and then it looks like a dead short.*

Well that symptom is very similar to what I was observing using my breadboard a month ago. Once I soldered all the components together, things were much happier.

*You shouldnt be skeptical about getting an inductor with dc R less then 0.1 ohms, i already posted that i had a small construction that has about 0.026 ohms.*

What I'm trying to say is that an inductor with such a low DCR will either have unacceptably high AC resistance due to skin effect, or it will saturate well under Ipeak, or it won't the necessary 68uH minimum inductance. Could you possibly post more details of your homemade inductor, so that we can run it through the formulas?

*An LS that drops 3.5 volts at 350ma cant be more electrically efficient then one that drops 3.1 volts at 350ma, now can it?*

Seems kinda odd, doesn't it? I guess I shouldn't have used the word "drop" in this case. The new LS caused the output voltage to be higher, while output current and input power remained constant, thus increasing circuit efficiency.

*Are you going to make that output ripple voltage measurement?*

Well the good news is that I'm getting a nice digital voltmeter for Christmas



The bad news is that I have to wait until Christmas!





By the way, how did you measure the voltage drop across the Schottky diode? It's more complicated than simply measuring it with a meter.
<HR></BLOCKQUOTE>


----------



## MrAl (Dec 3, 2001)

(quotes appear between >>> and <<<)

Hi again Duggg,

>>>
What I'm trying to say is that an inductor with such a low DCR
will either have unacceptably high AC resistance due to skin
effect, or it will saturate well under Ipeak, or it won't (have)
the necessary 68uH minimum inductance. Could you possibly post more
details of your homemade inductor, so that we can run it through
the formulas?
<<<
Im not sure why you are trying to relate low DCR to high AC resistance
or to saturation current or to minimum inductance. It's very possible,
indeed already done, to construct inductors with a variety of DCR while
attaining any other characteristic, be it high or be it low, as well.
And what formulas do you intend to run it through?
I'm trying to find out the manufacturer, so that i can find out
what material it is. So far it looks like Magnetics type "F" material
and it's 3/8 inch diameter, with about an 1/8 inch hole. It's about
0.1 inches thick. It's now got 10 turns of #24 wire, but there is
room for a larger diameter wire (not that much though i guess) meaning
the DCR can be brought down a little more. I suspect that if we
try to get other cores we may find one that works even better, but
since this works ok i guess for now i'll use it. From the way it works,
i would guess it's best range of frequencies is about 20kHz to 500kHz.
I would bet that other cores like this would work too, perhaps some
on the surplus market.

That's great to hear you are getting a digital meter soon, and since
we havent been rushing this project anyway, another 20 days or so should 
be ok right?  Make SURE it has a 10 megohm input or greater.
In the mean time, if you want to use the impedance transformed network,
that should work with an analog meter.

>>>
By the way, how did you measure the voltage drop across the Schottky diode?
It's more complicated than simply measuring it with a meter.
<<<
I simply used an oscilloscope  This gives the exact waveforms.
When the diode conducts, the voltage never goes above 0.21 volts.
I'm hoping all the Zetex 2000 diodes have this same property.
There is a simple static method too:
Run a current of 1.5 amps constant DC (possibly from a battery in series
with a resistor) and measure the dc voltage across the diode with a dc meter.
If you use one 1.5v alkaline cell, start with a 1 ohm, 2 watt resistor.
Because the equivalent parallel diode capacitance is so low, a measurement
like this at 1.5 amps would be very close to the diode's actual drop
when running in the circuit at 300kHz at the peak point of 1.5 amps.

I use the scope to do all the ac measurements like ripple and
stuff like that. If you switch it to ac coupling, you can see
the ripple up close by switching to a lower voltage range.
The network i posted does almost the same thing, but doesnt
amplify the signal.
If you cant get access to a scope and you want to know what a 
particular waveform looks like, i would gladly test it for you
if you dont mind paying postage both ways. I would bet small
inductors are very very cheap to mail, probably 34 cents one way.
I dont know about a whole circuit board though, probably a few dollars
with insurance.
I'm thinking of getting a cheapy digital camera just so i can
take snapshots of some waveforms on the scope and post them on the web.
I'll then even be able to enhance them digitally so they appear more
'readable' thanks to the fact that the color of the grid lines are
different then the color of the phosphor. Drawing up these waveforms
after viewing them takes up too much time 

It shouldnt be long now before we have a completed circuit for the LS, 
as well as lower current apps like a few LED's in parallel.

Well, take care for now and good luck with your LED circuits,
Al


----------



## papasan (Dec 3, 2001)

how about this part?...

M9711CT-ND
data sheet

kind of pricey at $3.10 a piece, but getting it right may cost a little more...very similar specs/size to the coilcraft coils i got, but i got all 100uH...

a question...how are you getting .01 and .02 resistance for Isense?...using a big fat 1~2W resistor?...wouldn't running a bunch of resistors in parallel do it?...let's see if i remember right, if you have 1 ohm resistors 10 in parallel would be .1 ohms, right?...so you would need 100 in parallel?...ouch...i can't seem to find any small wattage small resistance resistors in digikey, am i just blind?...perhaps a resistor array?...

here's my shopping list so far...i think that i too am going to wait until after christmas to start ordering stuff, for time/money considerations...

01 x ZXSC310CT-ND = Zetex IC @ $0.81
01 x ZHCS2000CT-ND = Zetex Schottky diode @ $1.29
01 x FMMT617CT-ND = Zetex NPN transistor @ $0.99
01 x M9711CT-ND = JW Miller 68uH .20 DCR inductor @ $3.10
01 x P11314CT-ND = Panasonic 150uF 10V tantalum capacitor [email protected] $21.40
--
01 x 15FR005-ND = Ohmite 5W .005 ohm 1% resistor @ $1.85 (for testing)
00 x various 1/8W resistors from .01 to .02 ohm

also, i think it was wayne asking about the dimentions of the LM2621 board...the guy here says that it is 1/2 by 3/4 inch with the leads cut...national claims efficiencey up to 90%, but it's got twice the number of parts...


----------



## **DONOTDELETE** (Dec 3, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Im not sure why you are trying to relate low DCR to high AC resistance or to saturation current or to minimum inductance. It's very possible, indeed already done, to construct inductors with a variety of DCR while attaining any other characteristic, be it high or be it low, as well.*

Michael Faraday would probably disagree. Electromagnetism is sensitive to physical size. Inductance is proportional to core area and saturation current is dependent on the effective length of the flux path. And while certain core materials allow for small size, small size leads to low saturation current.

*And what formulas do you intend to run it through?*

Well, here's one that will determine how many turns an inductor can have before it will saturate:

N = Bsat x le / Iµ

where Nsat is the number of turns at saturation, Bsat is the saturation flux density, le is the effective length of the flux path, I is the saturation current, and µ is the absolute permeability (which you can find from the spec sheets by multiplying the relative permeability by the permeability of free space, 1.257 uH/m).

*I'm trying to find out the manufacturer, so that i can find out what material it is. So far it looks like Magnetics type "F" material and it's 3/8 inch diameter, with about an 1/8 inch hole. It's about 0.1 inches thick. It's now got 10 turns of #24 wire*

F cores have a relative permeability of 3000 and a Bsat of 490 milliteslas.

The effective length can be approximated by simply averaging the inner and outer diameters, namely 1/4 inch or 6.3mm, and multiplying by pi. I get about 20mm. However, let's say 18.5mm, since most of the flux is concentrated nearer to the center. The core's spec sheet may indicate the correct value.

With I=1.5 amperes,

N = 0.49 x 0.0185 / (1.257^10-6*3000*1.5) = 1.6

That means your inductor saturates with less than two turns.

An N-turn inductor has an inductance of L=N^2µA/le, where A is a little less than the area of the core's cross section, again because of flux concentration.

For your toroid, A is approximately 7.3 square millimeters, so the inductance with two turns is 4*3000*1.257*10^-6*7.3*10^-6/0.0185=6uH.

Your inductor has ten turns, so its inductance is 150uH, which is good. But it saturates at only 240mA. To handle 1500mA without saturating, you either need a larger diameter core (or one with a more annular shape) or a different core material, or you use a small air gap.

Will respond to the rest of the message tomorrow!<HR></BLOCKQUOTE>


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## **DONOTDELETE** (Dec 4, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*how about this part?...

M9711CT-ND*

I have some of those due to arrive from Digi-Key on Thursday. MrAl feels the 0.2 ohm DCR is too high. I'll test it and report the results.


*how are you getting .01 and .02 resistance for Isense?...using a big fat 1~2W resistor?*

Yes, unfortunately. At $1.11 a piece, I'm not happy about either the price or the size. If we can find some less expensive 1/8-watt (or even smaller) SMD resistors in those values, that would be most ideal.

*i can't seem to find any small wattage small resistance resistors in digikey, am i just blind?...perhaps a resistor array?*

Resistor arrays don't come in small enough values. We either need another vendor, or we have to cough up $1.11 each, or we carefully make our own resistors.

*here's my shopping list so far...i think that i too am going to wait until after christmas to start ordering stuff, for time/money considerations...*

That may be wise. By then we may have a more refined list.

Two items on your list are reason for concern. First, the ZXSC310 won't be available until mid-January, although the 300 is available now for just $0.24 more. Second, the Panasonic TE series tantalums are not low-ESR type, and in fact have ESRs well above one ohm!

If you want something small, suitable, and in stock, check out Digi-Key PCE3269, 150uF, 6.3v, SMD Aluminum Polymer. Although the 6.3v is a little low for comfort, it has an ESR of 0.015 ohm! But, they're $7.42 EACH. You can get 16 low-ESR electrolytics for that price. 

*also, i think it was wayne asking about the dimentions of the LM2621 board...*

It was me asking... Wayne responded saying it was 13x25mm. Right now Mercator is targeting 16x23mm for the Zetex board, and it may end up a tad smaller.<HR></BLOCKQUOTE>


----------



## MrAl (Dec 4, 2001)

Hello Duggg:

I'm not sure how you ended up with a relative perm of "3000 Henries per meter"
when relative permeability is a scaler quantity without dimensions.

Also, you shouldnt really speak for Michael Faraday because he's not here to
agree or disagree with you  When you increase the wire diameter, you
decrease the DCR and also decrease the skin effect ac resistance, so there is
no reason to think ac resistance would some how increase when we decrease
DCR.

In any case, i think what your trying to do is determine the core material
by the saturation characteristics? In that case, i come up with a saturation
current of 5 amps with 10 turns around the core for "F" type material.
To allow for temperature variation, i would cut that in half to 2.5 amps.

I could in fact test it for this approximate 5 amps around 25 deg C, but 
i'd have to set up a circuit with a power MOSFET. I dont know if i well
get around to doing this or not, perhaps it would be interesting enough
to do it.

In any case, the inductor measures 220uH and certainly doesnt saturate at
1.5 amps.

As far as testing the construction, it is enough to know that a certain
core does or does not saturate before a given pulse time ends, with a
certain height flat topped voltage wave applied. In our case, we are applying
a voltage wave about 2.4 volts high. If a certain inductor saturates 
before about 2us, it wont work. If it doesnt saturate, it might work ok.
If it doesnt saturate at about 80 deg C, it will probably work ok forever.
For comparison, the Delevan 100uH inductor saturates at about 1us or less.

I'll take a look at the other inductor posted too. This time i'll try to
get more specific information about the device. I thought looking up
the current rating would be enough to tell how an inductor would 
operate, but apparently this isnt enough. I'd like to see everyone get
both a store bought inductor and a hand wound inductor, if both are 
possible, and compare results using both. These parts are easy to swap 
in the circuit.

In closing, i just wanna say im glad your interested in this circuit too,
enough to bring up some interesting points about the circuit itself and
the parts that make it up.

Good luck with your LED circuits,
Al


----------



## MrAl (Dec 4, 2001)

Here's an inductor:

M9775-ND, $3.10, 0.13 DCR

check it out at Digikey.

--Al


----------



## **DONOTDELETE** (Dec 4, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I'm not sure how you ended up with a relative perm of "3000 Henries per meter" when relative permeability is a scaler quantity without dimensions.*

That's a good point. Only the absolute permeability and the permeability of free space have units attached. Thanks for pointing that out; I have edited my earlier post.

*When you increase the wire diameter, you decrease the DCR and also decrease the skin effect ac resistance, so there is no reason to think ac resistance would some how increase when we decrease DCR.*

I didn't say that AC resistance increased---I said the AC resistance was greater than the DC resistance (for 24AWG and larger wire diameters at 400kHz), and I pointed out that efficiency losses would be greater than expected as a result. For 20AWG wire, for example, the AC resistance is almost twice the DCR.

Using larger diameter wire also means you would need a larger core in order to fit in the same number of turns (to get the same inductance).

*In that case, i come up with a saturation current of 5 amps with 10 turns around the core for "F" type material.*

How did you come up with that figure?

*As far as testing the construction, it is enough to know that a certain core does or does not saturate before a given pulse time ends*

True, but the nature of our circuit is that the pulse time will not end until inductor current reaches Ipeak, and it's critical that the inductor not saturate before then.

*I'd like to see everyone get both a store bought inductor and a hand wound inductor, if both are possible, and compare results using both.*

I'm just skeptical about your basic premise that commercially available inductors are crap, and that we can easily make homemade ones are many times more efficient.

The various inductor manufacturers employ hundreds of engineers whose job it is to come up with more efficient inductors, so why haven't they yet?

Probably because those pesky laws of physics keep getting in the way





MrAl, I truly appreciate your efforts. Your testing equipment and extensive circuit building experience are invaluable for the development of our circuit, and I hope this kind of "heated discussion" doesn't discourage you from continuing to contribute.
<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Dec 4, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Here's an inductor:

M9775-ND, $3.10, 0.13 DCR

check it out at Digikey.*

My analysis:

1. Why 100uH and not 68uH? The 68uH version has almost half the DCR, M9774-ND.

2. At 19x19x8mm, it's larger than the SMD inductors we've been looking at, and would require a board size of 19x30mm (although I suppose we could stick some components inside its center).

3. Because toroids have no air gaps, I'm concerned that they will saturate prematurely. Hehe, "premature saturation" reminds me of something else




<HR></BLOCKQUOTE>


----------



## MrAl (Dec 4, 2001)

Hi there again Duggg,

Communicating via written word isnt always that simple.
Misunderstandings may abound at times.

Ask yourself this:

If i had any core on earth and any kind of wire on earth
and the design formula to produce the best inductor for
my application, would i sit down and design one or
try to find and buy one that 'sorta' fit the app?

But inductors are out there  we just have to find them. (Read to the tune
of the X-Files).

There are some at digikey that are very high priced, over $7 US.

>>>
How did you come up with that figure?
<<<
From the dc magnetization curve for F type material.
Also, while i had the book out i looked up a similar toroid and found
one that looks the same but it's "J" type material. I must have remembered
"F" because i was wanting to test a toroid of the same size but
made in that material. The toroid im using now looks more like J type material,
not F type. The J type is higher mu, and calculates out to almost exactly
220uH, exactly what i measured with scope and function generator.
The toroid has an AL=2200mH. I hadnt yet tried to verify the saturation
characteristic for J type material, although since we have been talking about
that too, i may do that just to see what shows. With these types of materials,
i would like to see about twice the sat at 25 deg C then we really need.
BTW, the J type material saturates a little lower then the F type material.

>>>
True, but the nature of our circuit is that the pulse time will not end until inductor current reaches Ipeak, and it's critical
that the inductor not saturate before then.
<<<
"then" is the end of the pulse period, that's why i said:
"As far as testing the construction, it is enough to know that a certain
core does or does not saturate before a given pulse time ends".
Recall that v=L(di/dt).
Since the transistor can be on for as long as 2us, we can use this as a starting
point. If the inductor saturates before 2us time period is up with 2.4 volts
across it, it wont work in our circuit. Sure we might need longer then that,
but if it doesnt work with 2us, it sure wont work with 4us 

When i said:
"Here's an inductor"
I meant to point readers to the page, not that specific inductor only.
I was also hoping they would see the other more expensive ones too as well
as other values.

>>>
I'm just skeptical about your basic premise that commercially available inductors are crap,
and we can easily make homemade ones are many times more efficient.
<<<
The good ones are more expensive, and digikey doesnt have every available 
inductor on earth. Also, if you are skeptical about something ask yourself
how you could prove or disprove it absolutely. Come up with a test that will
end the wonder once and for all, otherwise you will be doomed to wonder forever.
If you feel like building a high current square wave generator, we might
be able to come up with a test to test the inductors for saturation
that only requires a meter. Perhaps something like the peak detector network.

>>>
The various inductor manufacturers employ hundreds of engineers whose job
it is to come up with more efficient inductors, so why haven't they yet?
<<<
'they' arent all working on inductors made for switching regulators.
A lot of inductors are made for ac sine wave applications.
Also, quite a few companies that make power supplies also wind
their own inductors and transformers. This not only keeps costs down
it also enables them to create application specific constructions
that may be very hard if not impossible to find on the market.
And again, there are inductors out there, you just have to find them and
be willing to pay for them 
Also, there is a surprising lack of knowledge out there even from people
who are very involved in the industry. To give you a really good example:
in our quest for the perfect capacitor i had called three rather large
electronic supply houses in the area. I've known these three places
have been around for at least 20 years or more. Now you know THEY know what a
'low ESR' capacitor is right? Well if you said 'yes', take another guess 
None of them had any idea what a low ESR capacitor was. Needless to say,
not one of them had one. They all deal in parts, yet they wouldnt know one
if they saw one.

>>>
Probably because those pesky laws of physics keep getting in the way
<<<
It's not the laws of physics, its the laws of economics. Often a company
will make what another company wants to buy, regardless of how well it 
may or may not fit 'our' little application  or even dc-dc converters
in general. They then add that to their
product line.

>>>
Because toroids have no air gaps, I'm concerned that they will saturate prematurely.
<<<
Well, that's one reason they make test equipment. If they saturate prematurely
you scrap 'em, if not you keep 'em  It only takes one prelim test and
one final test at elevated temperature. It also really only takes one
sample core as well. If it turns out that it doesnt work for any reason,
perhaps it will work in something else. If you want to wait, i can probably
get one in a couple weeks to test and i'll certainly post the results.
If you like air gaps that much, try using an air core inductor (just kidding

>>>
it's very large.
<<<
Yeah your certainly right. Why they dont stock smaller ones i dont know.
If mine works i would think they should be able to make one too.


>>>
MrAl, I truly appreciate your efforts. 
<<<
I appreciate your interest as well. Hashing this stuff out is good for 
our circuit in the long run


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## MrAl (Dec 5, 2001)

SOME EXTREMELY GOOD NEWS REGARDING THIS CIRCUIT:

I was kicking the idea around about using an output filter circuit in place of a single capacitor, but didnt get around to trying anything concrete out. Since after pricing
the capacitors i was a little disappointed in the higher price for low esr caps, which we needed, i decided it was time to try out an output filter circuit instead of a single cap. What happened was pretty amazing.
Before i go any further though, i should
mention that i only did a simulation so far,
and havent built up the filter yet to try
on the real world circuit. But the results
of this simulation look so good, i have to
conclude that we can cut the price tag
if we use an output filter instead of just
a single capacitor. Let me state some of the
details now:
1. instead of one output cap alone, we use
two output caps of lower value.
2. between the two capacitors, we place a
second inductor.
The nice thing is,
intead of requiring one 100uf or larger cap
with 0.1 ESR or lower, we can now use two
10uf caps with ESR 1 ohm or lower.
The other nice thing is that the second inductor need only be about 5uH or larger,
and this can be obtained by wrapping about
maybe 5 turns of #32 wire around a ferrite bead that is about 1/4 inch long and about
an eight inch in diameter(very small).
With the second inductors series resistance
set at 0.1 ohm or less, we only see about a
1 percent drop in efficiency max.

Let me Recap:
Instead of the 100uf cap with 0.1 ESR we now
might be able to get away with using two 
10uf caps with ESR 1 ohm or less and a single
5uH or larger inductor.

Sound good?
I hope to be able to try this out on the 
real world circuit either today or tonight or
tomorrow sometime. Of course i'll post the
results.

In the mean time, i'd like to hear opinions
on how you like replacing one part with three parts
(although they will be much smaller now and
cheaper too, and much easier to get).

--Al


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## Mercator (Dec 5, 2001)

MrAl...

Regarding the addition of more parts to our circuit. I personally don't like the idea for two reasons.... The main reasons we all became excited about the Z300 was the low parts count as compared to other driver options. The second reason is overall size of the completed circuit design. Both are important considerations. I think that if the circuit is going to require a few more expensive components in the end that will keep our parts count down as well as meeting our overall size objective, them the few extra dollars might be the trade off we have to make.

With that said, and in spite of how I feel about "more parts" I'd like to submit something I recently read in the MAX1759 datasheet (pg. 8) regarding low ESR caps.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*
Note that capacitors must have low ESR (20m) to maintain low output ripple. Ceramic capacitors are recommended. In cost-sensitive applications where high output current is needed, the output capacitor maybe a combination of a 1µF ceramic in parallel with a 10µF tan-talum capacitor. The ceramic capacitor’s low ESR will help keep output ripple within acceptable levels.<HR></BLOCKQUOTE>*

From what I gather, they recomend using a small cermaic cap in conjunction with a tantalum capacitor to acheive a lower output ripple. 

Could this method also work in our application? I beleive that there are some lower priced SM tantalum capacitors available that might not normally meet our strick requirements and I'm sure there are SM ceramic cap as well. Perhaps using two lesser rated caps is another approach to solving our problem of acheiving low ESR, low ripple. If this does work, then we would be adding just one more part as opposed to two. Also, the additional parts in the above concept would most likely be smaller than two electrolytics and another inductor.

Mercator


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## papasan (Dec 5, 2001)

considering our rather strict requirements for both the cap and the coil, i think adding a few components to work around these maybe a good idea...

as far as size goes, i think a small (under 1 inch square) board is important, but it looks like if we stick to original idea then the main coil will be by far the largest piece...it sounds, from a laymen's POV, that the size will be similar with MrAl's ideas, just more, but smaller, parts...

i too was impressed by the small piece count for the 3x0 board, and i'm sure that simply driving a few .02A LEDs the circuit could be kept very simple, but for our needs we should think about expanding the count by a bit to get the desired results...

my considerations, in order of importance...
<UL TYPE=SQUARE>correct output, enough to drive an LS at peak output for an extended time...
efficiency, getting good run time (90%+ would be great)...
size, keeping this circuit small enough to fit into alot of 2 cell lights (especially AA)...
cost, no super-specific hard to find parts...
[/list]

check out the board diagram i made for the 3x0 in the 'batteries not included' section...it's about 3/4 by 3/4, made with a coilcraft coil and the panasonic electrolitic cap which are by far the largest components...


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## **DONOTDELETE** (Dec 5, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Instead of the 100uf cap with 0.1 ESR we now might be able to get away with using two 10uf caps with ESR 1 ohm or less and a single 5uH or larger inductor.*

We can already obtain 0.1 ohm ESR with a $0.63 14x8x8mm electrolytic, and I doubt the new solution could be cheaper than that.

With the second inductor at 6x4x4mm and two 10uF caps at 7x5x6mm each, the footprint will be larger, although we can trim the height by 2mm, which is significant.

I dunno, right now I'm leaning toward using that low-ESR tantalum MrAl spec'd originally (P11289), because it can make the PC board much smaller.

I heard in another thread that the release of the Lambertian white LEDs has been pushed back until next summer, so waiting the 1.5 months for the tantalum to become available from Digi-Key is no longer a major factor.
<HR></BLOCKQUOTE>


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## **DONOTDELETE** (Dec 5, 2001)

My latest Digi-Key order just arrived.

I quickly soldered on the first SMD inductor (68uH, 0.14 ohm measured DCR, M9711CT) and the first SMD electrolytic (220uF, 16v, 0.2 ohm ESR, PCE3400CT)

Considering these are relatively substandard components, I was amazed to measure an efficiency of 85%!






I attribute the 5% increase to the fact that this inductor doesn't saturate until 1400mA, and Ipeak is well below that. It also confirms MrAl's suspicions that the Delevan inductors are inefficient at our frequency or current.

I added a second 220uF in parallel in order to cut the ESR in half, and observed the expected ~3mA increase in output current, though it's quite subtle on my analog ammeter set to the 500mA range. (Can't wait to get that digital one!)


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## MrAl (Dec 5, 2001)

Hi there again everyone,


Ok i guess for now we stick with the original game plan.
We'll use the one output cap and try several types like
the SM part (when it comes in and if we can get one) and
Duggg's choice. This will give us a low cost solution and
a small size solution.
I'll test the output pi filter as a side to this project
and see how that comes out also, and compare cost. If it
looks like it will provide a significant savings in cost
or some other benefit, i'll post the news also.

Mercator:
I tryed the parallel combo of 3.3uf tant with the 100uf cheapy
we got, and it did bring the ripple down. I dont have
any 1uf ceramic caps though. I might have a 1uf cap of
some other type, im not sure what kind it is though, i found
it laying around also. It might be silver mica.
It's possible that 1uf in parallel with a 10uf could work, but
i dont have the right caps to test this idea with, but also
10uf of any kind of cap didnt work out well in the original
simulations i did. I would be very willing to test this out too
though in the real world if we get one of each to test.
Perhaps we can pick up one or two of each and try it?
They would probably be fairly low cost parts. I'd like to
see the results myself. Since in the simulation i used
an ESR of perfectly zero ohms, i dont think 10uf will be
enough, even with a perfect capacitor. I did however make
the mistake of using zero ohms for the inductor's series
R too, but if we use a high quality inductor the R will 
be very low anyway. Used in conjuction with a series R of
0.1 ohms though, perhaps a lower capacitance could work
to some degree due to the low pass filter action of the
series R and the output capacitance. It's very doubtful
that we can get down to 10uf though, because the RC time
constant of 0.1 ohms and 10uf is only 1us, and our cycle 
time is about 3us, but perhaps 50uf could work. This would
have to be tried too of course. I think i'll run a simple 
simulation including a few series R values and lower output
caps and see what gives.

Duggg:
The point of using a 10uf ceramic with a 100uf low cost 
cap is a good idea too. I just dont have any ceramics that
high in value. I dont even have the 1uf one to test.
What is the cost of these high value ceramics?
Perhaps we can get one to test it.

papasan:
Regarding parts selection, it looks like we may end up with
more then one solution depending on your budget and desire to
wait for parts ordered via mail order, etc. So far it
looks like at least two to start with:
1. smallest size possible.
2. lowest cost possible/easier parts to find.


Well take care everybody, for now...

Al


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## **DONOTDELETE** (Dec 6, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*From what I gather, they recommend using a small ceramic cap in conjunction with a tantalum capacitor to acheive a lower output ripple. Could this method also work in our application?*<HR></BLOCKQUOTE>

That solution is similar to what MrAl proposed, except without the extra inductor.

We would need larger values, though, because our output power is higher than that of the MAX1759.

I had suggested using a single 10uF multilayer ceramic (PCE1894, 2 millohms ESR) a while back, but we later rejected it because the capacitance was too low.

However, wouldn't such a ceramic allow the use of a general purpose (high-ESR) 100uF tantalum behind it?

Would such a solution be better than a single 150uF tantalum with an ESR of 100 millohm?


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## **DONOTDELETE** (Dec 6, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Using a 10uf ceramic with a 100uf low cost cap is a good idea too. I just dont have any ceramics that high in value. I dont even have the 1uf one to test. What is the cost of these high value ceramics? Perhaps we can get one to test it.
*<HR></BLOCKQUOTE>

Digi-Key only sells them in lots of 10, but after a lot of digging I found some 3.3uF SMDs "on sale" for a pretty reasonable price, 10 for $1.75.

311-1196-1-ND 3.3uF/16v multilayer ceramic

Put three in parallel to simulate a 10uF.

If it checks out, we can later order the 10uf/10v PCC2170CT-ND at 10 for $7.80.

Or maybe the 3.3uF will be good enough, and we can save $0.60/board.


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## MrAl (Dec 6, 2001)

I would like to test some of those out too.

Since two people were saying they were getting at least some results with the
68uH Delevan inductor, i went back and reinstalled that into the circuit.
I noticed that the sub harmonic oscillation problem that i originally didnt like
doesnt look like sub harmonic oscillation, it looks like external interference.
Something is interfering with the circuit that makes it turn off every so often
at a very low sub harmonic. The other problem here though is, there is
still a sub harmonic related to the inductor. Instead of oscillating at
something like 300kHz, it oscillates mainly around something like 30kHz,
which is 10 times less then it should be. This would make the circuit
appear to be operating somewhat normal when using only meters to measure
quantities. The problem with operating at 30kHz is we might need a
bigger capacitor.

Also, i decided to check the 617 transistor to see if it would operate
at lower input voltage (like 1.2 volts). I found out that there isnt 
enough base drive at this lower voltage as suspected. The transistor
starts to heat up because the saturation voltage goes up to 0.6 volts.
If you try to run at 1.2 volts or so, feel the copper clad around the
transistor to see if its warm. Dont run it like this too long.
I'll next test the 688B transistor to see how well it performs at
the lower input voltage.

Let me order these problems and number them:

p1. some kind of external very low freq interference.
p2. 1/10th sub harmonic oscillation, although it is stable.
p3. low voltage operation with the 617 transistor looks bad.

Now to look at the significance of each problem:

I'll start with p3, because thats the easiest:

p3:
p3 isnt that much of a problem because we decided run time with
only one cell isnt going to be that great anyway. We can pretty
much ignore this for now, unless the problem comes back
with low battery and higher temperature operation. We will have to 
be careful that we dont burn out the little transistor with low
battery conditions 

p2:
We might be able to live with this, as long as we can keep the output 
current ripple peak below 500ma. I'll be happy with any freq as long as
we can get this current limit value.

p1:
This is the most unusual problem. Since one difference between
the toroid inductor and the Delevan is that the toroid's mag field
is almost completely contained within the metal and the Delevan
has an open frame design, im now wondering if it might be picking up
some stray magnetic field from something. I'm going to test for this
more carefully once my NiCd's are recharged.
Somehow we have to figure out why this is happening. At one point it
was occurring at around 60Hz or so and another time it was only once
every quarter second (250ms). When this happens, the output drops suddenly
to zero for maybe 50ms or so, interrupting the output to the LS simulator.
I'm also wondering if we might be better off using a lower value inductor.
This leads me to want to try several cores out now. I have a range of
different core sizes laying around so im going to try out a couple other
designs to see what happens. I also noticed that the inductor i made
originally changes inductance quite a bit with dc bias current, although
it still works like an inductor. The smooth operation with this inductor 
also leads be to believe maybe we do need a lower value.

On the plus side, i did a few more simulations with series R and all and
found a new discovery: the output ripple doesnt center around 350ma, it's
got a bit more below the 350ma mark then above it. On the down side,
with the 68uH delevan and ignoring the interference, the output peak 
current reaches about 650ma with the crappy 100uf and 3.3uf tant in parallel.
Perhaps with the better cap even with the lower freq oscillation it will
perform reasonably enough to get by with 

Any ideas?

--Al


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## **DONOTDELETE** (Dec 6, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*The output peak current reaches about 650ma with the crappy 100uf and 3.3uf tant in parallel. Any ideas?
*

Even a low-ESR tantalum has a substantial ESR (>0.6 ohm) at 3.3uF. You should see much better results testing with a 3.3uF ceramic.

*Since two people were saying they were getting at least some results with the 68uH Delevan inductor, i went back and reinstalled that into the circuit.*

I personally wouldn't spend much more time with the Delevans, since we're now at the stage where we should be concentrating on SMD-sized inductors.

Speaking of which, check out the Digi-Key M1011CT, $3.50, only 9x10x5.4mm!
<HR></BLOCKQUOTE>


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## MrAl (Dec 6, 2001)

Yeah thats a good point duggg, i think we should start moving
toward all SM parts. That inductor looks like it would be
worth trying also, even with the somewhat higher DCR.

I tested the Delevan 68uH inductor for sensitivity to
external magnetic interference, and it turned out that
it's not really that bad. What is causing problems with
this inductor and the 100uH Delevan in our circuit i dont know.
It's actually turning the transistor ON for an inordinarily 
long time period (typically 5ms). This makes no sense at all,
but it is happening. That's whats causing the output to drop to
zero for this time period. I removed the inductor again and went
back to my original toroid design.

Just for the heck of it, i tryed two other core sizes, one about
1/2 inch in diameter and one about 1 inch in diameter. Both
of these worked about the same as the smaller one. I tried 
a few different number of turns on the cores, and every one worked
about the same, except of course for the change in inductance,
which did lower the output ripple somewhat with the larger values,
but nothing to scream about.

The real amazing results came when testing the output pi filter
using an extra 6x3mm ferrite bead with 10 turns of #32 wire with
a tested value of inductance of 16uH.
With the cheapy 100uf still on the circuit output and adding
the ferrite bead and another 100uf $0.20 cent capacitor, the
output turned into PURE dc. That is, the output ripple went 
down so low that it wasnt possible to measure it even on the
10mv scale on the scope. This confirms that we have at least
one circuit to fall back on if everything else fails.
Since this worked so darn good, i decided to try a lower value
cap on the very output. I used a 3.3uf tant on the output,
replacing the second 100uf cheapy. The results were good
with this too, taking the output ripple down to about 10mv peak to 
peak. That extra inductor sure makes a difference.
All of the ripple voltage appears across the inductor, meaning the
inductor drops all the ac ripple leaving almost pure dc on the output.

I'm all in favor of trying the better caps too though next, SM types too.

The last problem, once we get the parts picked out and verified,
is what to do about the low input voltage problem. When the input
goes low, the base drive also goes lower, meaning the transistor
cant turn fully on, and so drops much more voltage which causes 
heating. I havent tried to find the limit on this heating, but
it does heat up pretty fast. It might mean that we need some 
way of detecting undervoltage condition? We cant have a circuit
that works very well at fairly high eff untill the battery runs low,
and then the circuit burns out, can we  Perhaps we can
think of something simple, any ideas?

--Al


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## **DONOTDELETE** (Dec 6, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*It might mean that we need some way of detecting undervoltage condition? We cant have a circuit that works very well at fairly high eff untill the battery runs low, and then the circuit burns out, can we  Perhaps we can think of something simple, any ideas?*<HR></BLOCKQUOTE>

Three ideas come to mind.

1. Don't worry about it. When a two-cell circuit finally hits 1.2 volts, there isn't a whole lot of current available, especially with NiMHs which seem to die quite fast. And let's do the math. Suppose it continues to draw 700mA at that voltage. 700mA times 0.6 volts is only 420mW, well below the 625mW rating of those SOT transistors.

2. Rely on the end user to turn the circuit off once the LS starts to dim. This is common sense. Of course, it's bad circuit design to expect the user to do anything rational





3. Exploit the 310's STDN pin. To make it shut down at 1.2 volts instead of 0.1 volts, make a simple voltage divider out of two SMD resistors, with one value twelve times the other.

While #3 is the most elegant, I'm not excited about adding more components, so I say go with #1


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## MrAl (Dec 7, 2001)

Hi again,

#1 Dont worry about it:
I like that idea too  but i guess what i need to do is get more
exact measurements on the heating and relate it to the heatsinking 
area of the copper clad. If we can get away with it great. I didnt
do too many tests because i was afraid if the transistor burns up 
during the test i cant do any more tests with it. I'll check the relationship
between copper clad area and device rating and see what it looks like. If you
feel like it, you might want to check this also. Higher heat output puts
a constraint on the allowable product packaging.
I think i'll try to get the test with the 688B transistor done soon now.
That may help if that transistor works down to a lower input voltage
as originally suspected.

#2 End user responsibility:
Your right about this being bad practice. Not only that, i can see myself
running the battery down and not realizing it if it happens too slowly, thus
leaving the circuit on longer then healthy.

#3 Voltage drop out using the shut down pin on the 310 chip:
Of course i like this the best, but as you said it will suck in more
parts. I would think the trip voltage would be higher then 0.1 volt 
though, but would still require a min of 2 SM resistors (not very big).
I'll check the min/max spec on the voltage sense at this pin and
see if this is a viable solution. If the level variation from chip to
chip is less then maybe 30% we could probably get away with this, even
if it requires hand selection of one of the two resistors on a per-chip
basis. I like this idea a lot though, because it would mean we could
guarantee the ciruit would always runs safely. If the voltage variation
is too much though, it might mean we need another solution. Same if
the variation is too much with temperature.

Thanks for the ideas 

Take care for now,
Al


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## MrAl (Dec 7, 2001)

Hi again,

Ok using the 310 shut down pin with two resistors wont work because of
the relatively high hysteresis. The device turns on at 0.7v or higher,
and shuts off at 0.1v or lower. This means if we use a 12:1 resistor
divider the device would turn off at 1.2 volts, but wouldnt turn on
untill 8.4 volts input. This means if we want to use this pin
we need an active device to use as an input voltage sense and then
drive the pin either high or low. Probably the min would require
at least one more transistor, and that probably wouldnt work very
well over temperature.

Before we look at this any further, perhaps i should get some better
measurements in. Maybe we can get by by just using a large enough
heat sink area. I looked at the spec sheet again on the transistor,
and they did all the measurements with the transistor attached to
a 'ceramic substrate'. Who the heck uses this? We are using copper
clad board, so i guess we have to do our own testing.

--Al


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## **DONOTDELETE** (Dec 7, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Ok using the 310 shut down pin with two resistors wont work because of the relatively high hysteresis. The device turns on at 0.7v or higher, and shuts off at 0.1v or lower. This means if we use a 12:1 resistor divider the device would turn off at 1.2 volts, but wouldnt turn on untill 8.4 volts input. *<HR></BLOCKQUOTE>




How annoying! We could get around the hysteresis by adding a THIRD component, a small capacitor, across the higher-value resistor. That way, at startup, STDN is briefly near Vcc. The size of the cap would depend on how long the 310 needs to see 0.7 volts or above in order to enable.

I'm wondering if this problem will be unique to the 617... I'm going be testing other transistors tonight anyway, so I'll report my findings.


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## papasan (Dec 7, 2001)

i got some smd tantalum caps from illinois cap, inc today...one is promising (157 STN004MD) but almost too close to the minimum specs...

when i talked to the sales rep about getting samples i didn't talk about purchasing later, but i did request other samples that he didn't send because, 'they have 1000 piece minimums', so perhaps, if they work out, we can order smaller volumes...

gotta call the zetex rep next and get samples of the 310, i don't wanna wait for digikey to get them...

looking around for ultra low ohm resistors still...no luck really...the smallest from digikey, panasonic .1 ohm, are like $15 for 10!!...i guess maybe we'll have to use a big-*** 2watt resistor after all...i did notice some 0.0 ohm resistors (??) at digikey but i have no idea what a 0.0 ohm resistor would be, anyone?...someone mentioned making resistors, but i have no knowledge of how to do this...links or something?...

keep on truckin'...


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## MrAl (Dec 7, 2001)

Hi again,

Duggg:
>>>
How annoying! We could get around the hysteresis by adding a THIRD component,
a small capacitor, across the higher-value resistor. That way, at startup,
STDN is briefly near Vcc. The size of the cap would depend on how long the
310 needs to see 0.7 volts or above in order to enable.
<<<
That's a good idea, however i didnt mention the other problem. The problem with
taking that "0.1 volt" spec literally is that im sure zetex wont spec that
within 1% for sure. What they would do is take out a new number for us
(such as 310A) and spec that parameter +/- whatever we wanted, if the
quantity we ordered warrented that.
There is a possibility of selecting one resistor per chip, if we could
get a guarantee on the temperature co. of the "0.1 volt" spec, and it 
turned out to be minimal. Also, since it would be a dynamic, time dependent
network, it would mean some oscillation could take place if the series
resistance of the batteries (which also increases with discharge) reacts
with the capacitance. This would have to be checked, but i bet it would
still be better then nothing at all. In other words, the circuit goes 
undervoltage, turns off, and then the battery voltage jumps up turning it
back on, then goes undervoltage again, then back on again, etc. The nice
thing here is if we can get it to oscillate the way we want it too, the 
worse that could happen is the LS would dim during undervoltage, while
the transistor stays safe, even with the oscillation.
I havent yet checked the extent of the problem: i.e. does it burn up or does
it just get a little hot?

papasan :
Sometimes they use 0 ohm resistors for jumpers, or for places that require
a resistor sometimes, and no resistor (jumper) other times.
Some of the digikey resistors are fairly small, like the 0.015 ohm one i got.
They might be 2 watt, but they are about the size of a 1/4 watt resistor only
a little longer. We hope to find SM parts here too.

--Al


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## MrAl (Dec 7, 2001)

Oh one thing i forgot to mention:
Did anyone check out Mouser?
They have a lot of parts too including
inductors.

Al


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## MrAl (Dec 8, 2001)

FALSE ALARM:

I went back to verify the 618 transistor
saturation problem with low input, and to
check that problem out further, and
found that this problem only occurred with
the DELEVAN 68uH INDUCTOR !
After going back to the original
hand wound toroid core (now with 5 turns)
the 'problem' doesnt appear even at 1 volt 
input.

So i guess that solves that 

Hopefully, we dont see too much
difference from chip to chip as far
as the base drive is concerned.

Good luck with your LED circuits,
Al


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## **DONOTDELETE** (Dec 8, 2001)

Yes, I was about to say, I didn't notice any unusual heating of any of the transistors during my tests last night.

I'm glad you found the problem seemed to go away. What power source are you using? I'm concerned it may reappear, for example, if using D cells or larger batteries, which may still provide decent current at that voltage.

I did determine that the FMMT617 is a tad more efficient than the 618 and the ZXT11N15DF.


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## MrAl (Dec 8, 2001)

Hi again Duggg,

Im using two sub C NiCd's in series for 2.4 volts, and one NiCd for
1.2 volts input. These batteries can easily put out 4 amps even at
about 1.2 volts. But the problem wasnt related to how much current
the input source could put out anyway because you have to assume 
a pretty high current like that with most decent batteries right?
and that the circuit will always try to pull 1.2 amps or so at
the peak.
I still cant explain why the delevan inductors do this when the hand
wound ones dont. You would think either way the current is limited
to the set point determined by the sense resistor right? so this
would turn the chip off as soon as the current reached maybe 1.2 amps or
so regardless what kind of inductor you used, but apparently the
delevan somehow interferes with the normal operation of the chip.
Perhaps more noise couples through the power supply connection,
i cant say for sure though what is happening. I also noticed that
using that inductor causes the chip to turn the transistor on for
very long time periods(relatively) like 5 ms, when it should be
at most a few micro seconds or so. I had to abandon the delevans for
this reason.
Perhaps it has something to do with the self resonance of the coil.

Luckily, it wont happen with every inductor  so we still have a
decent circuit here. In the end, it wont regulate current
perfectly, but i think it could be good enough. After this
circuit is pretty much completed, im going to work on miniaturizing
my 2 transistor 1 op amp circuit and get it working with near perfect
current regulation. The chip samples i got from National are super
small also, meaning really small board size too.

Oh BTW, Digikey does have the low value
chip resistors, and they are about $1.10
each and you have to get a min of 10 of them.

Good luck with your LED circuits,
Al


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## papasan (Dec 8, 2001)

what happens to this circuit when the voltage drops below .7 volts?...assume a 300, no shutdown...but the IC needs .7 volts to start-up anyways, doesn't it?...do the LEDs see it as a transparent circuit in that they will now get .7 volts instead of a regulated supply?...in this case the light would remain on but at a much lower light level...

so with a 310 and the shutdown connected does the whole circuit shut down when the threshold is reached?...

i would *much* rather that the light continue to burn at a much lower level then the circuit just shut down all together with no warning, leaving you in the dark...even if it meant risking a deep discharge (which should be very evident in this circumstance anyways)...

the only reason i cold see to shut the circuit down was if it was left for a very long time or it turned on by mistake...


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## **DONOTDELETE** (Dec 8, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mercator:
*I looked through the WWW.Mouser.Com web site and found that they do carry many SM parts that we might take a look at. Some prices were even better than Digi-Key. Same policy regarding only charging he "actual postage" on any order.*

Wow, cool! Mouser actually sells a better tantalum than the Digi-Key P11289 MrAl spec'd, and not only is it cheaper, it's actually in stock: 80-T520D157M010, 150uf, 10v, 0.055 ohm ESR, 1700mA ripple, 7.3x4.3x2.8mm, $3.00 each.

*I mainly looked for low value SM resistors. Same problem with Mouser as we found on Digi-Key. They only list the 1 watt values. But, actually those are not all that big. (length - .246, height - .136, width - .136) If I'm not mistaken, Mouser had the better price. The part number I saw was Ohmite RW1S0BAR015J*

Unfortunately, that's a wirewound resistor, and I think we might want to avoid a wirewound, as it may act like an inductor at 400kHz and the impedance may add to the resistance.

Phycomp makes a 0.020-ohm thick-film chip resistor in a low-power, small SMD package, I believe it's their LRC11 series. We just need to find a Phycomp distributor who will sell us a few dozen---or better yet, allow us to "sample" a few dozen




<HR></BLOCKQUOTE>


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## **DONOTDELETE** (Dec 8, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*What happens to this circuit when the voltage drops below .7 volts?...assume a 300, no shutdown...but the IC needs .7 volts to start-up anyways, doesn't it*<HR></BLOCKQUOTE>

It needs 0.7 volts to start working properly. With less than 0.7 volts, the IC may still apply enough transistor base current to steal collector current that would otherwise go to the LS, which is inefficient.

The circuit actually has three modes: a normal operating mode, where the inductor is charged until Ipeak is reached, then discharges; a deprived mode, where the IC can no longer provide enough base current to saturate the transistor, during which time the transistor stays closed indefinitely and may potentially heat up; and a shutdown mode where the IC actually shuts down and applies zero base current.

In deprived mode, much of the remaining battery power is wasted by the transistor as it tries but fails to adequately charge the inductor, so it would be much better to go into shutdown mode at this point.

Note that shutdown mode does not mean the LS is turned off. On the contrary, the LS is always in series with the battery, and with the IC and transistor turned completely off, it can more efficiently draw the remaining power out of the battery.


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## papasan (Dec 8, 2001)

ahh...i got you...i'm slowely learning =)...very excellent, i will definatly have to go with the 310 over the 300...but you could still have a deep discharge or reverse polarity issue if the light was accidently left on...


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## **DONOTDELETE** (Dec 8, 2001)

Well, the possibility of cell reversal and transistor overheating are certainly compelling reasons to look into the 310's shutdown feature.

For two NiMH cells, the circuit should shut down around 1.6 volts. With the chip disabled, a white LS should barely conduct at that low forward voltage, and the batteries should be spared.

(For those users who don't want the shutdown feature, they can either not buy and install the extra resistors, or if they purchase a completed board, snip out one of them.)

However, everything depends on whether we can get reasonable shutdown behavior out of the Zetex 310. The published 0.1-0.7 volt hysteresis is not reasonable, because it doesn't match any common battery discharge characteristic. I'm honestly wondering if there might be a misprint!

Mercator, since you're the only one with a 310 chip right now, can you set up a simple voltage divider and determine the exact voltage at which your chip enables and disables?


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## Mercator (Dec 9, 2001)

Good to know that the low voltage problem isn't something to be concerend with. If it was just related to the Delevan inductor, then that's even better since we've pretty much eliminated that as a final parts choice. Some interesting information was learned about the Delevan Inductors though.

In spite of there not being a problem when the batteries get down to around 1 volt,would it still bet a wise decision to consider the the ZXCS310's STDN feature to protect the batteries. I'm concerned about putting re-chargeable batts into a deep discharge condition. Is this a problem or would the ckt using the Z300 actually shutdown on it's own before it tried to suck every last bit out of the batteries?

I was wondering when MrAl mentioned that he didn't see any problems with the Zetex FMMT618 transistor in regards to the low voltage. I thought we had decided that the FMMT617 was the better choice. Duggg's testing and comment re-afirmed the FMMT617 decision.

I looked through the WWW.Mouser.Com web site
and found that they do carry many SM parts that we might take a look at. Some prices were even better than Digi-Key. Same policy regarding only charging he "actual postage" on any order.

I mainly looked for low value SM resistors. Same problem with Mouser as we found on Digi-Key. They only list the 1 watt values.
But, actually those are not all that big. (length - .246, height - .136, width - .136)
If I'm not mistaken, Mouser had the better price. The part number I saw was Ohmite RW1S0BAR015J

Mercator


----------



## MrAl (Dec 9, 2001)

(see #32 gauge wire replacement data below for replacing the
sense resistor with a short length of wire).

Hi again,

Duggg:
>>>
However, everything depends on whether we can get reasonable shutdown
behavior out of the Zetex 310. The published 0.1-0.7 volt hysteresis
is not reasonable, because it doesn't match any common battery discharge
characteristic. I'm honestly wondering if there might be a misprint!
<<<
Well actually this would be a typical 'logic' input rather then a 'voltage sensing'
input. The problem is, they probably dont spec a temperature coefficient for either
of these thresholds, meaning it would be impossible to use it for undervoltage 
sensing unless we got lucky and it happens to have the same temp co with every chip.
I guess we could test it, but we would have to test every single circuit we ever made 
before we 'ship' it, to make sure the temp co never changes too much. If it
only varies by 10 percent we would have it made, but logic inputs usually arent
guarenteed that close i dont think. I would bet if they say 0.1 then we could expect
0.05 to 0.15 easily over the temp range. I cant be sure of course without testing,
but its not as easy as it sounds to test for that.

Anyone working with this circuit:

I meant to get to this sooner, but just got to do a little testing this morning...

Using a short #32 gauge wire jumper for the sense resistor:

I used two number 32 gauge magnet wire jumpers (in parallel) measuring 1.75 inches
long (each) in place of the normal sense resistor (mine was originally 0.015 ohms).
The two wires in parallel provide about 0.0123 ohms total resistance at 26 deg C.
The circuit output measured 300ma with this combination running at 26 deg C.

Another possibility is to use a single #32 gauge wire 0.875 inches long, which
gives the same resistance.
I thought since i have a peak of about 1.4 amps that i would use two wires in parallel
rather then one single wire which may heat up a little. The increase in inductance with
two wires versus one wire is only about 10 percent (see chart below).

One thing that has to be mentioned when using copper wire in place of the normal sense 
resistor is that the temperature co of the wire is much higher then a resistor would
give, so this could mean more current output at lower temperatures. On the other hand,
if the typical temperature co of the sense voltage at the sense pin changes
the way the data sheet seems to imply it should, then using copper could actually
temperature compensate the circuit to some degree. Just in case you get a device
that doesnt have the typical spec'd value though, you should be aware that using
a copper wire will change the temperature profile of the output current. This means
at least one measurement at low or an elevated temperature should probably be made
to insure proper operation over a pretty wide temperature range.

Here is a chart of other wire sizes that can be used, but because
of the inherent difference in sense voltage from chip to chip,
it would be better to start at a 50% longer wire and measure the
output current. If the output current is too low, decrease the
length of the wire a little and measure again. Repeat this
untill you get the right length.


Chart of copper wire lengths for possible use in replacing 
the sense resistor
(the order here is "number of wires x length, inductance")
(for all 2 wire entries, parallel two identical wires of the indicated length):

#32
1 x 0.875 inches, 0.024uH
2 x 1.75 inches, 0.027uH (this entry was actually tested in the circuit)

#30
1 x 1.4 inches, 0.039uH
2 x 2.75 inches, 0.044uH

#28
1 x 2.2 inches, 0.065uH

#26
1 x 3.5 inches, 0.11uH

#24
1 x 5.6 inches, 0.18uH

#22
1 x 8.9 inches, 0.29uH

Im not really sure if wire gauges #26 and up should be used, but i included
the length data here anyway. The larger inductances with these longer
wires could cause other problems. If possible, use two lengths of
#32 starting about 2.5 inches long each and work the lengths down.
The wires should be soldered in place and cant be coiled up.
If the wires seems too long, fold them up like an accordion, but never
coil them like a hand wound air core inductor.
Also, when adjusting the wire lengths: after unsoldering and cutting
the wires a little shorter be sure to solder the ends of the wires
back to the same position on the copper clad as they were before
adjustment.

Here is the temperature data for any of the above lengths and
the possible effect it could have on the output current with
a nominal 300ma output at 26 deg C (and an other then typical
spec on the temperature coefficient of the sense voltage)
(the order here is "temperature: ohms, output current"):

0 C: 0.0110 ohms, 335ma
26 C: 0.0123 ohms, 300ma
52 C: 0.0135 ohms, 273ma

If the chip happens to have the typical temp co spec on the sense voltage,
then the output at 52 degrees C will be about the same as the output
at 26 deg C, as well as at 0 deg C, but it's hard to count on this.

Good luck with it,
Al


----------



## **DONOTDELETE** (Dec 9, 2001)

Do we want to use small inexpensive SMD resistors for Rsense, or just use the jumper idea for the final project?

Speaking of which, I had been using a #24AWG wire jumper in series with a 0.01-ohm resistor since almost Day One now. I originally calibrated the length by hooking my analog ammeter in series with the LS, stopping when the meter reported 350mA.

Later, I became concerned that the low-impedance meter was introducing signficant loss, so I put a 0.05-ohm resistor in series with the LS, hooked my meter across it, and adjusted the jumper length until the meter registered 18mV.

Sure enough, I got totally different lengths using the ammeter versus the voltmeter. I would think the voltmeter is more correct.

This weekend I decided to deduce the jumper resistance by replacing it with other small resistors I have been accumulating. I was extremely surprised to find its resistance to be around 0.025 ohm, because I was expecting a fifth of that.

Yes, with Rsense clearly at 0.035 ohm, my analog voltmeter is still reporting 18mV across the 0.05-ohm resistor (360mA).

This has huge implications for the value of Ipeak (now 543-686mA), so I'm now wondering if the meter is overreporting the voltage (and thus the LS current).

To determine this, I think it's time to ask Santa for that new digital meter NOW. I hope all my figures haven't been wrong due to a wacked up analog voltmeter


----------



## papasan (Dec 9, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Do we want to use small inexpensive SMD resistors for Rsense, or just use the jumper idea for the final project?*<HR></BLOCKQUOTE>

i, for one, would prefer a small (0805 package) resistor for rsense...much more polished and 'professional' in my opinion...of course, if we cannot find a distributor that will do small quantities...well, we do what we have to =)...

anyways, wouldn't a wire change resistance if it's a solid strand or multi strand and weather it's copper or aluminum or whatever (do they even make small guage wire out of anything but copper?)...even different purities of copper would change this value, wouldn't it?...

an SMD resistor seems to take the guess work out of it...for me at least...


----------



## **DONOTDELETE** (Dec 9, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*Anyways, wouldn't a wire change resistance if it's a solid strand or multi strand and weather it's copper or aluminum or whatever (do they even make small guage wire out of anything but copper?)...even different purities of copper would change this value, wouldn't it?...*

You're right, different materials and different manufacturers will make it difficult to determine the correct jumper length.

*an SMD resistor seems to take the guess work out of it...for me at least...*<HR></BLOCKQUOTE>

Yes, but SMD resistors, like all resistors, have a tolerance, and we'll be lucky to get +/-10% with such low values. That means a 0.02-ohm resistor may be anywhere from 0.018 to 0.022 ohm, and output current could vary considerably as a result.

And although the SMD solution is small and elegant, it's not only more expensive, it's completely untweakable.

Tweakability is important for two reasons.

First, the LS forward voltage appears to vary from unit to unit. Without tweakability, the same circuit board could overdrive some LS's and underdrive others.

Second, the tolerance concern applies to the other components. For example, some 310 chips may trigger at 21mV instead of 19mV, and some 68uH inductors may actually be lower than 55uH with their 20% tolerance. So output current could vary widely from board to board, using the same LS.

If we use an SMD resistor, it would behoove us to pick a "safe" value that would never overdrive any LS---but doing so would result in most LS's being underdriven, and that would be unacceptable to many users, considering the circuit is supposed to be a maximum brightness solution.

However, if we use a jumper, we could set the jumper to a reasonably safe value, and, if desired, the user could then carefully shorten it (by twisting or soldering) to provide additional output current.


----------



## MrAl (Dec 10, 2001)

Hi again,

>>>
anyways, wouldn't a wire change resistance if it's a solid strand
or multi strand and weather it's copper or aluminum or whatever
(do they even make small guage wire out of anything but copper?)...
even different purities of copper would change this value, wouldn't it?...
<<<
Not sure what you mean here papasan; if you do use wire, you want to
use copper wire only. The temperature coefficient of the copper
matches the typical temperature coefficient of the sense voltage
threshold, meaning with copper wire we get some temperature 
compensation for free 
You can probably find strands of #32 copper wire in a larger stranded wire
size wire. Simply unravel about 2 inches or so. I'll try to come up
with some typical wires sizes that contain #32 gauge strands unless
someone else wants to do that. I was using magnet wire myself, which
is real cheap for a piece 2 inches long. You have to do a one time
adjustment with your particular circuit anyway, while measuring current
output.


>>>
Second, the tolerance concern applies to the other components.
For example, some 310 chips may trigger at 21mV instead of 19mV,
and some 68uH inductors may actually be lower than 55uH with their
20% tolerance. So output current could vary widely from board to board,
using the same LS.
<<<
I couldnt agree more Duggg.
We are operating in the 'gray' area with this circuit because it wasnt 
designed for this high output current. Almost everything we do has to be 
carefully measured on a per-circuit basis. We cant expect to ever be able
to buy one value low ohm resistor and have it work for every circuit we
ever build. On the other hand, since adjusting the length of the tiny
wire isnt that hard, this makes a good way to tweek in the values like you said.
I was originally going to use a 0.010 ohm resistor in series with a
tweeking very short length of #32 gauge wire. I'll still try this out
when the 0.010 ohm resistors come in though.
At some point we should put the circuit in the oven and raise the temperature
up to maybe 50 degrees C and note the output change. I'd like to do this
with both wire jumper and standard low ohm resistor for the current sense
and see which one comes up better. According to the typical spec, the
copper wire jumper should come up better over temperature.
The down side is that if we set the output current to the full 350ma
and we get a chip with a zero temperature co characteristic (possible because only
typical is spec'd on the data sheet) at 0 degrees C we could see some
390ma average instead. Setting the output current to 325ma at 25 degrees C would
probably be a good compromise, unless you were willing to test your
circuit at 0 deg C and make a measurement to insure it doesnt go over 350ma.
Alternately, we could test at 50 deg C and make sure the current doesnt change
more then 10ma or so.

I tryed to test the jumper and chip temp co with the soldering iron.
I placed the iron very close to the jumper, and then close to the chip.
In both cases i didnt see much change on the output. This doesnt make
sense so ill have to try the test over again sometime. I think i'll heat
the whole circuit up next time though, or take it outside on a cold
winter night and see what gives.

Good luck with it,
Al


----------



## MrAl (Dec 10, 2001)

Table showing stranded wire sizes and number
of strands of what size each strand is:

#30: 7 x #38
#30: 19 x #42
#28: 7 x #36
#28: 19 x #40
#26: 7 x #34
#26: 19 x #38
#24: 7 x #32
#24: 9 x #33
#24: 19 x #36
#22: 7 x #30
#22: 9 x #31
#22: 19 x #34
#20: 7 x #28
#20: 9 x #29
#20: 19 x #32
#18: 7 x #26
#18: 19 x #30
#16: 7 x #24
#16: 19 x #29
#14: 7 x #22
#14: 19 x #27
#12: 7 x #20
#12: 19 x #25
#10: 37 x #26
#10: 105 x #30
#8: 133 x #29
#6: 133 x #27
#4: 133 x #25
#2: 665 x #30

For example:

if you have a #22 gauge stranded wire containing 7 strands
then each strand is #30 gauge wire.

--Al


----------



## Mercator (Dec 10, 2001)

Hello All...

If MrAl's list wasn't enough for you here's another ;-) This one is the AWG gauge diameters in inch. Info was copied from the following site:

Rea magnet Wire Company, Inc.

They have lots of useful info regarding various wires sizes, inductance, etc.

If you're like me and have several samples of lacquer coated magnet wire that you have no idea what gauge it is, this chart or the complete listing at Rea and the use of a micrometer will tell you for sure. Keep in mind that these measurements are for bare (unpainted) copper wire. 

```

```

Mercator


----------



## **DONOTDELETE** (Dec 10, 2001)

Well I found some 24AWG stranded speaker wire and sure enough, it had 7 strands of 32AWG wire! Thanks MrAl for that useful chart.

I took a 3-inch strand and hooked it in place as Rsense. Initial output current was less than 100mA. Using tweezers, I started a small twist in it, and twisted it until the ammeter read 400mA (with the batteries at 2.75 volts).

The strand ended up being 1.8 inches (4.6cm) in length for a resistance of 0.025 ohm.

With this much brighter setting and a ZXT11N15DF transistor, I am now measuring efficiencies around 83%.

My earlier 85% figures were with an Rsense of 0.035 ohm and the superior FMMT617 transistor.

I am getting a Fluke 87 meter for Christmas!



With it, I should be able to report a lot more info more accurately.


----------



## MrAl (Dec 10, 2001)

Hi again,

Mercator:
Thanks for the link. I couldnt find
the 'inductance' info you mentioned
on that site though, i wanted to double check
my wire inductance formulas. Could you
post a link? Thanks 

Duggg:
Sounds like you have some pretty decent
results there. Is there any possibility you 
could change your circuits' temperature and
get another reading to see how much your 
output current changes with say 10 or
20 degrees C change? It would be interesting
to see some data on this. I guess the circuit
needs to run for 4 or 5 mins in the alternate
ambient temperature for things to stabilize
before taking a new reading.

Good luck with your LED circuits,
Al


----------



## Mercator (Dec 11, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi again,

Mercator:
Thanks for the link. I couldnt find
the 'inductance' info you mentioned
on that site though, i wanted to double check
my wire inductance formulas. Could you
post a link? Thanks 
*<HR></BLOCKQUOTE>

Ok... Sorry, they didn't list "inductance factors" for the various wire gages. They do show the resistance correction factors for different temperatures. Also,I beleive, usefull in our applications.

Mercator


----------



## MrAl (Dec 12, 2001)

Hi again,

Mercator:
Oh ok, i have used 0.004 percent per
degree C for copper. Note this is
the same as the voltage sense temp co for
the Zetex chip, hence the possible free
temperature compensation 
Thats why i was thinking of going to 
pure copper instead of resistor and
trim jumper. Since Duggg also reports
getting good results (and he devised a
simple way of tweeking the length) i think
this could be the best way to go with the
sense resistor. I guess we need some data
now though, in the form of measurements at
a few different temperatures, just to make
sure.
One little question regarding the transfer
film copper clad layout patterns:
After you draw them on the computer, how do
you print them out so that they are the correct size?
In my printer setup, all they have is inches,
not pixels, so i cant set it the way i thought
i would be able to originally.

Duggg:
Would you be interested in testing one of
my hand wound inductors? I'd like to see
what kind of results you get with your
circuit.

Good luck with your LED circuits,
Al


----------



## Mercator (Dec 12, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi again,

Mercator:
snip, snip, snip......
Thats why i was thinking of going to 
pure copper instead of resistor and
trim jumper. Since Duggg also reports
getting good results (and he devised a
simple way of tweeking the length) i think
this could be the best way to go with the
sense resistor. I guess we need some data
now though, in the form of measurements at
a few different temperatures, just to make
sure.*<HR></BLOCKQUOTE>

Al, I now agree on the "no SMD sense resistor" approach. At first, I was leaning towards the trimmed SM resistor since it would make for a neater package. I've given some thought in regards to how the final circuit board can be designed in the smallest possile configuration and the inch of so of copper wire will nolonger be a problem. More on that design later once we get the the actual parts worked out. It seems that the inductor and the cap are going to take up the biggest chunk of realty. I can't wait until I see what we finally come up with and have better idea on how to conserve as much space as possible. Here's a hint....no bigger around that your little finger or, AA battery.

Temperatures factors for both the LS and any heat built up by the ckt. will be a major concern and will have to be tested and evaluated. Especially, considering that in most applications the driver ckt will be in close proximity to the LS.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Again...Originally posted by MrAl:
*
One little question regarding the transfer
film copper clad layout patterns:
After you draw them on the computer, how do
you print them out so that they are the correct size?
In my printer setup, all they have is inches,
not pixels, so i cant set it the way i thought i would be able to originally.
*<HR></BLOCKQUOTE>

The program I use.... 'Paint Shop Pro' gives me the ability to chose between using inch or pixels. At printing time I can specify the printed size of the image in either millimeters or 0.00 inch. Or, I can choose to have the image scaled to fit the page. Also, I can select where on the page the image will print. When I make a print-out using a 1/3 page of transfer paper, I use a page set-up for a #10 envelope on manual feed. I tape the transfer paper's leading edge onto a regular sheet (8.5 x 11) of bond paper in the same location as a single fed envelope would be in. Regarding the image editing programs. I've got several and only Paint Shop and Pagemaker allow me to be so precise in printed image size and location. PageMaker has too many "bells and Whistles" and is time consumming to learn. Paint Shop is a Shareware/Freeware program that's simple and easy to use. Worth taking a look at.

Mercator


----------



## papasan (Dec 12, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*One little question regarding the transfer
film copper clad layout patterns:
After you draw them on the computer, how do
you print them out so that they are the correct size?*<HR></BLOCKQUOTE>

mral, i use the eagle layout program...if you're using this go up to 'File' then click on 'CAD Processor' then i pick the output device to 'PS' (Post Script), make sure the scale is '1', choose an output file (if this is for a real transfer remember to 'Mirror' the top so it comes out right), choose the layers to process, and hit 'Process Job'...then i have a post script file (vector graphics, holds it's resolution like a true-type font) that i open in adobe illustrator and print out...there are some printers (plotters?) listed in the output devise section, but i didn't see mine and this seems to work well...if you don't have illustrator or some other post script reading program you could probably play around with it and find a different suitable format...good luck...


----------



## **DONOTDELETE** (Dec 12, 2001)

I just did a cold temperature test, taking advantage of rare freezing temperatures here in otherwise temperate southern Arizona.

The same pair of NiMH AA cells that provided 405mA of initial output current at 20°C provided 425mA at 0°C, although it dropped to about 410mA within about two minutes.

I attribute the initial surge to lower internal resistance of the LS, which quickly disappeared as it heated up.

The Rsense "copper resistor" also heats up to some extent when a single strand of 32AWG wire is used. Supporting this is the fact that I saw virtually no change in output current when I grasped the strand with my fingers. Yet, at room temperature, touching an ice cube to Rsense creates an immediate 20mA increase.

I'll next rig up a 50°C test. Hopefully it too will show little variation.


----------



## **DONOTDELETE** (Dec 12, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
Duggg:
Would you be interested in testing one of my hand wound inductors? I'd like to see what kind of results you get with your circuit.
*<HR></BLOCKQUOTE>

Sure! You can either send it to me directly, or save a little in postage by sending both to Mercator, then he can send it to me along with the other stuff he's ordering.

How big is it? What core material? How many turns? Are the cores available in small quantities and relatively affordable?

Note that we want a maximum height of 6mm and outer diameter no bigger than 10mm.


----------



## MrAl (Dec 13, 2001)

Hi again,

Mercator:
Yes it looks like the copper jumper is better then the resistor,
unless of course Zetex made a mistake on the data sheet and
the 0.004 percent per degree is really -0.004 percent, in 
which case we would be compounding the problem 
Assuming their spec IS correct, we should be doing pretty
good with the copper jumper, and it's not only cheaper it's
smaller and a heck of a lot easier to get.

What version of Paint Shop Pro are you using?

papasan:
I've been thinking of trying that program. How long does it take
to get used to it, like, how hard is it to learn?

Duggg:
That's great that you got to do that test and get some data on the
temperature characteristic. The results look very good.
I'm using two parallel strands of #32 to handle the current
a little better.
I'll be sending you an inductor to test also so you can check it
out for yourself and see what your ideas are regarding it's small
core. I would like to get more cores from Magnetics, Inc. so we
know exactly what we are getting. With the surplus cores, it's
hard to tell even after a few measurements. I guessed Magnetics
J type material because the initial permeability matched that
for a core size similar to this one of that material.
I'm sure these cores are dirt cheap.
I have your address now, but if you want to verify it email me before 
Saturday ok? I would like to make sure it's going to the right place 

I did some brief temperature tests with the
core also. Heating the metal up to a pretty
high temp with the soldering iron while
the circuit was running, i didnt see any 
change in the output current. I couldnt
go too high because i was using a plastic
coated wire, but it had to be at least 50
deg C. If i saw any change at all, i would
have tested higher using actual magnet wire.
According to most mag curves, the metal
Bsat at 100 deg C approximately halves
from that at 25 deg C.

Well i hope to do some more testing later myself.

Bye for now,
Al


----------



## MrAl (Dec 13, 2001)

Hello again,

I did a little testing with the inductors again.
This time, i broke a slightly larger core up
into four pieces, then glued two pairs of two pieces
back together again forming two halves of a toroid core.
The core when glued back together effectively now has
a small air gap.
Then i wound 10 turns on one half of the core.	
I used this half as an inductor, as well as holding
the two halves together to form a full toroid again
only with the four air gaps.

Other then the inductance value and its' effect on the output
current, i didnt see really that much difference, although there was
some slight difference. The best combinations were when the
core halves were held together tightly (forming again the full toroid)
and when an identical full core with no cracks in it was used with 
only 5 turns.

Once we get the right parts (and my LS order gets here) 
i'll do the test over again and take more accurate 
measurements to try to see if adding an air gap
and/or using less turns will improve efficiency.

One other thing was interesting, i was only joking about using
an air core inductor, but since i was doing some tests i thought
i would give it a shot. I found that lower inductances work too
so i build up an air core inductor.

Here's the inductor:
Wind 10 turns of #24 or heavier on 1/2 inch diameter form, then remove
the form and squeeze the turns together tightly so that it forms
a construction 1/2 inch diameter and about 1/4 inch thick. Secure the
turns with some glue or thread or other non magnetic non electically
conducting cord.
That's it.
Efficiency only suffers slightly. More turns might improve this too
though.

Alternately, perhaps wind 12 turns consisting of 3 layers of 4 turns each, 
one layer tightly wound on top of the other.

Modifications to the air core inductor:
More turns = more output current from the same battery voltage input,
but you may have to use heavier wire for a lot of turns.

Tested results:
With the above inductor, i got 180ma output. More turns would increase this.

Duggg, i hope you will try this and report your results. If you get the 
time, maybe you could try more turns also.


And now briefly back to the Delevan 100uH inductor (and i use the term
'inductor' very very loosely here  When i saw this device in the
catalog, the writeup said "inductor" hence i assumed it was really
an inductor 

I removed 16 turns (out of the 35 that were on there) and tested the
device, and it still didnt work. In fact, now it didnt work at all.
The transistor got red hot. Needless to say, the core (which is about
3/16 inch diameter) material must be either a very high frequency type or
a very low frequency type and cant handle the upper frequencies contained
in a rectangular waveform. It does test ok at 100kHz, but with a sine wave 
only. This leads me to suspect this device is made with a low frequency
core material.

If anyone else tries the air core inductor, please post your results.

Oh and if you decide to try breaking up your core to test with air gaps,
it helps to coat the core with (or dip it in) a heavy flexable glue like
"Goop" or even maybe silicone rubber to entirely cover all the surfaces of
the toroid core (inside and outside). Then, after it dries clamp it
lightly in a vise and turn the handle of the vise just a little. The core
will crack up into 2, 3, 4 or more pieces, all of which will be still held
together with the encompassing dried glue. After this, the core will 
now have 2 or more small air gaps and the inductance will have decreased
somewhat (maybe 5 times less then without the cracks). You can then
test the new inductor and see what changes it makes in your circuit
with the added air gaps.

If anyone tries this, please post your circuit results.

Bye for now,
Al


----------



## **DONOTDELETE** (Dec 13, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*question: when i do get around to testing out this circuit i was thinking of putting a couple/few 3.6v 5mm LEDs in parallel with the output in order to absorb extra output current just in case i screw something up so i don't fry the (ratehr expensive) LS...would this be good to do or not?...would it change the output of the circuit (meaning, after measuring the voltage and amperage with this set-up would it change signifigantly after removing the 5mm LEDs)?...*<HR></BLOCKQUOTE>

It would definitely affect things. The circuit is "tuned" by carefully adjusting Rsense to provide 350mA of current through the LS.

If you add extra LEDs, you'll need to lower Rsense to provide the extra current they require. But then if you take away the extra LEDs, the LS will be left to absorb that extra current by itself.

The best approach is to start with a high value for Rsense (i.e. a long strand of wire) and carefully shorten it by twisting it until you're comfortable with the current through the LS.

The biggest threat to the health of the LS is the capacitor---it can store a lot of energy. Even a momentary loose connection can allow the cap to gather enough charge to zap the LS when it reconnects. However, this is not a concern if the connections between the capacitor and the LS are tight at all times. 

This poses a challenge if you had planned to insert an ammeter in order to measure output current. It would be much safer to solder a small resistor (0.01-0.05 ohm) in series with the LS, measure the voltage across it, then divide that voltage by the resistance in order to determine the current.


----------



## **DONOTDELETE** (Dec 13, 2001)

Here are the high temperature results.

I stuffed the whole circuit inside a picnic cooler filled with six liters of water bottles at 40°C, in order to maintain constant temperature.

Initial current was just 350mA. It fell to 340mA within a few minutes and it was 325mA after a half hour, at which point I ended the test.

Final efficiency was actually quite high at 86%, perhaps due to the fact that the diode's voltage drop is less at higher temperatures.


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## papasan (Dec 13, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*If you add extra LEDs, you'll need to lower Rsense to provide the extra current they require. But then if you take away the extra LEDs, the LS will be left to absorb that extra current by itself.*<HR></BLOCKQUOTE>

well...what i was treating the LS + any extra LEDs as a single unit, not as seperate entities...meaning i would try to tune the output of the circuit to 350~400mA with the extra LEDs in place then when i got it right i would remove the extra LEDs and just run the LS...

so if i do this, if i tune the circuit output to 350mA with extra LEDs there just in case (since a 5mm LED can take pulses of 100mA a couple in parallel could really save my a$$) and then remove the extra LEDs from the circuit without chainging anything else would the output still remain 350mA or am i missing something?...

i'm just really aprehensive about runing an $18 LS off of a circuit that i don't fully understand, espicially since i am not anything even close to an EE...


----------



## Mike (Dec 13, 2001)

If you ran a Luxeon in parallel with some other standard 5mm white LEDs I think the 5mm LEDs would barely light since they take a slightly higher voltage than the Luxeon.


----------



## papasan (Dec 13, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Mike:
*If you ran a Luxeon in parallel with some other standard 5mm white LEDs I think the 5mm LEDs would barely light since they take a slightly higher voltage than the Luxeon.*<HR></BLOCKQUOTE>

that's fine...they're not there to be actually useful, just to be drains for excess current...they would be removed once i deemed the circuit to be LS friendly...besides, 3.6v LEDs light up pretty well at 3v...


----------



## MrAl (Dec 13, 2001)

Hi again,

papasan:
We are now using the LS simulator to test
the circuit before connecting the 'real'
LS to the output.
The simulator is just three 1N4004 diodes
connected in series with a 1 ohm resistor
also connected in series with the diodes.
The anodes of each diode connect to the
cathode of the preceding diode. That leaves
one free anode and one free end of the 
resistor. The anode becomes the + terminal
of the LS and the free resistor lead becomes
the - terminal, which connects to circuit
ground. A slightly better simulator would
also have one Schottky diode in series with
the other diodes also, like a 1N5817 diode.

Also, i posted a network which you can build 
up to test the output ripple to make sure
the LS doesnt see too much peak current. 
That's in a previous post in this thread.

--Al


----------



## **DONOTDELETE** (Dec 13, 2001)

Got this just today

-----Original Message-----
From: Neil Chadderton [mailto:[email protected]]
Sent: Thursday, December 13, 2001 1:36 PM
To: 'Bill Schaer'; 'Dave'
Subject: RE: zxsc300m - web forum


Dave, Bill, just to confirm - the ZXSC300 and '310 are now in stock at DigiKey.
Regards,
Neil Chadderton 
Applications Engineering Manager 
Zetex Inc., NY 
Tel: 631 366 5062 
Email: [email protected] <mailto:[email protected]> 
Website: www.zetex.com <http://www.zetex.com> 

-----Original Message-----
From: Neil Chadderton 
Sent: Friday, November 09, 2001 9:23 AM
To: 'Bill Schaer'; 'Dave'
Subject: RE: zxsc300m - web forum
Importance: High


Bill, Dave, thanks for this, this looks great! Please assure your colleagues that samples are available from our sales reps and distributors - they don't have to wait for DigiKey to stock if they need a few for evaluation.
Thanks again for this.
Regards,
Neil Chadderton 
Applications Engineering Manager 
Zetex Inc., NY 
Tel: 631 366 5062 
Email: [email protected] <mailto:[email protected]> 
Website: www.zetex.com <http://www.zetex.com>


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## papasan (Dec 14, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I've been thinking of trying that program. How long does it take
to get used to it, like, how hard is it to learn?*<HR></BLOCKQUOTE>

i found it easy to learn and use...took only a couple hours to figure out everything, probably would have been even easier if i'ld ever used a PCD layout program before...it builds schematics and will auto-route, but i just use it to make the layouts...

of course, having never used a PCB layout program i have nothing to compare it to...i have used autocad and quickcad and autosketch and found it much easier to figure out than autocad, similar learning curve to autosketch...

best of all is it's cost =)...the free version is limited to like 3.5x4 inches or something, more than enough...

www.cadsoft.de

i'm excited about the progress being made, i'll be ordering some stuff up soon...perhaps an SMD cap can be singled out...if i can avoid drilling that would be nice =)...

question: when i do get around to testing out this circuit i was thinking of putting a couple/few 3.6v 5mm LEDs in parallel with the output in order to absorb extra output current just in case i screw something up so i don't fry the (ratehr expensive) LS...would this be good to do or not?...would it change the output of the circuit (meaning, after measuring the voltage and amperage with this set-up would it change signifigantly after removing the 5mm LEDs)?...


----------



## papasan (Dec 14, 2001)

anyone seen these ricoh chips?...

http://www.ricoh.co.jp/LSI/english/spec/power/rh5rh/rh5rh-e.pdf

lots of cool graphs and stuff i can't begin to understand...the sot-89 package looks easier to solder, but perhaps bigger than wanted...


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## **DONOTDELETE** (Dec 14, 2001)

Thanks Clackcom---the 300 has been available from Digi-Key in single quantities for over a month now.

As far as the 310 goes, their website reports they have two 3000-piece reels in stock, and single pieces will ship on December 29. Of course, yesterday it said December 28, and tomorrow it will probably say December 30. Good ole Digi-Key, what a little jokester






And boy Papasan, that's some spec sheet Ricoh puts out on their RH5RH series, 29 pages! The last page of application hints was definitely interesting reading. Too bad its output is limited to 250mA---just a little more and it could have driven an LS directly. But without the direct drive capability, I see it as bigger than the Zetex chip, but not any better.


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## papasan (Dec 14, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*And boy Papasan, that's some spec sheet Ricoh puts out on their RH5RH series, 29 pages! Too bad its output is limited to 250mA---just a little more and it could have driven an LS directly.*<HR></BLOCKQUOTE>

i get bored and check these forums too frequently =P...

on page 14 they have a chart of the 302B getting close to 600mA with a 2.5V input...at less than 80% efficiencey tho and with an extra cap and resistor...going by that chart it will put out 350mA until the input voltage is about 2V, not bad with a 2 cell power source...unless i'm reading it wrong...

** edit **

btw, i asked about specs and availabilty of the zetex 320 chip, apparently it's been abandoned, they told me to just send a PWM signal to the shutdown pin of the 310 meanign that this would require even more junk thrown in there...bah humbug...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>...we have decided to put the '320 dev' on hold. It is very similar to the '310 but with a dimming function. This function can be obtained fairly easily already with the '310 by strobing the enable pin with a PWM signal. This is indicated on the datasheet.
Regards,
Neil Chadderton 
Applications Engineering Manager 
Zetex Inc., NY 
Tel: 631 366 5062 
Email: [email protected] <mailto:[email protected]> 
Website: www.zetex.com <http://www.zetex.com><HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Dec 14, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*On page 14 they have a chart of the 302B getting close to 600mA with a 2.5V input*

All the XX2B series require an external transistor---see page 2. The chart on page 14 shows performance using a 2SD1628G, if you read the fine print.

*btw, i asked about specs and availabilty of the zetex 320 chip, apparently it's been abandoned, they told me to just send a PWM signal to the shutdown pin of the 310 meanign that this would require even more junk thrown in there...bah humbug...*

Well, I wasn't really that interested in dimming an LS anyway... we can already do that using a large value for Rsense




<HR></BLOCKQUOTE>


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## MrAl (Dec 15, 2001)

Hi again,

papasan:
That is an interesting circuit too.
I'm wondering how well their chip really
works down to the low input voltages
too though.
I have been rekindling the idea of
running the Zetex circuit off of a single
cell by using a hand wound inductor/transformer
with a turns ratio of maybe 2:1.
Also, the waveforms they provide on the
data sheet are pretty much idealized.
In our circuit, we always have current flowing
and the inductance ends up being controlled
by the voltage across the inductor.
During the transistor on time the inductance
is lower then during the off time, so
the inductor charges up quickly, and discharges slower.

My next test will be with the transformer/
inductor instead of just a plain inductor.
I have a feeling the right turns ratio
(according to input voltage) could raise
efficiency. On the other hand, the core
doesnt eat up that much power anyway, so ill
have to see what happens.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Dec 15, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*In our circuit, we always have current flowing and the inductance ends up being controlled by the voltage across the inductor. During the transistor on time the inductance is lower then during the off time, so the inductor charges up quickly, and discharges slower.*<HR></BLOCKQUOTE>

The inductance should not be varying. If it is, it's a sign that the inductor is saturated, and when an inductor saturates, it behaves more like a resistor, causing a loss of efficiency.


----------



## MrAl (Dec 16, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*The inductance should not be varying. If it is, it's a sign that the inductor is saturated, and when an inductor saturates, it behaves more like a resistor, causing a loss of efficiency.*<HR></BLOCKQUOTE>

Well when you think about it, does it really matter if the inductance changes? I mean,
if it changed from 100uH to 99uH would that be a problem? Certainly every inductor
used in this kind of circuit will change inductance to some degree, depending on
dc bias. There is no way around this without using a core with an area so large
it wouldnt be practical. Besides, the bottom line is: "does it eat up too much
power and/or get too hot?". When the core is driven further toward saturation,
the BH loop necessarily gets wider, but just how much wider does it get? Once
you get way up there on the curve, the loop doesnt get that much wider. Even if
we assume 100mw/ccm, with a volume of only 13ccm this tiny core should only 
increase 4 degrees C in temperature. This cant be too bad.
Also, sometimes "saturation" is mistaken for "evil zone" without regard for the actual
construction under consideration (including the material), or the
application. Just because we might be operating on the upper flat of the mag curve
doesnt mean its bad. And besides that, the efficiency isnt that bad right now.

You will soon have a core to test yourself as im sending you one also 

Remember the thing that looks bad about an inductor operated
near saturation is 
that some apps require a certain minimum inductance in order to
operate normally because they are driving the construction with 
a square wave of preset frequency. When the inductance changes
to a lower value, the construction draws a whole lot of current
near the end of the pulse. If this current is too high, it
blows the transistor used to drive the core. In our app, as long
as there is some inductance (ie not zero) our circuit still operates
because for larger currents the pulse simply ends sooner. This is
very different from driving say a transformer with a constant frequency
square wave, where current is essentially not limited.

If you have any tests that you would like to see done on this
core, let me know. I'll test it and post the results.

So far i have tested it with sine waves with a variety of dc
bias currents, and i have seen the inductance change quite drastically
for some high currents, but it still acts like an inductor just the same.
I would like to do more tests with higher ac voltages but i have to 
build up a better drive circuit (right now i can only get about 20mv ac
100kHz voltage when the core is taken up to maybe 2 amps or so, so its hard
to measure quantities).

Take care for now,
Al


----------



## **DONOTDELETE** (Dec 17, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*If the inductance changed from 100uH to 99uH would that be a problem?*

Certainly not. But if the inductance changed from 100uH to 25uH or even 50uH, then that's a different issue.

*Certainly every inductor used in this kind of circuit will change inductance to some degree, depending on dc bias. There is no way around this without using a core with an area so large it wouldnt be practical.*

That's an interesting question. The commercial inductors state a saturation current, and it's usually the point at which the inductance has dropped by 10%. So it would appear manufacturers take the issue of saturation very seriously.

Toroids are notorious for saturating at low current, so I fully expect an inductance loss of greater than 10% even with Ipeak around 800mA. How that will impact the circuit and affect the efficiency, remains to be seen.


*Besides, the bottom line is: "does it eat up too much power and/or get too hot?". And besides that, the efficiency isnt that bad right now.*

Well that really is the key. Sometimes we tend to fixate on the "E" word, even though a few percent here and there really won't make that much of a difference in real world applications.

Don't get me wrong---if we can keep efficiency above 80% using your handwound toroids, and the cores are readily available at a good price in small quantities, I'm all for saving the $3+ we would have spent on the commercial bobbin inductor. And I'll happily give you full credit for suggesting the idea!

*You will soon have a core to test yourself as im sending you one also *

Cool, I'll test it as soon as it arrives! Thanks!!

*In our app, as long as there is some inductance (ie not zero) our circuit still operates because for larger currents the pulse simply ends sooner.*

Yes, but in order to obtain 350mA of output current, there needs to be a substantially nonzero inductance. It won't work with just any old inductor.

And we just can't keep shortening the pulse to compensate for poor inductors, because at some point the transistor or the IC won't be able to keep up. We're already operating at twice the 300's intended operating frequency.

And boosting Ipeak to compensate won't work either, as doing so will increase I^2R losses and cost us in efficiency, or possibly damage the LS.
<HR></BLOCKQUOTE>


----------



## MrAl (Dec 17, 2001)

Hi again,

An inductor whos' value doesnt change 
looks like this:

L=L1

which is simply a constant.
In the real world, the inductance changes
at least somewhat with dc current so we
change this constant to:

L=f1(Idc)

which simply means the inductance depends
on dc bias current.
But looking at the mag curve, the 
permeability changes with both current
and voltage, so for a more complete description we write:

L=f2(I,V)

which simply means the inductor changes
value with both current and voltage.

Now having established an equation
for the inductor, even though relatively
simple, there are a number of questions we 
could ask in order to determine the
allowable limits on the change of inductance 
in a given circuit application. Not all apps
are the same. Some can tolerate a huge change in
inductance, while others cant tolerate much at all.
Since our circuit measures current through the
inductor, ours can tolerate a huge change as long
as that change doesnt have very bad secondary effects
like power consumption.

First, establishing two equ's for both inductance values:

L1=f2(I1, V1)
L2=f2(I2, V2)

Now we have something we can work with, more or less.
The first inductance value (L1) occurs during the transistor
on time and the second during the off time (L2).

Now lets see what the values V1 and V2 come out to be.

Assuming 2.4 volt input and 3.2 volt output, the voltage
across the inductor during the on time is 2.4 volts, and
during the off time only 1 volt (assuming 0.2 volt Schottky 
diode drop). So now we have V1=2.4 volts and V2=1.0 volts.

Substituting these into the equations:

L1=f2(I1, 2.4)
L2=f2(I2, 1.0)

we get a little bit better picture of what is going on.

Although we havent yet pinned down the other values,
we can see that any inductor would see two values of
current through it and two corresponding values of voltage across it
during one cycle. From waveform inspection, i can tell you the current
increases faster during the on time then it decreases during the
off time, and that this change is disproportionately higher then the
voltage V across it would dictate if it were a linear inductor.
This means that inductance L1 is less then L2.
The other interesting thing is that since L1 is less then L2,
the on time is much shorter then it would be had the inductor
been a constant value equal to L2. This means core losses during
on time will be less because of this also. Since the on time
is reduced, we may actually see a gain in eff. It depends on
how much we save because of the shortened on time vs how much
we loose because of operation on the horizontal section of the
mag curve.

Another interesting thing we could do is establish a new inductance
value, and call it "average inductance". This would look like:
Lavg=(L1+L2)/2
Now we might establish a min or max average inductance value that would
work in our circuit.

An easier way around all this is to simply handle the circuit as
having two inductors instead of one. That is, during the time
that the inductor has value L1 we analyze the circuit for 
losses using it's dcr, core loss, and inductance value, and we do the same
for the time the circuit has value L2. We then add the losses
together and simply determine if it's too high or not, and if
the core heats up too much with these two values.

An even simpler way is to measure the efficiency, and if it's too low
we know its the inductor. If it's above 80% i wont complain, too much 

It will of course be interesting to test the newer store bought inductors
and compare them to the toroids. It's very possible that if they dont
change inductance quite as much as the toroid we might get higher
efficiency with those. If not, or if its not much higher, or even lower,
i'll have to go with the toroid. If the newer inductors act the same way,
we can keep them on the list of second sources.

Having established the other part selections, it seems to me that the
best final inductor choice now will be the one that provides our circuit
with the highest efficiency, period 


Good luck with your LED circuits,
Al

Added later:

Noting that the inductance is more
controlled by the voltage across it
then the dc current though it
(i.e. dL/di << dL/dv)
i decided to go to 20 turns instead of
5 or 10 turns. Sure enough, the inductance
value changes much less and the circuit puts
out more current. The dcr is still less then
0.05 ohm.

Duggg&Mercator:
Your inductors are now in transit so
you should have them in about 5 days.

--Al


----------



## MrAl (Dec 18, 2001)

Hi again,

This time i unwound the Delevan inductor
and wound 20 turns of #24 gauge wire
with plastic insulation (not magnet wire).
The inductor worked in the circuit to some
degree, but the efficiency dropped to 67%.
I also noticed that sometimes the circuit
wont start up properly when power is
applied, and the transistor gets very hot.
This makes a pretty good test for trying
out a new inductor--if the transistor
starts to heat up (it heats up fast too)
dont use that inductor. You have to hold
your finger on the transistor clad
connected to the collector while you
turn the power on.
(Of course make sure the LS simulator is
connected properly to the output also).
If the inductor is bad,
the transistor starts to heat up really
fast, so that you cant hold your finger on
it very long. If you feel any heat at all,
dont use that inductor. Turn the circuit on
and off a few times slowly to repeat the 
test several times. If the transistor heats
up once, dont use that inductor. Try another
one.

With the same rewound inductor connected in
series with the LS and another small tant 
cap (3.3uf) using the inductor as an output
filter, the output ripple goes way down to
very nearly 20mv or so. This indicates that
the inductor, once rewound, can be used to
filter the output if you want to be more sure
you are getting a pure dc output. Of course
this inductor core is a little large, so
you may not wish to use up this much space
when a smaller core will work just as well.
But if you happen to have ordered some of 
these inductors, at least you may have a use
for them in larger space applications.


For my own flashlight, im going to keep
the small ferrite bead inductor on the 
output for it's extra filtering action.
The efficiency isnt affected much at all.

--Al


----------



## papasan (Dec 18, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>A $5 handling charge is added to your order if the subtotal is less than $25<HR></BLOCKQUOTE>

ahh!...<grumble grumble>...too bad mouser doesn't carry zetex stuff...any way around this?...


----------



## **DONOTDELETE** (Dec 18, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*ahh!...<grumble grumble>...too bad mouser doesn't carry zetex stuff...any way around this?...*<HR></BLOCKQUOTE>

One way around it is to pre-pay your order, in other words, mail Digi-Key a check for the full amount. In return, you get free shipping. (Note that you cannot get free shipping if you order online and/or pay with a credit card.)

Now, if you had ordered from Mouser (or Hosfelt or any other mail order outfit), you would have saved the $5 handling charge, but you would still have had to pay the same for shipping, more or less. So it balances out.

Whenever I order from Digi-Key, I usually "invest in my kitbuilding future" by ordering extra components that I'm sure I'll use eventually, bringing the total to just over $25, so that I skip the handling charge AND get free shipping.


----------



## papasan (Dec 18, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*One way around it is to pre-pay your order, in other words, mail Digi-Key a check for the full amount. In return, you get free shipping. (Note that you cannot get free shipping if you order online and/or pay with a credit card.)*<HR></BLOCKQUOTE>

i've heard this, and it's true that there are no shipping charges when you mail your money in, but the order sheet for sending/faxing orders still says that they charge a $5 handling fee for orders under $25...i suppose i'll just have to be on the lookout for usefull stuff to pad the order with...


----------



## **DONOTDELETE** (Dec 18, 2001)

I got tired of looking at cyan photons, so I hooked up my amber LS to the circuit, since its electrical characteristics are different.

I was surprised that it used the same value for Rsense---approximately 0.025 ohm---to get the 350mA output, although the output voltage and input current was lower.

However, efficiency wasn't much better---around 86%, just 1 or 2% better than with cyan.


----------



## MrAl (Dec 19, 2001)

Hi again,

papasan:
Yeah that digikey ordering is interesting.
So that means if you send in for $25 worth
of stuff and mail in the check you dont
pay ANY extra charges? Sounds pretty good
to me. Most places charge at least $5.

Duggg: 
So you tested your circuit with the actual
LS? What kind of output cap are you using 
now, and what inductor and input voltage?

My LS just got here yesterday, so i'll be able
to test the circuit with the real thing now.
I did some real quick tests on the LS and
i can see it 'overshadows' multiple LED's
by a large margin. The brighness and beam
width are pretty remarkable even at only 150ma.
The only improvement i see is
that they could have made the board it's
attached to round instead of square, which
would have made a very slim 2 or 3 AA cell 
flashlight. Any ideas how to get the board
ground down to round like the LS/O itself?
The heat sink would have to be ground too,
or removed and replaced. Does it come off?

I'll probably modify the LS
simulator for testing the circuit with too.
Although the 3 diodes + 1 ohm resistor isnt
that bad, from looking at the data sheet
it looks like the dynamic impedance of the
LS is even lower then the simulator.
From the data sheet i created a new model of
the LS and compared it to the LS simulator
and found that 4 diodes plus a special
transistor simulate the LS even closer then
the diodes and resistor. I might build one
up and compare it, but i think test data
obtained from using the original LS simulator
can be scaled up and deemed good enough for
a go/no-go final circuit test.

BTW, i found that even the slightest inductance
placed between the LS and the output
of the circuit lowers the peak output current
substantially. Even two turns of #24 wire
through a tiny 1/4 inch ferrite bead works.
Of course you need another cap in parallel 
with the LS when this is done. The cap i used
was only a 3.3uf tant, so i would bet
a larger 20uf electro would work even better.
The DCR of an inductor like this is really
insignificant.

Well, i hope to have my first LS flashlight built soon.
I'd like to put multiple switched light settings on it,
but im not sure if the zetex 300 chip is suitable for this.

I dont recommend putting a switch in series with the sense
resistor unless maybe its a very high quality type and mounted
in close. Perhaps the highest value resistor in parallel with
the switch would work, that way if the switch were momentarily
open, the worse that would happen is the circuit would dim
the LS. Im now just wondering what kind of switch will have low
enough resistance at 1.5 amps and still be small enough?
I dont like doing this though, so i hope to find a better way.

I'm not sure that using the zetex 310 chip with the extra
control pin will make things any easier, since that would
require another chip like the 555 to pulse width modulate
the 310 chips' enable pin. That would require a few more
resistors and a cap or two also. Putting a resistor in
series with the LS could screw things up royally, as the
voltage across the transitor would increase too high.

Controlling the positive supply terminal of the
chip itself with a small pot is also not workable as
lowering the chips' supply voltage reduces transistor 
drive current which raises saturation voltage which
heats up the transistor.

Perhaps switching resistors in series with the transistor
collector. This would reduce efficiency at moderate
settings, but high and low settings probably wouldnt
be affected that much.

I guess a second transistor connected to the base of
the output transistor could steal all the base current,
thereby turning it off completely, but this too would 
have to be pulse width modulated which draws in a host
of other parts too.

Or, mounting a magnet on the end of a thumb screw, where
turning the screw brings the magnet closer to the core
thereby magnetizing the core higher up on the mag curve
thereby lowering the inductance therefore causing a 
reduction in output current without bothering the
efficiency as much as a series resistor. I think i'll
try this and test efficiency at various settings.

Any other ideas for providing multiple settings?

Good luck,
Al


----------



## **DONOTDELETE** (Dec 19, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Duggg: 
So you tested your circuit with the actual LS? What kind of output cap are you using now, and what inductor and input voltage?*

I haven't gotten any new components in a couple of weeks now, so I'm still using a 220uF SMD cap with an estimated ESR of 0.2 ohm. The inductor is the 68uH M9711, and I'm using 2 NiMH AA cells as the power source.

*My LS just got here yesterday, so i'll be able to test the circuit with the real thing now. I did some real quick tests on the LS and i can see it 'overshadows' multiple LED's by a large margin. The brighness and beam width are pretty remarkable even at only 150ma.*

Even at currents below 100mA, the LS is pretty impressive, and probably quite efficient.

*The only improvement i see is that they could have made the board it's attached to round instead of square, which would have made a very slim 2 or 3 AA cell flashlight. Any ideas how to get the board ground down to round like the LS/O itself?*

The approach that I'll be taking involves buying a plain Luxeon Star (without optics) which has a much smaller hexagonal board, only 20mm in diameter, and then mating that with the collimator I removed from the LS/O I fried last month.

I emailed Luxeon inquiring about the availability of just the collimators, but of course I got no reply.

*The heat sink would have to be ground too, or removed and replaced. Does it come off?*

The chip is integral to the board for maximum heat transfer, so it's hard to remove. You might consider using a Luxeon Emitter and arrange your own heatsinking.

*BTW, i found that even the slightest inductance placed between the LS and the output of the circuit lowers the peak output current substantially.*

Yes, I noticed that when I used my analog multimeter in ammeter mode. To get around the problem, I had to use current sense resistors and measure the voltage to derive the current.

This problem was even more dramatic on the input side.

*Any other ideas for providing multiple settings?*

If two settings are good enough, simply switching between one or two cells sounds pretty simple...
<HR></BLOCKQUOTE>


----------



## MrAl (Dec 19, 2001)

Hi again,

duggg:
what i meant by 
>>>
i found that even the slightest inductance placed between the LS and the output of the circuit lowers the peak output current substantially.
<<<

was that even the slightest inductance
used to filter the output helped clear
up the high peak current very well.
The small inductance of even 2 turns on
a small ferrite bead lowered the peak current
but didnt affect the average current.
If you can afford the room, the small
bead is very well worth it.

I built my first LS flashlight tonight 
Darn thing seems brighter then a room full of
regular LED's  I left leads on the 
LS so that i can test it with other circuits
without removing it from the flashlight.
I'm only running it at 250ma for now.

I think any flashaholic can easily
get hooked on these things 

--Al


----------



## **DONOTDELETE** (Dec 19, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Even the slightest inductance used to filter the output helped clear up the high peak current very well.*

Oh, I see, I misread your post.

I'm seriously hoping the new, expensive low-ESR tantalum capacitor will completely take care of any ripple, without the need to add an additional inductor, because even a small ferrite bead is relatively gigantic.
<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Dec 20, 2001)

I found an alternate supplier for the capacitor and inductor. www.newark.com. They seem to have good prices, but I have never ordered from them before, so _caveat emptor_ and check out their terms & conditions carefully.

They sell the Kemet 150uF, 10v polymer tantalum capacitor for $2.46 each, or 10 or more for $2.32 each. Compare to Mouser at $3.00 each.

They also sell a Bourns 68uH SMD power inductor, 1110mA, 0.22 ohm DCR, 10mm diameter, 6mm height for *$0.54 each,* which is $3 cheaper than similar inductors from Digi-Key. Not surprisingly at that price, they're out of stock for the next eight weeks.


----------



## MrAl (Dec 20, 2001)

Hi there again Duggg,

The second bead is 3/16 inch diameter by
1/4 inch long.

I have ordered from Newark before.
I got high voltage HEXFETS,
dual 50 amp Schottky rectifiers,
driver ic's and stuff like that.
They have a $25 minimum, if it's still
$25 that is. 
I had only one problem with them once, and
that was i had ordered a few types of 
HEXFET transistors and two of the lower 
priced transistors were being shipped from
a different location then the rest of the stuff so they tried to charge me extra 
shipping for the remaining two transistors
(like $6.00 extra or something). When i 
called them the only option i had was to
refuse the second shipment, so i couldnt
get the parts unless i was willing to pay
more shipping then i should have had to pay.
Possibly a way around this is to make sure
all the parts will ship from the same 
location before ordering.

BTW that inductor core site looks real nice.
Lots of different kinds of cores.

Good luck and thanks for the info,
Al


----------



## **DONOTDELETE** (Dec 20, 2001)

*WOW!*

I just tried one of MrAl's famous handwound mini-toroids. Efficiency went up by over 4%!

I just got a reading of 88.6% efficiency! And that's with a crappy transistor and capacitor!

I will do some more testing later this evening, but as of right now: 

*All Hail MrAl!*


----------



## MrAl (Dec 20, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*WOW!

I just tried one of MrAl's famous handwound mini-toroids. Efficiency went up by over 4%!

I just got a reading of 88.6% efficiency! And that's with a crappy transistor and capacitor!

I will do some more testing later this evening, but as of right now: 

All Hail MrAl!









*<HR></BLOCKQUOTE>

hee hee that's great Duggg.
The highest i got so far was about 85%.

I'm glad to hear you got that inductor.
I put 20 turns on that core, but it is possible that 10 turns might be even more 
efficient. When i tryed 10 turns vs 20 
turns, it looked like 10 turns was higher so 
you might want to try that next.
If you want to scrap a little enamel off
the wire at 10 turns, you can tack solder
a light gauge wire to it for a center tap.
You can then test it with 10 turns and 
compare eff. When i did that, it looked like
10 turns took it up a few more percent.

BTW, i'm pretty sure now that that core
is 'J' type material, but it would be
interesting to try the other materials also.

I'm glad your getting such good results.
The other circuits i've been reading about
are all under 80%, some much under.
I think the Zetex circuit is the highest of
them all so far, partly because of the 
transistor and partly because of that great
diode i think.

What kind of transistor are you using now?

I'm dying to try some of those other
core materials also. I saw the 'W' type
which looked really good for filter apps.
I might have to try a few samples.

Also, i found out that the material i was
using for my output filter right now is
only u=125, which means it requires lots
of turns to get any decent amount of inductance
out of it. So what im thinking about
doing is using a very small toroid
(like 1/4 inch diameter) for an output 
filter (made out of 'W' material)
which would only require a few turns,
and then minimizing the two cap's
required to form the pi filter. See,
i think if this works, it could reduce
size in the long run and certainly cost.
If we can use really cheap caps, that 
would be great. If the extra inductor allows
a much lower value of capacitor, that could
save money as well as space. Thats some of
the reasons im so interested in the output
pi filter. The little inductor im using now
is smaller then a cap. If i get the right
material, i can use less turns and lower
the dcr even more. Should be an azz kickin
circuit  (even though it is already).

I'd still like to try the more expensive caps
though, and compare results. If the caps
are smaller then the extra inductor and
lower value caps then i guess i'll have to
go with that for size.

I'm thinking of converting an AA mini mag
flashlight to LS with Zetex circuit now.
Since this circuit is getting smaller by the
minute, i think it might be possible.
I like the extra run time you can get from
2 AA's so i think this would work out really
good. Perhaps orientating the parts in 
a circular shape would make it more suitable
to this smaller case.
It is possible to use an even smaller inductor
albeit with some loss of eff.

I'll tell ya, right now im tired of
the light output from my current
mini mag AA to single LED conversion
with three N cells. Such a nice case
design with a sick little one LED at
something like 20ma.
If i can get an LS in that thing, that
would make the whole flashlight worth 
having, and using.
Right now it's 'useable', but that's about it. With an LS in that thing, that would
really be quite a flashlight 
I think anyone would want one.

--Al


----------



## **DONOTDELETE** (Dec 20, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I put 20 turns on that core, but it is possible that 10 turns might be even more efficient. When i tryed 10 turns vs 20 
turns, it looked like 10 turns was higher so
you might want to try that next.*

The 20-turn toroid produces an average efficiency around 87%. I even got a 90% once---our first! However, Rsense had to be shortened to 0.012 ohm, doubling Ipeak to 1583mA.

If it really is J material, then that's a pretty hefty inductor---I calculate 927uH. I also show that the core saturates at just
one turn, so its true inductance is far less, though obviously sufficient.

It will be really interesting to see what happens when we don't saturate the core.

I'll play around with the number of turns. It's a bummer, though, that every time the inductor is modified, Rsense has to adjusted. Oh well, life's rough sometimes





I'll report more test results tomorrow.

*BTW, i'm pretty sure now that that core is 'J' type material, but it would be interesting to try the other materials also.*

Materials 43 and 85 look very promising, IMHO.

*What kind of transistor are you using now?*

I'm using the Zetex ZXT11N15DF.


*If the caps are smaller then the extra inductor and lower value caps then i guess i'll have to go with that for size.*

The tantalum is 4.3x7.3x2.8mm, so I think you'd have a hard time making the pi filter smaller than that, but who knows?

BTW, I found our fancy Kemet polymer tantalums on www.arrow.com for only $1.57! Of course, they are out of stock... 

*With an LS in that thing, that would really be quite a flashlight  I think anyone would want one.*

I know, I can't wait to modify my MiniMag!

<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Dec 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*When i tryed 10 turns vs 20 turns, it looked like 10 turns was higher so you might want to try that next.*<HR></BLOCKQUOTE>

I concur, with 10 turns, efficiency is about 1% more on average, closer to 88%.

Rsense is now 0.01 ohm, bringing Ipeak to 1900mA.

The really amazing thing is, average battery (and inductor) current is still under 600mA, so the 1900mA must not last long!

However, I can see now why you're so worried about ripple current. The M9711 only drew 800mA max, so it was hard to imagine the LS getting much over 500mA, if at all.

At 1900mA, it's much more imaginable!

I'm also more concerned now about peak voltage. There must be quite a spike when the transistor opens. That spike must not exceed 10v, or else our expensive tantalum may get fried. MrAl, do you have any means of measuring the peak voltage across the cap?


----------



## MrAl (Dec 21, 2001)

Hi there again Duggg,

>>>
If it really is J material, then that's a pretty hefty
inductor---I calculate 927uH. I also show that the core saturates
at justone turn, so its true inductance is far less, though
obviously sufficient.
<<<
" You say
'saturate',
i say
'operates on the horizontal part of the magnetization curve' "

According to Magnetics, they spec saturation flux density at 15 oersted.
This is well onto the horizontal section. If we could find
a core that would stay on the lower more vertical portion, that 
would be great to try. I'm hoping
the u=850 material you picked out helps the situation by lowering
the Bdc. Should be interesting. Since this is 5 times less then the J
material, we could see an improvement as long as everything else
stays equal, such as the core losses at this frequency.

>>>
The tantalum is 4.3x7.3x2.8mm, so I think you'd have a hard time
making the pi filter smaller than that, but who knows?
<<<
Yeah that is small  I cant wait to try one. I think your right
though, that should clear up all our esr/ripple problems.
Perhaps a lower cost solution would contain the pi filter with
a little loss in space.

>>>
I concur, with 10 turns, efficiency is about 1% more on average, closer to 88%.
<<<
Oh ok, not that much i guess with your setup.
Perhaps that transistor is a little better then the Zetex 618 ?

>>>
The really amazing thing is, average battery (and inductor) current
is still under 600mA, so the 1900mA must not last long!
<<<
Oh yes, i have seen inductance changes over 20 to 1. The inductor
acts as a "voltage controlled inductor". As soon as the higher
battery voltage hits it, it switches to low inductance. With the
lower inductance, it charges up really really fast. As soon as the
transistor switches off, the lower battery minus output voltage
differential voltage switches it back to high inductance. The core
magnetization jumps from the horizontal curve section to the more
vertical section. It's really pretty cool. I was thinking of 
plotting this by cutting a small gap in a slighly larger core
and inserting a linear hall effect sensor and running the whole
thing at a much lower frequency (after frequency domain scaling
all the components of course) so that the sensor can pick up the
fast dc flux changes in the core. Of course i would also have to
drive it with a simple oscillator and transistor, just for the core
material testing.

>>>
However, I can see now why you're so worried about ripple current.
The M9711 only drew 800mA max, so it was hard to imagine the LS
getting much over 500mA, if at all.
<<<
Hmmm, i guess the difference in peak current is because of the
difference in inductance when the transistor is 'on'.
With a very low inductance, we need a high peak because we only 
get a very short time to charge.
The nice thing is, this is the main
area where core loss would come into
play, and its so short a time it helps
keep the core losses down low 
I havent measured much temperature
increase at all; less then 2 degrees.

>>>
I'm also more concerned now about peak voltage. There must be
quite a spike when the transistor opens. That spike must not
exceed 10v, or else our expensive tantalum may get fried. MrAl,
do you have any means of measuring the peak voltage across the cap? 
<<<
Yes, it's pretty easy using a Schottky diode and ceramic disc cap.
With the Schottky diode acting as rectifier and the cap as filter,
you can measure the dc voltage across the cap and add about 0.15 volt
for a regular 1N5817 diode (25 deg C). This comes out pretty close
to the peak. You have to use a high impedance meter of course, or
the FET op amp circuit elsewhere in this thread.
You can then compare this reading to the average voltage at
the output to determine how much above the average your peak goes.
Recently i found the dynamic impedance of the LS to be a little lower
then 1 ohm, so to get the added current from the ripple increase
multiply by 1.20. This means if you read 0.10 volts above average
you have ipeak=1.2*0.1 = 120ma above the average of 350ma which comes out
to 470ma peak to the LS.

An easier method though (and probably more accurate) is to use the
network to measure ripple voltage. You can then multiply the ripple
voltage by 1.2 to get the increase in current applied to the LS.
I actually tested this circuit to make sure it would work for
measuring ripple output. These tests should only be performed at
25 deg C though (or at least the diode has to be at 25 deg C).

You dont have to worry about the voltage 'spike' applied to the cap
that much though, because it wont be that large unless there is
high ESR in the cap. With the LS connected, the LS eats up the current
pretty well, because it acts like a super flat zener diode 

If the ripple voltage is lower then 0.1 volt, i think that is
a sufficient test to prove reliablilty at 350ma average output.
Since 0.1 volt corresponds to 0.12 amps, for every 120ma decrease
in average output current we gain another 0.1 volt safety margin,
meaning more or less at 230ma or so we can afford as much as
0.2 volts of ripple output without problems. I would bet
most people want to drive it all the way to 350ma though 

Good luck with it,
Al


----------



## **DONOTDELETE** (Dec 23, 2001)

There hasn't been much activity on this thread lately, so I thought I would publish some data obtained this evening using the handwound toroid provided by MrAl.

This toroid uses a ferrite core similar to the Amidon FT-37-J, available from many sources for about $0.75 each. I've been experimenting with the number of turns and also some winding techniques.

The more turns a toroid has, the higher its inductance, but also the higher its DC resistance, since more turns requires more wire.

I found it most efficient using 16 turns of #24AWG magnet wire.

Once I wound the 16 turns, I then played around with the spacing of the windings. Conventional wisdom says the turns should be evenly spaced, but I found the coil provided the best efficiency with all the windings bunched together, leaving about half the circumference of the core exposed.

The choice of core material is also important. "J" material, also known as Material 75, has a relatively high permeability of 5000 and a Bsat of 430mT.

For best performance, we want the ratio of permeability to Bsat to be as low as possible, so we'll soon be exploring several other materials, including 43 (perm=850, Bsat=290) and 85 (perm=900, Bsat=420).

The cores are on order, and once they arrive and are tested, we'll report the results.

We are so far very impressed with the efficiency of these handwound toroids, especially since they're much less expensive than most commercial inductors, yet comparable in size.

The following results were measured using the 16-turn toroid with a mediocre capacitor and transistor. Power source was two freshly-charged NiMH AA cells.



```

```

Hopefully even better results should appear in week or so, when the new cores, the Kemet polymer tantalum capacitor, and a replacement FMMT617 transistor arrives.


----------



## MrAl (Dec 24, 2001)

Hi again,

Merry Christmas to Duggg and Mercator and
anyone else following this thread 

Duggg, that looks like some really
good results. When we first started this
project, i didnt expect to see efficiencies
approaching 90%. I think 90% is very
reasonable and is only 10% off from
not having any converter at all.

I'm thinking of converting my Brinkmann now,
using this circuit. It has plenty of room
for the LS and for the circuit board and
inductor so it should be a fairly easy 
conversion.

Also, i hope to be able to use the same 
circuit for a 6v 'down converter' for the
LS. This way i hope to get high
eff with 6v inputs as well. The other nice 
thing about this chip is that it takes a
max up to 10v dc input.

Have a happy holiday,
Al


----------



## papasan (Dec 24, 2001)

i've been doing some reading but i'm still not sure on the relationship of all the stuff in an inductor/coil...hell, i'm still not sure on what they do/can-do/how-they-do-what-they-do exactly...i'm supposing that henries is a defining term for the amount of energy that can be stored in the coil and how fast it is stored...and that henries in a coil is defined by the core material and the height/width of the coil and the number of turns(there's probably a million other defining stats too)...so how do you measure henries and how many henries (or micro-henries) do these home-made coils represent?...

i'm asking because i want to be able to relate these home-made coils with a commercial product...


----------



## **DONOTDELETE** (Dec 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Also, i hope to be able to use the same 
circuit for a 6v 'down converter' for the
LS. This way i hope to get high
eff with 6v inputs as well. The other nice 
thing about this chip is that it takes a
max up to 10v dc input.
*<HR></BLOCKQUOTE>

Happy Holidays to you as well, MrAl. And to everyone on CPF.

I'm not sure if the circuit will work as a buck converter---let us know!


----------



## MrAl (Dec 24, 2001)

>>>
i'm asking because i want to be able to relate these home-made coils with a commercial product... 
<<<

It's probably harder to do that then to
just buy some cores and wind your own turns,
but we were trying to do something like
that too because we thought it would be nice
to be able to grab one off the shelf already
wound. The problem is, for all the specs
we have come up with so far i havent seen
any of them listed on sites that sell
inductors, so even if you knew all the specs
it might still be hard to get one without
maybe calling the manufacturer and finding
out what kind of material they use, etc.
The most important now is what material to
get. I havent seen one comercially available
inductor specify the material nor the core
area nor the number of turns, so i guess you
would have to get on the phone and contact
these places and try to pry some info out
of them before you buy. This is probably
why most power supply companies design and
wind their own inductors/transformers; not
only is it cheaper, you can get exactly what
you need with a custom inductor design, at 
the cost of a longer turn around time.

If you order the type of
material and the same size core and you wind
the same number of turns of the same wire
diameter you will get comparable results, no 
doubt, or else you can get someone else to
make them up for you perhaps. The toroid
core is a little harder to wind by hand but
then again there arent many turns involved 
with this applications' inductor design.

If you are interested in the value in 
Henries, you can test an inductor knowing
that
i=v/(j*w*L)
where
v is ac voltage in volts
i is ac current in amps
w = 2 * pi * frequency in Hertz
L is inductance in Henries
j=square root of -1

When using meters to measure ac current and
voltage, you can set j=1:
i=v/(w*L)

When dealing with rectangular voltage waves,
you can measure inductance with:
v=L(di/dt)
and when the current is a straight line ramp:
v=L((delta i)/delta t))
or
L=v*(delta t)/(delta i)
[in units this is Henries=volt seconds per amp, or webers per amp]

which means if you get, say, a 1 amp change 
in i within a period of time of say, 10us
with a rectangular voltage pulse of, say,
2 volts that would mean you have 20uH of
inductance.
If, on the other hand, the current ramped
up to 2 amps (instead of 1 amp) that would
mean you had 10uH instead of 20uH.

This is an easy way to measure inductance in
pulsing circuits.

Good luck with it,
Al


----------



## **DONOTDELETE** (Dec 24, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*i'm supposing that henries is a defining term for the amount of energy that can be stored in the coil and how fast it is stored*

Henries indicate the inductance. The actual energy stored is the inductance times the square of the current, divided by two.

*...and that henries in a coil is defined by the core material and the height/width of the coil and the number of turns*

Correct!

*...so how do you measure henries and how many henries (or micro-henries) do these home-made coils represent?...
*

For a toroid, the inductance is approximately the number of turns squared, times the absolute permeability, times the area of the cross section, divided by the average circumference.

The absolute permeability is the relative permeability (5000) times the permeability of free space, 1.257 uH/m.

Our 16-turn toroid has a cross section of about 8E-6 square meters, and an average circumference of 22E-3 meters, so its inductance is approximately 585 uH.

That sounds pretty high, doesn't it?

However, it needs to be, in order to compensate for saturation effects at the high currents we're using. A small core can only handle so much current before it saturates, at which point its ability to store additional energy is compromised.

As the core becomes more and more saturated, the coil behaves more and more like a resistor, and the effective inductance falls. Unfortunately, the formula for determining this effect is convoluted, especially with the DC component involved in our circuit.

Avoiding saturation is the main reason why we'll soon be looking at cores with better materials.
<HR></BLOCKQUOTE>


----------



## Mercator (Dec 24, 2001)

Merry Christmas to Duggg and MrAl and
Everyone who's following this topic.

Thanks Duggg for posting the test results with the various windings of MrAl's inductor. Very interesting and informative.

So far I have only tested using the original 12 turns. I'm running the 300 with a 617 trans, 2000 diode and a discreet 1000uf low ESR cap. Haven't tried the new tantalum cap until I can accurately measure output ripple. I'm not so much worried about problems with the new cap as much as I want to be able to compare the differences. Today, I did some efficiency testing and on average I'm getting 84%. That's with two AA batts and the LS current is set at 320mA.

Duggg, MrAl...
Everything has arrived and went back out today. Won't be long now





Have The Most Enjoyable Holiday

Mercator


----------



## **DONOTDELETE** (Dec 28, 2001)

I now have four ferrite toroid cores in my possession, and preliminary results are that the _smaller_ the core is, the more efficient it seems to be.

This means that I've been going in the wrong direction in looking for the largest core that will fit within the design diameter.

In retrospect, this makes sense, since inductance is proportional to the square of the number of turns, and for a given length of wire, a smaller core means more turns, and thus more inductance.

My mistake was in my premise that the larger the core, the more turns it can hold, and thus the more inductance it can provide. Although fundamentally true, the goal of this project is not to find the largest possible inductance, but a _particular_ inductance, namely somewhere in the vicinity of 100uH.

Although any of the cores can provide this inductance, and the smaller cores need more turns to do it, they actually accomplish it with a shorter length of wire---and thus have lower resistance (DCR).

As an example, an FT37-J core requires 6 turns to obtain 80uH of inductance. Each turn uses 11.1mm of wire. Total length=67mm.

Although a smaller FT23-J core requires 9 turns for 80uH, each turn uses only 5.8mm of wire for a total length of 52mm.

But there are two potential drawbacks in using a smaller core. First, the core can't be too small, otherwise the inner diameter won't be wide enough to hold the necessary number of turns. Second, the value of Rsense appears proportional to the DCR of the inductor. The lower the DCR, the lower the Rsense, and the higher the Ipeak.

At some point, a higher Ipeak may require a larger diode and/or transistor, so a practical goal is to settle on a DCR that requires a value for Rsense such that Ipeak remains below 2000mA. 

So if we fix Rsense at 0.01 ohm, and adjust the number of turns until Iout is exactly 350mA, the toroid that does it with the shortest length of wire should provide the highest efficiency.

Agree? Disagree?


----------



## MrAl (Dec 28, 2001)

Hi there again Duggg,

That's some interesting data there and
I'd like to comment on that stuff but
right now im going back to bed i
came down with something just before Christmas
and it looks like i wont be doing to much for
another day or two. It might be a flu or
something like that.

Take care for now,
Al


----------



## papasan (Dec 28, 2001)

looks liek digikey has pushed back the zetex 310 date again, it's now 1/12...guess i'll have to wait for awhile since they'll probably hold the 617 and the rectifier until then as well...sigh...oh well...i guess i can use this time to make some SMD to SIP adapters for the few parts that i do have =)...


----------



## MrAl (Dec 29, 2001)

Hi there again,

Duggg:
>>>
and adjust the number of turns until Iout is exactly 350mA,
the toroid that does it with the shortest length of wire
should provide the highest efficiency
<<<
Sounds like an interesting idea to me too. I havent ruled out
a bifilar winding yet though.

Oh, by the way Duggg, if you feel like testing the 'down converter'
out a little, you just take the current circuit the way it is and
connect the cathode of the LED or LS to the battery positive (+) terminal
instead of the minus (-) terminal. You have to make sure
the transistor rating is at least 15 volts or higher though. This
new circuit formed may require an inductor with more turns then usual
also. I would also start out with a higher R sense value just to make
sure the current setting from one topology isnt too high for the other,
although i dont see why it would be, and will probably require more
for the new. Of course the output cap still connects directly across
the LED or LS, not to ground.
I was intending to test this circuit at 6 volts input, but it may be
a few more days or longer untill i can do that now.
Also, i think we should keep in mind that if the new topology requires
more current thought the inductor, we may get up to a high enough 
value that the base drive problem comes back, which could easily fry the
transistor before reaching the desired current.
The efficiency in the new configuration would be very interesting.
With a series resistor and a 6 volt battery the efficiency is only
about 50%. With the down converter, i hoped to get at least a min of
75% one way or another, and hopefully higher.

I wasnt sure if you wanted to test this config out, but if you do
the circuit change is very simple 

Did you get your new meter Duggg? Is it 10megohm or more input?

Good luck with it,
Al


----------



## MrAl (Dec 30, 2001)

Hello again,

In addition to the above post, i wanted to
add some data.

I connected the new chip cap and checked
the output ripple. The ripple with this
cap is down to about 10mv peak to peak 
which is very very good and certainly
acceptable. There is also a very short
pulse about 50ns long of about 40mv peak
which is also very much within spec.

This means this cap should be quite good for 
a safe solution for driving the LS.

The cap part is:
150uf, 10v, 20% tolerance, "D",
Kemet SMD Polymer Tantalum chip capacitor.
Mouser part # BO-T520D157M010

I'll post more results as soon as i can test
some more. I wanted to get that at least
out of the way today.

Good luck with it,
Al


----------



## **DONOTDELETE** (Dec 30, 2001)

MrAl, that's great news about the capacitor. I figured with such low ESR that it would do a good job. I can't wait to test it myself---hoping it arrives Monday!

And yes, I got the new digital meter. It has a 4000-megohm impedance mode, so I'll do a ripple measurement using the old cap, and again with the new cap and present the comparison.

Speaking of comparison, I have made many different toroids using the four different cores I have, and will be posting the results soon. I want to repeat the tests using the new meter, since it should be more accurate and a LOT easier to use.


----------



## MrAl (Dec 31, 2001)

Hi again Duggg,

>>>
And yes, I got the new digital meter. It has a 4000-megohm impedance mode, so I'll do a ripple measurement using the old cap, and again with the new cap and present the comparison.
<<<
Wow 4000 megohm thats pretty good. What
model/manufacturer is it?

I got a couple new unknown cores in and
i'll be testing them soon i hope. i'm
really interested in seeing how some
different materials work out. The one
nice thing about the J material was that it
was pretty darn temperature stable. I
heated the toroid core up with the soldering
iron and didnt see much change at all on the
output at 350ma. I hope the other materials
stand up to this test, although i have a 
feeling our circuit will work ok with even
some core temperature instability -- another
side benefit of having a circuit that
measures current through the inductor.

Since im stuck at home anyway with this
nasty cold i hope to do a little more testing 
tomorrow on the cores.

I'm real interested in the numbers you get
measuring the ripple with the old cap
and the new cap. I see a really big difference between the old and new caps.

Take care for now, and Happy New Year!

--Al


----------



## **DONOTDELETE** (Dec 31, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Wow 4000 megohm thats pretty good. What model/manufacturer is it?*
<HR></BLOCKQUOTE>

It's an older model Fluke 87. It has a normal 10 meg input, but a power-on option gives it 4000 meg in the 400mVdc range.

In the 4000 meg mode, I measured about 16mV of ripple across the LS with the cheapie electrolytic capacitor in place. In the 10 meg mode, it was around 0.3mV lower.

But with the new Kemet capacitor, ripple is less than 2mV! Wow!

BTW, Digi-Key now sells the Kemet cap for $3.38, and since they're the only practical source for the Zetex components, it may be worth the extra $0.38 (over Mouser) to simply order from them, especially since part no. 399-1770-1-ND has an even lower ESR than the ones from Mouser.


----------



## MrAl (Jan 1, 2002)

Sounds good Duggg, i would like to
order from one source mainly myself, rather
then two. That cap works real nice too 

How did you measure the ripple in those
tests? Were they with the real LS or the
simulator?

Al


----------



## **DONOTDELETE** (Jan 1, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Sounds good Duggg, i would like to order from one source mainly myself, rather then two.*

Along those same lines, I'm getting near 88% efficiency out of those little 29-cent FB73-287 bead cores Mercator discovered on Digi-Key. Not only is that really good bang for the buck, but it means we could get all five components from DK, which is a huge plus, especially with their free shipping.

So I think I'll focus my energy there, and see if I can't squeeze out 90% through the right combination of turns and wire gauge.

*How did you measure the ripple in those tests? Were they with the real LS or the simulator?*

I used the circuit you posted on page 14 of this thread, with a real LS in place. Have you dared hook up your new LS yet?
<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Jan 2, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*So soon i will hook up the real LS to see how well it works. I dont have any doubts now though, do you?*

None at all. I think the LS is actually quite tough. It took several 20+ volt capacitor discharges to kill mine!

*I guess we do have to test low battery drop out characteristics also. If the battery runs down and the transistor burns out, that wont be good. I think we should do this with any new inductor choice.*

I seem to recall you saw the problem only in certain single-cell tests. With a single cell, Ipeak is on the order of two amps, so we would need to employ a two-watt transistor to handle the heat. Or, a shutdown circuit.

For that reason, I thought we pretty much settled on a two-cell design? 
<HR></BLOCKQUOTE>


----------



## papasan (Jan 2, 2002)

finally got enough parts today to build a test circuit...driving 3 5mm nichia LEDs and without the cap or diode...thanks for turning pics back on davidw =)...











you can see the .01 5W resistor in-line with the input there...when i try to measure the dc voltage accross it i get .001 out of my fluke which i doubt is correct...what am i doing wrong?...i've got another that i'll put on the output in a minute...there's a .1 ohm resistor on iSense...the LEDs are not drivin to peak i don't think...probably more than 20mA, but not over 40 for sure...when they're in parallel they have very different light emitions, so series it is...oh, and the coil is the 68uH jw miller...i've got a few of the 10v tants from mouser, i'll hook them up next...


----------



## MrAl (Jan 2, 2002)

Hello again,

papasan:
0.001 volts across 0.01 ohms means
100ma is flowing, but for low currents
like that i would use a higher value
resistor, like 0.1 or even 1 ohm.
Keep the 0.01 for higher current measurements.

duggg:
oh ok, we decided two cell apps wont be
harmed because the cells die out too 
fast at that low voltage?

Take care for now,
Al


----------



## MrAl (Jan 3, 2002)

I just got the cap the other day. I was
waiting for that cap to come and so soon
i will hook up the real LS to see how
well it works. I dont have any doubts now
though, do you?
I guess we do have to test low battery
drop out characteristics also. If the
battery runs down and the transistor 
burns out, that wont be good. I think
we should do this with any new inductor choice.
I have a new core also to test and im going
to do that as soon as possible.
I'll be posting any results here as soon as
i can.

--Al


----------



## MrAl (Jan 3, 2002)

Hello again,

Took some more accurate measurements of
the original hand wound core. It 
definitely looks like J material because
the initial permeability measurement comes
out to 4500, which is pretty close to
the published 5000 for J material.
I took a good deal of time to verify
the measurements, using a frequency counter
to measure the 1/2 voltage frequency
of the test inductor in series with a
100 ohm resistor using:
vL=Vin*(sL/(R+sL))
Setting vL=0.5 and Vin=1 and solving for L
from the resulting equation:
0.5=sL/(R+sL)
Then substituting the resulting L in the equation for inductance and solving for u.
To verify the measurement, the phase angle
between vL and Vin is checked to be
very close to 60 degrees.

I also measured another core
which i recently got and it turns out
that it has u=650 or so. It's also
about 3/8 inch diameter. Because the u
enters the Bdc equation as a scalar factor, 
the lower u means it will maintain a higher inductance
while the transistor is 'on'. This could
boost efficiency, although how much i cant
say just yet. I hope to test it in the
actual circuit tomorrow sometime.
The drawback is that with less u, more turns
will be required to attain a nice value of
inductance, so that will increase dc and ac
resistance. If the eff goes up though, i'd
say it's better in any case.

Hopefully more data on the new core tomorrow.
--Al


----------



## papasan (Jan 3, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*0.001 volts across 0.01 ohms means
100ma is flowing, but for low currents
like that i would use a higher value
resistor, like 0.1 or even 1 ohm.
Keep the 0.01 for higher current measurements.*<HR></BLOCKQUOTE>

your definatly right about using a bigger ohm resistor...after hooking up my LS with the output filter, i read a .006 dc voltage accross the .01 resistor in-line with the input...since my meter only read three digits this could be anywhere from 500 to 700 mA input, a large margin...i got the .01s because i wanted to have the least impact on the circuit but i now regret buying the .01 resistors, shoulda gotten .1 at the least...radio shack, which hardly seems to have what i want, had a lowest ohmage resistor of 10...blah...oh well...i don't seem to be getting the output i should be with my solderless breadboard, so i guess my next step is to make a test board and etch it...

it's too bad that the 3x0 chips need such small iSense values to function, this is the biggest detracting feature of the crcuit in my opinion...i suppose in the end it will be nice on the efficiencey side tho...

so has anyone got any figures on how well this circuit regulates throughout the discharge curve of the batteries?...there is a definate output difference between 1 and 2 cell inputs, so i'm wondering how the output is going to look at different time slices...

if i read my readings right it looks like i have about 85% efficiencey, not bad considering the breadboard set-up...there's 2 .01 ohm resistors in the circuit now...


----------



## MrAl (Jan 3, 2002)

Hi again papasan,

I didnt realize you were using a solderless
breadboard. I wouldnt use this because
there is too much risk of blowing out
a component if something becomes disconnected. I would definitely solder
all the parts in place making sure they cant
pull apart. I even go as far as to disconnect
power in between tests, because one mistake
could take out a part.

There is some data regarding regulation
over input battery voltage in this thread
i posted after doing a circuit simulation.
The results told me that the circuit
doesnt regulate perfectly, but its not 'too'
bad using NiCd's. My actual measurement
was only at two points so far: with
2.4 volts input and iout set for 300ma, at
1.2 volts input i get 100ma output, but
the two NiCd's in series will die out at about 2 volts, so there should still be a reasonable
output current at normal input voltages
over the discharge of the NiCds.
Alkalines wont show up quite as good as the 
NiCd's because 
they have a different discharge curve.
If you look back in this thread, you 
should find the simulation data for
both NiCd's and Alkalines.

Good luck with it,
Al


----------



## papasan (Jan 3, 2002)

test board i drew up...anyone see problems before i make a few?...it's about the size of the base of the LS/O, and made with the coilcraft coils in mind (which are the largest i have)...could be made alot smaller with a smaller coil and without room for the output filter...





clicking on the image should get you a post script file of the layout if you wanna make your own...


----------



## **DONOTDELETE** (Jan 3, 2002)

The circuit is not a regulator. As a result, it doesn't regulate particularly well. Here are some general results, obtained using a pair of NiMH AA cells.


```

```

Fortunately, the LS is reasonably bright even at 240mA, and the circuit does provide over three hours of useful light from 2 AAs at very low cost and with good efficiency.


----------



## **DONOTDELETE** (Jan 3, 2002)

90% efficiency remains elusive, even after hours of trying in vain.

Using 24AWG magnet wire, I'm only able to get 88% efficiency using the 29-cent Digi-Key bead cores. These are made out of material 73, which has a permeability of 2500.

Oddly, only two turns are required. Maybe because the bead cores are relatively massive for their volume. More than three turns, and efficiency falls off, presumably due to increased resistance. Less than two turns, and there's not enough inductance.

Pursuing the resistance angle, I thought for sure I would see an improvement when I twisted two 24AWG strands together, and wound it twice around the core. I even tried winding two strands in a parallel bifilar technique (4 turns in all) and saw no improvement whatsoever.





Very frustrating!





One bright spot is that Rsense is now around 0.016 ohm, so Ipeak is under 1200mA. I didn't like it up near 2 amps!

Given that 2% of three hours is only 3.6 minutes of extra run time, I'm wondering how many more hours need to be spent? On the other hand, 3.6 minutes on a mountain bike could mean another mile of night riding, so I'll spend a few more hours on it this weekend.


----------



## papasan (Jan 4, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*The circuit is not a regulator. As a result, it doesn't regulate particularly well.*<HR></BLOCKQUOTE>

ahh...my lack of experience is showing again...i thought that this would be a better regulated set-up...sigh...so hard to have your cake and eat it too...i suppose i'll have to start looking for a regulated charge pump or something...i like the idea of rock-steady regulation, even if it's only down to 2V...


----------



## MrAl (Jan 4, 2002)

papasan:
Try the circuit out first before forming
an opinion. Although it is true that
it doesnt try to regulate current though
the LED(s), it still works pretty good
anyway.

Tests on Digikey inductors and 650u core:
I tested two of the digikey inductors
and one other new core with a u=650.
Both of the two digikey inductors 
brought the efficiency down by about 4%,
as well as the new core with the original
8 turns. I havent tried 10 or 20 turns yet
on the new core, which i intend to do next.

Both of the two digikey inductors dont
change inductance much at all, like the older
core does. The current ramps up and down 
very cleanly, although it forces the circuit
to oscillate at a sub harmonic (although stable, not like the Delevan inductor did).
The lower frequency (about 10 times lower)
causes a little more ripple, but not as much
as expected. It still looked safe for the LS,
although like i was saying the eff drops about 4%.

The new core with 8 turns already on it
works about the same (using all 8 turns)
although the inductance is much lower.
I expect better results with a few more
turns, so i intend to try this next.
So far this too caused a drop of about 4%
in eff. The u of this core is about 650
meaning it isnt as sensitive to dc current
and this shows up in the waveform, where
it's inductance doesnt change as much as
the original core did. It does change more
then the digikey inductors though.
I havent found a cross ref to the material
yet, it might be something like #43.

Apparently, the J material core performs
best, although the peak current is higher
and the inductance changes alot. 
Because this material has u=4500, im
now wondering about trying cores in the
other direction, that is, with even
higher u like 10,000 or so. That would mean
a good temperature stability test would be
required, but i would bet it would work.
I'll have to try to get a core or two 
of this type somewhere.

--Al


----------



## remuen (Jan 4, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
... when you insert a small resistance in a circuit you can measure the current through the resistor by measuring the voltage across the resistor. 

... This is a good trick to use because you can insert resistors into
the circuit and make measurements without constantly disturbing the circuit.

... Of course you have to also compensate for the drop when you determine efficiency 

... I use 1 ohm a lot during a circuit start up to see how things look. This way i get current limit action as well protecting the parts untill i can see how it looks. Then i switch to 0.1 ohm resistors. Hopefully i'll be able to use 0.010 ohm resistors also, although i havent tried these yet. These insert very little loss into the circuit, but dont offer any protection to the circuit during intial trials.
Al*<HR></BLOCKQUOTE>

MrAl, if I understand everthing right what you said then I could reduce the target of these 1/0.1/0.01 ohm resistor on two points:
- *making measurments without disturbing the circuit*
Would a second DMM which I could let in the circuit as ampmeter do the same?
- *limiting the possible current with the 1 ohm resistor if something is going wrong*
Would a power supply with a current limiter not be better means safer?

I'm really out of any practice and just try to remind what I've learned almost 30 years ago: To get the right power consumption for calculating the efficiency I must measure the voltage behind the ampmeter (or the 0.1/0.01 ohm resistor) to "compensate" the voltage loss across the resistance. Is this correct?


----------



## MrAl (Jan 4, 2002)

Hello there remuen, welcome to the forum/thread,

It's better to use a resistor of about 0.1 ohm to measure
current because:
1. you know exactly how much resistance you are inserting into the circuit.
2. ammeters might have too high an internal resistance.
3. eliminates extra lead length associated with typical ammeter leads.
4. eliminates any extra ammeter inductance.

One way to compensate for the extra resistance insertion (instead 
of calculating voltage drop) for calculating efficiency is to measure
the voltage on both sides of the resistor and then (using ground as common):
1. on the input side, use the lowest voltage on either side of the resistor.
2. on the output side, use the highest voltage on either side of the resistor.

This works out to the same as doing the following:
1. on the input side, measure the voltage across the circuit input, after
the resistor (not across the battery).
2. on the output side, measure the voltage across the circuit output before
the resistor, (not across the load).

This means you are always measuring voltage across the circuit's input
or output, and never across the battery or load. This compensates for
the inserted resistance, although it's still a good idea to stick
with about 0.1 ohm.

The above assumes you insert one resistor in series with the battery and
another resistor in series with the load in order to measure input current
and output current in order to calculate the electrical efficiency of the
circuit.

If you wish to calibrate your two chosen
resistors, simply insert them in series
with your ammeter and measure the voltage
drop when applying say, 500ma. Note the
readings and use those to scale your future
measurements with both resistors. You may
come up with a slightly different factor
for each of the two resistors.

Good luck with it,
Al


----------



## **DONOTDELETE** (Jan 4, 2002)

I also "give credit" for the power consumed by the test resistors. On the output side, I add the power consumed by the resistor, and on the input side, I subtract the power.

It may not seem like much, but the test resistors in my case eat up around 18mW, and that's about 2.5% of the total power.

(That should read 12mW, and 1%---Ed.)


----------



## **DONOTDELETE** (Jan 5, 2002)

Well I now know why I don't see an efficiency improvement by using larger-diameter wire.

The two-turn inductor uses only 6cm of 24AWG wire, for a DC resistance of only 0.006 ohm. The copper loss through the inductor is the square of the average current times the DC resistance. Since the inductor is directly in series with the battery, the average inductor current is the average input current, around 550mA. So the power wasted by the winding is only 2mW! So even if DCR were eliminated completely, efficiency would rise by only 0.2%.

There are two other losses in an inductor--- hysteresis loss and eddy current loss. But these are related to the material and core construction, and we can't do anything about that.

So we have 88% efficiency with the 29-cent cores from Digi-Key. I'll turn next to MrAL's core of J material, which has twice the permeability, and see if there's any improvement there.


----------



## remuen (Jan 5, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
It's better to use a resistor of about 0.1 ohm to measure current because:
1. you know exactly how much resistance you are inserting into the circuit.
2. ammeters might have too high an internal resistance.
3. eliminates extra lead length associated with typical ammeter leads.
4. eliminates any extra ammeter inductance.

.....
*<HR></BLOCKQUOTE>
MrAl, thank you for the very good explanation. Thanks also to Duggg for confirming it. I think I now understand why using a resistor! 

I've already made my two 0.1 ohm resistors by parallel switching ten 1 ohm 0.25 watt resistors because in our company we don't have lower values except some 0.5 and 0.1 ohm huge and wired resistors with heat sink bodies (or how you say to that). And according to what you wrote I think this solution is better than an additional inductance because of such wired resistor.

_For your background information: 
From time to time I take a look into this thread. But what you experts make is beyond me so I will not be an active participant. Maybe I'll ask you some more questions. In the Converting Minimag thread we (means mainly Wayne Johnson, Jeff1500 and me - but me only with the help of an electrical engineer of my company in the background) try to make at least one small regulator for the Minimag which can drive up to 10 Nichias. I don't know wether one can later push such a small regulator to drive a Luxeon or not. In every case it would be a new challange to make a Minimag mod with a Luxeon and a good regulator. Maybe your Zetek circuit will fit into a Minimag?_


----------



## MrAl (Jan 5, 2002)

Hi there again remuen,

>>>
Maybe your Zetek circuit will fit into a Minimag?
<<<
Although it might be a tight fit, i 
think it can be done. The Zetex circuit
components are all very small. I might
attemp this conversion myself if i can find
an LS/o with a round heat sink, or else try
with an LS emitter. I havent found any
emitters sold in single quantities yet
though. The inductor can be formed out of
one half of a 3/8 inch diameter toroid core
(after carefully breaking it in half) if
space gets too cramped. The eff goes down 
to 75% but it does work. I've tried an air
core inductor also, and that works too with 
some loss in eff and reduced output.
With at least some magnetic material in the
core, it works better then air alone.
I havent tried a whole lotta turns with air
core yet though, because i suspect the 
extra wire will eat up more eff anyway.

Also, that's good that you remembered to 
NOT use wire wound resistors for the current
measurements as i forgot to mention that.
Some of those aluminum heat sinked resistors
are excellent though, being marked 
explicitly with "NI" for 'non-inductive'.
I have a 0.2 ohm resistor of this type,
i use for current measurements sometimes.
It's rated about 10 watts i think, and the
nice thing is the high rating means the
resistance doesnt change that much when current
starts to flow through it causing a slight 
heating effect.

I once designed an 'active shunt' that 
theoretically drops 0.000 volts, unlike
a resistor. The device works by compensating
a sort of regular shunt by increasing the
voltage at the 'low' voltage end of the shunt
to match the 'high' voltage end of the shunt
while measuring how much current is required
to do this. The actual current flowing 
through the shunt is then related to that
measured current and thats how the measurement
is made without dropping any voltage. 
The thing is, for high enough
frequencies (even 300kHz) the op amp that
does the measuring has to be a very wide
bandwidth type (probably at least 20MHz),
but because our circuit here operates
at low duty cycles at 300kHz even that
may not be enough. Perhaps a 100MHz
op amp would do the trick, but it would 
have to be built up and tested, so
it's just too much easier to use a resistor 
The active shunt is still useful for lower
frequency circuits though.

Take care for now,
Al


----------



## MrAl (Jan 5, 2002)

Hello again Duggg,

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I also "give credit" for the power consumed by the test resistors. On the output side, I add the power consumed by the resistor, and on the input side, I subtract the power.

It may not seem like much, but the test resistors in my case eat up around 18mW, and that's about 2.5% of the total power.*<HR></BLOCKQUOTE>

When i use a purely resistive circuit,
i see only 0.2 percent error 
(that's two tenths of one percent) in the
efficiency calculation when using the
circuit's actual input and output voltages
and two 0.1 ohm test resistors as compared
to not using any resistors at all, so,
could you explain exactly why you are 
doing this?

--Al


----------



## remuen (Jan 5, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
... I once designed an 'active shunt' that 
theoretically drops 0.000 volts, unlike
a resistor. The device works by compensating
a sort of regular shunt by increasing the
voltage at the 'low' voltage end of the shunt
to match the 'high' voltage end of the shunt
while measuring how much current is required
to do this. ....
*<HR></BLOCKQUOTE>

Hi MrAl

How many hours have your days - 36 or 48? Even if I would have the knowhow I wouldn't have the time doing all what you do! And beside all these things you find some time to help newbies like me!

Just an idea to improve your time management: Why don't you implement some kind of processor into your active shunt to calculate and show the actual current and voltage direct on a display? Would safe you xx seconds per day because you had no longer to measure and calculate. You could win a few more seconds if it would display also the efficiency in %.












<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
Although it might be a tight fit, i 
think it can be done. The Zetex circuit
components are all very small. I might
attemp this conversion myself if i can find
an LS/o with a round heat sink, or else try
with an LS emitter. .....
*<HR></BLOCKQUOTE>

Concerning the 'Luxeon Minimag': With a tailcap switch one could glue the Minimag head on the body in its utmost position (forget the O-ring and seal it with the glue). This would give about 10mm more height in the Minimag head for placing the LS and the circuit board. And as the thread inside the Minimag head isn't used any longer one could drill it out. Gives an additional 1 - 2 mm in the diameter. The circuit board could be hard wired to the bulb socket because you don't srew/move the head anymore. Therefore you wouldn't need an epoxy adapter like I've just 'developped' for my Minimag mod. 

BTW, somewhere I read about a Luxeon in a Minimag. I don't know any details like which LS and how it was built into the Minimag but I will make a search when I've a bit more time. I'll come back on this issue in the next days and give you the link if I find it again.


----------



## MrAl (Jan 5, 2002)

Hi there again,

remuen:

>>>
How many hours have your days - 36 or 48?
<<<
More like that divided by pi^3 

>>>
Why don't you implement some kind of processor into your active shunt to
calculate and show the actual current and voltage direct on a display?
<<<
That's a great idea for sure, but i have a feeling doing all that would
take on the form of a new project that in itself would take quite a bit
of time to build up. I certainly like the idea though, and including
an analog to digital circuit would eliminate the meters. Im sure
this would be quite an undertaking though, not your average Saturday 
afternoon project 
One interesting thing though, i have a 100MHz digital scope that interfaces
with the computer 90% completed that i could probably incorporate into it,
but i think i would go for more versitile useage by constructing the current/eff 
circuit as a plug in, and display all the data on the computer monitor instead
of a separate display to save cost.

>>>
Concerning the 'Luxeon Minimag'
<<<
Some very good ideas. I was hoping to keep the original switch myself,
but im not against a tail switch if its a good one and waterproof.
I was thinking even if the LS/o sticks out the top a little i wouldnt
mind too much. The LS emitter should fit in there though i think.
Our circuit here has a max height of about 3/8 inch now, so that may
be enough if a special head/bulb adapter is made. I guess it would
really be a trick to get the original switch to operate the same way though.
I imagine it would require a careful mechanical head layout.
When i did my Nichia white LED AA minimag conversion, i reamed out the hole
with a rat tailed file and drill instead of drilling, and reinforced
the remaining diameter with a round plastic insert epoxyed to it. This
kept the original switching mechanism working the same way. Im almost
positive there is a way to do the LS also and keep the switch the same too.
If someone didnt do it already, i might tackle it one day. I have a number
of things to do before that though, including a pretty simple 6 volt lantern
light to LS/o conversion. Im using a dropping resistor for now, but hope
to modify our little Zetex circuit here to work as a down converter for 
this application too. That will make the Zetex circuit the most versatile.
Im still not worried about perfect current regulation (yet) although when
i get back to another circuit i had been working on i'll fix that 
It's interesting that the Zetex 310 chip and SMD 555 oscillator might 
solve the current regulation 'problem', if you can even call it a problem.
I think Duggg mentioned a 'flat' shaped toroid, which would save even more space.


If you find that minimag link, that should prove very interesting also.
I'd like to see that one very much.


Duggg:

The simplest exact form for the eff i can find is:
eff=(Iout*v3-Iout^2*R2)/(Iin*v2-Iout^2*R2)
Notice R1 is not in this equation
(although of course you still need to know R1 in order to measure Iin).
where
R1 is the input current resistor (typically 0.1 ohm),
R2 is the output current resistor (also typically 0.1 ohm),
v2 is the voltage measured directly at the circuits' input, not across the battery,
v3 is the voltage measure directly at the circuits' output, not across the load.
Notice also the only difference between that equ and:
eff=(Iout*v3)/(Iin*v2)
is the "-Iout^2*R2" terms.
With these terms included, the eff calculation is exact, and without
these terms the eff calculation is pretty close. Both terms enter as
subtractive terms however.


Take care for now, and thanks to both of you for the ideas and input,
Al


----------



## **DONOTDELETE** (Jan 5, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*so, could you explain exactly why you are doing this? (Adding & subtracting test resistor power in order to compute efficiency)
*<HR></BLOCKQUOTE>

I have a 0.02-ohm resistor in series with the battery. Typical voltage across it is about 12mV, which corresponds to 550mA of input current. The power consumed by that resistor is 7mW.

On the output side, in series with the LS, I have a 0.05-ohm resistor. It drops 17.5mV to represent an output current of 350mA. It also consumes 6mW.

So the two test resistors together use up 12mW of power that could otherwise be going to the LS, so I don't count it. With average input power around 1200mW, 12mW is 1%.

I'm not sure how I came up with 2.5%, I thought that was a little high myself


----------



## dat2zip (Jan 5, 2002)

Hello all. I've been reading this thread which is getting rather long. I have wound some cores and inductors myself and have built several switching regulator circuits using Maxim, Linear Tech IC's and National. 

Just thought I'd offer some Litz wire if you are interested. It helped out my Q and surface current problems on the WWV receiver I was working on. Don't know if it would help your efficiency or not. I think it will lower your DCR. It's cool special plastic coated version instead of magnet wire coating which means it is very easy to tin the ends. It's a little more delicate to work with. Let me know if one of you want some. That person can share it with the rest. Only one piece of wire is available.


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## remuen (Jan 6, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*


Concerning the 'Luxeon Minimag'
<<<
Some very good ideas. I was hoping to keep the original switch myself, but im not against a tail switch if its a good one and waterproof. ...

....I was thinking even if the LS/o sticks out the top a little i wouldnt mind too much.

....I guess it would really be a trick to get the original switch to operate the same way though. I imagine it would require a careful mechanical head layout.

... If you find that minimag link, that should prove very interesting also.
*<HR></BLOCKQUOTE>

Hi again MrAl
Coherence has modified a Minimag with a luxeon but without a regulator. You will find the infos here: http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=3&t=000696. 
Unfortunatly the link to the pictures does not work. I already asked Coherence because of that.

Coherence also uses a tailcap switch. But I agree with you it seems not easy to find a good one.

But on the other side keeping the original switch is IMHO not a good idea, because
1. The original switch is not the best regarding its contact resistance and it causes sometimes contact problems
2. You have to make some kind of adapter to bring it to work. This adapter steels you some room in the head.
3. You need a wiring from the switch/bulb socket to the circuit board. Because you're moving/screwing the head all the time I think you will have problems with this wiring.

And last but not least I think letting stick the LS out of the top of the Minimag is a bit dangerous for the LS because it could be damaged. And what's about the sealing? You don't need a sealed tailcap switch if you do not seal the top of the Minimag. BTW I can imagine that the original Minimag glass will get damaged because of the heat. So one had to take another glass to keep the Minimag head sealed.

Because of the above mentioned problems with the original swith I made a special epoxy adapter for my Minimag mod which replaces the original switch. This switch is similar to the one in the ARC AAA. 

See here my drawing of this adapter: 
http://edusite10.tripod.com/remuen/adapter.html. 
An explanation to this drawing you will find here: http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=3&t=001221&p=6 
Up to know this adapter/switch works perfectly with 0 milliohm resistance - and it is self cleaning. But for a mod with a Luxeon I think my kind of adapter would take to much room in the head so a Luxeon together with the Zetex circuit board wouldn't fit in the head.

BTW, Coherence used a tailcap switch from Brinkman. Here is the link: http://www.brightguy.com/detail.tpl?cart=10079523572784&sku=KROAM2A666 
And here some pic's John N made of this tailcap switch: http://www.navitsky.org:4601/index/minimag/ 

Good luck


----------



## **DONOTDELETE** (Jan 6, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by dat2zip:
*Just thought I'd offer some Litz wire if you are interested. *<HR></BLOCKQUOTE>

Hi Dat2zip,

Sorry to not get back with you earlier. 

Litz wire is superior to ordinary enamel wire of the same gauge, especially at high frequencies, because its strands reduce skin effect losses, and the soft insulation helps the windings stay parallel to one another.

However, the inductors we've been making seem to require relatively few turns and we can use pretty hefty wire, so we've got copper loss down to virtually nothing.

Therefore, I doubt would we see much improvement by using Litz wire. Appreciate the offer though!


----------



## **DONOTDELETE** (Jan 6, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*I havent found any emitters sold in single quantities yet though.*<HR></BLOCKQUOTE>

White Luxeon Emitters can be purchased from www.future-active.com for $11.55 each, part number LXHL-BW01.


----------



## MrAl (Jan 6, 2002)

dat2zip:
How many conductors does your wire have? What is the equivalent
wire gauge size?

remuen:
Thanks for the many interesting and certainly informative links.
I especially like that tail switch link. Looks like it simplifies
problems with converting a minimag to LS.

I didnt have any problems with my single Nichia white LED conversion
wire connections though, i just gently filed the leads round and inserted
them into the original bulb socket pins. When testing the idea, i did the 
same with regular round copper wire about #24 i think. The wire stayed
connected in the bulb socket pins pretty well.

Duggg:
Thanks for the LS emitter purchasing link. Do they sell LS/o 's too?


Take care for now,
Al


----------



## **DONOTDELETE** (Jan 6, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Thanks for the LS emitter purchasing link. Do they sell LS/o 's too?*<HR></BLOCKQUOTE>

Yes, Future Active sells the complete Luxeon line of products, from Emitters to Floods and everything in between. 

However, they charge $7 for UPS ground shipping, which makes them less than desirable for small orders, and for some items there is a minimum quantity order.


----------



## MrAl (Jan 7, 2002)

Thanks Duggg,

I see now the trick with Active is
that you have to know the Manufacturers'
part number BEFORE you try to find the part.
I like those sites where you can look up
the part and see a pic and read a description
better  At least they have them though.
At first i tried to look up 'leds' in 
general and that brought me to over
1000 different parts, all of which wouldnt
even display (only the first 300 would show
up). Finally i went to the Lumileds site
and looked up the part number, then went back
to Active and looked it up by part number.

Take care for now,
Al


----------



## MrAl (Jan 7, 2002)

Hello again,

I forgot to mention in the last post
that i found a very simple way to
measure the efficiency in a circuit
when using two small value resistors
(typically 0.1 ohm) to measure current.

The simple equation is:
eff=Vro*(Vco-Vro)/(Vri*Vci-Vro*Vro)

where 
Vri is voltage across input resistor (input resistor is typically 0.1 ohm)
Vro is voltage across output resistor (must be exactly equal to input resistor)
Vci is voltage measured directly across circuit input, not across battery.
Vco is voltage measured directly across circuit output, not across load.
All the voltages measured are average.
Note that both current measuring resistors must be exactly the same,
or at least pretty close. You can use a resistance bridge to match both resistors
by paralleling the higher one with some large value resistors untill they match
pretty close. It doesnt matter if they are 0.1, 0.11 or 0.12 with this method,
as long as they are both the same.
This is a pretty neat method i think
because you only have to measure voltages,
which you have to do in order to determine
current anyway, so it sort of saves a step.

If for some reason you cant use matched resistors, then you can still use:
eff=R1*Vro*(Vro-Vco)/(R1*Vro*Vro-R2*Vri*Vci)
instead of the other equation, but you'll have to know the value of both resistors.

The two equations are both an algebraic consequence of the most basic efficiency calculation:
eff=P(load)/[P(loss)+P(load)]
and are therefore exact.

Good luck with it,
Al


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## dat2zip (Jan 7, 2002)

Mr. Al

I'm not sure what it is. I think it 5-7 silk laced with the final wire conductor size around 26 AWG??? I'm not sure since I got a few small bundles. Each bundle was wound on a hand and there are ~10-15 turns for each bundle.

BTW: My 3 AA cell flashlight in a battery holder which I built three of them. I added one inch of 30 gauge as per one your previous messages and took a voltage reading and determined I was drawing or driving 0.750 Amps thru the one LS I measured. <Ooops> But, the LED works quite well in this overdrive mode and I only use in intermittent mode. I just wanted to let you know I didn't kill them.

Also, I converted my Maxim converter to get maximum current out it and then measured my efficiency at 81.5%. Sadly, I reviewed the IC data sheet and it said the IC was good for 82%. I also have looked at the current Maxim IC's and found a uMax 10 pin that has syncrounous FETs built in. This converter will achieve 95-96% effiency and was going to do some additional work to see if the physical space would be smaller. It switches at much higher frequency and so the caps and the induction (3uH) would be physically smaller too. Do you or want me to look into this for the group?

The Maxim IC I have and have been using is now 




obsolete and I don't see it listed at the Maxim web site. It was one of the first 0.9 volt step up converters and I had a design idea published many moons ago in conjuction with Maxim driving the Super HP LED of the time.


----------



## MrAl (Jan 8, 2002)

Hi again dat2zip,

That wire sounds interesting.

0.750 amps through the LS? That's very much over the manufacturers'
recommended max you know? The max pulsed is 500ma, and the average
is 350ma max. I dont think your LS will last very long like that. I really
think you should lower the current.
Try lengthening the wire to twice it's current length.

That Maxim ic sounds very interesting too, i wouldnt mind taking a look
at that one. If it's really obsolete, then if i have the part number 
i'll look for a similar ic on the Maxim site. What is the part number
you have now?
The syncronous FET's sound like it might have a minimum voltage spec
fairly high when used like that?
I'd like to see more of this chip and if you feel like looking into it
thats great too. Post whatever you find here.

Thanks for the info.

Take care for now,
Al


----------



## papasan (Jan 8, 2002)

i think he's talking the 1674...
http://dbserv.maxim-ic.com/quick_view2.cfm?qv_pk=1878
i've requested samples from them last week, hopefully i can check 'em out soon...


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## dat2zip (Jan 8, 2002)

Mr Al

The Maxim IC that I have (obsolete) is the Max 778 (777,778,779). It was the first low voltage step up converter. It has an internal charge pump up converter to generate the MOS gate drive voltage. As such the switching devices are MOS and only the die size (RDS on) limits the efficiency. Todays parts are much better and higher frequency. The one that caught my attention is the MAX 1760. Because of the constant voltage design, the drawback to this would be that you will probably need to tune each one for Vout ~ 3.1 - 3.6 as needed to set the current of 0.35. Also, constant voltage might not be that attractive since the diode characteristics over temperature will probably mean that once set it will draw more or less depending on the ambient. What you really want is constant current which most up converters aren't designed for.

PS. If you are looking for Litz for other applications I just saw some on EBAY.


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## papasan (Jan 8, 2002)

alright...finally got one built, here's some pics...













i forgot to flip the layout before i etched it, good thing it's a simple circuit =)...i used the wire resistor trick, but i'm still not thrilled with it...there's a 2 inch piece of very fragile wire just sitting there waiting to get shorted or broken...

the LS is noticably brighter than without the circuit, it gets *very* hot to the touch pretty quickly now...unfortunatly i only have one LS and my digital camera has very few manual controls so i can't get a comparison shot...

too bad this isn't a regulated circuit, it's nice and simple and small...


----------



## **DONOTDELETE** (Jan 8, 2002)

Wow Papasan!

Very cool. What kind of efficiency are you getting?

I hope you're not too disappointed at the lack of regulation. A more strictly regulated circuit would go through batteries much faster.

One suggestion regarding the fragile Rsense wire: tape it to the underside of the circuit board.


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## MrAl (Jan 8, 2002)

Hi again,

papasan & datzip:

Thanks for the info and the pics, very nice. I see you got the circuit board
pretty small there papasan? I like that idea too. Did you have any problems
soldering the parts or the leads to the LS ?
BTW, the test i did with a similar inductor (that you have pictured there)
showed that the circuit oscillated at a lower then normal frequency.
Although this might not hurt the LS, you might want to keep this in mind.
That Kemet capacitor seemed to keep the ripple down even at the lower freqency.
Also, i noticed a gain of 4% in efficiency with a core that is allowed to
operate on the 'more' horizontal part of the magnetization curve.
After carefully reviewing waveforms, i can only attribute this gain in
eff because in the zetex circuit the bulk of the eff loss is due to the
transistor 'on' sat voltage. This means the longer the transistor is on,
the more eff it eats up. Cut the duty cycly, and you increase the eff.
By forcing the core to operate on the horizontal part of the mag curve
during the transistor on time, the inductance is decreased dramatically,
even though temporary. This means the current increases much faster then
it normally would, which also means the core charges up much faster,
which also means the peak current is reached much faster, which also means
the transistor turns off much sooner, which also means the transistor 'on'
duty cycle is much lower. Once the transistor turns off, the inductance
again increases to its 'normal' value and discharges into the cap and LED,
which takes much longer then it takes to magnetize the core. This results
in a low 'on' duty cycle which increases eff. Apparently, the core losses
during the 'on' time are much lower then the losses due to the transistor
being on for a longer time with a coil that doesnt operate as far out on the
mag curve. I noticed the same effect with several different coils, some hand
wound and some store bought especially for this project. The coils that cause
about a 4% decrease in eff are those with a lower permeability between about
650 and 1000. The core that provides the 4% boost in eff has a perm of about
4500. I dont have any intermediate mu valued cores to test yet, nor do i have
any cores with a higher mu to test yet either. Originally i though that maybe
using a core that doesnt operate as far out on the mag curve would work better
because the core loss would be less, but after the tests i can see it could very
well be the exact opposite: it might be that even higher mu cores will work
better because they will cause the transistor to turn off even a little faster
then with the 4500 mu core. There may be a limit, however, between the gain
because of duty cycle and the core loss due to mag curve operating point so i
guess if the core loss becomes greater with higher mu then too high a mu might
cause even more loss then an intermediate value. This will have to be tried,
and in the mean time i'll take a look at the core loss curves published on the
Magnetics, Inc. site. It will probably be a tough call without testing an
actual core though, because the 'on' time shortening would have to be predicted
as well as the core loss during the 'on' time in order to get an idea what
effect this will have on the eff.

Take care for now and thanks again for the info and pics,
Al


----------



## papasan (Jan 8, 2002)

i don't have the right resistors to do any good efficiencey testing yet, so all i can give you is the voltage in and out which is 2.533 in and 2.969 out...an interesting note, the Vin was dropping pretty steadly (more than .001V a second) but the Vout was staying fairly steady...with the meter on 300mA it read OL on both in and out...this was two fairly fresh and very new (stiff chemical) NiMH AAs...

soldering wasn't too tough...plenty of flux and have a braid handy =)...the hardest part is getting those damn flea sized chips to sit still until you tack a corner down...i used fairly stiff 18 guage (7 strand i think) wire, next time i'll use smaller and not so stiff wire as i really had to put pressure on it sometimes to bend it (especially after soldering it)...other than that it went pretty smooth...

i understand about wanting to get the inductor to be the best match possible, it sounds like, from MrAl's explanation, that we need a fast switching choke that can take more than 1A...i'm not up on the physics and theory of coils and power storage through EM fields and all that stuff, so i'll leave that to those that know better...i'm thinking that, if we ever want to put this circuit to real use, we need to come up with a simple shopping list of items that anyone can buy (hopefully all at one place) and solder at home...along these lines i think we need to translate our coil needs into a readily available commercial product...even, perhaps, at the cost of a little efficiencey...

here's my parts list, in case anyone is 'just tuning in'...

from digikey
ZXSC310CT-ND = Zetex 310 IC (not out yet, got samples) = $0.81
FMMT617CT-ND = Zetex NPN transistor = $0.99
ZHCS2000CT-ND = Zetex Schottky diode = $1.29
M9711CT-ND = JW Miller 68uH coil = $3.10

from mouser
T491D157K010AS = Kemet 150uF tant cap = $2.30

someone mentioned that digikey sells the kemet tants now, but i couldn't find 'em or the post...


----------



## **DONOTDELETE** (Jan 8, 2002)

Digi-Key now has the Kemet caps available, part number 399-1770-1-ND, $3.38 each.

The Zetex 310's, part number ZXSC310CT-ND, $0.81 each, are also now available.

And I found a 3-5% efficiency improvement over that JW Miller inductor by simply winding two turns of 24AWG wire around a bead core, M2310-ND, $0.29 each. Although it stands about 2.5mm taller, its footprint is 4mm narrower. The material has a published permeability of 2500.


----------



## papasan (Jan 8, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I found a 3-5% efficiency improvement over that JW Miller inductor by simply winding two turns of 24AWG wire around a bead core, M2310-ND, $0.29 each. Although it stands about 2.5mm taller, its footprint is 4mm narrower.*<HR></BLOCKQUOTE>

do you use bare 24G wire or does it need to be insulated?...if it needs to be insulated do you use extra-thin insulation or what?...spending over $3 for a simple coil does seem a bit much...


----------



## **DONOTDELETE** (Jan 8, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*Do you use bare 24G wire or does it need to be insulated?*<HR></BLOCKQUOTE>

Material 73 has a relatively low volume resistivity, which means it will conduct electricity, so using bare wire may be problematic. Moreover, I got best results when the two turns were right next to each other, which could possibly short circuit with no insulation between them.

I used about 6cm of 24-gauge enamel-coated magnet wire, ten feet of which I got for free from a local electric motor repair shop. You remove the enamel coating using sandpaper, and you tin the exposed copper leads before soldering them to the board.

The bead core has a fairly narrow inner diameter, so larger diameter wire, or wire with thicker vinyl or plastic insulation, may not fit. You can use smaller diameter magnet wire, but efficiency will suffer due to the increased resistance.

The picture below shows two views of the bead core on the left, and the ubiquitous M9711 inductor on the right, for size comparison.


----------



## remuen (Jan 9, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*
... i'm thinking that, if we ever want to put this circuit to real use, we need to come up with a simple shopping list of items that anyone can buy (hopefully all at one place) and solder at home...along these lines i think we need to translate our coil needs into a readily available commercial product...even, perhaps, at the cost of a little efficiencey ...
*<HR></BLOCKQUOTE>

Papasan, thanks for the pics! The board already looks quite small and that's great.

If you, MrAl and Duggg and all others working on this circuit want to share your work with us 'non-participants' and beginners outside of this thread it would by absolutly necessary to come up to standard compononts (kind of shopping list). Most of us are not able to make such a special inductor you're talking about. The challange to bring the components on a small board and solder them is already big enough ...

The efficiency of this circuit is of course important - but a good efficiency will be nothing if we are not able to make the circuit board. 

Thanks for all what you experts are doing for us!


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## papasan (Jan 9, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*The picture below shows two views of the bead core on the left, and the ubiquitous M9711 inductor on the right, for size comparison.*<HR></BLOCKQUOTE>

excellent, much clearer in my head now...looks like the core is much larger than it needs to be, perhaps break it in half and make 2 half (semi-circle) cores?...is this the smallest core that digikey has?...

also, i wonder why the digikey kemets are almost 70% more than the mouser ones...another good deal i've found from mouser is their copper clad board, a sheet of 4x6 fr-4 was like $1.50 from mouser...a similar fiberglass sheet from digikey is like over $4...


----------



## **DONOTDELETE** (Jan 9, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*Looks like the core is much larger than it needs to be, perhaps break it in half and make 2 half (semi-circle) cores?*

The large volume of the core has a lot to do with its performance. I suspect if you reduce its size, at a minimum you will need more turns, and that will increase the DC resistance and may reduce efficiency.

*...is this the smallest core that digikey has?...*

Actually, it's one of the largest. The next smallest one is M2308-ND, $0.22 each. At that price it may well be worth ordering and testing, if size is more critical than efficiency in your application.

*also, i wonder why the digikey kemets are almost 70% more than the mouser ones*

Digi-Key charges $3.38, which is only 13% more than the $3.00 Mouser charges, and only 37% more than the $2.46 Newark charges.

However, if you factor in shipping and handling charges, and the fact that only Digi-Key has all five components, ordering just from Digi-Key may be cheaper.

Disclaimer: I have no affiliation whatsoever with Digi-Key.
<HR></BLOCKQUOTE>


----------



## papasan (Jan 9, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*



Digi-Key charges $3.38, which is only 13% more than the $3.00 Mouser charges, and only 37% more than the $2.46 Newark charges.<HR></BLOCKQUOTE>

Click to expand...

*
hmm...i guess mouser's prices went up since i ordered mine...and yeah, i did my math backwards, 2.30 is 70% of 3.38, it's only about 47% more in price...


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## papasan (Jan 9, 2002)

some very informal runs...i installed the board into my children's adventure headlamp as shown in another thread...this is with an amber lambertian...

puts out some real nice light with two fresh NiMH AAs...much much better than the mini-mag type lamp that came in it...can't wait to try it out with some urban or cave spelunking...my dog and my 15 month old son are in love =)...

let it run for a few hours on some not-so-fresh NiMHs, i think about 5 hours, but i wasn't watching the clock...within an hour and a half (probably closer to an hour)before i stopped the run it got very dim (i had it up-side down so the dog would stop barking and snapping at the walls for awhile, i didn't observe the change)...as a note the case gets warm, but not hot at all, when the batteries are fresher...

so i shut it off and checked the batteries...one read .090V!...the charger is telling me it's a goner, hopefully it'll recover...

i jumped the Vcc with the shutdown hoping that power wouldn't be wasted on the transistor when the juice got low...opening it up i felt the transistor and it didn't feel warm...

all in all it felt good...with the realization that this circuit wouldn't regulate at all made my heart sink a little, but seeing how quick the output fell perhaps it's not all that bad...although, this could be characteristics of NiMHs, even more so because they are new...i'll have to get some alkalines and run them into the ground and see what happens...


----------



## MrAl (Jan 9, 2002)

Hi there again,

papasan:
>>>
i'll have to get some alkalines and run them into the ground and see what happens... 
<<<
I was thinking of trying this out too
just to see how low it would take them
and still provide decent light, and of 
course not burn up the transistor 

I did some other testing regarding the
input cap. I had been using 100uf cap
with about 0.2 ohms esr across the
batterys (2 NiCds). After removing
the input cap, i see about a 3% drop
in efficiency, as well as a high change in
input ripple voltage: 0.5 volts of ripple.
The valley in the input ripple occurs
when the coil is drawing max current
while the transistor is on (at the end
of the 'on' part of the cycle). Since
0.5 volts means the voltage at the input
has dropped to 1.9 volts, which would cause
a drop in eff. This could be related closely
to the type of batteries im using.

Duggg:
If you could try using and not using an
input cap and notice the change in eff
that would be great.

Oh yeah, i tested that little bead core
with the 1/16 inch diameter hole, and
with 2 turns it works pretty good, but
i dont like the waveform im seeing with
it. Sometimes it decides to cause 
oscillation at a lower frequency, depending
on input voltage or output current. It 
causes the circuit to 'skip' a cycle by
turning the transistor on and off really
fast. Not sure if i like this operation
with this circuit. The eff is only a little
bit lower then with the white core or
Mercator's 4+4 turns black core with 13 turns.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Jan 10, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*After removing the input cap, i see about a 3% drop in efficiency, as well as a high change in input ripple voltage.

Duggg: If you could try using and not using an input cap and notice the change in eff that would be great.*

A possible 3% efficiency improvement is certainly worth firing up the test circuit for.

Efficiency using a 100uF input cap: 85.8%
Efficiency not using it: 86.0%

So unfortunately, I did not observe your findings. In fact, I found the circuit slightly less efficient using the input cap.

It's possible my test caps had too high an ESR. I tried two different ones, a brand-new 16-volt one with an ESR of 0.3 ohm; the other was an old 35-volt one with an unknown ESR.

*Oh yeah, i tested that little bead core with the 1/16 inch diameter hole, and with 2 turns it works pretty good, The eff is only a little it lower then with the white core or Mercator's 4+4 turns black core with 13 turns.*

That's interesting, I found the bead core outperformed the white core by 0.5% and Mercator's core by 1%.

Did you place both turns right next to each other, or did you space them apart? Are you sure you tested the right core---the M2310 has an inner diameter of 2.26mm, which is a bit larger than 1/16 of an inch...
<HR></BLOCKQUOTE>


----------



## remuen (Jan 10, 2002)

MrAl, Duggg and papasan and all the other experts in this thread
I was not sure (and am still not) wether it is good to post this info because I'm quite sure it is 'old poop from yesterday' (this is a direct translation from German into English) for you. But if it's not that old then maybe it could help you so I post it.

I had just a short discussion with Thomas who's an electronic engineer in our company developping also such regulator (stepup/stepdown) circuits with LT ic's. He told me that it is very important to make also all test circuit boards as small as possible to avoid any unwanted inductivities and capacitivities. With his first switcher circuit he had a lot of troubles until he made a really compact circuit board.

Hope this hint will help you - and if it is old stuff for you please forgive me because I don't want to offend you.


----------



## MrAl (Jan 10, 2002)

Duggg:
>>>
Efficiency using a 100uF input cap: 85.8%
Efficiency not using it: 86.0%

So unfortunately, I did not observe your findings. In fact, I found the circuit slightly less efficient using the input cap.

It's possible my test caps had too high an ESR. I tried two different ones, a brand-new 16-volt one with an ESR of 0.3 ohm; the other was an old 35-volt one with an unknown ESR.
<<<
Ok thanks. I find the best eff came from using a 100uf cap with not-so-good
esr. The low esr input cap actually lowered the eff a little. I see the
best results with the original 100uf electro we acquired. The 100uf low esr
cap i have lowers the eff, while the 0.2 ohm esr cap raises it. A 3.3uf
cap raises it by less, about 1.5% with my circuit.

>>>
Did you place both turns right next to each other, or did you space them
apart? Are you sure you tested the right core---the M2310 has an inner
diameter of 2.26mm, which is a bit larger than 1/16 of an inch...
<<<
Yes that's the core, and yes the center is actually just a little bigger
then 1/16 inch. I put the 2 turns right next to each other. What did
you do?

Which core do you like best now?

Oh one other thing: I tried the bifilar winding on the best core, and
it didnt help at all. In fact, since there were two windings, both of
which were #28 gauge (that you sent), i ran it with both windings connected,
then disconnected one of the windings (one of the two bifilar) so that
there was again only one #28 gauge, and it performed the same both ways.
It seems neither the ac nor the dc resistance has much to do with those
few turns (9 turns, white core), as doubling (or halving) both would have
shown a difference. I also increased the wire size to #22 and also did
not see an improvement (single winding, not bifilar, 9 turns, white core).

Mercators' black 4+4 core: i had found 13 turns to be about the best.
It fell behind only maybe 1% (if that) of the white core after increasing 
the number of turns to 13 (the white core seems best with 9 turns).

remuen:
>>>
I was not sure (and am still not) wether it is good to post this info
because I'm quite sure it is ' old **** '
<<<
That's ok, any info MIGHT be repeated, or we might not have seen it yet.
Also, I dont want to offend you either, but just in case
there are any young tot's reading the post i think most
CP members try to avoid using uncolorful words 

Take care and good luck with your led circuits,
Al


----------



## papasan (Jan 10, 2002)

i must be over-driving the luxeon like mad, because i only get about 2-2.5 hours of good level light when running it off of duracel pro alkaline AAs...i'm on about 5 hours now and it's pretty dim, my arc-aaa completely blows it away...guess i need more resistance for isense...gotta order me some .1 ohm test resistors soon...

i guess this set-up qualifies as a high-drain device =)...if i turn th elight off for a few moments it will get very bright again for a very short time...actually measured them and watch as the voltage went from .9 up to 1.2 in about 10 seconds =)...waiting for it to get below .7 to see what happens, currently it's at .82 in and 1.8 out and holding pretty steady...


----------



## MrAl (Jan 10, 2002)

Hi papasan,

If you are going to use alkalines or
NiMH cells, you might be better off using
an input capacitor also of about 100uf.
Alkalines and NiMH cells dont work as well
with high current pulse drains as NiCd's
so you should see a longer battery life
when using an input cap. NiCd's dont
seem to mind the higher pulse drain current,
but i suspect the life would be enhanced for
those too somewhat.

Good luck with it,
Al


----------



## papasan (Jan 10, 2002)

i pretty much only use nimh and alkalines...the occasional lithium...what would you suggest, like 100uF?...and i would assume that an electrolitic would do fine (and sparing some cost)...too bad it'll make the board bigger, i got it down to 3/4 of an inch square...

btw, i use nimh batteries in my digital camera all the time, no problems...with alkalines i can take about 5 pictures, without anything 'extra' like the LCD panel or the flash...with nimhs i can take over 100...most things i've read on the digital photo boards say that nimh batts work fine for 'high drain devices'...


----------



## remuen (Jan 10, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
Also, I dont want to offend you either, but just in case there are any young tot's reading the post i think most CP members try to avoid using uncolorful words 
Al*<HR></BLOCKQUOTE>
Thanks for your advice. I didn't think about it because it's a word we - and that means also the kids - use here in our country very often without thinking what it really means. I'll keep your words in my mind .....


----------



## dat2zip (Jan 10, 2002)

Hello all again.

Just some FYI and food for thought. I got back an email I posted to someone who works at National Semiconductor. He said you can covert a step up converter to a current converter by putting the LED(s) in place of the upper feedback resistor used to set Vout. When you do this you control the current instead of the voltage.

I thought about this and did some additional reasearch and the many IC's from National, Maxim, LT and others will indeed do this if I'm thinking correctly. I found the VREF sense is around 1.2 Volts which would mean you would need a sense resistor in series with the LS LED for example to develop 1.2 @ 0.35 = 3.4 Ohms. This is lost or wasted power in the sense resistor. The other way to do this is use a very small current sense resistor and use a small sot23 CMOS opamp to add some gain. This would reduce losses in the current sense resistor but either adds a nasty pole or gain to the feedback. Some spice or simulations will need to be done to make sure the feedback loop is still stable.

Just food for thought...


----------



## **DONOTDELETE** (Jan 11, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi papasan, If you are going to use alkalines or NiMH cells, you might be better off using an input capacitor also of about 100uf.*<HR></BLOCKQUOTE>

Using a pair of fresh AA NiMH cells, I repeated the test I did last night, and found only a 0.2% improvement using a 100uF input capacitor---statistically insignificant.

Using MrAl's formula for calculating efficiency, the M2310 bead core now scores 86.2% and 13 turns on the Mercator 4+4 core scores 84.6%. I'll test 9 turns on the MrAl white core Friday evening.


----------



## MrAl (Jan 11, 2002)

Hello again,

It looks like almost any input cap improves efficiency with my circuit.
I'm wondering if perhaps my NiCd's have unusually large internal resistance.
I'll have to do a test on this, but i'm now thinking the input cap should
be an option. At best, it will only improve eff a few percent. The
battery life test with and without the cap is an almost impossible test 
to run in any resonable amount of time and without holding exact 
standards in check for every single run, so it's hard to make a strong
point for including it. I'll check my batteries internal R sometime
and see if it looks high. Perhaps i'll pick up a set of NiMH cells 
and repeat the test also.
BTW, an expensive cap didnt work very well. The best choice was a rather
high esr cap (0.2 ohm).

Im also wondering if battery ageing might
affect the efficiency without an input cap.
I guess this would be pretty hard to test
for too, unless you have an old set of 
batteries laying around.

I didnt see any instability caused by not having the cap in at least.

Thanks for doing the test Duggg.

Take care for now,
Al


----------



## MrAl (Jan 11, 2002)

Hello again,

>>>
The other way to do this is use a very small current sense resistor and use a small sot23 CMOS opamp to add some gain. This would reduce losses in the current sense resistor but either adds a nasty pole or gain to the feedback. Some spice or simulations will need to be done to make sure the feedback loop is still stable.
<<<

There is no problem with the feedback loop
when regulating current this way. As long
as you set the loop frequency low enough,
it works just fine. I would say at least
20 times lower then the converter's oscillator. I did this with two different
converter circuits and it works really good.
I think it was about 1ms time constant in
the feedback circuit.
It might even be lower then that, but it's
still plenty fast enough to regulate the
current as there isnt any chance of abrupt
output current changes like there is with a
regular power supply. There is only one
thing i found to worry about, and that is
what is sometimes referred to in the 
power supply industry as 'soft start'.
This means when the circuit is first turned on, you dont want to bang the LED with the
maximum current available from the circuit
(which is always set higher then normal to
account for low battery voltage), so you
build in a mechanism for turning the LED
on somewhat slowly, untill the regulator
takes over. After that, it's near perfect
current regulation. I'm doing this with
my 4 transistor circuit, but only using
two transistors for the converter and
one combination op amp/ voltage reference diode, but you can use almost any op amp
that can run on about 3 volts in combination
with almost any voltage reference diode.
With the op amp, the current stays regulated
to within less then 1%. With the SO package,
it still comes out pretty small, but of course
there are more parts (like resistors) then
in the zetex 300 circuit. I hope to get back
to this circuit as soon as we are pretty much
done with this zetex circuit. One nice thing
about it is if you dont need super small 
parts, you can get the parts almost anywhere,
including Radio Shack, except maybe for the
voltage reference diode unless maybe special
order.

Al


----------



## papasan (Jan 11, 2002)

as a follow-up...i've left the light on all night...it looks exactly the same as when i went to bed, it's a dull orange glow and still reads 8.2V in...says to me that there is still alot of juice left in them, just how to get it out...

so how effective is another 150uF kemet tant going to be?...i mean, putting it in parallel with the input how much longer will it allow the light to stay at full?...if i turn off the light the output cap doesn't keep powering it for very long, so i imagine that 150uF isn't very much juice...

i really want to be able to use this for all battery situations, not specifically nimh or alkaline...

oh, and i thought about it a little and i actually shrunk the board a little with an input cap =)...it's under 3/4 x 3/4 of an inch now...need a decently small coil tho, the jw miller 680 is the largest that'll fit...


----------



## **DONOTDELETE** (Jan 11, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*I really want to be able to use this for all battery situations, not specifically nimh or alkaline...*<HR></BLOCKQUOTE>

Since the different battery families each have their own distinct discharge voltage curves, it may be hard to come with a single value for Rsense that will produce satisfactory results in all three cases.

I'll experiment with different batteries over the weekend, including some input cap tests.


----------



## MrAl (Jan 11, 2002)

Hi again papasan,

8.2 volts input?

It's hard to say how much longer the batteries will last with an input cap,
but in any case dont use another Kemet low esr cap, use a cheapy electrolytic.
The low esr cap actually lowered the efficiency, so use a cheap cap.
20uf should be enough. It's not a question of 'juice' however  it's 
how high the maximum pulse drain on the battery is. The higher the worse
it is for any battery. Most batterys last longest when the drain is low,
and die out faster when the drain is high, normalizing for time that is.
You will notice that even NiCd's show less ampere-hour output at high
drain currents then low ones. Some good 6v lantern batteries seem to last
forever at very low currents (like a single Nichia led). That is, the
apparant storage capacity goes up as current goes down. Just how much
the input capacitor helps is very hard to say though, as many tests would
have to be done to determine this. It does help during the high current
surges drawn by the transistor being turned on, as much of the current then
comes from the capacitor, not the battery. During the off time, the cap
charges back up from the battery, but its a lower current draw. The cap
therefore helps to average out the current drawn by the circuit.
If the battery has to put out 1.5 amp surges every cycle, it could mean
we will see a depreciation in the apparent ampere hour rating. Now the
difference between 10 hour discharge and 1 hour discharge is about 15%,
which looks like another 15% efficiency as far as battery life is concerned.
With our circuit though, it looks more like the difference between
1 hour discharge and 4 hour discharge, which would only be about 6%.
A good estimation therefore would be about 6% longer battery life with
an input cap using NiCd's. Since alkalines dont handle high current surges
as well as NiCd's, there could be a much greater impact when using 
alkaline batteries. Dont get me wrong though, im not saying alkalines
(or any other battery) cant handle high currents, im just saying that
when they are forced to handle higher currents their apparent storage
capacity falls off. That's one of the reasons EverReady Battery Co. came
out with their e squared line of batteries. These batteries are (supposedly)
better at handling high current surges.
I think it would take some pretty careful measurements to measure the
effect of the input cap on battery life, unless you get the results i get
with my circuit and battery combo, where you can see a decrease in efficiency
without even considering the current surge phenomenon.

As far as size of the pc board, im hoping to get down to 3/4 inch round max.
This will fit into the AA MiniMag head.

Take care for now,
Al


----------



## MrAl (Jan 11, 2002)

Hi again,

>>>
0.82 volts
<<<
Ahhh, that makes more sense now 

I think the input cap should be optional so that very small apps
can take advantage of the very small board size. I think i'll need
this when i try to do the minimag conversion.

As a side note, i was able to pick up some more 0.1 ohm 2w resistors
today and some test leads and stuff, and while i was at the store
i noticed they had a digital meter on sale for 7 dollars, so i picked 
one up just to see more or less how well a 7 dollar meter would work.
Well, it's kind of funny, because the manual says it takes a 12 volt
battery (those little #23 batteries) but after opening it up, i find
SIX little 1.5 volt AG12 cells SCOTCH TAPED in series !! ha ha.
I wasnt sure at first if they were maybe 2v cells, because the manual
said "12v" so i took the pack apart to check, and found out they
are really 1.5v cells. Trying to get them back together is another
story: ever try to stack 6 little cells in series under spring
pressure from a cheap battery holder? ha ha. When you go to put the
last one in, the middle one pops out. It's like a little circus.
Finally, getting them to stay in place, i put a new piece of scotch tape
on top to hold them in place. Well what do you expect for 7 dollars? he he.
On the plus side, it does have lots of dc ranges and dc current ranges too,
and it's only about 2 inches by 4 inches by 3/4 inch thick. Since the 
batteries add up to about 9v dc, they can be replaced, albeit with some
increase in case size, with a single standard 9v battery and a battery clip.
The only real drawback is that it only has a 1 megohm input impedance.
My other two cheapy meters do have 10 megohm input, but no current scales
and they were $15 each.
I guess it's not bad for 7 dollars though. The accuracy seems pretty good
at least at 23 deg C.

Take care,
Al


----------



## papasan (Jan 12, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*8.2 volts input?*<HR></BLOCKQUOTE>

er, .82 volts...

small SMD electrolitic caps don't seem to be all that much cheaper than tants...at least not in the 100uF range and not from digikey...why do you think the higher ESR is better?...beacuse the cap is less transparent to the circuit and discharges a little slower?...also, am i correct in thinking that the larger capacity the cap the more steady the draw from the battery?...following this logic, a 100uF cap would do much better than a 22uF if you had a bad high-drain battery like an alkaline or a 'heavy duty' type?...i suppose there comes a point where the cap leaks too much power and becomes negatively desirable...

i appreciate you taking the time to explain things to me in a way that i can understand, MrAl...patience is a virtue =)...

i actually have a couple 16V 100uF SMD electrolitics from illinois cap, i'll try one out and let you know how it goes...


----------



## papasan (Jan 12, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Since the different battery families each have their own distinct discharge voltage curves, it may be hard to come with a single value for Rsense that will produce satisfactory results in all three cases.

I'll experiment with different batteries over the weekend, including some input cap tests.*<HR></BLOCKQUOTE>

in this case i would probably gear it towards most voltage/current input (lithium AAs) and take the slight hit if i chose to use alkalines, nimh, or anything else...another good point in using an input cap, to help average out widely varying battery sources...


----------



## papasan (Jan 12, 2002)

okay...got the 3/4" board with the input cap all soldered up...it's sitting right beside my original doing some comparison testing right now: the original has NiMHs and the mark II has alkalines...

not a very scientific test because i still have no good way to get correct current readings or check the R value of Isense, but i'll get a general feeling of how good the cap will work to help drain the alkalines more fully...

btw, the alkalines powered the original board for almost 3 days straight...i would turn it off now and again to let the batteries 'rest' to get some good light for 15-20 minutes...

i'll take some pictures of the board later tonight...


----------



## papasan (Jan 12, 2002)

hmm...something must be out of whack...i'm getting like 1.5 hours of good solid light...the new board with the input cap has been running on 2 alkalines for about 2:45 and it's down to a very unusable dull glow...even the NiMH, while definatly better, is a little dimmer than my arc-aaa le, not very usable in LS terms...i wasn't really watching the clock and was doing other stuff before in the other runs, now that i have the times are much shorter than i thought originally...

comparing this to the arc-ls, the only other LS light i know anything at all about, which is supposed to run at full for 5 hours this seems very off...perhaps i'm over-driving the LSes like mad, but the light output doesn't suggest this...perhaps something else is wrong...here's my board layout...about the only things to scale are the SOT components...Vin is left, Vout right, GND is bottom...replace the 0805 R near the bottom middle with a 2-3 inch piece of small wire =)...any thoughts?...







also, how do you test a capacitor?...i'm thinking that maybe i left the iron on it too long and maybe fried it?...or perhaps, because the board is so small, the Isense R has to be alot greater...or perhaps the coil is crap for this circuit (the jw miller 680 for both)...really need to get some .1 or even 1 ohm resistors...


----------



## **DONOTDELETE** (Jan 12, 2002)

Regarding run time, the LS consumes about 1 watt, more like 1.15 watts if you take the efficiency of the converter into account.

To get 5 hours of full brightness, you would need a battery capable of supplying 5.75 watt-hours of power.

1600mAh AA cells provide 3.84 watt-hours, so you should expect 3.3 hours of run time, and that jives with my experience.

Although AA alkalines are typically rated around 2800mAh, they provide this rating only under low current discharge. At 1.15 watts, according to Duracell data at http://www.duracell.com/oem/Primary/Alkaline/mx1500.asp, typical service life is only about 2.5 hours!

For that reason, I think I will save some money and pass on testing those alkalines


----------



## papasan (Jan 12, 2002)

i've read that the arc-ls goes beyond this 2.5 hour expectation, but i don't have any first hand knowledge of such...and into 'moon mode' very much longer beyond that...it has something in it to suck the juice out of the batteries better than what i'm using...

there's, obviously, plenty of charge in the batteries: i turned it off for 30 minutes and got another hour of good run-time after...this, however, is not a good trait for using this light for caving or urban spelunking or other zero light environments where it would (or should) be on steady for hours...

my thinking now is that r-sense is just too small and that i need to up it to better match the battery's discharge curve by not driving the LS as hard...possibly under-driving the emitter, definatly, but for me it's better that the light be able to stay on until the batteries are dead...

i've tried seperating the emitter from the board (had them mounted back to back) thinking the heat might have been an issue, but didn't help...

i'm looking for a good all-around circuit, i don't want one that restricts me to one battery type, that's what drew me to the project in the first place...if i just wanted relatively flat discharge i would have just stuck lithiums in there and been done with it...that's the beauty of doing it yourself, you can customize it completely...


----------



## **DONOTDELETE** (Jan 12, 2002)

I got some very interesting results this evening using MrAl's white core with 9 turns of #24AWG. This core has the highest permeability of all the ones tested, around 5000.

With the same high value for Rsense that the M2310 bead core uses, efficiency was almost 88%! Unfortunately, average output current was very low, only around 270mA---too low for a valid comparison.

Lowering Rsense to increase average output current to around 335mA, efficiency fell dramatically to 84.9%. Perhaps due to saturation and additional I^2R losses.

I then added a 35-volt, 100uF capacitor across the battery. Efficiency rose to 86.0%! So the cap really does help in some circumstances, after all.

However, considering the M2310 bead core achieved 86.2% without the need for an additional capacitor, I think it remains the leader in the great Battle of the Toroids.


----------



## MrAl (Jan 13, 2002)

Hello again,

Here is the calculated run time for the Zetex circuit driving
the LS at 350ma average. The 'NiCd' set takes into account 
a 6% drop in storage capacity due to cyclic current surges
(discussed previously in this thread)
while the 'Alkaline' set takes into account a 12% drop.
I dont have any data on the NiMH cells yet. If anyone knows a
web site with some data for these cells, please let me know.

---------------------------------------------
ZETEX RUN TIME DATA 01/13/2002, I(LS)=350ma
---------------------------------------------

Alkaline:
AA 2.3hr
C 5.0hr
D 11.6hr

---------------------------------------------

standard NiCd's:
AA 1.0 hr
sub C 2hr
D 2.5 hr

---------------------------------------------

Good luck with it,
Al


----------



## papasan (Jan 13, 2002)

this help?...

http://www.sanyo.com/industrial/batteries/industrial_specs.html

guess i just expected more out of the run-time...2.3 hours, that's like halogen run times which, while the bulb doesn't last as long, seems to put out more light...

perhaps the answer for me is a switch or a jumper to change rsense and do a high-low type set up...


----------



## papasan (Jan 13, 2002)

an interesting and desirable, for me, side affect of using an input cap...the LS stays brighter longer and dies faster (and harder) than without...even with NiMHs driving it...

question:
if i wanted to put a resistor between Vcc and SHTDN on the 310 chip so that it shuts down at say 1V (instead of the rated .1V), does this equation follow?...

R = .9/.000005 = 180000 = 180K

i got the 5uA from the 310 datasheet...i realize that this would send the circuit into an oscilation where it turns off until the batteries recover a bit (get back to 1V or more) and then turns back on and that this may cause an undesirable blinking effect, but i thought it may be fun to experiment with...


----------



## MrAl (Jan 13, 2002)

Hi there again,

Thanks for the link papasan. According
to that data, the NiMH cells' data can
be added to the calculated run time list:

--------------------------------------------
NiMH:
size AA 1600mAh run time = 2.8hr
--------------------------------------------

>>>
does this equation follow?...
R = .9/.000005 = 180000 = 180K
<<<
Yes that looks correct, but you must realize
that either the 5ua or the 0.1 volt spec 
might be temperature dependent, so you will
have to try a resistor and then test it
with maybe a variable power supply or maybe
a 1k pot (to vary the voltage) and run the
test at elevated and decreased temperatures
in order to determine the effect (if any)
of ambient temperature variation on the
set point voltage. The reason i say this is
because logic inputs arent usually that good.
It may still be acceptable though, or you
might try using an appropriate thermistor
once you determine the temperature effects.
A test at +10 deg C and another test at
+30 deg C while varying the voltage applied 
to the resistor would confirm the operation 
to at least some degree of accuracy.
You're right though about the circuit 
turning back on almost as soon as it turns
off because the battery voltage will
'recover' fairly quickly once the circuit
stops drawing current and so it might turn 
back on, unless the upper trip point is
high enough. If the upper trip point is
too high though, the circuit will never turn
back on again! I'll take a quick look at the
data sheet and try to determine this.

ADDED LATER:
Ok, the spec sheet says something like
turn on at 0.7 volts and turn off at
0.15 volts, therefore a resistor wont
work here because if you select a value
that turns off at 0.15 volts when the battery
runs down to about 1 volt then the circuit
will require something like 4 or 5 volts 
input in order to turn back on again.
This means the series resistor wont work,
nor any combination of resistors in a 
voltage divider type network.

One possible way around this is to add an
active device, like a transistor. When
the output voltage rises, it drives the
transistor who's collector pulls down
on a point in your resistor divider network.
When the circuit input falls and the circuit
turns off, the transistor turns off and
therefore makes the input divider more
sensitive again. The whole arrangement would
be a kinda trick and might require freq 
compensation with a small capacitor also.
A better way would be to use an SM ic 
comparator circuit, which would require a
few resistors and probably a voltage reference diode. It wouldnt take up
'that' much more room, but it would make
the circuit larger. I guess it all depends
how bad you want this to work and what your
app is.


Good luck with it,
Al


----------



## papasan (Jan 13, 2002)

ahh...yes, i didn't account for the grey area...

even still, wouldn't it only take a .7V addition to the voltage from the source in order to turn back on?...if it takes 3-4 volts then the circuit wouldn't even turn on at all with 1.2V batteries...

the reason i'm thinking of this is because i took the dead NiMH batteries that were putting out very little light and bypassed the 310 circuit with them and it put out considerably more light...i'm thinking if i can find the 'sweet spot' where the direct battery current works better than the switched current i could put the correct ohmage resistor there and conserve as much power as possible...

with the all on or all off thing this won't help as much with alkalines as i was thinking it would...still, it would be a small step in making it a little better with a $.10 very small footprint part...

just thinking out loud, as they say =)...


----------



## MrAl (Jan 14, 2002)

(See input cap problem below too)

Hi there again,

>>>
even still, wouldn't it only take a .7V addition to the voltage
from the source in order to turn back on?...if it takes 3-4 volts
then the circuit wouldn't even turn on at all with 1.2V batteries...
<<<
In a word, 'no' 
Calculate the voltage needed to drive the input up to 0.7 volts
at 5ua through the same resistor that you use to set the 1 volt
turn off point and you'll see why.
We talked about connecting a cap in
parallel with the resistor which could
work to some degree, with the side effect
of some oscillation, possibly not harmful
though.

>>>
bypassed the 310 circuit with them and it put out considerably more light
<<<
Not sure what you mean here, what do you mean by "bypassing the circut" ?


INPUT CAP PROBLEM REVISITED:

One thing that worries me is that without an input cap when we disconnect
the battery with a presumed power switch, where does the energy from the
inductor go assuming we turn off near the highest current point through
the inductor during a typical cycle?
Answer:
When the battery is disconnected, the low impedance normally provided by
the battery goes much higher. Now the inductor normally discharges 
through the LED and output cap, but also through the battery to provide
the LED with the battery voltage plus the voltage across the inductor.
Without the battery, the + power pin on the ic would be driven low,
possibly negative. This could have a distructive effect on the ic chip
itself, and so will have to be looked at. There may be a minimum cap
value require on the input to take care of this, or at least a reverse
connected diode to absorb the power from the inductor should we turn off
at an undesirable time in the switching cycle. I'll be taking a look at
this new phenomenon which i originally 
overlooked.
The ic chips' power supply pin is rated at
-0.3 volts to 10 volts.

--Al


----------



## papasan (Jan 14, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Not sure what you mean here, what do you mean by "bypassing the circut" ?*<HR></BLOCKQUOTE>

i took the output of the batteries and connected them directly to the LS instead of the circuit input...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Calculate the voltage needed to drive the input up to 0.7 volts
at 5ua through the same resistor that you use to set the 1 volt
turn off point and you'll see why.*<HR></BLOCKQUOTE>

that's the thing...i sat here for a while last night trying to figure it out...it seemed that it should be easy to, that it was 'on the tip of my tongue' so to speak, but i couldn't come up with a formula...R=V/I, so if we know R and I then V is always the same...or do i convert the energy to watts and do something there?...bah, i should have paid attention in school =P...


----------



## **DONOTDELETE** (Jan 14, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Without the battery, the + power pin on the ic would be driven low, possibly negative. This could have a distructive effect on the ic chip itself, and so will have to be looked at.*<HR></BLOCKQUOTE>

Perhaps the Zetex designers already looked at it. If they put a snall resistor in series with a reverse diode, it could easily absorb the one pulse of excess energy.

I've personally disconnected the batteries hundreds of times with no apparent ill effects, so I don't consider this a major issue.

It's time to get this show on the road, not get sidetracked with adding additional components at the last minute.


----------



## papasan (Jan 14, 2002)

ran my first 'real' test...my efficiencey is horrible...i suppose that has alot do to with the coil...anyhow, here it is...


```

```

here's a nifty graph...the labels got cut off in the translation somehow, but you got those above...







this is with an EL 100uF input cap and the kemet 150uF output cap...the coil is the jw miller 68uH...two 0.1ohm resistors were used to get the current...it stays pretty good until the two hour mark, but it doesn't take long before its output is unusable...the NiMH batteries i used may still need a few charge cycles...


----------



## **DONOTDELETE** (Jan 14, 2002)

Papasan,

What power source are you using?

Your output voltage seems rather low. My cyan and white LS's are typically in the 3.3-3.4 volt range. What color is yours? 

Also, you don't seem to be taking into account the power wasted by the current sense resistors. Try using the following formula:

Eff = Vout*Iout / (Vin*Iin - Iin*Iin*Rin - Iout*Iout*Rout)


----------



## papasan (Jan 14, 2002)

i was using 2 generic 1600mAH NiMH batteries...fresh out of the smart charger...the measured 2.80V unloaded before the test began...after the test they rose back up to 2.08V unloaded...

the LED was an LS lambertian amber...the orange/red LSes have a 2.95V typical forward voltage, not the 3.42 of the blue/green/white colored ones...something about the chemestry of the LED...

no, i didn't use the large formula because i neglected to notice MrAl's statement that the voltage should be measured on the circuit input and output, i was measuring the battery output instead...next time...

i just measured the other board i made, same set up but with no input cap...after 10 minutes it was at 73% using the simple eff formula, slightly better but nothing to write home about...i did find out that i guessed a little short on the sense R, it was driving the LS at over .5 amps!....539 at 0, .492 at 10...guess that explains it's angry orange color =P...

considering that all the parts i'm using are the same as what you guys are using except for the coil i have to assume that's the reason for the 20% efficiencey gap...my next digikey order will definatly have some ferrite beads on it...

somehow i quoted MrAl's post that was made *after* this one...hehe...
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by : MrAl
*>>>
i took the output of the batteries and connected them directly to the LS instead of the circuit input...
<<<
If you are saying that you get more light out of the LS with 2.4 volts then by
using the circuit, then something is wrong *<HR></BLOCKQUOTE>

no, i'm saying that when the batteries got very low (like around the 150 minute mark on my chart) i disconected the circuit and the LS put out more light...mind you, it wasn't a whole lot of light, still very dim compared to the original, fresh output, but better than through the circuit...from my chart the eff drops down to 15% at 150 minutes, even with a better over-all eff circuit i would think it'ld be fairly low...it would be better to, at this point, turn the circuit off and just run the LS directly...

i'll try your resistor test on the 310, but it may be a little bit as the shutdown pin is very attached on my current prototype board...i have actually designed a new one, just need to etch it...


----------



## MrAl (Jan 14, 2002)

papasan:
>>>
i took the output of the batteries and connected them directly to the LS instead of the circuit input...
<<<
If you are saying that you get more light out of the LS with 2.4 volts then by
using the circuit, then something is wrong 

I made a mistake when i quoted the 5ua input current for the enable pin
on the zetex 310 chip. If this is in fact a constant current input, then
perhaps a series resistor would work to some degree with perhaps a little
temperature sensitivity. If its more like a resistance (which i assumed)
then the battery voltage would have to go up to 7.0 volts dc to turn the
circuit back on. Since i dont have a 310 chip, you yourself will have
to test this pin and see what happens.
Perform the following tests:
Using 200k, 100k, and 20k resistors
for the series resistance connect each
one in turn between the battery + terminal
and the enable pin and measure the following
(using a 10megohm input meter):
1. battery voltage.
2. voltage at enable pin to ground.
3. whether or not the output is actually enabled (turned on).

We can then determine
if the pins' input looks like a constant current or a resistor input.

Also, your efficiency looks very bad. I dont have one of those coils
to test. Perhaps you should try another coil and repeat the test. So
far we all get at least 80% and typically 85%. The coil has a lot to do with it.
I'll be getting more cores soon i hope, if
you want one let me know.

Duggg:
>>>
I've personally disconnected the batteries hundreds of times with no apparent
ill effects, so I don't consider this a major issue.
<<<
That sounds good, i just like to be sure that's all. I'll be able to do
that test myself. I've been using a 100uf input cap the whole time except for
a few tests without it and a few tests with a smaller 3.3uf cap.

Take care for now,
Al


----------



## papasan (Jan 15, 2002)

this test was on my original 310 board...same components minus the input resistor, about 1/4 bigger on both dimensions...in the last test i used aligator jumpers to connect the batteries to the circuit, everything on this test was soldered...an interesting note, the sense R is about 1.5 times longer on this board...

2 1600 NiMH AAs, 1.44 unloaded voltage, lambertian amber LS...efficiencey gotten using this formula...

eff=Vro*(Vco-Vro)/(Vri*Vci-Vro*Vro)


```

```

a little better...wonder if the increased run-time is due to the lack of input filter or perhaps the battery's chemicals where 'looser'...

*** edit ***

added more efficiencey ratings...which is correct?...


----------



## **DONOTDELETE** (Jan 15, 2002)

I know the JW Miller inductor is grabbing around 4%, but where the other 5-6% is going I don't know!

I assume you are using:

<UL TYPE=SQUARE><LI>Kemet 150uF 10v polymer tantalum cap
<LI>FMMT617 transistor
<LI>ZHCS2000 Schottky diode
[/list]

BTW, I wouldn't recommend running your NiMH's down like that---stop the test when Vin reaches 1.8 volts, and you'll get more recharge cycles out of them.

I'm just did a test similar to yours, except I used a white hexagonal LS I got in the mail yesterday. 


```

```

Power source is two freshly charged NiMH 1600mAh AA cells, initial open circuit voltage 2.93v. Inductor is the infamous M2310 bead core with two turns. Transistor is a sub-optimal FCX688---an errant solder blob between Vcc and the base briefly turned the 617 I had been using into an LED


----------



## papasan (Jan 15, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I assume you are using:

<UL TYPE=SQUARE><LI>Kemet 150uF 10v polymer tantalum cap
<LI>FMMT617 transistor
<LI>ZHCS2000 Schottky diode
[/list]*<HR></BLOCKQUOTE>

yep...add to that he jw miller 68uH (digikey M9711CT-ND), the zetex ZXSC310, two ~3.5" strands of #30 copper twisted together, and about 1x1" of 1oz. single sided copper clad fr-4 board and you have my whole set-up.

i, too, am surprised at the low numbers...i'll try replacing the jw miller with a coilcraft coil and see what happens...at least until i get some beads...

hmm...i just figured out the efficiencey of my last test by just dividing input watts by output watts and i get higher numbers (almost 80%)...shouldn't it go down because it's not figuring in the 0.1 ohm resistors?...


----------



## **DONOTDELETE** (Jan 15, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*added more efficiency ratings...which is correct?...*<HR></BLOCKQUOTE>

The formula for column 3 is correct if you measured the voltages at the battery and at the LS. Those efficiency figures are reasonable considering you are using the M9711 inductor.


----------



## papasan (Jan 15, 2002)

ahh...as per MrAl's statement with the formula he posted in the first column, the ratings were taken at the circuit input and output...


----------



## **DONOTDELETE** (Jan 15, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*ahh...as per MrAl's statement with the formula he posted in the first column, the ratings were taken at the circuit input and output...*<HR></BLOCKQUOTE>

Papasan, 

If you adjust your t=0 input and output voltages to take the voltage drop across the resistors into account, column 3 yields 74.67%, which is a lot closer to column 2 than column 1 is.

In fact it's so close to column 2, that I propose we simply adopt column 2's simple formula as *the standard method * with which all of us measure and report circuit efficiency. The math's a lot easier, too!





Simply measure the voltages at the board's input/output terminals, and multiply by the input/output current to get input/output power, and then divide the output power by the input power to get efficiency.

All in favor say aye!


----------



## MrAl (Jan 16, 2002)

Hello again,

>>>
Simply measure the voltages at the board's input/output terminals, and multiply by the input/output current to get input/output power, and then divide the output power by the input power to get efficiency.
<<<
That was the original method i was talking
about, but then i started looking for methods
that would produce the highest accuracy.
It is possible to match two resistors to
a very high percentage, while not specifying
their exact values, so i developed a formula
that would be void of resistance values with
the only requirement that they be matched.
I dont mind going back to the original
method, but it should be stressed that
measurements will depend very much on 
the value of everyone's actual resistors.
Keep in mind that a current measurement that
depends on a resistor that is 5% can only be
as good as 5%, and that leads to an efficiency
calculation that can only be as good as
+/- 5%. This means that if we measure 85%,
then the actual efficiency can be as low 
as 81% or as high as 89%. Of course this
assumes one isnt low and the other high.
Using 1% resistors helps a lot.
As a minimum, however, i would recommend
testing the resistors using a test current
around 1 amp and measure the voltage drop
and the current through the resistor in 
order to obtain a calibration factor for 
each resistor. If not 1 amp, then at least
100ma.
To match two resistors, an easy way is to
run approx 1 amp though both resistors 
connected in series, and using the same
meter measure the voltage drop across
each resistor and adjust the lead length
and/or parallel higher value resistors untill
both resistors measure the same voltage drop.
A better way of course is to use a bridge
method, using 4 resistors and adjusting
the two sides of the bridge for a null
reading even after swapping resistors in
each leg. It's theoretically possible
to match the resistors to within about
0.0001 percent (that's one ten-thousanth of
one percent) of each other with a digital
meter and an approx current source around
1 amp.
With accuracy like this, the bulk of the inaccuracy
falls on the meter.

I dont mind using the original method,
but again, the resistor values should be
checked in order to obtain at least some
decent accuracy.

Good luck with it,
Al


----------



## **DONOTDELETE** (Jan 16, 2002)

Hi guys, whadaya talkin' about???

I'm sorry but I'm afraid unless you can condense, dumb down, and explain to me the previous 28 pages, or, offer me a nifty product to buy like an Arc aaa flashlight, (which Gransee did in well under 28 pages, I might add) I must ask you on behalf of the other 998 members who aren't taking part in this discussion, to finish up whatever it is you think you're doing and lock the string...thanks.


----------



## papasan (Jan 16, 2002)

ted, we're trying!...i wish it were so simple...

output watts divided by input watts is fine by me, makes it easier...i could only find 5% resistors locally and digikey shows no 1% stock so getting super technical with it probably wouldn't matter much for me anyhow...

put in a digikey order for some ferrite beads and parts for the maxim 1674 today, it'll be good to try out...

i replaced the jw miller 68uH coil with a coilcraft 100uH, not much change...a little worse if anything...missed a few readings, oh well...


```

```


----------



## MrAl (Jan 16, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Ted the Led:
*Hi guys, whadaya talkin' about???

I'm sorry but I'm afraid unless you can condense, dumb down, and explain to me the previous 28 pages, or, offer me a nifty product to buy like an Arc aaa flashlight, (which Gransee did in well under 28 pages, I might add) I must ask you on behalf of the other 998 members who aren't taking part in this discussion, to finish up whatever it is you think you're doing and lock the string...thanks.

















*<HR></BLOCKQUOTE>

What's the problem Ted? Some of us have
found this project and associated discussion
pretty interesting. Did you ask all 998
members personally? 

--Al


----------



## Badbeams3 (Jan 16, 2002)

I don`t have any idea what everyone is talking about...but it makes me feel like I belong to a pretty smart forum...I say...talk away...and if you all come up with something great...well...I`ll buy one.


----------



## **DONOTDELETE** (Jan 16, 2002)

oh, man, MrAl, I didn't think _anyone_ would take that post seriously...
(didn't the winky and smiley faces come through?) I was kidding..keep up the good work.


----------



## **DONOTDELETE** (Jan 16, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*i could only find 5% resistors locally and digikey shows no 1% stock so getting super technical with it probably wouldn't matter much for me anyhow...*<HR></BLOCKQUOTE>

Resistor tolerance isn't important at all, as long as you know the actual resistance to within 1% or better.

That's easiest to do using 1% resistors, but as MrAl noted, with larger tolerance resistors it's easy to calculate using a fixed, regulated power source---fix the current, measure the voltage, and determine the resistance by dividing the voltage by the current.

BTW, although Digi-Key is out of 0.1-ohm resistors, they do have some 0.05-ohm, 1% ones in stock, #12FR050, $1.45 each.


----------



## **DONOTDELETE** (Jan 16, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*What's the problem Ted? Some of us have
found this project and associated discussion
pretty interesting. Did you ask all 998
members personally?*<HR></BLOCKQUOTE>

Woohoo! Way to go MrAl!





Actually, Ted, I think the finish line is in sight---good things come to those who wait.


----------



## MrAl (Jan 17, 2002)

Hello again,

Ted:
<handshake>



Good luck with your LED circuits
and of course with your LED lights,
Al


----------



## MrAl (Jan 18, 2002)

Hi again,

Just in case anyone is interested, NTE has
150uf solid tant caps. I wonder if they
are fairly low ESR. Anybody have any idea?

--Al


----------



## bikeNomad (Jan 18, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi again,

Just in case anyone is interested, NTE has
150uf solid tant caps. I wonder if they
are fairly low ESR. Anybody have any idea?

--Al*<HR></BLOCKQUOTE>

Well, their radial solid tant caps have a DF of <0.1 in that cap range; this would be an ESR of around 0.88 ohms (at 120Hz), probably higher because of inductance, etc. at higher frequencies.

It's interesting that the SMD ones don't specify DF or ESR.


----------



## MrAl (Jan 18, 2002)

Hi there,

Yes, NTE is a little strange with their specs.
Funny too because they carry quite a few parts.

BTW, Duggg, Mercator, etc:
do we ever intend to test out the zetex
100 chip? We seemed to forget all about this,
and now after reviewing the data sheet i can
see this has features we might want in a
cicuit. It looks like one implementation is
almost exactly the same as the 300 chip
circuit, so why not go with the more featured
chip and select options as required?

--Al


----------



## **DONOTDELETE** (Jan 18, 2002)

Several drawbacks to the ZXSC100:

<UL TYPE=SQUARE><LI>Published efficiency only 82%
<LI>Only operates above 0.93 volt
<LI>At 5x4mm, twice the size of the 300/310
<LI>8 pins, harder to solder
<LI>The $1.75 price is more than twice the 
310's
<LI>1-watt circuit requires a lot of components
[/list]


----------



## **DONOTDELETE** (Jan 18, 2002)

I thought I would bring everyone up to speed as to where we are in this project.

Next week we'll be testing some actual-size 13x13mm boards, which can be trimmed to the diameter of an AA cell, 14mm.

Since the board carries significant current and there are magnetic fields involved, we need to ensure the board performs properly with the components close together, and that efficiency remains above 86%.

Also, in about a week, some M2308 bead cores will arrive from Digi-Key, and we'll see how they turn out. Right now board height is 11.5mm with the M2310; the M2308 would reduce it to under 9mm, if it works.


----------



## MrAl (Jan 20, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Several drawbacks to the ZXSC100:

<UL TYPE=SQUARE><LI>Published efficiency only 82%
<LI>Only operates above 0.93 volt
<LI>At 5x4mm, twice the size of the 300/310
<LI>8 pins, harder to solder
<LI>The $1.75 price is more than twice the 
310's
<LI>1-watt circuit requires a lot of components
[/list]*<HR></BLOCKQUOTE>

<LI>Published efficiency only 82%.
Untill we get ahold of it 

<LI>Only operates above 0.93 volt.
Yes thats a little higher.

<LI>At 5x4mm, twice the size of the 300/310.
Ok, but thats still small.

<LI>8 pins, harder to solder.
Well, if we make a pc board it's ok.

<LI>The $1.75 price is more than twice the 
310's.
Well, twice the price twice the functionality.

<LI>1-watt circuit requires a lot of components
Well, the SM resistors are small, but we'd
have to order a lot of them probably.

I guess it wont hurt NOT to use this chip,
but i'm still keeping it in mind.

If nothing else, at least i know how to use
'bullets' in my posts now 

Take care for now,
Al


----------



## papasan (Jan 20, 2002)

question:

what would two 68uH (or any value, but matching) coils in paralell act like?...one bigger 68uH coil with twice the saturation level and half the DCR?...

just waiting on parts from digikey, specifically the miller beads...just been working on my 3 LED mag-light retrofit in the meantime...


----------



## **DONOTDELETE** (Jan 20, 2002)

Inductors in parallel behave like resistors in parallel---the inductance is cut in half, but so is the DCR. But, the inductor can now handle twice the current, or, if current is kept the same, inductors will be less saturated and may operate more efficiently.

By putting inductors in series, you double the inductance, but also the DCR.

Both techniques may be of use with the new M2308 bead cores, because I suspect there will be an efficiency loss using just one.

But two M2308s can fit in less space than one M2310, so that's something to be investigated.


----------



## MrAl (Jan 21, 2002)

Hello,

I'm looking for some parts/test wire.

1. I'm looking for a second source for
low Vsat transistors (other then Zetex)
for our circuit here. The transistors
typically have less then 0.2 volt vsat
at about 1.0 or 1.5 amps
Any ideas?

2. I'm looking for rubber coated
(or silicone rubber coated) wire typically
about 1/16 inch outside diameter
(including insulation). It's typically
used for test probe wire and it usually
comes in red and black. Any ideas?

Thanks,
Al


----------



## MrAl (Jan 22, 2002)

Hi again,

Here are some more notes on measuring the efficiency.

Using the method of measuring circuit input voltage (not acoss the battery)
and circuit output voltage (not across the LS) and multiplying the
output current times the circuit output voltage and then dividing
by the input current times the input circuit voltage to calculate
the efficiency leads to an error in the efficiency calculation
of very close to ten times the value of the output resistors' value
with a purely linear circuit. With our very nonlinear circuit there
will be another error because of the drop in input voltage which might
add another small percentage when using 0.1 ohms, but that isnt accounted
for here and it should be quite small.

Inclusion of an output resistor of 0.1 ohms lowers current as much as 9
percent, but it only effects the output efficiency calculation by about
1 percent. Adding 1 percent to calculation corrects for this error.

<UL TYPE=SQUARE><LI>The amount to add varies by the value of the output resistor.
<LI>The amount to add is: ten times the value of the output resistor.
[/list]

Add this to the efficiency calculation for correction.
Very small values of R dont affect the calculation very much.

Here is a short table with an example for each using 85% and showing
correction:

<UL TYPE=SQUARE><LI>0.01 ohms add 0.1 percent, (85.0+0.1=85.1%)
<LI>0.02 ohms add 0.2 percent, (85.0+0.2=85.2%)
<LI>0.05 ohms add 0.5 percent, (85.0+0.5=85.5%)
<LI>0.10 ohms add 1.0 percent, (85.0+1.0=86.0%)
[/list]

Since a lot of us are using 0.1 ohms, it means we have to add
1 percent to our calculation if we use this method.

Good luck with it,
Al


----------



## **DONOTDELETE** (Jan 22, 2002)

Well that's very good news.

The adjustment now puts your efficiency figures more in line with my original ones, and we're now close to 88%.

It will be interesting to see how efficiency will be affected with the new 13x13mm board, with the parts closer together.


----------



## ElektroLumens (Jan 23, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi again,

Here are some more notes on measuring the efficiency.
*<HR></BLOCKQUOTE>

MrAl,

What is the resistance of some of the inductors you are using? In some of my circuits, I'm using the M9711CT-ND 
68uH inductor for one of my circuit designs. I was curious of the resistance, and it measured .3 ohms, which seems like a lot to me. The recomended resistance Maxim has recomended for the MAX757 is .03, so I see this measurement is way to high. I'm sure this is killing some efficiency. I have found some inductors from Coiltronics with a .06 rating at 22uH, and I have requested a few samples.

Wayne Johnson


----------



## **DONOTDELETE** (Jan 23, 2002)

The long-awaited M2308 bead cores arrived from Digi-Key today. As you know, the M2308 is 2.5mm shorter than the M2310, and reduces board height by that same amount.

With two turns of #24AWG, efficiency appears to be around 86%. That's the bad news, but expected given that the M2308 is only 62% of the volume of the M2310.

The good news is that there's room in the MiniMag head for two M2308s (at no cost of space), so I'll be experimenting with various combinations and see if I can't bump the efficiency a bit.


----------



## remuen (Jan 24, 2002)

Duggg, MrAl, papasan

Do you already have the 'shopping list' for the parts for your Zetex booster which papasan recently mentioned?

If not when can it be expected?


----------



## MrAl (Jan 24, 2002)

Hi there,

Wayne:
0.3 ohms would take the eff down a lot more then 0.1 ohms would.
We are typically obtaining about 0.05 ohms or less by winding our 
own inductors on toroid cores. If you want to experiment to
find out the effect of having a higher series resistance in
your coil, simply add one or two 0.1 ohm resistors in series 
with your coil and take efficiency readings. Note the difference
with the extra resistors and without them.
Also, 22uH might not be enough, but it's worth a try i guess.

remuen :
Didnt doug post a list a few posts back?
If you have trouble finding it or with any parts let us know.

Good luck with your LED circuits,
Al


----------



## remuen (Jan 24, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
[QB]
Didnt doug post a list a few posts back?
If you have trouble finding it or with any parts let us know.
/QB]<HR></BLOCKQUOTE>

Hello MrAl
I found a list posted by papasan - but it is very old, dated somewhere 10/01/02




. Here it is:

_
from digikey
ZXSC310CT-ND = Zetex 310 IC (not out yet, got samples) = $0.81
FMMT617CT-ND = Zetex NPN transistor = $0.99
ZHCS2000CT-ND = Zetex Schottky diode = $1.29
M9711CT-ND = JW Miller 68uH coil = $3.10
399-1770-1-ND = Kemet 150uF tant cap = $3.38
from mouser
T491D157K010AS = Kemet 150uF tant cap = $2.30
_

Since then you have worked on your design means optimized some parts. If one is not really involved it is not easy to follow all your steps and improvements and tests and .... Therefore I really don't know if papasans 'old' list is still up to date.


----------



## MrAl (Jan 24, 2002)

<UL TYPE=SQUARE><LI>ZXSC300CT-ND = Zetex 300 IC
<LI>FMMT617CT-ND = Zetex NPN transistor = $0.99
<LI>ZHCS2000CT-ND = Zetex Schottky diode = $1.29
<LI>M2310 ferrite bead with 2 turns of #24 wire
<LI>Kemet 150uF SM cap
<LI><LI>short piece of #32 wire or equivalent for sense resistor
[/list]
You adjust the wire length to set output current.
Im not sure what the part number was for teh Kemet cap,
but all these parts are obtainable from Digikey, except maybe
the wire. Also, some of us are using a cheapy 100uf input cap
for the dual purpose of protecting the ic chip during turn off
and also for making the battery look like a lower impedance
extending it's apparent charge capacity somewhat.
I havent found ANY store bough inductors that work as well
as the hand wound toroids, so i gave up on testing store
bought inductors for now, but if anyone want to send me
the Miller coil i'll test it and send it back if you want
after the test is complete (allow about 3 days for this).
I would doubt it would perform as well as the hand wound 
inductors though, because these hand wound ones happen to
have some very very nonlinear characteristics that happen
to work out in our favor for this particular kind of circuit
for the purpose of raising the efficiency.

As a side note, for running one or two standard LED's in parallel
i think almost any very small inductor would work.

Good luck with it,
Al


----------



## MrAl (Jan 24, 2002)

Hello again,

In addition to the above post with the
parts list, i decided to inquire about
the Zetex's ic chip equivalent input.

Here is a copy of the letter i sent,
and after i get a reply i'll post it here.

--------------------------------------------
(begin quote)

Hello again Geoff, and thanks for your info in the past which 
has proven to be very useful.

My question now is regarding the ZXSC300 ic chip made by Zetex using an output
Schottky diode and output cap in the typical max brightness solution
application as shown on the data sheet and using around 100uH inductor.

The question sounds a little complex, but it's really quite simple.
With the usual circuit, the battery is connected via a switch to the
circuit and power is applied to the circuit when the switch is turned
'on'. The inductor charges up to Imax and the sense resistor senses
this and turns the transistor off. The cycle repeats.
Imax in our application is 1.5 amps, but the typical discharging
current is less then that, being about 500ma or less because of
the nonlinearity of our inductor. In other words, the max 
discharge current is less then 500ma always.

Now here is the catch:
After some time, the input switch is turned 'off' in order to
turn the circuit off and turn off the LED on the output.
Turning the switch 'off' disconnects the battery from the circuit and
so the power supply input to the ciruit now looks like a high impedance,
when before the switch was opened the input supply looked like a
very very low impedance.

My question is this:
If the inductor happens to be charged up to Imax close to the very
moment when the switch is turned off, at the instant the switch is
turned off the battery (+) side of the inductor starts to drop negative
in an effort to dissipate it's energy through the output diode
(which the other inductors' lead is connected to) and LED.
Since this inductor lead is also connected to the chip's positive
power supply pin, it's very possible that this pin gets driven
negative for the short time the inductor dumps its' energy for
the last time. Now since this pin drops negative, it brings into
question just what is on the input of the chip internally.
Is it a reversed diode, and if so what is the non repetitive 
current rating?
The max negative spec of the ZXSC300 chip is -0.3 volts, but it's
obvious from examination of the typical apps shown on the data sheet
that if there is no internal clamping diode almost any inductor
would drive this pin more negative then that and would mean
sometimes when the circuit is switched 'off' this would occur at
least once while the inductor discharges. You see what i mean here?

This raised the question of whether or not an input capactor
or even a diode clamp of some kind across the input power
supply pins will be required to insure
the safe operation of the ZXSC300 chip over a reasonable period 
of time. Of course adding an input cap increases the pc board
space requirement, and so it becomes a fairly important design
decision for our application, which requires extremely small size.

Thanks much.

Sincerely,
Al


(end quote)


----------



## remuen (Jan 24, 2002)

Hello MrAl

Thanks for checking the shopping list and the additional explanations.
I will look around if these parts are also available here in Switzerland.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
As a side note, for running one or two standard LED's in parallel
i think almost any very small inductor would work.
Al*<HR></BLOCKQUOTE>

For only a couple of LED's I intend to make a smaller booster (LT1932?) even it will not be as optimized as your Zetex design and have a worse efficiency. But I also want to have a bit of fun



. 
A smaller board will also fit in flashlights and headlights where one has even less room than in the Minimag.

I will for sure use the Luxeon Star too and then I don't want or better am not able 'to reinvent the wheel again' (hope you understand this simple translation). 

Therefore I plan to use your Zetex booster for driving the LS - if I'm still allowed to use your design after all my criticism



. 

Btw, you and Duggg always explained and convinced me why you did this an that in this or that way .... Only if one asks and claims one will get an answer and explanation! And that's the way I learn most of all this stuff. It's the same as in the school: If your are just sitting there you will not learn as much as when you are discussing, asking, claiming, trying ...


----------



## ElektroLumens (Jan 24, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hi there,

Wayne:
0.3 ohms would take the eff down a lot more then 0.1 ohms would.
We are typically obtaining about 0.05 ohms or less by winding our 
own inductors on toroid cores. If you want to experiment to
find out the effect of having a higher series resistance in
your coil, simply add one or two 0.1 ohm resistors in series 
with your coil and take efficiency readings. Note the difference
with the extra resistors and without them.
Also, 22uH might not be enough, but it's worth a try i guess.
*<HR></BLOCKQUOTE>

Hello Al,

I suspected that the resistance was a problem. Thanks for the reply, even though it's not specifically related the the zetex project. Thanks for the update on the parts for the Zetex chip. I do hope to construct one of these Zetex regulators, because they are so small, should work great in the Mini Mag. You guys are doing a great job here.

I did receive the samples from Coiltronics, and I tested the resistance. I could not get a reading with my DVM, so the resistance must be really low. They are rated at .06 ohms resistance. The MAX757 calls for the 22uH, and since the resistance was so low with these inductors, that is what I ordered. I hope 22uH is sufficient. Anyway, when I put this regulator together, I'll see what improvement, if any, I get. The Coiltronics part # is: CTD03316P-223. They sent me 5 free samples. They do have higher inductance values, and it might be worth your checking into these higher quality inductors. They seem to be a better quality than the Miller inductors? At least the resistance is much lower.

Here's the web page for the Coiltronics inducors:

Wayne
Inductors, Inc.


----------



## papasan (Jan 24, 2002)

i've tried one of the 100uH coilcraft inductors with the zetex circuit...it's about 50% bigger than the jw miller and the efficiencey went down a little...but perhaps a 68uH would work better...

i recieved the miller beads today but i've drivin around to several different places looking for enamel coated wire and came up short...so i'm taking some 24guage hook-up wire and dipping it a few times into some nail polish...let you know how it comes out...


----------



## papasan (Jan 24, 2002)

part one of the bad news...the nail polish didn't work out very well...i couldn't get a nice even coat and when i tried to wrap the magnet it seemed to me that too much of the insulation scraped off...perhaps i didn't wait for it to dry long enough...

parts one and two of the good news...another radio shack near me had the 3-pack of magnet wire...and 22 gauge wire fits in there just fine (could probably go to 20 gauge, plenty of room left)...

part two of the bad news...my efficiencey stills bits the big one...i have no idea how i'm doing so poorly compared to duggg's readings...i'll post a picture in a minute, perhaps someone could notice any shortcomings...

here's my chart so far for this run...


```

```

here's some pics...


----------



## **DONOTDELETE** (Jan 24, 2002)

One thing that stands out is that those current sense resistors appear to have a tolerance of +/- 5%.

You can't measure efficiency to an accuracy of 1% unless you use 1% resistors.

Try switching resistors and see if there is any difference. I bet there will be.

Meanwhile, I'll hook up my amber LS and do another M2310 test tomorrow. You would think the amber LS would produce higher efficiency results, since the required output voltage is closer to the input voltage.


----------



## MrAl (Jan 24, 2002)

Hi there papasan,

Strictly speaking, you've got a total of 
THREE turns on your core, not TWO.
Technically, the number of turns is determined
by the number of times the wire goes
through the CENTER of the core (toroid),
not how many turns appear on the
outside of the core.

You'll notice your wire goes through
3 times, therefore you have 3 turns.

Now i dont know if this is what Duggg used,
but i tested mine with exactly two turns.
If this is in fact what Duggg used, then
i'll have to go back and retest mine with
3 turns.

Also, you might try calibrating your resistors by
running a known current of around 1 amp and measure
the voltage drop across it. You can then determine
the value of the resistor to a closer tolerance.
If your interested in matching your resistors to
a very very tight tolerance, i'll post the procedure
here too, but the matched resistors are only of use
with the other method.

Good luck with it,
Al


----------



## **DONOTDELETE** (Jan 24, 2002)

Actually, a turn is just that; one complete revolution around the cross section of the core. If you don't go all the way around, then you have a fractional turn.

So strictly speaking, papasan's inductor has 2.37 turns, and is the same number of turns as the one showed in the picture I included several pages ago.


----------



## papasan (Jan 24, 2002)

in wrapping the core i just followed the picture duggg had taken...i was wondering about the two and a half turn thing too...

5% is the best i've found so far, the decent surplus store is a ways off so i haven't checked them yet...

the problem with calibrating to a known voltage and known amperage is that i don't have such a source...i don't have a lab power supply or a variac or anything, just batteries and 'wall warts'...any ideas on something sitting around in an average home to calibrate the resistors on?...

if the readings are off because of resistor variance then this inductor is just as efficient as the jw miller 68uH coil as the readings were very similar...


----------



## **DONOTDELETE** (Jan 25, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*I've drivin around to several different places looking for enamel coated wire and came up short...so i'm taking some 24guage hook-up wire and dipping it a few times into some nail polish...*<HR></BLOCKQUOTE>

Another option is to visit your local Radio Shack and get their magnet wire set, #278-1345, $3.99. You get 40 feet of #22AWG, 75 feet of #26AWG, and 200 feet of #30AWG.

The #22AWG should work as well as the #24AWG. The big question is, what do you do with 200 feet of #30AWG?


----------



## papasan (Jan 25, 2002)

i was thinking that enamel coated wire for the isense resistor would work out better, it wouldn't short and be a little stronger...but my local radio shack only had some 30gauge that wasn't enamel, it was a thicker coating...


----------



## **DONOTDELETE** (Jan 25, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*if the readings are off because of resistor variance then this inductor is just as efficient as the jw miller 68uH coil as the readings were very similar...*<HR></BLOCKQUOTE>

That was certainly not the case with me. The 68uH inductor was much less efficient, 3-5% as I recall. I'll run another test this weekend using that inductor as well.


----------



## **DONOTDELETE** (Jan 25, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Well duggg according to that definition you would say that the typical ferrite bead with a single, straight piece of wire going though the center and out the other side without curving back would have only one half of a turn? *

Well, you're not describing a toroid. Instead, you're talking about the inductance of a long, straight wire, a portion of which is surrounded by a relatively high permeability material.

*Im not really sure either where you got that extra 0.37 of a turn from *

The M2310 has a length of 7.29mm and a cross sectional perimeter of 19.71mm; the length of the hole is 7.29/19.71 = 0.37 turn.

*When i talk about turns, i talk about the electrical number of turns, not the actual number that may be counted from the outside of the phyiscal construction. See, when you refer to the number of turns as the number of turns through the core center you then have a way to calculate transformer ratios and increases in inductance with added turns and such.*

Certainly such an approximation is useful when calculating ratios, as (A+x)/(B+x) is pretty close to A/B when A,B >> x, but it would produce horribily inaccurate inductance results if the number of turns is small.

*The reason for this is because the wire though the center has great influence on the magnetic field, whereas the wire outside the center has very little effect on it.*

Nonsense. Inductance of a toroid is proportional to the square of the number of current _loops_ surrounding the cross section. Every millimeter of each current loop contributes to the total magnetic flux. If you don't believe me, see what happens to the inductance of a toroid when the loops are wrapped tightly around the inner diameter, but loosely around the outer diameter---it goes way down, as the effective permeability plunges due to the large portion of each loop now surrounded only by air.

*As a simple example, consider one turn (or one half turn) of perfectly straight wire going though the core, with an ac current flowing through it. Then consider a second wire of the same gauge also going though the center; this creates one primary and one secondary.*

Again, what you are describing are two long, straight wires in parallel to one another. The effect you describe would be true regardless of whether this simple coupler was surrounded by ferrite, or free space.

*In fact, the only reason for putting any wire on the outside at all is so that you can
loop the wire around to create more turns.*

What!? The windings on the outside of a toroid are vital to the electromagnetic shielding which are a feature of toroidal transformers. In fact, a tightly wound toroid confines the entire magnetic field to the core itself---there's no field outside the core. Nor in its center, for that matter.

*Note also that you could wind 100 turns around the outside of the core without going through the center once, and you would have exactly zero turns, certainly not 100 *

Now you're describing a third beast, a ferrite rod inductor, and the number of turns around the rod would most certainly be 100, not zero!





See, the bead core's unique shape can make it behave like a straight wire, a rod inductor, or a toroid inductor, depending on the core's aspect ratio, the number of turns, and how closely they are spaced.

*Did you get one of those really flat cores that are roughly about 0.1 inch thick and about 1/2 inch diameter with a small hole
about 1/16 inch in diameter?*

No, I didn't. I definitely would have tested something that large, and such a washer shape might lend itself well to flashlight apps. Did you happen to test it?<HR></BLOCKQUOTE>


----------



## **DONOTDELETE** (Jan 25, 2002)

Here are some results from several amber LS tests I performed earlier today. As usual, all tests were performed with a pair of freshly recharged AA NiMH cells.

1. M2310 bead core with 2.37 turns: 86.9%


```

```

2. M9711 68uH commercial inductor: 80.5%


```

```

On a lark I also managed to squeeze 3.43190975 turns (4 inside turns to MrAl



) of #24AWG around the smaller M2308 bead core, and preliminary results indicate efficiency around 87.3%, which is very encouraging!


----------



## MrAl (Jan 26, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Actually, a turn is just that; one complete revolution around the cross section of the core. If you don't go all the way around, then you have a fractional turn.

So strictly speaking, papasan's inductor has 2.37 turns, and is the same number of turns as the one showed in the picture I included several pages ago.*<HR></BLOCKQUOTE>

Well duggg according to that definition
you would say that the typical ferrite
bead with a single, straight piece of wire
going though the center and out the other
side without curving back would have
only one half of a turn? 
Im not really sure either where you got that
extra 0.37 of a turn from 

When i talk about turns, i talk about
the electrical number of turns, not the
actual number that may be counted from the
outside of the phyiscal construction.
See, when you refer to the number of turns
as the number of turns through the core 
center you then have a way to calculate
transformer ratios and increases in inductance
with added turns and such. The reason for
this is because the wire though the center
has great influence on the magnetic field,
whereas the wire outside the center has 
very little effect on it. As a simple
example, consider one turn (or one half turn)
of perfectly straight wire going though the
core, with an ac current flowing through it.
Then consider a second wire of the same
gauge also going though the center; this createsone primary and one secondary.
Now short out the secondary and you effectively short
out the 'transformer' which would draw 
heavy current on the input side. Now 
remove the second wire from the center and
place part of it on the outside of the toroid
close to the surface, without going through
the center. Now again short out the second
wire by looping it and connecting the 
ends together, and note there is no longer
a heavy current drawn on the input side.
In other words, the wire on the outside
has very effect, so only the turns that
go through the center count. In fact,
the only reason for putting any wire on
the outside at all is so that you can
loop the wire around to create more turns.
That is why the number of turns is usually 
referred to as the number that actually go
through the center.

Note also that you could wind 100 turns around
the outside of the core without going through
the center once, and you would have exactly
zero turns, certainly not 100 

One other thing:
Did you get one of those really flat cores
that are roughly about 0.1 inch thick and
about 1/2 inch diameter with a small hole
about 1/16 inch in diameter, and if so,
did you try testing it in our circuit?

When i set up my next test, i'll include 
a test with an 'additional' turn on the small
ferrite bead and see if it boosts the
efficiency.

Take care for now,
Al

ADDED LATER:
Ok i reviewed my personal notes and
found that i had already tried 1, 2 and
3 turns 'through the center'.
The 2 turns 'through the center' gave me
the highest eff readings (which looks like
only one turn on the outside of the core).


----------



## MrAl (Jan 26, 2002)

Hello again,

Duggg:

It's up to you duggg how you want to define
how to count the number of turns, but i'll
have to stick to the electrical definition 
which is the number of turns that actually 
go though the center.

Take care,
Al

Added later:
I tested the flat core, and i found that 
it brings the efficiency down to less then
70 percent. I would have tried more turns,
but the hole in the center only accepts
3 diameters of wire though it. Not only 
is the eff bad, it only allows about 100ma
to flow in the output with 2.4 volts input.

I also tested the input cap potential problem.
Without any input cap at all, the chip's 
voltage DEFINITELY goes negative SOMETIMES
when the input switch is turned off and 
the batteries are disconnected. It happens
maybe once every 10 times. I theorized that
this could happen if the switch was turned 
off and the inductor happened to be fully
charged (or nearly so). It turns out that
it is really true. The pulse is quite
short, but is in fact present. This poses
a potential problem for the chip if the
chip has to see that negative voltage/current
unless the chip can absorb that energy
without harm. This is what im waiting for
the reply from Zetex for. I had gotten
an email stateing that the question would
have to be forwarded to another dept, so
it could take another few days. Untill then,
it's hard to say how much input cap will
absorb all the energy, but with 100uf the
negative pulse never appears at all,
but rather ramps down to about 0.7 volts.
I suspect a smaller cap will work too,
as the inductor then has the job of
supplying all of the power without the
aid of the battery, so it will have about
3.5 volts across it which will make the 
inductance go down quite a bit meaning
if will be able to supply less energy.
An external reverse connected diode wont 
really work either, because it's drop will
be higher then 0.3 volts, unless another
Zetex 2000 diode is used. I myself prefer
an input cap. 
The final decision can only come after we
hear back from Zetex. If they already 
have an input diode and that diode can
handle the energy from the inductor, then
there is no problem. I suspect that with
some inductors (not the ones we have been using)
there will be much more energy available
during turn off. Most of the store
bought inductors produce a more linear 
response, so they would be capable of 
producing the most damage.


----------



## papasan (Jan 26, 2002)

i think i've figured out where my efficiencey loss is coming from...

thinking about MrAl's concerns on harmful negative voltage it occured to me that since i was jumping the shutdown pin with the Vin it too was recieving negative voltage and therefore shuting down until the voltage came back up...turning on and off quickly through the coil cycle...oops...

so i made up a new board (actually had it anyways so i could do the resistor test for MrAl) and i get about 87% now...been using my batteries playing around with the white LSes i got today so a full run will have to wait...

i'm not 100% sure that this is the issue because it's a newly soldered board and i'm using a white 'lo-dome' luxeon instead of teh normal amber 'high-dome', but i'm fairly certain...


----------



## **DONOTDELETE** (Jan 27, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*i get about 87% now*<HR></BLOCKQUOTE>

Yay






I did a complete run with the M2308 this afternoon and again got 87.4% and a run time of 190 minutes. That's good enough for me!


----------



## MrAl (Jan 27, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
*
thinking about MrAl's concerns on harmful negative voltage it occured to me that since i was jumping the shutdown pin with the Vin it too was recieving negative voltage and therefore shuting down until the voltage came back up...turning on and off quickly through the coil cycle...
*<HR></BLOCKQUOTE>

Yes, i forgot to mention that 

There are two very bad points here:
1.
The coil will ALWAYS be at or near max current when the enable pin shuts the chip down,
meaning, just like you said, the circuit oscillates and the (+) supply pin sees
a negative spike EVERY cycle!!
2.
This isnt something particular to the 310 chip, as the 300 chip will also shut
down; just at maybe a slightly different voltage. Think of the 300 chip as a 310
chip with an internally set shut down set point.

Since this is going to happen every cycle, it could be very dangerous to the chip 
when the battery starts to run down. The only way to specify an input cap 
though is to find out what the equivalent input to the ic chip(s) are, unless we
assume it will cause damage and then go with the minimum capacitance that will
prevent ANY negative voltage from ever appearing at the (+) terminal of the 
chip during turn off or low battery hyper oscillation (by the way:
the oscillation itself might not be possible to stop with a reasonably
sized capacitor, so we have to deal with it).

As an interesting side line, im sure this problem isnt particular to our 
zetex circuit here, but plagues other converter circuits as well.

The best solution awaits Zetex's response. I hope they say that the
internal diode will withstand the reverse kick from the inductor 

In the mean time, i'll do a circuit simulation of the circuit at the
time of turn off and see what the minimum input cap would look like
in order to prevent the input from going lower then -0.3 volts.
One thing we have going for us here is that with some input cap
the inductor has to expend energy in order to discharge it by
approx 2 volts, or maybe a little lower then that, before it can
pull it negative, if in fact there is enough energy left for that.
I guess with a lower input voltage though this level isnt quite 
accurate, but then there will be less energy left in the inductor anyway.
I'll post results here too.

Good luck with your LED circuits,
Al


----------



## papasan (Jan 27, 2002)

here's a short run with a 47uF El cap...


```

```

average eff of 86.37%...so i lost about .8% by using this cap over no input cap...not bad, i think it'ld be a good idea for using alkaline batteries, so i'll prolly run with it like this...


----------



## papasan (Jan 28, 2002)

okay...a partial run...kinda busy lately, work has picked up alot...

2 1600mAH AA NiMHs and a white LS with optics...


```

```

average eff of 87.17%...not too shabby...i'll put an input cap on that board and check it out like that too...


----------



## MrAl (Jan 28, 2002)

Hello again,

Some interesting developments with the Zetex 300 & 310 circuits:


It appears that an input cap of 15uf (or higher) is sufficient
to swamp any negative turn off transients during battery disconnection.
The rated ESR of the cap should be 2 ohms max. Any higher ESR leaves
room for the negative transient to go too low to meet the specs of
the chip.

The simulation was done with 0.7v input and 300uH inductor with various
output capacitances. This simulates worst case scenarios duing turn off.
With a little higher input voltage, like 1.0v, 10uf works ok, but that
doesnt cover the circuit when the battery goes lower then that, so
15uf is the recommended minimum capacitance.

There was an interesting development that came about when doing the 
simulation, and that was that there is not only a negative transient 
on the input side of the circuit when the battery is disconnected,
but there is also a negative transient on the transistor collector
side of the inductor as well. There is more then just a single transient
though, it's actually an oscillatory wave that, if allowed to go undamped,
will go as low as -5.0 volts or lower, causing the transistor's collector
base junction to forward bias and cause apply about -4.3 volts to be
applied to the current sense input pin of the ic chip. Since examination
of the voltage waveform shows this waveform to be clamped to approx 0.7
volts, it is assumed that this pin's equivalent reverse voltage input also
looks like a diode. The approximated maximum current that appears 
to flow through the 'diode' is about 2ma, which isnt that high, but
it's not possible to determine the tolerance of this 'diode', or
even if it is in fact a diode at all without contacting Zetex again,
because the only published spec is -0.3 volts minimum.
In the mean time, i have found that a standard 1N4148 diode connected
across the transistor's collector to emitter swamps out ALL the oscillation,
and due to the forward bias of the collector to base junction voltage drop
the minumum negative voltage that the sense input pin ever sees will be
-0.1 volts to 0.0 volts, which is well within Zetexs' spec. The diode is
to be connected between collector to emitter with the cathode (banded) end
connected to the transistors' collector and the anode connected to its'
emitter. The diode will conduct only when the circuit is turned off.

As as side note, some MOSFET's have this diode integrated with the transistor already
to act in apps that have inductive loads.

Just to recap:

1. 15uf input cap required with maximum ESR of 2 ohms.
2. 1N4148 diode connected across transistors collector emitter junction with
the cathode connected to the transistors' collector and the anode connected
to the emitter.

Now it's entirely possible that the circuit will perform for years without
the diode, and even without the cap (i have been running my circuit now
without the diode, albeit for not that long of a period of time yet) but 
it should be noted that leaving either component out of the circuit will
subject the ic chip at one time or another to specs that are outside of
Zetexs' recommendations.
In other words:
LEAVE OUT AT YOUR OWN RISK 

Good luck,
Al


----------



## remuen (Jan 28, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Hello again,

Some interesting developments with the Zetex 300 & 310 circuits:


It appears that an input cap of 15uf (or higher) is sufficient
to swamp any negative turn off transients during battery disconnection.
The rated ESR of the cap should be 2 ohms max. Any higher ESR leaves
room for the negative transient to go too low to meet the specs of
the chip.
....

Just to recap:

1. 15uf input cap required with maximum ESR of 2 ohms.
2. 1N4148 diode connected across transistors collector emitter junction with
the cathode connected to the transistors' collector and the anode connected
to the emitter.
....
*<HR></BLOCKQUOTE>

Hi MrAl

It's awesome how you are examining every single part and possible problem and trying to find a solution. How much time do you spend for all this? 

And a question not to be answered: Why does not Zetek give all these recommandations on their datasheet?


----------



## MrAl (Jan 28, 2002)

Hi there again,


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by remuen:
*Hi MrAl
It's awesome how you are examining every single part and possible problem and trying
to find a solution. How much time do you spend for all this? 
*<HR></BLOCKQUOTE>
I spend a varied amount of time on this project, from one hour to about 
three hours in one 'sitting', depending on what im looking for and what comes up.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*
And a question not to be answered: Why does not Zetek give
all these recommandations on their datasheet?
*<HR></BLOCKQUOTE>
The answer to this and many other amazing questions can be answered very simply:
The people who design some things dont have to use them. Sometimes a few tests are done
and that's that. They arent building flashlights, they are building chips.
We are building flashlights, therefore we pay more attention to the final details
because only we are very concerned about getting together a flashlight that is
reliable. They are only concerned about the final details of the chip itself. If it 
works, ship it 

Now here's another very interesting question:
How can you spec -0.3 volts minimum input to an ic pin and then find -0.5 volts or
less riding on that pin and expect to get long life out of a chip, even after using
the recommended circuit?
For answer, see above 

There are a couple good reasons:
1. They have an internal static discharge diode that has a forward drop of about
0.7 volts and they absolutely dont want to see that diode conduct, ever, except for
static discharge which is assumed to be fairly low current, so they spec the voltage
to always be 0.4 volts higher so that you dont use it in a circuit that will cause that
diode to conduct on a regular basis.
2. They made a mistake on the data sheet and the real min is 0.7 volts or so.

It's too bad i havent heard back from them yet. Zetexs' 'Principle Device Engineer'
thought it was a good question though, and didnt have the answer yet, so we have to 
wait for the answer. After reviewing the data sheet spec of -0.3
min and seeing that the internal diode (if it is a diode) drops at least 0.5 volts
in forward conduction mode, the only possibility is that either they made a
mistake on the data sheet spec or they dont want this diode conducting.
If the latter is true, then their data sheet 'reference' designs are also at fault,
so it will be interesting to see what they have to say about it.
It's clear from the simulations that the input does go negative because of the choke,
and if it were not for their internal diode (that has to be rated at least 0.7 volts
forward)it would go VERY VERY negative, like -35 volts or something. Since it doesnt go
THAT negative in real life, there must be something limiting it -- hence the diode theory.
Since this can occur in any one of their reference designs, i would bet they didnt do
much testing on the turn off phenomenon.

To us, all this doesnt have to matter that much, as 15uf and a 15 cent diode will
make sure it never bothers us again.

Now lets take a quick look at the possible answers they might give:
1.) It's an internal diode that drops 0.7 volts forward and they dont want it conducting.
2.) It's an internal diode that drops 0.7 volts forward and they dont mind if it conducts
and they made a mistake on the data sheet by spec'ing -0.3 volts min, as long as it
doesnt conduct more then 10ma dc current, with a non repetitive current of 1 amp
for 1 ms.

Now if case (1) is true then we need the input cap and external sense pin reverse 
diode.
Now if case (2) is true then we dont need any extra parts, for this reason alone,
but there are other reasons for using an input cap that are not related to the 
negative spike problem. A second very good reason is to stop the circuit
from shutting down prematurely when the battery voltage drops causing
oscillation which will at the very least cause premature led dimming
as the batteries die down. A third reason is to promote longer life from
batteries that dont like high currents drawn from them, and even ones that do
to a certain extent also. It's only about 6% difference here, but that 6% is
equivalent to a 6% increase in efficiency.

Next:
After testing the circuit for these turn off transient problems, i realized
that without a storage scope the problem cant be studied as well as i would
like too, or at least without building a turn-on/turn-off circuit that will
cycle the circuit on and off repeatedly at about 10 to 100 Hertz. This would
allow me to inspect the turn off transient a bit closer at the sense input
pin, as this is the hardest to see while turning the circuit on and off
by hand at an irregular frequency. Also, this would allow me to test the
circuits' ability to withstand a multitude of turn off's and see how it
holds up. Within a week's testing time, i could simulate a lifetime of
running the circuit, cycling it some 200,000 times on and off.
Im not really sure if i can get to do this or not, but it sure would
be interesting. I'd hate to lose a chip doing it though, and one chip
might not be enough to be conclusive; rather requiring 1000 chips or more
all cycling 24 hours a day 7 days a week for a week or two under conditions
of elevated temperature.

One other thing come to mind here:
I dont remember seeing any other converter
circuit without an input bypass capacitor,
could it be they simply forgot to include it
on the data sheet?

I cant wait to hear back from Zetex. As soon as i do, i'll post the 
answers. Untill then, to partly quote your own entertaining quote:

Fly with the eagle or scratch with the chicken ->
Either cover all the bases or sit back and hope it continues to work well.


Good luck with it,
Al


----------



## papasan (Jan 28, 2002)

so what are the characteristics of a 1N4148 diode?...looking for an SMD alternative but not sure what i'm looking for...

all i know about diodes is they're supposed to block power flow in one direction =)...and that schottky diodes are better because they lose less power...


----------



## MrAl (Jan 28, 2002)

Hi papasan,

Im pretty sure the number is almost the same
as 1N4148 with a letter suffix. If you
still cant find it, let me know.
These diodes are pretty tiny anyway
even though non SM. I would bet we could
tack solder one to the existing copper 
traces and do well enough.
1N4148 is a high speed low current 
silicon diode.
Cant get away with a 1N4001 here because
the diodes capacitance might be too large
and the diodes switching time not fast 
enough.

Al


----------



## **DONOTDELETE** (Jan 28, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*Within a week's testing time, i could simulate a lifetime of running the circuit, cycling it some 200,000 times on and off.
*<HR></BLOCKQUOTE>

Whoa, whoa, whoa! Enough already. All this overanalysis is getting to be quite a drag.

This is a six dollar flashlight circuit, not a six million dollar spacecraft circuit.

The concern about negative voltage---HELLO, under normal conditions the battery is STILL connected across both the + and - pins of the chip. What has more oomph, a little inductor or a big battery? Are you really suggesting that the battery reverses its voltage upon every inductor discharge? Come on.

Now, you DO have a point when it comes to the batteries being suddenly disconnected from the circuit. There, the chip has no choice but to absorb the final discharge pulse.

But, chances are good the engineers at Zetex had a sneaking suspicion that an inductor might get hooked to their chip, and that maybe the battery might get disconnected somehow---so they probably added the necessary protection. 

The presumption that Zetex never actually built the circuit they published is unfounded, and the fact that they "neglected" to include an input cap shouldn't be viewed as an oversight, but perhaps a feature.

Nevertheless, we can keep adding components to the circuit until the cows come home, as each new component results in weirder and weirder waveforms at all the various new junctions, suggesting catastrophic failure is imminent.

Or, we can build the original Zetex circuit with its minimum of external components and actually get something that will fit in the head of a MiniMag.


----------



## MrAl (Jan 29, 2002)

*
Whoa, whoa, whoa! Enough already. All this overanalysis is getting to be quite a drag.
*
I knew you were going to like this information Duggg <chuckles>.

*
This is a six dollar flashlight circuit, not a six million dollar spacecraft circuit.
*
Sure, but none of us want our flashlight failing prematurely either.
In some situations if your flashlight fails you might as well be
in deep space, or deep something or another 

*
The concern about negative voltage---HELLO, under normal conditions the battery
is STILL connected across both the + and - pins of the chip. What has more oomph,
a little inductor or a big battery? Are you really suggesting that the battery
reverses its voltage upon every inductor discharge? Come on.
*
Yes your right, and i think the batteries will have enough 'oompth' left
in them to absorb the transient, at least while they are still in the circuit,
even when run down. The internal resistance is probably still low enough to
constitute a workable circuit. Im not willing to bet on it myself though.
However, the other problem surfaced while exploring the original problem with
the battery disconnection. This problem may occur every cycle even during
everyday use without disconnecting anything at all and with a full battery.
As you probably know, an inductor and capacitor create a resonate circuit
which can self oscillate when excited by a square wave. Our circuit has
a bit of this high frequency oscillation also, which occurs when the
Schottky diode stops conducting while the transistor is still off.
This oscillatory response causes the collector of the transistor to
go very low every cycle, which puts a negative pulse on the sense input pin.
The diode is very small, very cheap, and does the job of damping any 
unwanted oscillation, hence the addition of the diode.
As you also would have read, if you dont believe these parts are
necessary, then dont use them; but dont blame me if one day the 
light doesnt turn on for no reason at all.

*
Now, you DO have a point when it comes to the batteries being suddenly disconnected
from the circuit. There, the chip has no choice but to absorb the final discharge pulse.

But, chances are good the engineers at Zetex had a sneaking suspicion that an
inductor might get hooked to their chip, and that maybe the battery might get
disconnected somehow---so they probably added the necessary protection. 
*
Well, if you dont mind tossing the dice every time you turn your flashlight off,
then by all means feel free to do so.

See, in my explanatory post (or at least i thought it was) i tried to
explain how you couldnt have both unless something was wrong with the
data sheet. It cant be both ways: either they must allow lower then 
-0.3 volts input or they overlooked something. The only other possiblity
is that they are using a low current Schottky on the input and it's 
being overdriven to -0.5 volts or a little lower.

*
The presumption that Zetex never actually built the circuit they published
is unfounded, and the fact that they "neglected" to include an input cap
shouldn't be viewed as an oversight, but perhaps a feature.
*
I never said they never tested it, just that maybe they didnt test it
enough, and their tests were not directed at understanding the turn off
transients and their effect on the long life of the ic chip. What leads
me to think this comes from their data sheet ambiguity.

But perhaps they did, and they have that info somewhere and they will disclose
it soon. Untill then, its a bit of a gamble.
Also, common sense tells me that inductive circuits always have kickbacks
that must be controlled or else they fry the circuit. You know what happens
when you charge up an inductor with a battery through a switch and then
open the switch: you get a tremendously high (or low) voltage spike who's
amplitude is limited mainly by the remaining circuit impedance. Since the
impedance of an open switch is very very high, so is the voltage spike.

*
Nevertheless, we can keep adding components to the circuit until the cows
come home, as each new component results in weirder and weirder waveforms
at all the various new junctions, suggesting catastrophic failure is imminent.
*
I have to disagree, as the waveforms become clamped to known safe voltage
levels as they become much more controlled and predictable. But i have
a feeling the cows are now almost in the barn 

*
Or, we can build the original Zetex circuit with its minimum of external
components and actually get something that will fit in the head of a MiniMag. 
*
Yes it will fit once, and then again when we have to replace it with a new
circuit with a diode and input cap 
The extra cap shouldnt be too large and
the diode certainly wont take ANY more
space.


In closing, my feeling on this is that they made a mistake on the data sheet.
You have to realize that although Zetex makes some of the best 
parts in the world, their data sheets and specs on those parts
are probably about the worst in the world. Unfortunately for
us, we have to go by what they publish, but when there is a
contradiction in their published data all we can do is ask and
hope for a reasonable answer.

Good luck with your LED circuits,
Al


----------



## **DONOTDELETE** (Jan 29, 2002)

Woohoo! This afternoon I actually managed to fit the Zetex driver and an LS inside the head of a MiniMag.

Can't wait til it gets dark and I can really see the beam in action. It's bright!

I took pictures during the modification process which I'll be posting on the web over the next few days.


----------



## MrAl (Jan 30, 2002)

Hi again,

Sounds cool Duggg, i want to do that too!
Now that i've traded a Dorcy LED light for
a 2 x AAA Minimag (not the 2xAA one) im
thinking about fitting that 2 AAA Minimag
with a Lux Star next  he he
This is a reallllllyyyyy small flashlight
so it's going to be a challenge for sure!

Take care,
Al


----------



## MrAl (Feb 3, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I'm wondering if anyone has implemented the max-brightness single-cell LED driver circuit described at http://www.zetex.com/3.0/pdf/ZXSC300.pdf 

Although the circuit is designed for the white Nichia NSPW500BS, I wonder if it would drive an amber Luxeon Star with R1 set to 0.04 ohm, which should pulse the LED at 475 mA.*<HR></BLOCKQUOTE>

So Duggg, 

Does that answer your question?



--Al


----------



## **DONOTDELETE** (Feb 3, 2002)

Hehe, I always laugh when I read that first post of mine.

With Rsense set to 0.04 ohm, the amber LS wouldn't be very bright





But, the question certainly got the ball rolling, didn't it?


----------



## remuen (Feb 4, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*I'm wondering if anyone has implemented the max-brightness single-cell LED driver circuit described at http://www.zetex.com/3.0/pdf/ZXSC300.pdf 

Although the circuit is designed for the white Nichia NSPW500BS, I wonder if it would drive an amber Luxeon Star with R1 set to 0.04 ohm, which should pulse the LED at 475 mA.*<HR></BLOCKQUOTE>

Duggg, MrAl, mercator, papasan and all others worked on this project

First I was wondering what you guys are doing here. Next I was a bit smiling about it. And then I began to understand ...

After all I see you've done a terrific job here in the CPF!! And I have learned a lot about what to consider when designing a booster circuit. 

You've put all your knowledge, your knowhow, a lot of your time and energy into this puplic project - not only for you but also for all of us other CPF members. Thank you very much!


----------



## papasan (Feb 5, 2002)

so any word back yet from zetex on their architecture and the effects of negative voltage upon the chip?...


----------



## MrAl (Feb 7, 2002)

Hello again,

I've got some good news regarding the Zetex circuit ( + some responses below ).

I finally heard back from Zetex regarding the transient
spikes found on one or more pins when the battery is
suddenly disconnected. The Zetex applications engineer
assured me that there are special clamping diodes on
both pins, and that the diode connected between the 
power supply pin and ground can absorb the remaining
energy in any 'reasonably' sized inductor used with
this circuit even without an input cap connected between
the (+) supply terminal and the (-) supply terminal.
He said that the -0.3 volt min spec should be taken
as a purely DC quantity, so that constant voltages
less then this shouldnt be applied to the chip, while
short spike-like transients will not cause damage to
the chip.

This of course means we have confirmation that we dont
need an input cap based on this reason alone
(although we may wish to use one anyway for the battery
reasons), or the reverse connected 1N4148 diode across
the transistors' collector to emitter.
You may wish to take efficiency measurements with various
input cap sizes and ESR ratings and compare.
You may also wish to test battery life with and without
various input cap sizes and ESR ratings as well and
compare.

Summary:
1. Absolutely dont need the diode.
2. Dont NEED the input cap, and this is now optional.

If you DONT use any input cap at all, keep the battery leads as
short as possible, as any extra lead length contributes to the
batteries' series resistance and inductance and affects the
undervoltage turn off characteristic of the circuit very markedly.


Duggg:
>>>
Hehe, I always laugh when I read that first post of mine.
<<<
Yeah me too, but mostly because 
here we are 4 months, 32 pages, and almost
500 posts later to answer that one little
interesting question  he he

papasan:
(see above) 

remuen:
Your welcome! It turned out to be a very
interesting endeavor for us all. Im
sure we all learned a great deal in this
discussion. I hope we came up with something
that many people will be happy using, and
im pretty sure we did.


Good luck with it,
Al


----------



## **DONOTDELETE** (Mar 8, 2002)

I have been reading this thread on the Zetex Single Cell LED Driver today with some interest. I am new to this forum, but certainly not new to the Zetex ZXSC300 and the Zetex ZXSC310 part. These constant power DC



C convertors are fantastic. Zetex will sell the products only in full reel quantities. (Certainly this is no problem if you have a marketable product.) But for you hobbiests and prototype makers, you can get them in single unit quantities from DigiKey. Zetex says that that is why they hire distributors such as DigiKey. You will find that they will cut a Zetex reel of product and append the Zetex ZXSC300 or ZXSC310 part with the suffix CT for cut tape. 

As for the Luxeon Star question and the Lumileds question- the answer is YES .. the part is the killer chip for LED driving. The part number is means Zetex Single Cell LED driver. The ZXSC300 part is the intital offering, and the Zetex ZXSC310 variant adds an enable pin so that you can put the thing into a sleep mode, or even use brightness control. 

If you want to make a great little evaluation project, Zetex even lays out the PCB for you on their datasheet. I would suggest you stick with the particular Schottky and Transistor that they recommend because they are well matched to the part. As for the magnetics- their datasheet lists a few options on page 6 of the '300 datasheet. I don't know about the Zetex ZXSC310 datasheet off the top of my head.

As I understand it.. the whole point of the product was to power a white LED from a single cell.. hense the name. It differs from other types of products out there in that it is a CONSTANT POWER convertor, and the Zetex part will make sure that the LED will maintain the same power and hense brightness as its battery source drops down to it's bottom threshold of operation. 

The max brightness reference design that Zetex provided does increase the brightness by smoothing out the rfectified pulses off of the transistor, and keeping a bit of a charge in the cap. It doesn't change efficience much for most applications and gives you more light for the cost of a little tiny capacitor. Certainly, without the cap, the batteries will last a bit longer due to the higher efficiencies... But from what I read in this forum, most of you are using 3V or more wereas this will work of a single double-A or even a tripleA battery. 

Up and coming is an even newer Zetex part for driving white LEDs for emergency lighting, flashlight applicatons, and LCD and Keypad backlighting (same applications as the Zetex parts I mention above). I would love to know what the upcoming part involves. Anyone have info on that? I would also love to hear about anyone's designs using the Zetex parts. I haven't found anything that works any better, and I have been looking around and experimenting quite a bit. 
biaspoint


forgive my typos... I type too fast to spell


----------



## **DONOTDELETE** (Mar 8, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
*Yes, I saw the ZXSC100 too, but I rejected it mainly because of the efficiency difference of 82% versus 94%, and the 1-watt circuit (needed to drive the LS at full brightness) was considerably more complex than its 300 counterpart. (Note the 100 has twice the pins of the 300.)

But, you certainly have good points in that the 100 is available right now, and the SO8 is easier to work with than the SOT23-5, although the extra pins take away some of the advantage.

Still, I'm an efficiency freak so I'm holding out for the 300



*<HR></BLOCKQUOTE>

The ZXSC100 and theZXSC300 are essentially the exact same chip in different pacakaging, with the Zetex ZXSC100 package giving the user access to more of the chips funcitons and capabilities at the expense of more elaborate packaging with more pins. The Zetex ZXSC300 is a reduced pincount packaged version of the ZXSC100, from what I understand, to keep the cost down for volume applications. 

The ZXSC100 reference design in their datasheet is remarkably similar to the Zetex ZXSC300 reference design when it comes to driving white LEDs and it does specifically claim an efficience in excess of 90% if the inductor is carefully chosen. 

Both package styles are easy enough to do hand laboratory work or prototyping work with and still tiny enough to stuff into a little tiny flashlight or other unique application.

The SO8 pacakge allows more power to be handled by the controller chip itself.

Anyone else play with this part at their bench? 

BP


----------



## MrAl (Mar 8, 2002)

Hi there Bias,

I've been meaning to, but im not sure
if i want to go with another chip that
doesnt provide absolute current regulation.
I had intended to try the 310 next and use
a pulse width modulator at the enable pin
if that works out, with feedback from
a sense resistor in series with the LED.
It would take one more ic package and
maybe 4 more resistors though  although
the resistors could be chip resistors
keeping the size down.
Perhaps someday..... 

I havent even gotten back to my 2 transistor
plus one (combo) op-amp/reference diode 
design, which is also very small but
has more parts then the zetex 300 design.
Seems every other design has more parts then
the Zetex 300 chip design.

Good luck with your LED circuits,
Al


----------



## dat2zip (Mar 8, 2002)

I think I've worked out the equation for Iout and it's close but not actual constant current or voltage. That is true at any one given voltage point and I've plotted on that I have on the bench against my computed formula version and they two match almost exactly. In order for me to get the numbers I got, I had to use a larger size inductor. One that did not bias into saturation. Plotting the Iout VS Vin for the ferrite bead the calculated and the measured did not line up. That would be expected since the ferrite bead is pretty non linear. My graphs are on my web site at 
comaprison between zetex and maxiim 167X ICs.

As for constant power, if you can hold the voltage to the LED constant, you achieve pretty much the same thing. There are differences between constant current and constant voltage and I'm not sure which one is actually better. The LED current with constant voltage will vary depending on the temperature of the actual die. So, constant voltage is not constant over temperature.

But the Zetex IC from what I've measured is not constant current either. I've got the formula and if it is correct the current out is dependant on Vin.

That's why I think it's rather tricky to setup. You need to use a fresh set of batteries and adjust Ilim very carefully. Use a different set of batteries with higher intial voltage and you could possible toast your LS.

The Zetex design is by far the simplest and still the smallest. The Maxim IC design is possibly more efficient, but, it's all a matter of taste. Just like fine wines!


----------



## MrAl (Mar 9, 2002)

Hi there again Dat,

Some very interesting data and waveforms.
How much did the Tek current probe set you 
back?

As far as the nonlinearity of the inductor goes:
I've found the simplest method is to measure the two di/dt's, one when the
transistor is on, and the other then the transistor is off.
In other words, the inductor acts as
a voltage controlled inductor, who's
value varies with voltage across it.
You can then compute the two L's and use the respective one
during the corresponding time period. If you want you could then
work up a formula relating the two L's and the core type.

It would be a good idea to stress what you were talking about
when you said increasing the input voltage to 3 volts after 
running at 2.4 volts or something. The increase in output current
could fry the LED as you said. I think i mentioned somewhere in
this thread that for every new input battery/voltage the Rsense
resistor should be adjusted. I guess the thread is so long now
it's hard to read the whole thing 

Good luck with your LED circuits,
Al


----------



## dat2zip (Mar 10, 2002)

MrAl,

Yes, I probably didn't explain that very well. I'm still trying to work out the exact equation on how the Zetex IC works and comparing it with the math equation version. There is another part similar to the Zetex and that is National new White LED driver LM2703. It too has a fixed off time (400nS) and can use a very small inductor. In order for the National IC to regulate the LED current it uses a current sense resistor in series with the LEDs and when it reaches the set current limit it will skip cycles till the output capacitor and LED current go down below the fb trip comparator. The Zetex IC works similar but runs every cycle and I would extrapolate that the Zetex cannot really regulate in a true sense.

From my observations it appears that the
Zetex IC increases Iout as Vin increases and decreases Iout as Vin decreases.

Their data sheet tends to make you believe that Iout is constant irregardless of Vin.

It would be nice if Zetex provided the actual formula for Iout. 

As for the ferrite bead inductor, the lower the Ilimit is the more linear the ferrite bead is. I think the scope waveforms I show are for the 0.9A switch inductor limit. I don't think it matters how linear it is as it has been shown to have good efficiency numbers. I'm just planning on adding it to the graph so that people that are trying to design other version can compare the differences.

More specifically, one of my experiments is to set the Ilimit to drive 3-4 white Nichias and see if that works. If that works I'm hoping the efficiency is high and then the ZLT+ could be used to drive both the LS and a series string of Nichias.

I'm not sure how much the tek current probe cost since I do this work after hours at work and this piece of equipment was just lying around collecting dust. I've seen it many years ago sold as used for $1500 or so if I recall correctly. I used to use the exact same model some 16 years ago, so, I knew what a nice piece of equipment it was and had my eye on it ever since I saw it lying around a shelf.

It's nearly impossible to measure the voltage waveform across the small Rsense resistor on the Zetex IC and get accurate readings. The current probe is an invaluable asset for doing DC/DC converter designs.

I should have the plots done for the calculated curves of Iout vs Vin and actual data collected from my ZLT+ board. I can post the resulting data on the web site.

I'm also trying to come up with the efficiency formula too. In that way substituting different inductor values and inductor resistances can easily be plugged in to see the effect on efficiency.

It's faily staightforward but I need more time to work this out.

Also, I found a Micrel app note that shows how to calculate a copper trace sense resistor. From that I've added one to my ZLT board. When you fire it up, it comes up in a low current Iout mode. You can then short out sections of the sense trace to increase Iout or add an external wire to parallel the Rsense to increase Iout. This eliminates the wire that has to be tucked in somewhere.

I totally agree about this thread. I still enjoy thumbing through it now and again. Is there some way to extact all this into one text file?

Thanks for setting me straight. I tend to write in babble code.


----------



## Evan (Mar 13, 2002)

MrAl, Duggg:

I've been wadeing thru this thread you left behind over the last week or so. It is full of good, practical information on circuit design that I havn't found anywhere else.

I have a question about your efficiency measurements. I was surprised that the addition of a capacitor to input or output sometimes reduces efficiency. Other than a really leaky capacitor adding in a substantial load, I'd have expected those capacitors to always have a zero to positive effect.

I'm not sure how a digital meter will respond to a waveform that is not true DC. I think there is a good chance that the meter is giving the peak voltage; that is, if the voltage is actually 3 volts with a 3 volt peak-peak ripple on it, the meter would call this 4.5 volts, while it's RMS value for a power calculation is really 3 volts. Since all 4 measurements that go into your efficiency computation are subject to the same source of error, it may be that the capacitors you've added to input and output are having more effect on the waveform presented to the meter than on the actual efficiency of the circuit. The waveform on the input would likely be different than the waveform on the output, so the whole ratio of input to output could be thrown off. In this respect, Duggg's old analog meter may have been superior for these measurements as it would always read more or less RMS. 

I'd also like to hear more about the 4 transistor regulating circuit that was mentioned early on. I have in mind a light that runs on one "D" cell (or one 2 volt lead-acid "gates" cell) and it seems the 300 won't really do that. I expect that your circuit that uses an op-amp won't either as 1.5 volts is pretty low for any op amp I know of.

I have in mind to try to build the 300 circuit, but in a novel way. I have breadborded TTL circuits by super-gluing the ICs to an aluminum plate and then wire-wrapping the pins. By accident I discovered that super glue is strong but brittle, and by flexing the plate ever so slightly, the glue bond would break leaving the circuit fully wired and functioning, but without any circuit board. If I can handle these tiny chips and the even tinier connections, I wonder what kind of problems this technique might cause. I would like to glue the 300, the transistor, and probably all the other smt parts to the plate, then connect them with solder bridges. Once the circuit works, I could just pot it to the plate, pop it off the plate and pot it, or pop it off and epoxy it to some non-conducting surface in the final light. The plate would provide some heat sink to *to the case* while I test, but my impression is that this small parts may depend on heat sinking *via their leads* to the copper traces of a circuit board.


----------



## **DONOTDELETE** (Mar 13, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Evan:
*I'd have expected those capacitors to always have a zero to positive effect.*

Hi Evan,

On the input side, you are right, especially if the battery has high internal resistance.

However, on the output side, ESR---effective series resistance---is critical. Even with an ESR of 0.25 ohm, if you figure the average capacitor charge/discharge current is 350mA, then the I²R loss is almost 31mW, which represents a 2-3% reduction in efficiency.

By carefully selecting a capacitor with an ESR around 0.05 ohm, we managed to get the cap loss well under one percent.

*I think there is a good chance that the meter is giving the peak voltage... In this respect, Duggg's old analog meter may have been superior for these measurements as it would always read more or less RMS.*

The problem with my old analog meter was its lack of sensitivity and relatively low 50k impedance, so I bought a Fluke 87 meter, which reports true RMS values.

*My impression is that this small parts may depend on heat sinking via their leads to the copper traces of a circuit board.*

Because efficiency is relatively high, I don't think heat sinking is a major concern as far as the SMD components go. The diode is the major power waster, and it comes with six little heatsinks built right on the chip




<HR></BLOCKQUOTE>


----------



## MrAl (Mar 18, 2002)

Hello there Evan,

Im glad to see you're getting some use out of this circuit too.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Evan:
*MrAl, Duggg:
*
*
I have a question about your efficiency measurements. I was surprised that the addition
of a capacitor to input or output sometimes reduces efficiency. Other than a really
leaky capacitor adding in a substantial load, I'd have expected those capacitors to
always have a zero to positive effect.
*
Capacitors have another rating called the ESR rating. This is basically
a resistor connected in series with the ideal cap. The primary concern
is that since this resistor absorbs energy, it wastes power. The secondary
concern is how both this resistor and the capacitance interacts with the
other circuit elements, which can be either positive or negative with
respect to power lost in these other elements as a result of the introduction
of an averaging capacitor into the circuit. Sometimes the result is
positive (overall circuit wastes less power) and sometimes it's 
negative (overall circuit wastes more power then before adding the cap).
The reason for this is usually because the cap loads the input part of
the circuit differently then when not connecting a cap, and sometimes
because the output part of the circuit gets a different kind of waveform
then before the cap was introduced. All of the voltages and currents
present in this circuit are very dynamic in nature, never true dc.
In the low power case, leakage becomes a concern as well.

*
I'm not sure how a digital meter will respond to a waveform that is not true DC.
I think there is a good chance that the meter is giving the peak voltage; that
is, if the voltage is actually 3 volts with a 3 volt peak-peak ripple on it,
the meter would call this 4.5 volts, while it's RMS value for a power calculation
is really 3 volts. Since all 4 measurements that go into your efficiency computation
are subject to the same source of error, it may be that the capacitors you've added
to input and output are having more effect on the waveform presented to the meter
than on the actual efficiency of the circuit. The waveform on the input would
likely be different than the waveform on the output, so the whole ratio of input
to output could be thrown off. In this respect, Duggg's old analog meter may
have been superior for these measurements as it would always read more or less RMS. 
*
I did tests to verify that my meter was very good at averaging dynamic dc voltages,
checking the waveforms with an oscilloscope and comparing the calculated values
to the values measured directly by the meter. I found that at least my meters
average dc voltages very very well, therefore i came to rely on them.

*
I'd also like to hear more about the 4 transistor regulating circuit that was mentioned 
early on. I have in mind a light that runs on one "D" cell (or one 2 volt lead-acid
"gates" cell) and it seems the 300 won't really do that. I expect that your circuit
that uses an op-amp won't either as 1.5 volts is pretty low for any op amp I know of.
*
Yes, you are right, but the op amp version uses bootstrapping to get the min
voltage for the op amp (+3vdc). The 4 transistor version doesnt need this.

*
I have in mind to try to build the 300 circuit, but in a novel way. I have
breadborded TTL circuits by super-gluing the ICs to an aluminum plate and then
wire-wrapping the pins. By accident I discovered that super glue is strong but
brittle, and by flexing the plate ever so slightly, the glue bond would break
leaving the circuit fully wired and functioning, but without any circuit board.
If I can handle these tiny chips and the even tinier connections, I wonder what
kind of problems this technique might cause. I would like to glue the 300, the
transistor, and probably all the other smt parts to the plate, then connect them
with solder bridges. Once the circuit works, I could just pot it to the plate,
pop it off the plate and pot it, or pop it off and epoxy it to some non-conducting
surface in the final light. The plate would provide some heat sink to the
case while I test, but my impression is that this small parts may depend on
heat sinking via their leads to the copper traces of a circuit board.
*
That's a very interesting idea! I would first solder some copper strapping
to the heat dissipating parts like the diode and the transistors' collect
before potting. These parts do need to conduct some heat to the ambient.

<HR></BLOCKQUOTE>

Good luck with it,
Al


----------



## ake (Mar 19, 2002)

I have question regarding this driver (zxsc300)..
From the final project of (http://www.5thcolumn.org/zetex/project/), If I want to vary the Iout (output current) can I just play with the Rs by using formular I =19mV/Rs as stated in zetex doc? Do I have to chage the value of other parts?

I just want to modify it to use with 1-10 nichias as well when the battery life is more important than the brightness.

Thanks,

Ake


----------



## MrAl (Mar 20, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ake:
*I have question regarding this driver (zxsc300)..
From the final project of (http://www.5thcolumn.org/zetex/project/), If I want to vary the Iout (output current) can I just play with the Rs by using formular I =19mV/Rs as stated in zetex doc? Do I have to chage the value of other parts?

I just want to modify it to use with 1-10 nichias as well when the battery life is more important than the brightness.

Thanks,

Ake*<HR></BLOCKQUOTE>

Hi there Ake,

You sorta can do that, but it doesnt always
work out to exactly that value. Maybe start
with a higher value of resistance and
work your way down while measuring
output current with a series resistor.

Good luck with it,
Al


----------



## remuen (Mar 20, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> Originally posted by ake:
*
I just want to modify it to use with 1-10 nichias as well when the battery life is more important than the brightness.
*<HR></BLOCKQUOTE>

*Just a few points to consider when using Nichias with the ZLT+:*

Connecting LEDs in parallel means that the LED's will be driven almost for sure with different currents. These LEDs can vary quite a lot. I have measured a couple of them myself. Here the currents on 3.6 volts:

LED 1 53.5mA
LED 2 32.2mA
LED 3 14.8mA

LED 1 and 2 are for sure white Nichias, LED 3 possibly from another manufacturer.

Therefore you should connect the Nichias in series so they will be driven with exactly the same current. A current controlled booster like the ZLT does enable this.

As the FMMT617 (output transistor in the ZLT+) has a maximum rated CE voltage of 15 volts the output voltage must be lower. IMO you shouldn't connect more than 3 Nichias in series. If you need more than only three LEDs connect two or 3 chaines of 3 series-connected LEDs in parallel. In this case you will probably also have different currents in the chains but the difference will be lower than with only some parallel connected LEDs.

Another point: The output cap recommanded here in this thread for the ZLT+ has a maximum rating of only 10 volts. This works very well for driving an LS or some parallel-connected LEDs with this booster. But if you connect the LEDs in series the output voltage will be higher and therefore you have to replace this cap by another one with a higher voltage rating. This is because a tantalum cap should have about a two times higher valtage rating than it is connected to. So for three LEDs in series you would need a 20volts tantalum cap (3 x 3.6 volts = 10.8 volts operating voltage x 2).


----------



## ake (Mar 27, 2002)

I was reading the ZTX300 doc. and came aross thier 2 example circuits. The first one is the brightest LED driver. They use Rsense for only 0.1 ohm. Based on the Iout formular, Iout = 19mV/0.1 ohm = 190 mA! How is that possible? Even for thier max battery life module, Rsense is .33 ohm so Iout is still 57 mA. Isn't it to much to drive a single white Nichia?
Am I missing something here?

Aso how can I calculate the Vout if I want to use 2 LED in series?

Ake


----------



## **DONOTDELETE** (Mar 27, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ake:
*Based on the Iout formular, Iout = 19mV/0.1 ohm = 190 mA! How is that possible?*

190mA is the peak current through the transistor, not the LED. When the transistor opens, much of that current is absorbed by the capacitor, which is in parallel with the LED.

*Even for thier max battery life module, Rsense is .33 ohm so Iout is still 57 mA. Isn't it to much to drive a single white Nichia?*

Again 57mA is the peak current. Although there is no capacitor to absorb excess current in the max batt life circuit, Nichias are rated to take short pulses of up to 100mA. Since the LED is off part of the cycle in this circuit, average LED current is probably closer to 30mA.

*Aso how can I calculate the Vout if I want to use 2 LED in series?*

Vout is normally the sum of the forward voltages of the two LEDs at a specified operating current.

For example, for two LS's in series, one would expect Vout to be around 6.8 volts if they are being driven at 350mA.
<HR></BLOCKQUOTE>


----------



## ake (Mar 28, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> <HR></BLOCKQUOTE>*null**"Vout is normally the sum of the forward voltages of the two LEDs at a specified operating current.*


I mean if the Vout is 6.8V , How do I calculate the value of parameter in circuit to get 6.8V out? Isn't this circuit designed to get ~ a constant 3.3V out? Maybe I am confused again here.

Also has anyone try this circuit with 3 cells? I just would like to see how much the run time increases with 3 cells. 2-3 Hrs on 2 AA w/o changing battery is not good enough for me on a night hike.

Ake


----------



## **DONOTDELETE** (Mar 28, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ake:
*I mean if the Vout is 6.8V , How do I calculate the value of parameter in circuit to get 6.8V out?*

There's no easy formula. I managed to power two LS's in series from a pair of C cells, but it requires almost an ampere of input current, so you'll need a beefier inductor.

*Isn't this circuit designed to get ~ a constant 3.3V out? Maybe I am confused again here.*

No, the ZXSC300 is not a fixed voltage regulator.

*Also has anyone try this circuit with 3 cells? I just would like to see how much the run time increases with 3 cells.*

The closer the input voltage is to the output voltage, the less current is required from the batteries, so the longer they'll last.

In the two LS case, you might even consider using four cells.
<HR></BLOCKQUOTE>


----------



## remuen (Mar 30, 2002)

Hi MrAl

I have just constructed your Ripple Detect Network. I've built it all in SMD with ceramic caps. Instead the 1N5817 Schottky diode I took a ZHCS1000.

Trying to measure the output ripple of a ZLT+ I have got a result of only 0.3 ... 0.8 millivolts at 350mA output current. Can this be correct or is the result influenced by the ZHCS1000 and its different forward voltage? If this is the case, what output voltage would be a good result and what a bad one? (Unfortunatly I do not have a scope to make any comparisons.)


----------



## MrAl (Mar 31, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by remuen:
*Hi MrAl

I have just constructed your Ripple Detect Network. I've built it all in SMD with ceramic caps. Instead the 1N5817 Schottky diode I took a ZHCS1000.

Trying to measure the output ripple of a ZLT+ I have got a result of only 0.3 ... 0.8 millivolts at 350mA output current. Can this be correct or is the result influenced by the ZHCS1000 and its different forward voltage? If this is the case, what output voltage would be a good result and what a bad one? (Unfortunatly I do not have a scope to make any comparisons.)*<HR></BLOCKQUOTE>


hi there again remuen,

The best i can do is a simulation because
i hadnt built up any networks with the
Zetex 1000 Schottky diode, but rather
always used 1N5817 because i thought it would
be easier to obtain.
I'll run a simulation and see what happens.

--Al


----------



## MrAl (Apr 1, 2002)

Hi again remuen,

Here are the results of the simulation.

As usual, the Zetex part shows it's
superiority over the standard parts.
For comparison, i've shown another
Schottky diode as well as the 1N5817.

ZHCS1000===> 60mvdc
MBR140====> 47mvdc
1N5817=====> 53mvdc

These would be the limits on the
dc voltage out of the network using
the different diodes. Each diode
provides a slightly different output
with the same input, so your particular
limit will depend on what diode you are
using.

ADDED LATER:
I found a second model for the 1N5817
diode and ran a simulation on it too.
The results follow.

1N5817 (2nd model) =====> 42mvdc


Good luck with it,
Al


----------



## remuen (Apr 1, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*

Here are the results of the simulation.

ZHCS1000===> 60mvdc
MBR140====> 47mvdc
1N5817=====> 53mvdc

These would be the limits on the
dc voltage out of the network using
the different diodes. 
<HR></BLOCKQUOTE>*

Hi MrAl

Thank you very much for this comparison











I have three more questions:

<UL TYPE=SQUARE><LI>Just to make it clear to me: When you introduced this RDN (= Ripple Detect Network



) in the Zetex thread you wrote: 'Anything over 0.100 volts is no good. Anything under 0.100 volts is good.' 

Are the above mentioned figures the limits for the tested diodes instead the 100mV you mentioned earlier? If yes would it be correct to say: Anything over 0.060 volts is for sure no good. Anything under 0.040 volts is for sure good. 

<LI>I've checked my RDN a couple of times and everything seems to be ok. No bad soldering joints, no shortcuts, the right parts on the right place, all pins correctly soldered. 

Could it be that teh astonishing result of 0.4 ... 1.8 mV with the RDN is the result of the 10uF low ESR ceramic cap I used instead the 150uF Kemet tantalum cap? 

<LI>added later:
What are the ripple peak limits for your good/no good limit with a scope? Is there eg. a 1 : 1 correlation between the output voltage ripple an the DC voltage?
[/list]

For your background information: I'm a bit experimenting with the Zetex 300 chip to get a smaller board I need for a specific application. Therefore I used a 22uF SMD inductor (low DCR) and this ceramic cap. The efficiency is only about 78% but in my very specific case the much smaller board is worth this loss of efficiency. I have the parts for one more original ZLT+ left so I will build this one later. The other ZLT I've built (without any problems



) is already running in Klaus' Minimag ...


----------



## dat2zip (Apr 2, 2002)

In another Zetex thread I posted some actual scope measurements on using a ceramic 22uF capacitor and the output ripple I measured.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> I just started testing a two changes to the ZLT+.
1) I changed the output capacitor to a ceramic 22uF/10V capacitor that is in a SMT 1210 footprint with Digikey part number PCC2172CT-ND. With Ilimit set to 800mA and Vin of 1.5V @ ~.5A input the output voltage ripple was less than 30mV and the LS ripple current was 20mA P-P with the 22uF ceramic capacitor. Using this capacitor makes space on the board for the a standard 400mW zener protection diode. Output voltage ripple and LS current ripple remained approximately the same P-P value over the complete Vin Range of 1V to 2.6V.

<HR></BLOCKQUOTE>

Hope this helps.


----------



## Klaus (Apr 2, 2002)

As René mentioned he built up the ZLT+ for me - let me add that while being a pain to put everything together (even without the SMD soldering René was so nice to do for me) and fit in that tiny Maglite head the final product is much bright and fun - recommended.

While I´m lucky and can use the standard mag on/off function as possibly the wires going into the mag socket disconnect somewhat when turned and re-connect when turned back I do believe that the switching function is something still missing in this design.

As I worte I absolutely like the Mag/LS/ZLT+ as it is but without my luck being able to use the on/off switch the final product would have been not as usable at least to me.

Klaus


----------



## remuen (Apr 2, 2002)

dat2zip, thank you for reminding me




. 

I have read your post earlier but forgot that you have also mentioned the ripple voltage in this post. Therefore I think I'm not wrong when I say that the output voltage ripple with my 10uF ceramic cap is almost for sure below 50mV. I think I have to ask my friend here in the company I'm working to measure this ripple for me so I can 'adjust' my RDN circuit (means knowing what ripple voltage leads to which DC voltage with the RDN)


----------



## remuen (Apr 2, 2002)

MrAl, dat2zip
I could manage to get my Zetex circuit in a short time here in the company. My friend (a r&d engineer) has measured the output voltage ripple (output ~300mA/3.15V). It is about 40mA peak to peak with the 10uF ceramic cap and the 4.7uH inductor. 

MrAl
I am still confused because of the low DC output voltage with the RDN. It is only 0.32xxmV at this output voltage ripple measured with a calibrated DMM. Therefore my RDN has at least not a 1:1 correlation between ripple voltage and DC output voltage. We cannot make more testings because we don't have a HF generator. 

Is there also some non linearity in the RDN or can I multiply the measured DC output voltage of the RDN with a factor of 40mVpp : 0.33mV = 125 to get an approx. output ripple voltage?

added later:
Just to be sure here the drawing of the RDN I've built (from page 14 of this thread):

```

```


----------



## MrAl (Apr 6, 2002)

Hi again,

Note first that the cap C3 was changed to
0.1uf. It was increased in order to detect
low frequency oscillations better.

Regarding the non linearity of the 
network:

It is very non linear in the sense that
the actual ripple measured with a scope
does not correlate to a constant ratio
to the output of the network.
For 100mv actual ripple peak , you will measure about 50mv out of the network.
For 150mv actual ripple peak, you will
measure about 88mvdc out of the network.

These notes are being updated on Mercator's
web site also.

Good luck with it,
Al


----------



## Mercator (Apr 7, 2002)

Hello, All....

Been awhile since I've posted here, but haven't been able to keep away from the ZLT+ Project.

Just wanted to let you know that I have up-dated the ZLT+ Webpage. Made some corrections and added a new page that lists all the precautionary circuit building information and included up-to-date instructions on building the LS simulator and the Ripple Detect Network.

To see the changes.... 
Zetex 300 Driver and MiniMag Conversion Page

I hope this helps clear up some questions and alittle confusion since the page was originally placed online.

*-Mercator-*


----------



## remuen (Apr 7, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
Note first that the cap C3 was changed to
0.1uf. It was increased in order to detect
low frequency oscillations better.
*<HR></BLOCKQUOTE>

I will make this change too and see how it influences the output voltage.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
*
It is very non linear in the sense that
the actual ripple measured with a scope
does not correlate to a constant ratio
to the output of the network.
For 100mv actual ripple peak , you will measure about 50mv out of the network.
For 150mv actual ripple peak, you will
measure about 88mvdc out of the network.
*<HR></BLOCKQUOTE>

MrAl, thank you for these additional notes!


----------



## ake (Apr 9, 2002)

I just notice that the maximum peak pulsed forward current for the Luxeon is at 500mA for the white one, how much harm it will do to the LED if I adjust the curent to be more than 350 mA? I may be a bit confused here, I think that the ZLT+ circuit is a pulsed regulator.
So what kind of current do we get when we measure it aross the R (0.1 ohm), instaneous => pulsed current, or RMS => average current?

Thanks,

Ake


----------



## MrAl (Apr 14, 2002)

Hi there ake,

The output from the ZLT circuit is a ramping waveform
with an average of 350ma. It never reaches zero though,
staying about 250 to 300ma above zero, with a peak of
about 450ma or less.
The harm that can come from overdriving the led
to average currents above 350ma or to peaks higher
then 500ma is difficult to evaluate. The most likely
effect will be reduced LED life, but again, it's very
hard to say exactly how much life is reduced for 
a given amount of overdrive. The companies that make
things like this usually rate it as high as they can
get away with without risking a high rate of returns
due to premature failure. They usually use a statistical
method based on hundreds or even thousands of tests.
They elected to specify 350ma average and 500ma peak,
so unless we are ready to do a few hundred tests in
order to determine absolutely whether or not we can
drive them at higher currents and not reduce life
significantly, we have to trust their recommendations.
Unfortunately, we cant test just one piece and 
assume they all perform the same either.
This is the same with most electrical/electronic
parts, but with quite a few parts usually you
assume it's the other way around: it's better to
run a device LOWER then the manufacturers spec's.

We used to have a saying for this:

*Don't run it at 'fool' load *

Good luck with it,
Al


----------



## Klaus (Apr 17, 2002)

Hi Mr. Al,

seems some guys are quite happy "overclocking" their LS-ses ..... 

One question though on the ZLT+ circuit ..

When initially setting up the circuit (René soldered up for me using I think a mercator board) in a MiniMag I just used a DMM in series and measured > 1A current through the 2 NiMh cells.

Using the recommended 0.1 Ohm resistor its 630ma which is in the area it should be IMO.

Now interestingly when I use the DMM in series AND the 0.1 Ohm resistor too to measure the current twice - BOTH do show > 1A current flow which confuses me.

Just doing runtime tests I get around 3hours out of Sanyo 1700ma cells which also confirm the 630ma is the right number.

What makes me wonder (and my actual question) is what could cause the circuit to draw so much current when the DMM is in series ??

Klaus


----------



## Klaus (Apr 17, 2002)

Hi Mr. Al,

seems some guys are quite happy "overclocking" their LS-ses ..... 

One question though on the ZLT+ circuit ..

When initially setting up the circuit (René soldered up for me using I think a mercator board) in a MiniMag I just used a DMM in series and measured > 1A current through the 2 NiMh cells.

Using the recommended 0.1 Ohm resistor its 630ma which is in the area it should be IMO.

Now interestingly when I use the DMM in series AND the 0.1 Ohm resistor too to measure the current twice - BOTH do show > 1A current flow which confuses me.

Just doing runtime tests I get around 3hours out of Sanyo 1700ma cells which also confirm the 630ma is the right number.

What makes me wonder (and my actual question) is what could cause the circuit to draw so much current when the DMM is in series ??

And I´m not too srewed up - René confirmed my measurement with the DMM in series.

Klaus


----------



## remuen (Apr 17, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Klaus:
*
What makes me wonder (and my actual question) is what could cause the circuit to draw so much current when the DMM is in series ??
*<HR></BLOCKQUOTE>

Hi Klaus

I'm certainly not MrAl and I would be happy to have his knowledge. But maybe this could be an answer to your question:

Could well be that some additional inductivity from the DMM or the cables could cause this effect. Each switcher circuit is very very sensitive to such influences. From my own experience I've learned that eg. on a surf board it is almost impossible to bring such a circuit to work. Then it shows various curious effects. All parts have to be very close together with as short as possible connections between the pins.

Mr. Slaughterhouseman



, you could try to connect an additional 100uF cap between + and - pin of the input (very close to the ZLT+ board!) and look wether something will change or not. A change of the input current would confirm my theory.


----------



## PsycoBob[Q2] (Apr 18, 2002)

If anyone has a few PCB's for the Zetex ZXSC300 LS Driver that they'd be willing to sell me, I'd appreciate it. 

I'm trying to avoid having to go buy a PCB etching kit, let alone getting my damned HP Laserjet to work right. (And I'd rather just buy parts and assemble them, instead of playing kitchen-chemist.... chalk it up to laziness.)

_-edit: Wonderful, now I just made this monster 35 pages..... _


----------



## MrAl (Apr 18, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Klaus:
*Hi Mr. Al,

seems some guys are quite happy "overclocking" their LS-ses ..... 

One question though on the ZLT+ circuit ..

When initially setting up the circuit (René soldered up for me using I think a mercator board) in a MiniMag I just used a DMM in series and measured > 1A current through the 2 NiMh cells.

Using the recommended 0.1 Ohm resistor its 630ma which is in the area it should be IMO.

Now interestingly when I use the DMM in series AND the 0.1 Ohm resistor too to measure the current twice - BOTH do show > 1A current flow which confuses me.

Just doing runtime tests I get around 3hours out of Sanyo 1700ma cells which also confirm the 630ma is the right number.

What makes me wonder (and my actual question) is what could cause the circuit to draw so much current when the DMM is in series ??

Klaus*<HR></BLOCKQUOTE>


Hi Klaus,

How's the 10 cell power light coming?

With the Zetex circuit, you should initially set the current level while measuring the
OUTPUT current, not the input current. The input current will vary quite widely
with 350ma output and various input voltages. The reason we dont use meters in series
is because most meters have a rather high internal resistance, except on the higher
scales like 10A or so, as well as extra inductance as remuen was saying. Either 
of these can cause all sorts of problems. On the output, the extra resistance/inductance
causes the output voltage to have to go higher, drawing more input current, while on
the input the extra resistance/inductance causes a reduced input voltage to the circuit.
Also as remuen was saying, extra lead wire between some points in the circuit can
cause all sorts of curious effects mainly because of the increased 
point-to-point inductance. Inductance causes ringing too, which can cause inefficiencies
at best, or even worse, blow out parts due to high ring peaks.

You can 'calibrate' your 0.1 ohm resistor first by putting a known dc current through 
it and measuring the voltage drop. You can use a battery to do this. If you put say
500ma through it and you read 55.0mv, you know your resistor is a little high, so that 
55.0mv correspondes to a real current level of 500ma, or
50.0/55.0 times 55.0 equals 50.0mv, which means 500ma is flowing.

Now, with this resistor if you measure 57.8mv then:
57.8 times 50.0/55.0 equals 52.5, which means 525ma is flowing.


Good luck with it,
Al


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## ake (Apr 18, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PsycoBob[Q2]:
*If anyone has a few PCB's for the Zetex ZXSC300 LS Driver that they'd be willing to sell me, I'd appreciate it. 

I'm trying to avoid having to go buy a PCB etching kit, let alone getting my damned HP Laserjet to work right. (And I'd rather just buy parts and assemble them, instead of playing kitchen-chemist.... chalk it up to laziness.)

-edit: Wonderful, now I just made this monster 35 pages..... *<HR></BLOCKQUOTE>


You can easily use a cutter to etche it. I use a cutter to etche mine (I think I use MrAl PCB). It takes me less than 10 mins to get it done. Have to be abit patient, but it works. Just make sure each part is totally separated, by checking the connectivity.


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## InTheDark (Apr 18, 2002)

I use a small woodcarving chisel to make mine. It has a V-shaped tip so I just cut a V-groove where the lines are. Not as nice looking as an etched board, but a lot faster and cheaper.


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## Klaus (Apr 18, 2002)

Hi Al,

its a 12 cell / 20W for now (and the 24 cell / 35W version is in the works too) and I finally got that charger to load them at 1C ~ 3.4A using a transistor with higher amplification - thought I emailed you about ?

Just modified the original 2D proto to use 12 1600ma NiMhs with the 20W bulb and a new switch / slight modifications for better usability - at approx 750 lumens / 1 hour runtime at that ridiculous low price I´m quite content at it. William in the US is readying the housing for the 24 cell one and most everything is in place - still working on some heat-shielding though ...

But back to topic:

I used 10 1 Ohm 1% resistors in parallel to get 0.1 Ohm and this should be pretty accurate as far as my math goes .... which kind of seems to tell me that this thing is at 0.1% accuracy now, can handle 6W and was dirt-cheap too - I just like such creative setups.

And your explanation does absolutely make sense and adds nicely to René´s thoughts too. As I´m pretty pragmatic I stopped loosing sleep after the rundown test at 3 hours which showed the serial setup was just screwed up - but I was still curious and as I was never befor involved with such a switching circuit I dind´t understood it at first why just a DMM (at 10A anyway) would change the current flow so dramatically. And I was quite shure I wasn´t screwing up the measurement as the double take with the additonal 0.1 Ohm part showed the >1A too.

Thanks again

Klaus


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## PsycoBob[Q2] (Apr 20, 2002)

Mildly silly question time (Might have already been answered, I'm still reading the back-pages.... more than 10 a day seems to give me a headache).

Would an input capacitor have any effect? I'm going to be mounting one of these drivers in the head of a 2D Angle-head, so it has HUGE amounts of space, so circuit size isn't the issue it is for mounting in a AA minimag. I happen to have a few 5v low-ESR caps of a dead VP6 motherboard...... I'm tempted to replace the output cap too. (expensive *******- I only bought 2, compared to 5 for everything else.)

Thanks guys, this thread and the pages it's spawned have been a big help.


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## The_LED_Museum (Apr 21, 2002)

*MODERATOR HAT ON*

Just to let you know, this and other threads primarily related to power supply circuitry, drivers, boosters, inverters, and the like are being transferred to the _Electronics Forum_.

This is being done for two main reasons:
<UL TYPE=SQUARE><LI>1: So you don't have to wade through 2,000 threads on the LED Forum looking for ZLT or Satcure circuits.
<LI>2: To help streamline the LED forum just a little bit. Those looking for LED flashlights and not necessarily interested in circuit designing won't have to wade through quite so many ZLT threads.
[/list]
Those who protest the move will be connected to a Zetec driver and fed 450 milliamps.











The original threads will remain available (read-only) for a time until you get used to looking for them in the Electronics Forum. And only those threads specifically discussing this type of topic will be moved. I won't move every single one that has the word "Satcure" buried somewhere in it if that isn't the main discussion going on.





Thanks, and I hope this isn't too much of an inconvenience, especially those who may have specific threads bookmarked.

*MODERATOR HAT OFF*


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