# Power Supply with Switching Pre-Regulator



## MrAl (Oct 4, 2004)

Hello folks of CPF,

Here's the start of a power supply which is linear but
has a switching power supply pre-regulator to reduce
heat output of the linear. It also uses fairly common
parts.

Right now it's still in the preliminary stage, but it
shouldnt be long now until it's ready.

Feel free to comment, make suggestions, etc.

Take care,
Al


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## tonyb (Oct 4, 2004)

Why wouldn't you make it completly switching and off-line so as to avoid using bulky expensive line transformers. Is there some issue with ripple or load reg that would cause you to go with a linear design? MOdern switchers perform quite well- i.e. personal computer supplies uses them exclusively. Heres a 100-240 volt AC input to 12 volts at 1 amp DC output supply that measures only 4"x2"x3/8"


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## PEU (Oct 4, 2004)

yipeee

can't wait for the final drawing /ubbthreads/images/graemlins/popcorn.gif 

Pablo


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## vicbin (Oct 5, 2004)

Yesss..... finally ! /ubbthreads/images/graemlins/smile.gif 

Al, just take your time !! /ubbthreads/images/graemlins/popcorn.gif

Question, what is the lowest output voltage ? 1.2 V ?


Hi Tony,

This project is planned for CPFer with "limited access" for electronic components and the learning process. /ubbthreads/images/graemlins/grin.gif

Of course , if you can share how those "isolated" idea can be applied "easily", I think it will be very nice. 


Vic


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## MrAl (Oct 5, 2004)

Hello again,

Tonyb:
Yes, that would be a good idea, but i have a feeling
it would be a bit more dangerous for most folks on CPF here.
If you'd like to share some design ideas though please
feel free. We'd like isolation from the main line too.

Vic:
I overlooked the fact that this should probably adjust
down to zero volts. I'll have to correct that.
Also, i shouldnt have jumped in with the complex
circuit first...rather, i should have started with the
simplest configuration and worked up. With this in mind,
i'll take a step back and post the more simple circuit
so people can see how simple this can really be...that
was the main idea anyway. Then later, if anyone wants
to upgrade to the more advanced design they can simply
add parts /ubbthreads/images/graemlins/smile.gif
The LM317 (and similar) already are capable of voltage
regulation and current regulation by itself without all
the extra op amps and voltage regulators, so the first
design should take advantage of that, which was what
was supposed to happen anyway. The upgraded version
will include all the added features.

I hope to have more on this posted today.

Take care,
Al


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## PEU (Oct 5, 2004)

Al,

does the digital meter affects in any way the voltage or current regulation? It should be measured at the output or in a stage in between?

Pablo


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## vicbin (Oct 5, 2004)

Hi Al,

Yes, I think adjustability below 1 Volt is handy, especially at observing single cell circuit behaviour on drained cell. /ubbthreads/images/graemlins/smile.gif

I agree with you on starting a simple one and advancing step by step for more features, and I really like the knowledge gained during that process. /ubbthreads/images/graemlins/blush.gif


Pablo,

For voltage measurement just connect as usual, parallel with the PS output and it won't affect it since for measuring volt the resistance is very high.
Even for the el'cheapo DMM, most of them are built based on ICL7106 ic and it needs only 1 pA (typical) and max at 10 pA (pico Amp) to measure voltage. With these pico amp, I don't think it will affects the V-out.

For current, *DO NOT * put the DMM in series with the PS since it has quite high resistance, especially on low current ma resolution. 
Just use the sense resistor (the one connected to and below the load symbol) and *measure the voltage drop* across that resistor to get the current reading.
If it is 0.1 ohm then it is pretty straight forward using I = V /R formula, if not, you'll need one multiturn potentiometer 1K or 2K parallel with that sense resistor and will need some tuning for the correct reading.

Let's wait for Al to finalise the circuit and see how much resistance he decided for that sense resistor.

Vic


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## PEU (Oct 5, 2004)

ok Vic! 

Yesterday I ordered samples from maxim and included a pair of 7107, the usually don't ask much, so I hope I'll receive them...

/ubbthreads/images/graemlins/popcorn.gif


Pablo


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## vicbin (Oct 5, 2004)

Pablo,

I pray for you... ! Geezzz... I have a feeling that both our PS at final stage will looks like twins ! /ubbthreads/images/graemlins/grin.gif

So you also decided to treat your DMM like me too ? ..he...he... /ubbthreads/images/graemlins/grin.gif 






Al, with all respect, if you find this kind of pic is distracting in this serious discussion, I'll delete it.

Vic


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## MrAl (Oct 6, 2004)

Hello again,

Pablo:
As Vic was pointing out,
measuring the output voltage wont affect operation, and
measuring the current output can be accomplished by 
measuring the voltage across the sense resistor, and if you
like we can use one of the left over op amp sections to 
create a meter amplifier so you can read directly: as 1.000v
on the meter means 1.000A output.

Vic:
Ok then, the more advanced unit will adjust below that, down
to either 0.000 or very close 0.010 volts.

The selection of the sense resistor is a bit of a tradeoff,
i'd like high (1 ohm) resistance but then at 3 amps that eats
up not only power but available voltage also (3 volts), so,
we'll probably end up with half that, 0.5 ohms. Of course i'll
also try 0.1 ohms first and see if the current regulation
stability AND adjustment checks out ok.

Actually i like the humor Vic, and i was going to draw some
cartoon up too but it takes too much time :-(
Eventually perhaps i'll get to it also.
I dont know how this affects loading however, when someone tries
to load the page(s). I like it though /ubbthreads/images/graemlins/smile.gif I've always liked
joking around and comedy, and i think your cartoons are really
a good idea. I think it would be fun to start an Electronics
Cartoon thread too, just for laughs. You could be on to 
something new.

Back to PS...

I hope to have a very simple version posted today.
This will be very simple to build and very useful
also, and will take advantage of the already present
advantages of the chips.

BTW, Pablo and Vic, i need to know what the max output
you wanted to get... is it 50v or what?
That will be one of the advanced units because
it requires extra parts to get up that high.
I've noticed that the small electrolytics go up
in price quite a bit once you get past about 35v ratings.
Price jump from about $1 to about $3 each.


Take care,
Al


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## PEU (Oct 6, 2004)

[ QUOTE ]
*MrAl said:*
BTW, Pablo and Vic, i need to know what the max output
you wanted to get... is it 50v or what?
That will be one of the advanced units because
it requires extra parts to get up that high.
I've noticed that the small electrolytics go up
in price quite a bit once you get past about 35v ratings.
Price jump from about $1 to about $3 each.

[/ QUOTE ]

Hi Al / Vic

In my case I have a 30+30 transformer, so that's the limit for me /ubbthreads/images/graemlins/smile.gif

And I guess the magic number should be around 30-40v because as you said prices&problems go quickly up after 40-50v for all the parts.

/ubbthreads/images/graemlins/popcorn.gif

Pablo


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## vicbin (Oct 6, 2004)

Greetings Al & Pablo,

[ QUOTE ]

Ok then, the more advanced unit will adjust below that, down to either 0.000 or very close 0.010 volts.


[/ QUOTE ]

Wow !! /ubbthreads/images/graemlins/ooo.gif This is better than I expected ! And I'm not complaining ! /ubbthreads/images/graemlins/grin.gif

So does it need a precision opamp for that ? Although I don't have problem with that (e.g. OP07 opamp is available here), but I'm thinking if other CPFer might have a problem with it. Just a thought.

About the sense resistor selection , if we use low resistance such as 0.1 Ohm , what's the catch ? I mean worst case scenario ?








For me, I don't have any problem with high voltage as you can see at the above picture. "But", is it possible let say other CPFer only has access on lower voltage one , say 15VAC out transformer ?

Realistically, at least for me, I think the highest voltage I used in the past was only to simulate car battery 12V, but looking what I got here, I really like to have the one that can put out at least 24 Volt (truck battery) or 30 Volts ..such testing series of leds ! /ubbthreads/images/graemlins/grin.gif

Again, as agreed to make it simple 1st, *is it possible that your design to accomodate this difference requirement on the max. V out "without" major re-designing. e.g.: only change some resistor or reference ?*

Another questions about the transformer and the rectifier part :

- Does it require a centre tapped transformer ? I got both though...psstt..only $2 a pop /ubbthreads/images/graemlins/grin.gif

- In the circuit drawing at the rectifier part I see you use 2 types, two (1N5402) for high amp connected to switcher, the other two (1N4003) for the opamp supply. My rectifier is the one at top of left transformer ? It is rated 1000V at 35 Amps /ubbthreads/images/graemlins/cool.gif , should be fine right ?

Hey .... its cost me only $40 cents ! I know it is *overkill*, but for that price, I can not bear not to buy it ! /ubbthreads/images/graemlins/smile.gif

Thanks & regards,
Vic


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## MrAl (Oct 6, 2004)

Hello again,

The simplest circuit is now here...







Vic:
It doesnt really need a precision op amp, although that would be nice,
but it has to be fast. I'd like even faster than LF347 but that might do.
OP07 will be too slow. OP27 if you feel like spending the money.
Now you see what i've been dreaming about, and how many many options
there are for a circuit like this. So many choices, it's hard to
decide /ubbthreads/images/graemlins/smile.gif

Worst case for 0.1 ohm is that the response to a current overload
step is too slow or rings too much. Im shooting for 1us max with
maybe 10% overload. I'll take 2us, but i think 100us is too slow.
Also as i was saying, a left over section of the op amp can be used
to scale the voltage meter to read directly in Amps with something like
two additional standard resistors.

Transformer doesnt have to be center tapped, but for the advanced
unit some means of supplying a negative bias has to be employed, so
that means either center tapped or an additional wall wart or small
transformer (100ma only).

The main reason for the simpler design is so that people who dont
want to have to connect lots of parts can still build one and get
very good performance and versatility. This means two parts lists
more than anything else, but the connections are a little bit 
different too for voltage mode and current mode operation.
See the schematic for a better explanation.

The reason for two types of rectifier diodes is mainly because the
negative supply only has to supply maybe 100ma or less while the
positive supply has to provide maybe 3 amps. This means smaller
diodes can be used for the negative supply, but of course this
isnt mandatory so if you want to use a bridge rect that's rated
for the max positive supply (or more) that's ok too.
Note however that if you use a single winding transformer
(no center tap) you need four 1N5402 diodes (as well as
another transformer).


Take care,
Al


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## PEU (Oct 6, 2004)

Hi!

adding to what I said, I want to start from almost 0v to 30v

I don't understand the 2 different loads, this means that if I want to limit the current supplied to a circuit I have to choose a diferent output? or I'm totally wrong? /ubbthreads/images/graemlins/smile.gif

Pablo


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## MrAl (Oct 6, 2004)

Hi again,

Pablo:
This 'simplest' version (001) only adjusts from 1.2v up.
The more advanced version will adjust from 0.00v and up.

Yes, this 'simplest' version has the load applied to 
a different place in the circuit depending on whether or
not you want to run constant current or constant voltage
mode. Again, the more advanced version will have the load
connected the same for either and will have both simultaneously,
so that the current is also limited by the set point you
choose, not by the device itself (note that the simple
version 001 current limit is set by the device itself,
unless you're operating in constant current mode).

The more advanced version will go from 0.00 up to
whatever your building for, and current limit and set point
from probably around 1ma up to full current.

Does this make more sense?

The simplest version (001) is there to minimize
parts count yet still get some of the benefits of
doing this in the first place, that's all.

Vic:
I guess you want to go 0 to 30v too then?

0-30v seems like a reasonable range.


Take care,
Al


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## PEU (Oct 6, 2004)

[ QUOTE ]
The more advanced version will go from 0.00 up to
whatever your building for, and current limit and set point
from probably around 1ma up to full current.

Does this make more sense? 

[/ QUOTE ] 

YES!






/ubbthreads/images/graemlins/popcorn.gif

Pablo


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## vicbin (Oct 6, 2004)

Hi Al,

Ok, since you asked for it, here are my wish lists /ubbthreads/images/graemlins/grin.gif

1. Adj. 0 - 30 Volt (with 0.1 volt or better resolution)
2. Adj. 0 - 3 Amp (with 1 ma or better resolution) ... stage I
3. Adj. 0 - 5 Amp (same as above) .................. stage II
4. Output voltage that will not overshoot during switching off or on of the PS main supply (during off caused by collapsing negative supply)
5. Low ripple , dunno how low yet, to be tested with various cap and/or LC filter as you describe OR double caps & inductors

Planning to separate switcher and linear board (modular), stage I will be 3 Amp switcher and stage II 5 Amp switcher. Linear part already 5 Amp capable.

Another bell & whistles : /ubbthreads/images/graemlins/smile.gif

1. Constant Current mode indicator (either LED *and/or* switchable mini buzzer ) just in case it got shorted by accident or trouble shooting circuit without turning our head to see if the CC mode was activated ..... /ubbthreads/images/graemlins/grin.gif

"Enhancements" which I'm planning to do it my self later :

2. Coarse and Fine (10% of coarse value) potentiometer for both Volt & Amp adjusment
3. Digital meter with BIG 7 seg. LED display (size 3.5 X 2.5 cm / digit) for Volt & Amp
4. Ripple meter using bar graph IC -> LM3914 indicator utilizing your ripple detect circuit, wondering if this is necessary once we got a low ripple, if the ripple is consistent then I don't need it
5. High temperature activated *low noise & long life* DC fan (Panaflo), just *ON or OFF only*, no variable speed. Adjustable temperature threshold.
6. Output disconnect & connect switch, possibly driven by semiconductor based (MOSFET) rather than mechanical swicth or relay. (need to discuss with you "later" for this switch to avoid disrupting the regulation loop)

These enhancements will added step by step if I got time for it. /ubbthreads/images/graemlins/grin.gif






Ok, did I miss anything ? Hope this wish list is not too much ! /ubbthreads/images/graemlins/smile.gif 

Vic


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## MrAl (Oct 7, 2004)

Hello again,

Pablo:
Funny cartoon /ubbthreads/images/graemlins/smile.gif

Vic:
0-30 volt should be possible with high enough input and HV devices.
0-5 amp can only be had with a higher power switcher and the 5 amp linear reg.

I'll keep an eye on the negative supply so it stays active longer
than the positive supply.

We'll have to see what kind of ripple we get, but it should be pretty
good because we'll have the linear reg on the output.

Im going to build my switcher separate too...for one thing, the switcher
itself will be very handy to have for some regulation needs too, even
without the linear on the output.

Constant current move indicator shouldnt be a problem.

Take care,
Al


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## vicbin (Oct 7, 2004)

Hi Al,

Great, you've thought of the neg supply ! /ubbthreads/images/graemlins/smile.gif

[ QUOTE ]

Im going to build my switcher separate too...for one thing, the switcher itself will be very handy to have for some regulation needs too, even without the linear on the output.


[/ QUOTE ]

Are you saying that you're planning to make the switcher part detachable and as independent PS ? That is great idea ! 

Vic


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## PEU (Oct 7, 2004)

Hi 

can this IC be used for the negative part of the PS ?

it transforms a positive voltage to negative.

And again, I may be totally wrong /ubbthreads/images/graemlins/smile.gif


Pablo


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## MrAl (Oct 8, 2004)

Hello again,

Vic:
Yes, i think it would be good to have a decent switcher
circuit to work with things like wall warts and automobile
supples (for Luxeon and similar). It would be nice
if it didnt get too warm. As you know, a linear will get
warm powering a luxeon from the car 12v battery.

Pablo:
Yes, that could work, but i think something a little more
high powered would be better (100ma or more).
That would help relax the need for two windings, but then
the person building would have to order that part too,
so it's a tradeoff.

Take care,
Al


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## vicbin (Oct 8, 2004)

Hi folks,

Pablo,
That ICL7660 is capable only at 10ma or below, I got it too, and its only suitable for low current needs below 10ma such as your ICL7107 DMM display. I tried before and even driving LEDs at 20ma the Vout dropped about 3 volts ! /ubbthreads/images/graemlins/frown.gif

Remember, you'll need another positive regulator for it since the max Vin only at 10 Volts !

Al,

I know you already provided the way of supplying neg supply but it is from transformer with center tapped. 
Please take a look at this pic below, is this ok (and *safe*) for generating negative supply ? 

Any recommendation for the D1,D2 and C2,C3 value especially for 100ma or more ? Or maybe you have other better solution ?








About inductor you put 200uH, could you explain where or how did you get this value ? Because from the datasheet there is only a formula for fixed output (for Adj. version). I'm lost how to use those formula for this kind of circuit since the output can be starting very low to high with very low current to high too ? (Adjustable Volt and Amp)

Your idea separating those modules is very handy too, think of other CPFer that interest or can afford building the linear part only ! /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


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## MrAl (Oct 8, 2004)

Hi Vic,

I'll take a look at your idea of generating the minus 
supply and let you know what i find ASAP.
I'll also try to explain the inductor value selection.
I should have this info a little later today ok?

In the mean time, here's the next version of the PS,
so you can take a look and see what you might find.
Note that i'll still be looking at replacing the neg
supply shown here with your idea Vic.

Version 002:





Take care,
Al


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## vicbin (Oct 8, 2004)

Hi Al,

Again, take your time ! /ubbthreads/images/graemlins/smile.gif

This is interesting, I noticed something new here, what are those D6 (1N5226), 2N4401 transistor and the 10K resistor used for ?

The linear C-in, how big for 5 Amps ? and are those Cout for switcher still the same 3 X 300uF even for 3 or 5 Amps ?

Regards,
Vic


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## MrAl (Oct 8, 2004)

Hi again,

Vic:
Your idea seems to work very well, so i included it on
the new schematic for the new version...(see below).

The new parts (incldg. 2N4401) is to swamp the FB pin in
case the neg supply goes away before the pos supply as
you mentioned earlier. This will kill the output voltage
in case input power goes down while powering something
critical, so the output wont jump up unexpectedly.

Actually, the 3x300uf might be an overkill, probably 
one 1000uf would be ok, but it will probably end up
being 1000uf for every amp output, so that's
3 x 1000uf for 3 amp output, etc.
I'll double check this too.

Here's the new version with the simpler neg ps:





Take care,
Al


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## vicbin (Oct 8, 2004)

Hi Al,

Great ! Actually those are *not* my design, I'm sorta copy it from my other circuit. (the other Adj. PS with so many-many discrete components) /ubbthreads/images/graemlins/grin.gif
Finally after hours of staring those new parts, I finally understand how it works when the neg. supply collaped and how it shutoff the whole thing ! 

It is so simple and pardon for my "noobeeness", another great thing I've learned today ! /ubbthreads/images/graemlins/bowdown.gif -> Mr.Al

Hi Pablo,

You can save those ICL7660 ICs now /ubbthreads/images/graemlins/grin.gif , trust me, you'll need it for those ICL7107 based DMM for good accuracy and consistent measurements.

Regards,
Vic


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## PEU (Oct 8, 2004)

Hi Al/Vic

yeah! I ordered 2 sets of samples from maxim, and both of them included icl7107/7660 ics /ubbthreads/images/graemlins/smile.gif

They will go to friends there and then forwarded via usmail here.

Also ordered some lm338 from national this way also /ubbthreads/images/graemlins/smile.gif hope they deliver this time (but I'll use the lm350 for the PS)

So, as you can see, I'm in no hurry, and learning a little every day it passes /ubbthreads/images/graemlins/smile.gif

I wait for the single output version

/ubbthreads/images/graemlins/popcorn.gif 

Pablo


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## Burnt_Retinas (Oct 9, 2004)

Should the 50uf electro for the -ve supply should be a non-polarised one?. The current polarised one will have reverse charge on it for some time which may lead to premature failure.

Chris


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## MrAl (Oct 9, 2004)

Hello again,

Vic:
I hope you like the way the power is shut down if the neg supply goes
away first. It's interesting that with light load, the thing could
put out power for some time without it.
We're all learning here 

Pablo:
So i guess you are making your own volt meters? What are you 
going to use for the display?
Were you able to get the 338's as samples or no?

Burnt_Retinas:
Thanks for the input!
Well, when the ac input goes negative at the top (+) of the 50uf cap
diode D4 conducts, and with enough current flowing to the Cin caps
it might drop 1v or so, which means the top (+) of the 50uf cap sees
about -1 volt, and since the second 1N4003 diode drops about 0.8 volts
or so, the difference is -0.2 volts (approx). This means the 50uf
cap will at most, see about -0.2 volts. Since it's rated at 50uf
i think it can take this small neg voltage.
Did i miss something or does this seem ok? I'll double check too.
[LATER]
I've found that there could be 1/4 to 1/2 cycle reverse
voltage across the 50uf cap, if the input power is turned
on during the negative half cycle of the 60Hz input.
Changing this to 500uf reduces the voltage to about
1 volt or so, so i guess we'll just do that.
This change makes the 50uf cap 500uf instead.


Take care,
Al


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## PEU (Oct 9, 2004)

[ QUOTE ]
*MrAl said:*
Pablo:
So i guess you are making your own volt meters? What are you 
going to use for the display?
Were you able to get the 338's as samples or no?



[/ QUOTE ]

I already have the voltmeter, but is nice to receive free stuff and I may end building a second one for current reading /ubbthreads/images/graemlins/smile.gif

Pablo


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## MrAl (Oct 9, 2004)

Hi Pablo,

Oh yes, i thought so, but what are you going to use for
the display of the second one?

Take care,
Al


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## vicbin (Oct 9, 2004)

Hi all,

Just did a little shopping at local shops today, look what I got ! /ubbthreads/images/graemlins/smile.gif






Al,

The sense resistors are ready to serve at 5 Amps even at 1 Ohm ! (by 2 X 2 matrix 40 watts or 0.5 Ohm at 20 Watts !) ...psstt.... 5 cents a pop /ubbthreads/images/graemlins/cool.gif Wondering what that "J" means ?

Have you decided the sense resistor value ?

Also got a new MAX724 (PDF) switcher with 5 Amps capability and the shop keeper said it is better, this will be used for the second phase (5 Amps) after the LM2576 settled.

Regards,
Vic


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## MrAl (Oct 9, 2004)

Hi Vic,

Gee, where do you find those shops? Wish we had a few
around here 

Oh good, im glad you got the sense resistors already.
Im thinking of going with 0.5 ohms, because 1 ohm
eats so much power and voltage. I'd like 0.1 ohms,
but i'll have to do a few tests to make sure this will
work ok... havent gotten to that yet, but soon.

The Max724 looks interesting, but they cant seem to decide
on what value for the resistor in the compensation network.
Did you compare the switch voltage drop in the Max chip
to the LM (5 amp) chip?
Also, how much are those Max chips (5 amp)?

Take care,
Al

SOME INDUCTOR SELECTION THEORY

With 100% duty cycle at 50kHz we have a period of 20us,
so 50% duty cycle is 10us.
We then can apply the equation:
dv=L*di/dt

which can be read as:

"The change in voltage (dv) is equal to the inductance (L)
times the change in current (di) with respect to time (dt)".

For our purpose, 'dv' becomes the input - output differential
volts, 'di' becomes the ripple current, and dt is the period (10us).

Since we know the input voltage and the period, we can assume any
output voltage we want in order to determine what the ripple current (di)
will be, and we simply look for a max.

Lets say we have 20vdc input, 10vdc output, and the period is 10us.

Solving the above equation for di, we get this:

di=(dv*dt)/L

Using this equation with our chosen value of 200uH for the
inductor, we end up with the following values:

dv=20-10=10 volts
dt=0.000010 seconds
L=0.000200 henrys

and after inserting them into the equation for di we end up with:

di=(10*0.000010)/0.000200 {amps}

which when we do the math we end up with:
di=0.5 amps

This means at 50% duty cycle we'll end up with about 0.5 amps
ripple current through the inductor.

Hope this helps.


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## vicbin (Oct 9, 2004)

Hi Al,

Btw, I'm really sorry for delay on ferrite core shipment cause didn't have a chance to visit the nearest post office (approx. 1 hour drive) /ubbthreads/images/graemlins/frown.gif . Will do this on next week. Two of this hunkee resistor will go to NJ too , no big deal, just 10 cents ! This will suitable for your 1.5 Amp (LM317) linear on both variation either 1 or 0.5 Ohm at 1.5 Amps ! /ubbthreads/images/graemlins/grin.gif

I'm ready what ever sense resistor value you choosed, 1 Ohm or 0.5 Ohm or even other. Anyway as you said we will have one spare/free op-amp that will be used as multiplier/divider for sensing the drop for measurement using DMM. Just focus on the best result for the current overload loop as you said.

[ QUOTE ]

The Max724 looks interesting, but they cant seem to decide on what value for the resistor in the compensation network.
Did you compare the switch voltage drop in the Max chip to the LM (5 amp) chip? Also, how much are those Max chips (5 amp)?

[/ QUOTE ]

Sorry, can't answer your question about the voltage drop caused I never build 5 Amps switcher before and also this is way beyond me since I don't understand what is that "<font color="red">*compensation*</font>" used for ? Is this suitable for our need on variable voltage and current ?

Also I found out other brand switcher non National such as this Maxim, Linear or On-Semi has this compensation pin. 

Example non National switcher :

- Linear : LT1070 - 5A and 2.5A High Efficiency Switching Regulators Datasheet (PDF) 
- On Semi : MC34167: 5A, Step-Up/Down/Inverting Switching Regulator Datasheet (PDF)

Why National "Simple Switcher" family (0.5 to 5 Amps) doesn't have it ? Is this an advantage or disadvantage ? or maybe National has a better design (more "*simple*") ? Please explain if this compensation network pin for if you got a chance. 

Anyway, that MAX724 cost me approx $5.5 a piece ! Not cheap, and if it is not suitable for our project, I can return it and have a refund ! /ubbthreads/images/graemlins/grin.gif

Thanks & regards,
Vic


----------



## MrAl (Oct 9, 2004)

Hi again Vic,

the LM2678 doesnt required a compensation network, while
the Max724 does. Since they arent clear on what the 
value of the resistor is supposed to be, it might
have to change with output voltage and/or current.
I dont know for sure, so i cant say for sure, but it
looks like the National part will work. It's not that
i think the National part is better, just that there is
nothing to adjust so it should work the same as the
3 amp version (almost).

I'll have to check the LT and MC parts you showed, and
see. 

It might even be possible that the Max724 can be adjusted
to have a slightly better response than the National part,
but without more information i cant be sure, and i wouldnt
want to take the chance because this sort of adjustment
pretains to the transient response, something most people
cant check once they build the power supply.

For now i think we should stick with what we 'know' (however
little that is /ubbthreads/images/graemlins/smile.gif ) and perhaps later try some new parts
too, which i sure wouldnt mind. Other makers parts would
be interesting too, im sure, and i'll check them out next.

I'd like to get to the most advanced design soon, so im
looking at various ideas. I think the major part of it
isnt really the switcher itself though, that's pretty
straightforward...it's the current limit and 0v adjust
with only one output. I'd like it to work very good
without any problems and nothing to check except a few
simple tests once someone builds one up.

Max724 comp pin:
The pin on the Max724 is for compensating the error
amplifier. Pick the wrong parts and the switcher could
become unstable for some inputs or for some loads.
Pick the right parts and it might have a better response
than the National part. Trouble is, im still in the dark
about it's exact nature, so i'll have to look more into
it. What i did find out so far is that the resistor
has to be chosen carefully, and the data sheet seems to
be kind of vague about what it should be. If it ends up
that it has to be chosen according to output voltage or
output current or even input voltage range (on the 
breadboard) then we're out of luck, because ours will vary
from 0 to probably 30v output with current from 10ma to
3.00 amp (or higher) so we probably not have the luxury of 
selecting only one value. It could be tested of course.

I made some adjustments in my previous post...we should
start with 50% duty cycle for the inductor selection.

If your inductor takes a bit longer to get here that's
perfectly all right...might be just in time for when i
get the other parts 
Please dont make that trip just for that alone, but 
rather wait until you have another good reason to
go there too. No reason to rush... the longer we
take to find a good solution, the better it is /ubbthreads/images/graemlins/smile.gif
I thought i would have my parts ordered already too,
but im still looking at a few things. Once im sure,
i'll get what i need. I'd like to make only one
order for everything, and i think i can get that done.


Take care,
Al


----------



## PEU (Oct 9, 2004)

Hi Vic/Al,

one question related to the inductor, can I use the ones found in PC AT suplies? they are about 1.5in in diameter and the core is about .5in? I have many of these.

If not, I know a local shop that sells toroids, so doesn't matter.


Pablo


----------



## vicbin (Oct 10, 2004)

Hi Al,

Thanks for the explanation on the inductor, really clear few things out of my mind. 

But again, lets forget those switcher, National switcher LM2576 simplicity beats out of those switcher with "compensation" feature. I've read all their datasheet and to my surprise, they're not clearly explained on how to utilise it. Looks like they left their customer in the dark and assuming we build em first and solve it later method. /ubbthreads/images/graemlins/frown.gif


Hi Pablo,

Dunno how to answer that, but I believe it is a switcher's inductor hence you can try it ! /ubbthreads/images/graemlins/grin.gif

Regards,
Vic

PS:
Folks, I will be "offlined" for few days ahead, on the field assignment ! Feeding the family first ! /ubbthreads/images/graemlins/smile.gif


----------



## MrAl (Oct 10, 2004)

Hello again,

Pablo:
Gee, im not sure about the inductors inside the switcher.
Im sure some of them would be suited, but you'd need a
way to test them--which means you at least need a way to
measure the ripple current though the inductor.
Perhaps build the Ripple Detect Network and measure 
ripple voltage, im not sure. Normally you would use a
scope. A scope is a very important tool for these kinds
of power supplies, because there is much concern about
the dynamics which can usually only be observed with
a scope.
Some of the tests points about an inductor would be
1. It's inductance
2. It's change of inductance with dc current or it's 
ripple current when used with the chosen switcher ic.

More than likely there is one you can use, but we'd have
to be able to make sure it worked ok.
If you hook it up with the switcher and maybe turn the
input voltage up slowly, you can check the ripple current
to get an idea if it's working or not, or perhaps check
the ripple voltage across the output cap. If the ripple
current is too high (inductance too low) the output
caps might get hot.
When you purchase a ready made inductor, it's got a rating
for highest current so you know if it will work before
you use it.
Sorry this probably doesnt help you that much.

Vic:
Yes, the National switchers look like they will be the
best choice, at least to start with. It takes some of
the guess work out of it. And yes, it's funny that the
data sheets on the comp networks arent that clear with
the other manufacturers. I guess they figure mostly
fixed output applications, which is probably 99% of the
uses of these things.


Take care,
Al


----------



## MrAl (Oct 11, 2004)

Hello again,

Update:
Just to let you know im still working on this
circuit. Almost done 

Take care,
Al


----------



## PEU (Oct 11, 2004)

Hello Al,

take your time, we got plenty of /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/smile.gif

Pablo


----------



## MrAl (Oct 12, 2004)

Hi Pablo,

I have to do a few more tests yet.
I'd like to be reasonably sure this is going to work
well...the next version will have everything.

Take care,
Al


----------



## MrAl (Oct 14, 2004)

Hello again,

This is close to the final version. The output
is adjustable from 0 to 30v with the 30vCT transformer
and of course the right version of switcher ic and linear
device.
The next version will eliminate the requirement for
the center tapped transformer, so that a single winding
transformer can be used.

Take care,
Al


----------



## PEU (Oct 14, 2004)

Hi Al

this is looking great, 

questions:
do you have the list of all the materials?

could you give more specifics on the inductor, may be we can find some premade at digikey.

The transistor at the output of operational thru the 10k is a 2n4401?

searched digikey for 1000uf and 500uf and found none reasonably priced, I tried 4x1500uf or 5x1200uf and none also, I guess I'll look here locally. The 500uf one can be replaced for other more common value?

I'm also updating the list at digikey.


Pablo


----------



## MrAl (Oct 14, 2004)

Hi there Pablo,

I dont really have a list yet, because i've been looking at
so many versions  Each version will have to have
it's own list i guess. It shouldnt be hard now though,
as most of the parts are known.

The inductor will have to support at least 1 amp above
nominal output, so that means if 3 amps out, then
4 amp inductor. If you're going to be looking for
5 amps out later as Vic wants to do, then maybe a
high rated inductor would be better for your purpose.
I'll check Digikey and have a part number by tomorrow
sometime if you like.

Yes, the other NPN transistor is 2N4401 also, but 
2N2222 would work as well.

I noticed that Digikey was a little high on some of the
caps too, so i wanted to order from Jameco. They have
very cheap caps which im hoping will work ok.

If i find anything worthwhile at Digikey i'll add it
to the list also, but keep in mind this is still in
the prelim stage, almost prototype, where we might have
to change something somewhere yet, and we havent actually
tried any known inductor yet either. I planned to start
with a slightly lower rated inductor i already had
from Digikey and work up from there.

The 500uf can be replaced with higher, like 1000uf.

Take care,
Al


----------



## MrAl (Oct 15, 2004)

Hello again,

I found an inductor which looks like it would work
very well for this app. There are two part no's,
one for vertical mount and one for horizontal mount,
depending on your pc board preference:

Horizontal Mount: 220uH, 5.8A, R=0.054, size=30x14,
DK part=M9827-ND

Vertical Mount: 220uH, 5.8A, R=0.054, size=14x30,
DK part=M9920-ND

Make sure to always double check the part number with
the spec's before ordering.

There's a chance this inductor could work up to
5 amps out also.


Take care,
Al


----------



## tonyb (Oct 15, 2004)

Why did you use a dual supply rail with your op amp current limit circuit couldn't you use a single supply instead seems over complicated for what you want to accomplish.


----------



## PEU (Oct 15, 2004)

I guess the negative rail is needed to overcome the 1.25v lower limit imposed by the lm350/317/338, this way you can go from 0 to 30. 
This is my basic analisis, I may be totally wrong... /ubbthreads/images/graemlins/smile.gif

Pablo


----------



## MrAl (Oct 15, 2004)

Hi tonyb,

Thanks for the comments.
The reasoning behind the neg rail is to get better control
over the LM317 type device. In order to adjust down
as low as 0v dc (one of the goals) you need to provide
a negative voltage of at least 1.2v to the LM linear device.
This brought in the negative rail to start with.

Eventually, i'll produce another version that doesnt
use the LM linear device, but instead uses a heavy current
darlington for the series pass element. This might not
require a negative rail if i can find suitable op amps that
also get down to 0v without the need for a neg supply rail.
I'd like to use faster op amps than the LM358 or similar
for this. This would require both high speed (hopefully
10MHz or better) and sensing near ground, or set up a 
different current sensing scheme.
The downside to this idea seems to be the relatively
high priced transistor (i think it's about $7.00).
Maybe find a cheaper one /ubbthreads/images/graemlins/smile.gif

Any ideas always welcome!

One think i forgot to mention (slightly off subject)
is that one of the other switching devices Vic was 
talking about has applications including using them
with high voltage transistors for direct off line
switchers. Except for the increased danger, this would
be interesting too. Imagine the result: no input
transformer (like you were mentioning before) for
current outputs of 5 amps or more may be possible.
Downside is special inductor to provide isolation,
not sure if everyone can get or wind one. Any ideas
here also appreciated.

Take care,
Al


----------



## tonyb (Oct 15, 2004)

Why not use the lm317 in a switching configuration - alot less parts are needed and has higher current handling capability -and efficiency is greatly increased. Refer to Nationals Linear Databooks. Also most circuits draw little if any power at 1.2volts input.


----------



## MrAl (Oct 16, 2004)

Hi tony,

How does using the LM317 result in higher efficiency than
when using the National LM2576 device?
One of the things i didnt like about using the LM317 part
as a switcher was that it requires an external switch
transistor in addition to the LM317 itself.

Yes i agree, most circuits dont draw much at 1.2volts, but
both Pablo and Vic want to go right down to zero volts
out, and if testing something that runs on a single
AA cell for example, you may wish to adjust down to
less than 1.2 volts to test for low battery.
My current built power supply (LM317 based) doesnt go
to zero either :-(

If you have any ideas about the LM317 in switch mode config
let me know.

Take care,
Al


----------



## tonyb (Oct 16, 2004)

The National Linear Data Book One has several designs utilizing simple 3 terminal linear devices (LM350, LM317 and others)configured to run in switch mode for higher current and higher eff. operation. I have built quite a few and have acheived 98% eff. in some designs. I ahve built simple and eff. switchers using a LM741 op-amp and a couple of other components.

tony.


----------



## Burnt_Retinas (Oct 17, 2004)

MrAl, or others,

What function is the 2nd half of the LF347 intended to do?

I at first assumed to provide to 0V capability, but why the need to sense current rather than just locking the ref to the - V ref volts + whatever via resistors? 

We don't learn if we don't ask questions do we.

Chris


----------



## PEU (Oct 17, 2004)

BTW, my friend in Miami received my 5 samples of LM338 from National, so I'll use them instead of LM350, but only to 3A since I don't want to purchase an according transformer /ubbthreads/images/graemlins/smile.gif

I guess the LM338 will work cooler if pushed only to 3A


You see Al, is good to wait /ubbthreads/images/graemlins/smile.gif


Pablo
PS: now waiting for some Maxim samples /ubbthreads/images/graemlins/smile.gif


----------



## MrAl (Oct 17, 2004)

Hello again,

[Please also see update later in this post]

I almost didnt get this posted today...couldnt get back
to CPF for some reason...web problems again i guess.

tonyb:
Oh ok, i thought you might have known of a circuit that
used the LM317 alone to do the switching 
I did some simulations with the LM317 and external PNP
power device and although it does look good, it requires
some extra components such as external PNP power.
I'd probably use a min 10A PNP device.
The other parts are resistors and caps, which set output
voltage and frequency. One thing that bothered me is
that i couldnt really put an upper limit on the max
frequency that is obtainable using their (Nationals)
data sheet app note.
With the National switcher ic, i was hoping most of
the work had already been done and it's a matter of
mostly just applying power 
After all is said and done, we still want a linear on
the output (not that all ps's will need this).
At least three of us want this so that's where the
linear post regulator comes from, which means it still
requires a switcher PLUS a linear.
What else i found out is also interesting (later update
below).

Hi Burnt:
If i understand your question right, you're asking about
the part of the LF347 that connects to the sense resistor
(0.1 ohm) to sense current. The reason for this op amp
is not really to sense current (although indirectly does)
but to sense the small but significant (for precision
operation) voltage that develops across the 0.1 ohm
resistor when the power supply is loaded. One of it's
purposes is to sense this voltage and add it to the
voltage that is already controlling the LM317 (and get
it to go to 0v), so that
the LM317 always puts out the required voltage (say
5 volts) plus the additional 0.100 volts (during say 1 amp
output). Thus, the LM317 puts out 5.1 volts when the
voltage is adjusted for 5 volts and there is an output
current of 1 amp flowing through the load. This keeps
the voltage getting to the load at exactly 5.00 volts.
Without this op amp, at 1 amp load the LM317 would only
put out 4.90 volts when adjusted to 5v and there is
1 amp output flowing, and without changing any adjustments
and removing the load the output voltage would return to
5.00 volts. So, without this op amp the output voltage
would vary with load current. Adding the op amp keeps
the voltage constant with loads zero to 3 or even more amps.
The analysis of that part of the circuit is simple: the
voltage increase that appears across the 0.1 ohm resistor 
with load also shows up at the bottom of the 2k pot and so
compensates for the drop across the 0.1 ohm resistor.

Yes, it's good to ask questions about this stuff.

Pablo:
Oh wow, you lucky!!! You should make out pretty good
with all those parts...you can build five of these (hee hee).

UPDATE:
This is mostly in relation to the new switchers Vic
was talking about (BTW where'd he go again ! /ubbthreads/images/graemlins/smile.gif )

It looks like the other switcher ic's supply a compensation
pin so that you may provide your own comp network -- of
course to get better response with your chosen inductor/cap
combo. It looks as if the response can be adjusted 
somewhat, to control overshoot and ringing on the output,
at the expense of about two to four more small components.
Some tests i've done (on the electro-makiwara )
indicate that there wouldnt be a change in the network
for different voltage outputs, as we intend to use a continuously
variable output.

Even so, how bad can the simpler National part be?
I dont have an 'exact' model to test for this, so
all i can do is guess with a model that i've guessed
at, until the parts arrive.

END UPDATE

Take care,
Al


----------



## Burnt_Retinas (Oct 18, 2004)

MrAl,

OK, I think can see where you are coming from, or heading too for that matter. It's not so much the circuit, but rather why that way. A tad unconventional, but so too is using an LM317 for such a task. Think I ve got that figured also as I can see minor issues with alternatives such as a fixed -ve bias to the 317 which though simpler will have some *issues*. Note, with a 317 ADJ reference to fixed -ve bias there is no need to consider the sense resistor drop, but of course you'll get drops in tracks etc. I feel you had considered this.

Good to see you are not thinking only simple and cheap as are 99% of what I see, but rather precision and accuracy, yet still simple and affordable.

Thanks,

Chris


----------



## MrAl (Oct 18, 2004)

Hello again,

Chris:
Now that you mention it, we could use another ref diode
and connect it directly to the sense resistor and
that might be simpler yet. I'll look into this
next as this would achieve the same goal.

Take care,
Al


----------



## vicbin (Oct 19, 2004)

Hi Al,

I'm back !! Was on field assignment ! again, feeding the family 1st right ? /ubbthreads/images/graemlins/smile.gif

Looks like I don't need to return my 5A switcher eh ? But as plan I'll proceed with LM2576 first then deal with the "compensation network" later, of course with your guidance as always ! /ubbthreads/images/graemlins/grin.gif

It is great to see how the final circuit is evolving through changes, great learning here !

By the way, it seems that other CPFer missed the final goal here. I think you should add/edit your 1st post in this thread about your plan, final design goal and the expectation. (incl. the learning process which I personally love to)

I feel readers still perceived why you, *our honourable CPF Electronic Guru* is doing a LM317 based circuit which supposed to be "so easy" ! NOT, if they know what is in your mind ! /ubbthreads/images/graemlins/grin.gif


Hi Pablo,

You're so lucky ! Congrats ! /ubbthreads/images/graemlins/smile.gif Did you get the 5 Amps switcher too ?


Hi Chris,

I really like this quote from you -> "*Precision and accuracy, yet still simple and <font color="red">affordable</font> *", this is exactly what Mr.Al is doing right now. /ubbthreads/images/graemlins/smile.gif

Imagine an accurate & stable adjustable PS with 0-30 Volt (mv resolution) , 0-5 Amps (mA resolution) with reliable constant current mechanism and what makes this design is special is this PS runs with "*minimal heat dissipations*" ! 
It can supply directly starting from a current devices such as tiny few mA LED up to charging a hunk & bulky SLA battery ! /ubbthreads/images/graemlins/cool.gif 

........and again...as you said, yet simple and affordable ! /ubbthreads/images/graemlins/smile.gif


Hi Tony,

Looks like you've experienced with a lot of switcher cicruits, why don't share your idea or experience "*here*" ? It is an open discussion ! 

I'm so curious and really like to know how did you manage using ordinary LM317 as a switcher can result a 98% efficiency ? /ubbthreads/images/graemlins/ooo.gif

Forgive me for my lack of knowledge, I thought this kind of result can only be achieved "*easily & simple*" using high end synchronous rectifier switcher type ?

Anyway, regarding the below 1.2 Volt requirement, in my case I've done a lot of low voltage circuits and some of them were as low as *0.4 Volt* ! 
Yes, its not a typo, 0.4 volt and that was using Germanium type transistors circuits !

One of my major problems while working on single cell circuits was to simulate the circuit at drained cell on certain level. Believe me, draining a cell is no brainer, but draining a cell to a level you wanted and expecting it to maintain same level is almost impossible. 

"You can tune a piano but you can't tuna fish !" Ha.. /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Oct 19, 2004)

Hi Vic,

Yes, the LM317 was supposed to be 'so easy' but the only
version that turns out so easy is the one that adjusts
1.2v to 20v and has separate output for constant current.

Controlling everything takes more parts :-(
At least these are low cost though, very low cost, parts.


QUOTE
"You can tune a piano but you can't tuna fish !" Ha.. 

Hee hee......
Yeah, but the tuna fish tastes a *little* better
than the piano, im pretty sure...and it
fits on a sandwich a little better too...hee hee.

Take care,
Al


----------



## vicbin (Oct 19, 2004)

Hi again Al,

[ QUOTE ]

It looks like the other switcher ic's supply a compensation pin so that you may provide your own comp network -- of course to get better response with your chosen inductor/cap combo. It looks as if the response can be adjusted somewhat, to control overshoot and ringing on the output, at the expense of about two to four more small components.


[/ QUOTE ]

TWO OR FOUR COMPONENTS ?? Don't have problem even a lot more than that !!! Remember, I survived my last PS project (the one with so many-many discrete components) didn't I ? /ubbthreads/images/graemlins/grin.gif

[ QUOTE ]

Some tests i've done (on the electro-makiwara ) indicate that there wouldnt be a change in the network for different voltage outputs, as we intend to use a continuously variable output.


[/ QUOTE ]

Thank you for the good news ! /ubbthreads/images/graemlins/happy14.gif

I've been google-ing the web for this "compensation network" and still can't find a good literature or explanation on it. /ubbthreads/images/graemlins/frown.gif

Now you have a very interesting and exciting information there ! Please share if you got a chance !

And are you sure you've read your "electro-makiwara" spec sheet ? I'm not worry about your limbs, it is the "Absolute Maximum Ratings" of that thing I'm worry about ! he..he.. /ubbthreads/images/graemlins/yellowlaugh.gif

Vic


----------



## MrAl (Oct 20, 2004)

Hi Vic,

Oh ok, i dont think i have a problem with two to four small components 
(small resistors, small disc caps) so this looks like the way to go
in the future sometime.

There are quite a few theories on designing a compensation network,
probably because there are different interpretations on what the
end goals should be, but then again there are different
approaches too.
Thing is, they all required a good deal of at
least complex number algebra or related to understand.

A simpler way to look at it is this:

Start with the basic output that we already have, an inductor (w/series R)
in series with a cap (w/ some ESR) where the output (Vout) is taken
at the center of the two components. This section is usually referred to
as the "Plant" in control theory.
Now in regulator design we basically want a steady state output
of a certain level and if something changes (disturbance such as line
surge or output load change) we want as little as possible change
to occur on the output and if it does change the change should end
as soon as possible. To see how our plant reacts by itself
(to see if we even need compensation) we can stimulate the plant with
a step wave (level change from one level to a higher level) and
see how the plant reacts.
We dont usually start with zero output, so let's say we already
have the plant running so it's input is at 10 volts (the desired
output). Because of the inductors series R and cap's ESR we might
get an actual output of 9.9 volts at some load current level.
We thus turn the input up to 10.1 volts and so we get close to
10.0 volts output, which is what we wanted.
To see how the plant reacts, we can apply a step change to the
input and look at the output. Applying a step of 1 volt, which
brings the input up to 11.1 volts, we see the output jump up
(or down) and then ring a few times and then after some time
increment it settles back down to a stead state value which is
smooth and unchanging. Measuring the output, we find that it
too has jumped by 1 volt, and stays that high! Clearly,
this would be a pretty crappy voltage regulator, so we look
for ways to keep the output near the desired 10v even if the
input jumps up by 10 volts or even more.

In looking for this solution, we first concentrate on the
steady state error (difference between what we want and
what we actually get on the output). We dont have to look
far to find that much has been done in control theory in
this area already and the basic approach is to use a 
feedback amplifier. The feedback amplifier is basically
a device that measures the error and provides a correction
signal to the driver of the plant so that the output 
steady state level stays at what we want it to be.
That's the first level of compensation, and is always a part
of any control system like this.
Now when we do the same step test, we still end up with
a changing wave output, but after some time increment the
changes damp out and we're again left with the steady
state output, and it's very close to what we wanted (often
VERY close, like 0.001 percent or something like that).

The only problem now is that when we look on the output we
still see ringing for some period of time before we get
the desired output. Our next goal therefore is to design
a amplifier that will either eliminate this or at least
minimize it to some degree. This is where the compensation
network comes in. There's various ways of looking at
this network, but most simply could be this view:

If you look at what we started with, we initially didnt 
look at the output to determine the error, and thus we
didnt generate a correction signal. We got a bad output
error mostly because we didnt measure it.
When we employed the feedback amp alone, we measured the
output level (only the level itself) to help generate the
correct steady state output. Measuring the output level
helped improve the output level's accuracy, but didnt help the
changing part enough.
It makes sense that if we could measure the output change as
well as the level we might be able to correct the changing
output part as well, and it just so happens that this
works, at least to some degree.

Measuring the change with time and using this result to
help improve the response is what it's all about.
In the physical model where you might have a motor,
the output voltage would be 'position' of the motor shaft
at any given time, and the change in position of the motor
would be the velocity. For this reason, the second form
of feedback is sometimes called "velocity" feedback, and
attempts to measure the change in position (voltage) in
order to correct the change in output to make it more
what we want it to be (jump up fast with little overshoot
and settle quickly for a servo, or little change
for a voltage regulator).

Other views work directly in what's called the 's plane'
where the poles of the response are pushed deeper into
the left half of this plane. The position of the poles
determine the response, so we try to move them to
better locations. These kinds of methods have been used
for years and there's quite a bit written on this.

Hope this helps.

QUOTE(Vic)
"And are you sure you've read your "electro-makiwara" spec sheet ? I'm not worry about your limbs, it is the "Absolute Maximum Ratings" of that thing I'm worry about ! he..he.. "
END QUOTE

Hee hee, im not worried either !!! As long as my parts dont blow up who cares /ubbthreads/images/graemlins/smile.gif

Take care,
Al


----------



## PEU (Oct 20, 2004)

This is why I love going to see factories (doing my work selling welding alloys) because I can see and understand how stuff is made and/or works.

Every explanation you give us Al, makes me remember of the good teachers I had in school, the ones that you enjoy listening. Or like reading a Richard Feynman book !!!!

Thanks


Pablo


----------



## vicbin (Oct 21, 2004)

Hi Al,

Great explanation, thank you very much. /ubbthreads/images/graemlins/happy14.gif

For practical approach in determining the value for the compensation network, scope is a mandatory tool right ?

Last time you've mentioned about the small sense resistor will make the current loop somehow slow to react, but the latest one you choosed 0.1 ohm ? 

Thanks & regards,
Vic


----------



## MrAl (Oct 21, 2004)

[ QUOTE ]
*PEU said:*
Every explanation you give us Al, makes me remember of the good teachers I had in school, the ones that you enjoy listening. Or like reading a Richard Feynman book !!!!

Thanks

Pablo 

[/ QUOTE ]

That's very nice of you Pablo and i take that as quite
a complement seeing what this guy has said and done
in the past! Some great ideas from him.
Thanks much.

Vic:
I hoped to get the idea across without using any math, but here is one place where not using math is hard to get around. I hope i was able to convey some information still so that it makes some sense at least.
I think a scope is needed because you need to see the dynamics in action, so you can improve them. Im not sure, but a 'peak' reading meter might work too (a meter that easures the peak and stores it) so that you can try to educe the peak. There's also the oscillatory part, which can be reduced too if you can see it happening. 
Also, dont forget there is always the simulation environment, which can show what values to start with.
I chose 0.1 ohm because in simulation i couldnt find
any difference between using 0.5 ohm or 0.1 ohm.
If it turns out that in the practical circuit we
have to use 0.5 ohm instead it will only mean changing
that resistor and one other 'regular value' resistor
so i dont think we should worry too much here, rather
forge ahead.

I'd also like to thank both Vic and Pablo:
Pablo, for thinking of the idea of powering the
voltmeter with a separate supply source, because
i've now got a meter that 'plugs in' to the wall 
so i can run it constantly by using a wall wart and
large cap replacing the six (count 'em, 6) small batteries
that powered one of my meters which kept running down.
All my other meters run on batteries too, so i have to
either keep buying batteries or keep turning them
off when doing long run tests. Now with this meter i can
plug it in and leave it to read constantly, so thanks go
to Pablo for this great idea!
And Vic, for thinking of doing this power supply in
the first place! Remember it was you, Vic, who started
the original thread for pre-reg switcher a long time ago...
Thanks!


Take care for now,
Al


----------



## vicbin (Oct 24, 2004)

Hi Al,

[ QUOTE ]
*MrAl said:*
I hoped to get the idea across without using any math, but here is one place where not using math is hard to get around. I hope i was able to convey some information still so that it makes some sense at least.

I think a <font color="red">scope</font> is needed because you need to see the <font color="blue">*dynamics*</font> in action, so you can improve them.


[/ QUOTE ]
.... and I've read through this Onsemi switcher data sheet (MC34167) and found an interesting quote which is so inline with your great explanation :

[ QUOTE ]
"The simplest way to optimize the compensation network is to observe the response of the output voltage to a step load change, while adjusting R and C for critical damping. The final circuit should be verified for stability under four boundary conditions. <font color="green">These conditions are minimum and maximum input voltages, with minimum and maximum loads.</font>"


[/ QUOTE ]
It is crystal clear, to be "*practical*" when playing with switcher circuits "*for an optimal & good result*", scope is a must ! /ubbthreads/images/graemlins/frown.gif
I've been desparately looking for a good scope such as this one BitScope 310 or this BitScope BS50U Pocket Analyzer /ubbthreads/images/graemlins/drool.gif (comments please) , but still there are other things in real life that got much-much more higher priorities ! /ubbthreads/images/graemlins/broke.gif /ubbthreads/images/graemlins/icon23.gif

Talking about contribution, idea is just an idea, wont make any good & value without "the real implementation" which is you. /ubbthreads/images/graemlins/bowdown.gif

Thanks & regards,
Vic


----------



## PEU (Oct 24, 2004)

FYI I'm /ubbthreads/images/graemlins/popcorn.gif reading this thread and turning some pieces in the lathe in the meantime Al finishes the prototyping phase /ubbthreads/images/graemlins/smile.gif

And I ordered some samples from onsemi, bad habits are difficult to leave /ubbthreads/images/graemlins/smile.gif


Pablo


----------



## vicbin (Oct 25, 2004)

Hi Pablo,

You are such a /ubbthreads/images/graemlins/evilgrin07.gif , but I'm wishing you good luck though ! /ubbthreads/images/graemlins/grin.gif

Turning some pieces in the lathe eh ? Can I request a "sample" once they're finished ? ..he..he.. just j/k /ubbthreads/images/graemlins/grin.gif

Vic


----------



## MrAl (Oct 25, 2004)

Hello again,

Pablo:
Oh making some new flashlight bodies? Any pic's we can see? /ubbthreads/images/graemlins/smile.gif

Vic:
Pablo made me a new end for one of my minimags so i can use a
three position switch (with Lux mod of course) to dim the thing
to three different settings. It threads right on the end of the
minimag. Very nice of him to do that...i looked everywhere for
a piece that would thread into the end of the minimag and
couldnt find anything pre-made. Thanks again Pablo!

Talking about the scope, i've noticed it's not *too* hard to
compensate by trial and error (trying different R and C values)
if you can view the output wave with a step change applied.
Like that paper said Vic, when you get (near) critical damping
you're about there. I shoot for slightly overdamped to make sure
that the component aging wont allow a future underdamped response,
that's perhaps the only difference. The math end of it however is
very interesting if you're into Laplace transforms or state space
methods, of even simply matrices. The thing i find with the rigorous
math approaches is that you have to know a lot about the response of
the particular op amp used as the error amp in the particular switcher
chip you've chosen. For example, if i 'pretend' that they used an
LM358 op amp circuit (internal to the switcher chip) as the error amp
then i can come up with a near perfect compensation network using one
or more methods. Problem is, it seems that the people who make the
switchers dont publish the data on the op amp, so i cant find anything
out about any of them (yet). Knowing nothing exactly about the op amp
means knowing nothing exactly about the comp network, pretty much.
I've guessed on the response using different op amps to try to get
around this and i think i've found a network that works with normal
to high freq op amps, but the proof will be in the breadboarding.
In any case, a scope definitely makes sense...a lot of sense.
I looked at the ones you (Vic) gave links to, and i must say they
look interesting and the one even seems affordable to a certain
extent ($300). 40MS/s doesnt seem that bad for what we are doing.
The way i figure it, you should have at least 10 samples per HALF
cycle, or 20 samples for a full cycle. Using this criterion, with
40MS/s you can view up to 2 MHz analog signals before you start to
run into problems with details at higher frequencies.
Since the switcher we intend to START with will be around 50kHz,
that will give you 800 samples per cycle, which isnt bad at all.
If we end up going to near 300kHz switcher ic's, that will reduce 
to 133 samples per cycle, which still isnt too bad at all and 
should give you a clear picture of the amount of damping (or lack
of it) when viewing the output.
Another idea is to buy an analog scope (say 20MHz or higher). These
are a bit more money (new) and wont provide storage like the
digitals, but will provide a very clear wave view.

I think next i'll try to get a picture of the complex plane posted
to show the responses obtainable with certain roots. It turns out
to be very interesting to compare various pole positions to the
output of a regulator.

BTW, Viren has offered to etch me a prototype pc board for this
power supply...Thanks very much Viren!


Take care for now,
Al


----------



## PEU (Oct 25, 2004)

Hi folks, there is a couple of threads in the homemade lights forum that shows the progress of 2 lights I'm building.

/ubbthreads/images/graemlins/popcorn.gif

Pablo


----------



## MrAl (Oct 25, 2004)

Hi Pablo,

I'll check them out.

In the mean time, we have to take a vote...

We can exchange the op amp (farthest to the right on the
schematic) and four resistors with another voltage reference
and single resistor. All in favor say 'aye' and against
say 'nay'.
Im asking for this vote because we can do it either way,
and using the op amp means slightly more
complex board and four resistors, and using the ref diode
means buying another ref diode.

Take care,
Al


----------



## vicbin (Oct 25, 2004)

AYE ! /ubbthreads/images/graemlins/wink2.gif


----------



## PEU (Oct 25, 2004)

If the part is common one I vote AYE! 

Pablo


----------



## MrAl (Oct 26, 2004)

Hi again,

That's three aye's /ubbthreads/images/graemlins/smile.gif It's in next drawing!

I like it too.

Take care,
Al


----------



## PEU (Oct 28, 2004)

Today my friend in Miami received more samples from National, this time the LM2576 /ubbthreads/images/graemlins/smile.gif

Now this project is even cheaper to build... /ubbthreads/images/graemlins/smile.gif

/ubbthreads/images/graemlins/popcorn.gif


Pablo


----------



## MrAl (Oct 29, 2004)

Hi again Pablo, Vic, Viren, other CPF folks,

Oh i guess the cost for you is coming to almost nothing then Pablo? That's great!
Vic has been very generous in sending off some parts for me to use for this power supply including a switcher LM2576 and a big toroid core, so my cost has already come down too!

UPDATE

I have some less than good news. Yesterday i did a few more tests and found that the second ref diode idea wont work as well as the op amp and four resistors solution, so im going back to that solution. I did a simulation at low current levels (output) like 1ma, 5ma, 10ma, 20ma, and found that the op amp works much better in insuring that the output level remains constant. Im sure people from CPF (me too) will want to use this power supply at some point to test low current LED's (20ma) at 5ma or even less, so i'd like to see it work down that low too without any problems. With the op amp it's looking very good, so i think we should keep it even though it means using four 1% resistors. They are still cheap (digikey). Im sorry i didnt see this sooner or i wouldnt have bothered anyone with mentioning it.

Cant wait to see this thing flying!

Vic:
With your original power supply, how hot did the LM2576
ic get at 3 amps output? Very hot or just a little,
and did you use a heat sink and if so how big?


Take care,
Al


----------



## vicbin (Oct 29, 2004)

Hi folks,

Pablo !!

Don't forget the LM2678 (5 Amps switcher) and LM1084 (max. 1.5 Volt drops @ 5 Amps) ! he..he.. /ubbthreads/images/graemlins/blush.gif

Too bad, I don't have that kind of luxury here ! /ubbthreads/images/graemlins/mecry.gif


Al,

From the 1st LM2576 experience, we got our 3 Amps (I think it was about 2.8 to 2.9 A) from the switcher alone not through the post linear regulator and powering a cheap incand 12 V car lamp. 

Using hi-tech, state of the art and god made "finger thermometer" /ubbthreads/images/graemlins/grin.gif , it was hot (I think I could not stick it for too long) and with moderate sized heatsink. Although I didn't notice there was any significant temp increase at the inductor. Anyway, is this normal ?

Since it was tested with incand lamp, dunno how big the ripple was.

Hey, no problem about the cancelled plan for new cc loop mechanism, no need to feel sorry, infact I'm curious how it looks even we're not going to use it ? Just want to learn a few kungfu tricks. /ubbthreads/images/graemlins/smile.gif

About the voltage control loop, how accurate or stability projected with your design ? mV resolution ? Does it need a minimal load for regulation ?

Regards,
Vic


----------



## MrAl (Oct 30, 2004)

Hi Vic,

Thanks for the heat sink info.

Here's the old drawing, using the ref diode instead of
the op amp...







See the 2.5v ref diode...the 1k resistor provides bias
current for it, but some of the current flows through the
0.1 ohm resistor (which normally wouldnt be too bad because
it's a low current typically 3ma or so). The only problem
is when you adjust the output current to a low value this
interferes with the current measurement and so it doesnt
work very well at low current settings like 20ma.

Min output current? There might be with the practical
circuit, but the simulations didnt show any needed.
I'll have to wait to test the breadboard and take a
few measurements.

The final version wont be long now, im almost done.
I've been juggling a lot of variables because of the
many options:

* 0 to 10v
* 0 to 20v
* 0 to 30v

* 0 to 1.5 amps out
* 0 to 3.0 amps out

For the very low voltage option i was trying to elminiate
the small 78L15 type regulators. Im probably going to
use +/- 6 volt regulators for my own version (12vac in).

I've got the final down to single winding input (no CT needed)
and other nice things, like fine tuning on the current
setting and the ability to adjust right down to 0.000 amps
output. I felt that as long as we were doing this, might
as well get some nice features built in.

If you want this drawing make a copy because it's not
really of much use right now so im going to replace it
with the current drawing (with all the updates) which i'll post once you've seen this one.

Take care,
Al


----------



## vicbin (Oct 30, 2004)

Hi Al,

Thanks for the drawing and its captured ! Another kungfu kicking styles learned today ! /ubbthreads/images/graemlins/huh.gif

Wow !!! Fine tuning & adjustment for current control down to <font color="red">*0.000 Amp !!!!</font>* /ubbthreads/images/graemlins/ooo.gif /ubbthreads/images/graemlins/buttrock.gif 
Does it include for the voltage control too ? 

The max output variations you're preparing (1A and 3A), add the 5A, please ! /ubbthreads/images/graemlins/grin.gif

Looking at Cin & Cout for the switcher at 5 A ? Is it Cin must be "huge" (12 X 1000uF or 6 X 2200uF) ? and also Cout at least 6 X 1000uF ? For me, space is not a problem !

Updating my shopping list for capasitors ! /ubbthreads/images/graemlins/naughty.gif

Regards,
Vic


----------



## MrAl (Oct 30, 2004)

Hi Vic,

Here's the most recent drawing.

Yes, fine turning for voltage too /ubbthreads/images/graemlins/smile.gif
I'll have to add notes for 5 amp output.

Cin: 2x1000uf per amp. (10,000uf for 5amp)
Cout: 1x1000uf per amp. (5,000uf for 5 amp)

We might get by with less Cout but i'll wait for the
breadboard to decide on the final value.
At least we know we'll get smooth voltages.

Here's the drawing:





Take care,
Al

P.S.
Pablo is that 470uf cap better for you than the
500uf one?


----------



## PEU (Oct 30, 2004)

Hi Al/Vic

I guess is more findable Al /ubbthreads/images/graemlins/smile.gif Can I order sample caps online? /ubbthreads/images/graemlins/crackup.gif

Vic, you're right, I can ask for the 2678, not sure if its going to be delivered on time (my friend sends me the stuff mid november). Will try. /ubbthreads/images/graemlins/smile.gif

/ubbthreads/images/graemlins/popcorn.gif


Pablo
Edited: Already placed sample orders for the ones you suggested Vic /ubbthreads/images/graemlins/smile.gif


----------



## Crux (Oct 30, 2004)

FWIW, rather than buying both 2.49k AND 4.99 1% resistors (Digikey minimum qty = 5), you can parallel two 4.99k to make 2.49k OR series two 2.49k to make 4.99k. Not a big deal, but something to keep in mind.


----------



## vicbin (Oct 31, 2004)

Hi folks,

Al,

Yes, finally..its here ! Its almost final right ? Or you still have other "hidden" kungfu blow to come ? /ubbthreads/images/graemlins/smile.gif

I'm also going to start breadboarding on the linear part soon !

Questions :

- Is it possible to increase the fine potentiometer to 500 Ohms ? While maintain the ratio of 10:1 to the coarse one, since 100 Ohms trimpot is easy to find but not for potentiometer here ! The lowest I can find is at 500 Ohms. /ubbthreads/images/graemlins/frown.gif I'm hoping it will not causing you trouble to change/adjust all other values. /ubbthreads/images/graemlins/blush.gif

- Is it possible to have a voltage trimmer as the current does ?

Finally, if you still have your typing stamina, "explain" the Voltage & Current control mechanism please ? /ubbthreads/images/graemlins/help.gif /ubbthreads/images/graemlins/bowdown.gif

My brain is starting slow and difficult to digest it ! /ubbthreads/images/graemlins/banghead.gif


Pablo,

What caps are you talking about ?


Crux,

Hey, thanks for that tips, you know in this kind of stuff, "*THE DEVIL IS IN THE DETAILS*" ! /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Oct 31, 2004)

Hi again folks,

Pablo:
With these filter caps a small difference doesnt make much difference,
like 470uf instead of 500uf. Samples online? Gee good question,
i dont know but maybe someone else does?

Crux:
Thanks for the suggestion and i'll keep this in mind.

Vic:
Yes final almost 
You can throw the linear part together and see how it works alone.

It's possible to increase the fine pot to 500 ohms if you increase all the
other resistors by 5x too, like 1k pot to 5k, 2.7k to (approx) 5*2.7k,
trimpot 5 times original, and 47 ohms to 250 (or closest standard).

It's possible to have a voltage trimmer (to adjust to 0.000v output
for both pots adj'd fully ccw, but it will take another op amp section
and one resistor and one trimpot. If you'd like this it's easy to add so
no prob.

I'd be glad to add some notes about the working of the voltage and current
control...i'll get back with another post possibly a little later or tomorrow.

About the cap: Pablo was looking for a 500uf cap and couldnt find one of
that exact value so i suggested a 470uf cap and changed the schematic too.
Usually i work with nice round numbers (like 500) and then later adjust
the schematic to show the real life obtainable values.

Take care, and Happy Halloween!
Al


----------



## vicbin (Oct 31, 2004)

Hi Al,

Thanks ! Since you already got this far, why not just add the adjustment for voltage ! /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/popcorn.gif

Will post the result on once I tested it.


Hi Pablo,

Well, if you still insisted on getting 500uF, you can parallel 470uF + 22uF + 10uF = 502 uF , that is quite close though ! he...he... /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Oct 31, 2004)

Hi Vic,

Yes, i agree. I little more circuit wont hurt 

No need to go through all that cap paralleling (hee hee)
as 470uf is good enough 

Take care,
Al


----------



## MrAl (Oct 31, 2004)

Hi again,

Here's the latest schematic...
This one has a meter amplifier to allow reading 1.000 volts
for 1.000 amps output.
Note that the trim pots MUST be adjusted BEFORE installing
to prevent problems. 
Also, when adjusting the pots dont adjust all the way to 
either end. This saves on parts.







Here's a brief explanation of the voltage and current
control...

Voltage contol...

IC6 pins 1,2,3 form a 2x amp which makes 2.4 volts from
the ref diode VR1. The pot allows adjusting this voltage
to make up for problems with the two voltage adjust pots
(R3 and R16) which dont allow them to go to 0 ohms, and
make up for a mismatch between R4 and R17.

The IC5 pins 5,6,7 form a adder/subtractor which
adds the voltage across the 0.1 ohm sense resistor and subtracts
two times the voltage across the upper 1.2v ref diode. It can do
this because the non inverting gain is 1 and the inverting gain
is -1. This puts the voltage at pin 7 equal to: 0.1*i-2.4

With no current output (0v out), v7 equals -2.4v, and
with the two voltage adj pots adjusted fully ccw
the two 100 ohm resistors (one at pin 7 and R4) divide
this down to -1.2v at the ADJ pin of IC2, which provides the
0v output.
When there is current flowing, this current times
0.1 adds to the -2.4v signal which adds to the bottom
of the voltage adjustment resistances (R3, R16, R17) to
raise the output level to an amount equal to the amount
across the sense resistor. This keeps the output between
Vout and the left side of the sense resistor constant with
load. This method is pretty accurate and should provide
tracking to within about 2mv with load. There will be more
drop in the external leads than that. This works to 5 amps
too.

Current control...

The heart of this is the secton of IC5 pins 1,2,3.
All this does is compare the voltage across the sense resistor
(which is 0.1v per amp) to the adjusted voltage at the wiper of
the 1k pot. When the voltage gets above the wiper setting the
op amp output starts ramping up from V- until the base of
Q3 (through the 10k) is driven high enough to
cause conduction collector to emitter. This
occurs pretty fast (fast op amp slew rate) and once this transistor
conducts it starts to pull the bottom of R4 down toward about
-3 volts or so. This causes the output to drop, which lowers
the current, hence the current limiting.
The setting is quite accurate, so that once set, the power
supply can function as a precision current source.
The trim pot is there to allow adjusting for 0.000 amps out
when both current set points (coarse and fine) are set fully
ccw. This is needed in case the offset of the LF412A (which can
be about 1mv) is such that it wont allow adjusting
to zero output. Without this trim, the output might still go
as low as 30ma, which isnt bad, and will elminate R12, R11, and VR2,
if R10 pot bottom is connected to ground. This is of course an option
for saving parts for those who dont require adjusting to exactly
0.000 amps output.
Also interesting is that if the trim pot is replaced with a 3.3k 
resistor (as shown on schematic) it will allow adjusting down
to 0.000 amps but may go down slightly negative, which doesnt
hurt either in most cases. The 47 ohm and second LM385 is still
required for this however.

Hope this helps.

Take care,
Al


----------



## PEU (Nov 1, 2004)

Hi Al,

Since the design is close to final, can we do a critical parts list?

Why I ask?

I have a friend coming from USA nov/18 and since some parts are difficult to find here, I can order them from digikey, I mean, 1% resistors, trimpots, multiturn pots, etc. I may even order many values for 1% just in case. What do you think Al?

The others I already have for free /ubbthreads/images/graemlins/smile.gif


Pablo


----------



## vicbin (Nov 1, 2004)

Hi Al,

Many thanks for the notes, its much-much more clearer now !!

Again, other noob questions (I hope you're not getting tired and bored of my questions) : /ubbthreads/images/graemlins/blush.gif

- Does the voltage loop stability depend "ONLY" at the reference diode (VR1) ? What happened if there is a drift at the LM317/350/338 internal reference (1.25V) ? 

- Any reason why R18 to R21 values are 4.99K for the voltage adder/subtractor IC5 opamp ? 

- As you said, if both trimmers (volt&current) value change to 500Ohm, just multiply the whole series of voltage divider by 5, please verify if these list of resistors are correct:

Current loop :
R8=2.7K -> 13.5K
R9(coarse pot)=1K -> 5K
R10(fine pot)=100 -> 500

Voltage loop :
R4=100 -> 500
R3(coarse pot)=2K -> 10K
R16(fine pot)=100 -> 500
R17=100 -> 500

Did I miss other components ? I hope this changes won't affect/compromise your design quality, if so, forget it, I'll try harder to find it. 

For other readers, please continue with the proposed value by Al, it is just my problem in finding lower than 500 Ohm potentiometer locally, no problem for trimpot though.

- Any chance for a CCM indicator /ubbthreads/images/graemlins/drool.gif , please ? /ubbthreads/images/graemlins/bowdown.gif 

Regards,
Vic


----------



## PEU (Nov 1, 2004)

Hi,

Just finished redrawing the schematics into expressPCB program. This is the 1st step into making a PCB board, please check it for errors:

Schematics Image

Power Supply Schematic file for ExpressPCB 

ExpressPCB program (free)

/ubbthreads/images/graemlins/popcorn.gif

Pablo


----------



## MrAl (Nov 1, 2004)

Hello again,

Pablo:
Ok, i guess it's time to start on a parts list.
Wow, nice drawing. How'd you do that drawing?
Note that the LM385's have a "1.2" suffix.
This is important because they have other types.


Vic:
I dont mind questions as long as i have answers for them /ubbthreads/images/graemlins/smile.gif

If the LM317/x/x internal reference shifts, that's life. It's
supposed to be pretty good however, so i dont think that's much
of a concern. Why did you see something somewhere that may have
suggested the reference would shift a lot?
One of the things about that regulator is the drift is much better
than other three terminal regulators, but let me know ASAP if you
find out any possible problem here.

R18+ should be 1% values to insure that they are all the same.
An error in one or more values relative to another could cause
the output current with load to track incorrectly (ie 5.000v with
no load, 4.980v with 1 amp load). Im hoping 1 percent is good 
enough.

Im sorry but you cant change the voltage loop resistor values.
You can still use a 500 ohm pot for the fine adjustment if you dont
change any other values, but it just wont be quite as fine. It may
help to parallel a 470 ohm resistor with the 500 ohm pot, you can try
that.

Yes, a CCM indicator sounds like a good idea. I'll add that right
away. Let me see if i can get back with a new schem a little later.

UPDATE

Im going back to the LF412 instead of the LF412A, because
the 'A' suffix part cost $5.00 each!!! on digikey!!!
The other one is $1.00, better /ubbthreads/images/graemlins/smile.gif

Take care,
Al


----------



## PEU (Nov 2, 2004)

I did the drawing with the ExpressPCB Schematic program (the link above).

The drawing process is not as simple as microcap, but when you have it, then doing the PCB is very simple, I liked the fact that you can draw a component if missing or redraw an existing one so the pin layour helps drawing the schematic.

Al, as soon you give me the OK on the drawing I'll start with the PCB.

I modified the schematic, because it was drawn using a wrong LM385, now the links above are updated.

/ubbthreads/images/graemlins/popcorn.gif

Pablo


----------



## vicbin (Nov 2, 2004)

Hi Pablo,

Thank you, that is very nice ! /ubbthreads/images/graemlins/smile.gif 

What size of board you're planning ? Is it in one piece for all components or separate board for linear and switcher part ?



Hi Al,

Thank you Sensei, for your patience and leniency with this humble, slow brain apprentice ! /ubbthreads/images/graemlins/smile.gif ..he..he..

[ QUOTE ]

If the LM317/x/x internal reference shifts, that's life. It's supposed to be pretty good however, so i dont think that's much of a concern. Why did you see something somewhere that may have suggested the reference would shift a lot?

One of the things about that regulator is the drift is much better than other three terminal regulators, but let me know ASAP if you find out any possible problem here.

[/ QUOTE ]

Ok Al, if you say it is good, then it is best for me ! /ubbthreads/images/graemlins/grin.gif
The reason I asked is in the past when I was toying with 5mm LED with constant voltage (not CC and it was on purpose) with LM317, the monitored current through the LED was increase when the regulator dissipates amount of heat. But I didn't keep the information.
Looking at the LM317 datasheet, the reference stability against junction temp is quite good right ? Maybe it is nothing as you said, forget it.

[ QUOTE ]

R18+ should be 1% values to insure that they are all the same. 
An error in one or more values relative to another could cause the output current with load to track incorrectly (ie 5.000v with no load, 4.980v with 1 amp load). Im hoping 1 percent is good enough.

[/ QUOTE ]

So for 3 Amp setting, are those resistors still at 4.99K ?

[ QUOTE ]

Im sorry but you cant change the voltage loop resistor values. You can still use a 500 ohm pot for the fine adjustment if you dont change any other values, but it just wont be quite as fine. It may help to parallel a 470 ohm resistor with the 500 ohm pot, you can try that.

[/ QUOTE ]

Ok, no problem, actually I did some shopping few days back and still no luck and the only one available is 10 turns Bourne pot which cost approx. $10 ! Will see how is the perfomace using your suggestion first then decide on it ! /ubbthreads/images/graemlins/smile.gif

[ QUOTE ]
Im going back to the LF412 instead of the LF412A, because the 'A' suffix part cost $5.00 each!!! on digikey!!!
The other one is $1.00, better /ubbthreads/images/graemlins/smile.gif

[/ QUOTE ]

Ouch, what a margin !! /ubbthreads/images/graemlins/eek.gif

Look ! What I got for 1 buck for those 5 LF412s ! /ubbthreads/images/graemlins/grin.gif






5 x 1.2 Volts VRs are ready and also 3 schottky diodes (2 X 45V/16A and 45V/10A) ! /ubbthreads/images/graemlins/smile.gif

That ICL7135 is for 4.5 digits voltmeter since you said for current the resolution is capable mA accuracy, 3.5 digits voltmeter won't cut it ! 

<font color="grey">pssssssst... Pablo, I hope your friend in FL still got a chance for carrying this new one ? /ubbthreads/images/graemlins/grin.gif </font>

Some other "small" things I bought on that day ! /ubbthreads/images/graemlins/grin.gif






Also found some new toy...err..... I mean new species of toroid !! man......I think I'm suffering an "IC" disease (IC=Inductor Cores) ! /ubbthreads/images/graemlins/crackup.gif
Planning to play with them in our switcher circuit ! /ubbthreads/images/graemlins/smile.gif






Regards,
Vic


----------



## MrAl (Nov 2, 2004)

Hello again,

Pablo:
I've been fine tuning some circuit values but i think
everythings been done now. I'm just ready to start
on the full parts list. Give me another day or so ok?

Vic:
hee hee.
Yes, the 4.99k resistors are for all versions. Im glad
we dont have to change every resistor for the different
versions.
BTW, i added the LED and i'll have the drawing up later or
tomorrow morning.
Guess what? i cant find the darn 100 ohm pot for less than
something like $6.00 !!! That's not good. Now i know
why those big power supplyes are $150.00 and up...those
darn pots are so expensive !!! hee hee.

WOW!! All those nice parts for 1$ ??? Wow, that's really
good and you're lucky you can find them for that price.
I'd like to be able to order from your supplier too!! /ubbthreads/images/graemlins/smile.gif
Nice toroids too! Looks like you're all set for making many
inductors right?

Oh, i forgot i was going to add notes for 5 amp version.
That's next.

Take care for now,
Al


----------



## PEU (Nov 2, 2004)

Vic, I plan to do a single board PCB because that suits me the best, but I can do a 2 part board if you tell me the split points for sure. 

Where do you source parts??? these are reaaaally inexpensive, I can pay here $1 for just a LF412CN or $12 for a LF412MH, may be you can buy for us the parts even with shipping is less expensive than digikey, I can sed the money via paypal.

You can check the prices I expect to pay in these sites: www.electrocomponentes.com.ar or www.elko.com.ar 

<font color="666666"> The ICL7135 sells here for about $3, the samples I ordered from maxim still aren't shipped, at the moment I "only" have 2 sample orders from National, plus one on the way that I guess will arrive on time, and a nice sample batch from Onsemi, they charge $11 for overnight delivery, but you can order A LOT of samples look:

SAMPLE 25 16792503 2N3773
SAMPLE 25 16792503 2N6509
SAMPLE 25 16792503 MMBT489LT1
SAMPLE 25 16792503 SS24T3
SAMPLE 5 16792503 MC33063ADR2
SAMPLE 5 16792503 MC34063AP1
SAMPLE 5 16792503 MC33063AVP
SAMPLE 5 16792503 MC34063ADR2
SAMPLE 5 16792503 NCV33063AVDR2
SAMPLE 5 16792503 NCV33063AVDR2G

(all those 33063/34063 are for building flashlight prototypes)

The value of just the 25x 2n3773 to3 transistors is more than $11 

Off topic, but I also have some liIon cells from foursevens and some board/lenses/LS from lambda waiting there too

</font> 

Al, no problem take your time /ubbthreads/images/graemlins/popcorn.gif 


Pablo


----------



## PEU (Nov 2, 2004)

Vic, how much do you paid for the 1000uFx100 caps? 

Best price here is around $0.8 for 1000x63 or $1.40 1000x100
Also found $3.8 for 5000x70 

do you have a link of your provider?

And BTW, why did you choosed 100v instead of 63v for the caps rating?


Pablo


----------



## vicbin (Nov 3, 2004)

Hi Al,

Yippee....CC indicator ! /ubbthreads/images/graemlins/clap.gif

[ QUOTE ]

Guess what? I cant find the darn 100 ohm pot for less than something like $6.00 !!! That's not good. Now i know why those big power supplyes are $150.00 and up...those darn pots are so expensive !

[/ QUOTE ]

If the final result is good, I'm thinking to skip the coarse and fine pot and choose to use the expensive 10 turns pot instead. It should be "adequate" for fine dialing right ? /ubbthreads/images/graemlins/smile.gif

$1 only for 5 LF412, not include those VRs, diodes and the AD chip ! C'mon, if all them cost $1, they're really dirts ! /ubbthreads/images/graemlins/icon15.gif ..he..he..

Too bad, because of the timing, I was hoping can pack some of those opamps & some new cores to you too. Btw, did you receive those "atomic bomb detonators"...err...cores ? he..he... /ubbthreads/images/graemlins/grin.gif

My suppliers are like traditional shops, sort of like Tokyo's Akihabara district with many-many small shops. There is no luxury of online shopping like Digikey here ! /ubbthreads/images/graemlins/frown.gif 
This kind of districts are common in the Asia region, and you can find this kind of electronic geek shopping districts ( GEEK ? Sorry, may its just me ! /ubbthreads/images/graemlins/smile.gif ) in every big cities like Hongkong.. and etc. For these shops, the electronic components actually are fast moving goods and sometimes to speed their cash flow they're selling stuffs for a very low margin. I believe the reason why some stuffs are so cheap is because nowdays most of electronic components were made in Asia region.











These pics are not mine, I just randomly grabbed from google since they looks almost the same here.

I had to visit lot of these shops to find the stuffs so there is no one stop shopping shop here, and most of the time it needs a lot of bargaining "from shop to shop" like hunting. Sure it needs a lot of walks & time, but sometime I could get a very good bargain. For example those 3 schottky diodes above, the shopkeeper was so nice that he allowed me to select from a pile of them and he even borrowed me their DMM for me to hunt down the lowest forward voltage diodes ! Spent almost 30 minutes just to buy 3 diodes, not bad eh ? he..he.. /ubbthreads/images/graemlins/grin.gif And the other fun parts was I can watch a lot of weird/exotic stuffs, hard to find or "ancient" electronic components. Remember I told you about tyre sized toroid ? /ubbthreads/images/graemlins/eek.gif

The constraint is time + energy, since they're closed at weekend, I need to take one full day off just to shop even for few components. /ubbthreads/images/graemlins/frown.gif


Hi Pablo, /ubbthreads/images/graemlins/smile.gif

I'm planning to split them into 3 pieces rectifier+powercaps, switcher part and linear part. I think I will design the PCB myself since the rectifier+powercaps and the linear part are already 5 Amps ready. plan to implement 3 Amp switcher first and then move on to 5 Amps. 

Thank you very much, really appreciate your offering ! /ubbthreads/images/graemlins/smile.gif

I'm not really planning to re-sell components since those shopping activities are very time consuming. I could help though but shipping cost is a bit expensive and I'm worry it will not justified. /ubbthreads/images/graemlins/frown.gif

A bit off topics, I was looking at your "other" project sample list...this is weird and what a coincidence, I also bought 4 MC34063s at that day too ! /ubbthreads/images/graemlins/ooo.gif




Do you mind share what are you working on with those 1.5A switcher ICs ? also some huge TO3 power transistors ? planning to power thousands of LEDs ? /ubbthreads/images/graemlins/grin.gif 
Plan to use them in my car for simple small sized buck converter for LSs and other project.

It is nice that your country has an online shops, but the price a bit steep, don't you think ? 

Now, price per piece I've got so far :

LF412CN : $0.2
LM385-1.2 : $0.8 (wrong shop ?) /ubbthreads/images/graemlins/thinking.gif
ICL7135 : $2.9 (need to improve my bargaining skill ?) /ubbthreads/images/graemlins/grin.gif ..he..he..
MBR1045/MBR1645 : $1.5 (with the luxury of choosing the best one/lowest VF, will maintain that good relationship) /ubbthreads/images/graemlins/naughty.gif
1000uF/100V : $0.9 (abit less than yours)
470uF/100V : $0.3 
MC34063A : $0.25

The reason why I choose 100V instead of lower one is these caps are just ordinary cap and their ESR is higher compared to specialized low ESR cap for switching circuits. And it is known fact that the higher the voltage rating, the lower their ESR. 

If there is no space limitation or other concerns like short switching power path on PCB, we can even use the 1000V one ! The higher the merrier ! Minimal voltage rating at least for the switcher Cin should be 63 Volt if you plan to use the 0-30V type. 

The low ESR cap price is "alot more" expensive and for higher voltage rating like 50V, it is even worst. /ubbthreads/images/graemlins/frown.gif 

For example, why 1000uF X 6 is better instead of 3300uF X 2 ? By paralleling more smaller caps are better than fewer caps with equal capacity (assuming same v rating), since they will have lower ESR and higher RMS rating "plus" better heat disspations too (larger skin surface) when the switcher on high load.
Cap temperature can increased by itself and if they're in a prolonged warm/hot environment, it will shorten their life span because of drying electrolyte inside them.

Again, I'm no expert, this is what I've learned through the switching literature, CPF and our sensei Mr.Al ! /ubbthreads/images/graemlins/smile.gif 

Regards,
Vic


----------



## MrAl (Nov 3, 2004)

Hi again,

Pablo:
Cant edit the page on the web site to post the latest
schematic. Is something wrong with the site?

Vic:
Oh ok i understand the pricing now.
Geeze, all those shops sell electronic parts? wow?
I wanted to post the latest schematic but the site is
not working or something so Pablo will have to look into
this.

Almost done with the parts list now too including
1.5 amp, 3 amp, 5 amp, 20v and 30v versions.

Take care,
Al


----------



## koala (Nov 3, 2004)

I've been following this from PEU's PC power supply, is it too late to join now? /ubbthreads/images/graemlins/grin.gif

If I am not wrong, this variable circuit can supply up to 0-30volts, 0-3amps with a 30vac transformer. Right? Question: 
1) How does a 30vac transformer supply 30vdc at 3amps? Or is it limited to 30vdc 1amps? 

2)So how do I know when I hit the limit? Is there a over-current trip or it will just blow up(sorry bad joke for MrAl /ubbthreads/images/graemlins/naughty.gif)? /ubbthreads/images/graemlins/grin.gif Fuses maybe?

3)Where is the most appropriate place to fuse? I am guessing before the primary, after the secondary and at the outputs?

4)I remember there's a pictorial essay where a bunch of talking dmm sitting in the bin cursing one another /ubbthreads/images/graemlins/hahaha.gif yes vic it was very funny. So How would I wire one up to monitor the output? The IC6 pin 7 goes out to meter. So if I wire up a dmm to read the outputs, what about the 9v power supply for the DMM? Can I have a LM340T9(9v) regulator connected to steal some power for the dmm? Using 9v batteries for me is just too impractical.

Sorry but you guys are listening to a software programmer who has alot of interest in building a powersupply. You may laugh at me but please correct my mistake.

/ubbthreads/images/graemlins/popcorn.gif
Vince.


----------



## PEU (Nov 3, 2004)

Solved Al, too many amps in a single page /ubbthreads/images/graemlins/crackup.gif ...nah, just a glitch, a flag file wasn't removed properly.


Pablo


----------



## PEU (Nov 3, 2004)

Hi Vic,

No I don't have an actual plan for those power transistors, just used them as a "filler". Same with the SCR's but these are the type my lathe uses, and if something blows these SCRs are the 1st ones ... /ubbthreads/images/graemlins/smile.gif
Tried to add power diodes but they weren't readilly available.

The 34063 will be used in Lambda IllPill configuration, I may add a schotky + cap at the output for better results.

We do have a street (3 blocks) with many electronics shops here too, even the online ones have branches in that street, but you cannot mess with the parts... and the prices aren't better than the online ones /ubbthreads/images/graemlins/frown.gif

Good tip on the caps, didn't know that fact.

Regarding the PCB, you should try expressPCB, once you link the schematics to the pcb program, drawing boards is a snap.

BTW, where are you in Asia?


Pablo


----------



## koala (Nov 3, 2004)

Ok... I just went through the latest schematic.. and things are looking OK for me so far... I need some help on component substitute..

*D1,D2,D3,D4 1N5402 200V 3A Rectifier Diode*
substitute: 1N5404 400V 3A Rectifier Diode?
http://www.onsemi.com/pub/Collateral/1N5400-D.PDF

*D5,D6 1N4003 200V 1A Rectifier Diode*
substitute: 1N14004 400V 1A Rectifier Diode?
http://www.onsemi.com/pub/Collateral/1n4001rev5dx.pdf

*D7,D8 1N4747A*
substitute: 1N4747 20v 1W Zener?

*D10 1N5822 40v 3A Schottky Rectifier *
substitute: 1N5882TR 40v 3A Scotty Diode?
http://www.onsemi.com/pub/Collateral/1N5820-D.PDF

*D11 1N5226 3V3 400mW Zener*
substitute: 1N4728 3V3 1W Zener?

*IC3 78L15 +15V 100ma Regulator*
substitute: 7815/LM340T15 +15v 1A Regulator overkill? /ubbthreads/images/graemlins/buttrock.gif

*IC4 79L15 -15v 100ma Regulator*
substitute: 7915/LM320T15 -15v 1A Regulator overkill? /ubbthreads/images/graemlins/buttrock.gif

*IC5, IC6 LF412A Dual op-amp*
substitute: OUT OF STOCK ??? /ubbthreads/images/graemlins/banghead.gif /ubbthreads/images/graemlins/twakfl.gif /ubbthreads/images/graemlins/rant.gif /ubbthreads/images/graemlins/jpshakehead.gif /ubbthreads/images/graemlins/icon23.gif /ubbthreads/images/graemlins/frown.gif

*Q1 2N4403 PNP ampliflier*
substitute: PNP 2N3906?

*Q2,Q3 2N4401 NPN ampliflier*
substitute: NPN 2N3904?


----------



## MrAl (Nov 3, 2004)

Hi there,

UPDATE:
Complete parts list on the way...about an hour from now /ubbthreads/images/graemlins/smile.gif
New schematic with several small changes...Check back.

koala:
No not too late to join, welcome! There's about 4 or 5 of
us building this power supply now.
Yes, the variable circuit will go 0-30vdc, 0-3 amps with a 30vac transformer.
The 30vac gets rectified to dc first.
There are various current limiting methods...
First there is the set point (via coarse current set) which forces
the output to be limited to whatever you set it for (2 amps perhaps?).
Second, there is limiting internal to the LM317/350/338.
Third, there is limiting internal to the switcher ic.
Fusing is a good idea, primary and secondary.
Your part substitutions look ok to me (1N4004 diode too) but double
check the new parts with the newest schematic as some small changes have
occurred.
If you'd like to power the meter with the existing supply, we *might* be
able to rig up two or so caps and some rectifiers that will run the meter.
Would you like to try this so you dont have to use batteries?
What kind of programming you do if you dont mind me asking?


Pablo:
Still doesnt work. Cant delete or add new schematic.
BTW, you'll have to update your schematic with this new schematic, and you
may want to check for errors because i saw a shorted cap, no ground for
one cap, and a few other things...might want to go over it?

Vic:
No didnt get any parts yet. How where they shipped?




Take care,
Al


----------



## koala (Nov 3, 2004)

Thanks for the help. I probably won't start building until I could find the LF412A Dual op-amp.


Offtopic What kind of programming? I am a pretty young programmer.

Currently
vb.net, perl, cobol

Previous commercial experience
c, c++, java, asp.net, php, python

Personal interest
Bash shell, Atmel AVR asm, Microchip PIC asm

RIP / rusty
Basic, Lisp, flex, bison, motorola mc64k


----------



## MrAl (Nov 3, 2004)

Hi again,

koala:
Ever hear of a language called Euphoria?
BTW, dont bother with the 'A' version of LF412.
Go for the non A version as it's a lot cheaper.
The Schematic is updated by Pablo did something to the
site so i cant upload the new schematic. He'll have
to fix it before i can post it.


UPDATE

Here's the parts list. There's two parts.
Part 1 deals with every version, while Part 2
is for specific versions.

PART 1

All resistors 1/4 watt, 5 percent unless otherwise indicated.


Parts list, all versions

R1 1k
R4 100 ohms
R5 10k
R6 10k
R7 10k
R9 1k pot
R10 100 ohm trim pot
R11 47 ohm
R13 4.7k
R14 4.7k
R16 100 ohm pot
R17 100 ohm
R18 4.99k, 1%
R19 4.99k, 1%
R20 4.99k, 1%
R21 4.99k, 1%
R22 10k trim pot (adj for approx 5k and 5k)
R23 10k trim pot (adj for approx 1k and 9k)
R24 100 ohm


C4 0.1uf, 50v ceram disc
C5 0.1uf, 50v ceram disc
C6 100uf, 25v electro
C7 10uf, 15v electro
C8 0.1uf, 50v ceram disc
C9 10uf, 35v electro
C10 0.01uf, 50v ceram disc
C11 10uf, 35v electro
C12 10uf, 35v electro
C13 10uf, 35v electro
C14 0.1uf, 50v ceram disc

IC3 78L15 voltage regulator
IC4 79L15 voltage regulator
IC5 LF412
IC6 LF412

D1 1N5402
D2 1N5402
D3 1N5402
D4 1N5402
D5 1N4003
D6 1N4003
D9 1N4739A (9.1v zener)
D11 1N5225 (3v zener)
D12 1N4148

VR1 LM385Z-1.2
VR2 LM385Z-1.2

Q1 2N4403 or similar
Q2 2N4401 or similar
Q3 2N4401 or similar

LED1 20ma, any color LED 



PART 2

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

20v output version parts

T1 Transformer with 24vac secondary
R2 18k
R3 2k pot
D7 (jumper)
D8 (jumper)
C1 100uf, 35v electro
C2 47uf, 35v electro
C3 470uf, 35v electro
Cin 35v electro (see also below output current selection)
Cout 35v electro (see also below output current selection)

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

30v output version parts

T1 Transformer with 30vac secondary
R2 27k
R3 2.5k pot
D7 1N4747A (12v zener)
D8 1N4747A (12v zener)
C1 100uf, 50v electro
C2 47uf, 50v electro
C3 470uf, 50v electro
Cin 50v electro (see also below output current selection)
Cout 50v electro (see also below output current selection)

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

1.5 amp output version parts

D10 3A Schottky, 1N5822 (20v version) or MBR350 (30v version) or similar
R8 6.2k
R12 10k trim pot (adj for approx 3.9k)
R15 0.1 ohm, 1/2 watt
IC1 LM2576-adj (20v version) or LM2576HV-adj (30v version)
IC2 LM317 (20v version) or LM317HV (30v version)
L1 200uH inductor, peak I=2.5 amps
Cin 2 x 1000uf (see also above output voltage selection)
Cout 1000uf (see also above output voltage selection)

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

3.0 amp output version parts

D10 3A Schottky, 1N5822 (20v version) or MBR350 (30v version) or similar
R8 2.7k
R12 10k trim pot (adj for approx 3.3k)
R15 0.1 ohm, 2 watt
IC1 LM2576-adj (20v version) or LM2576HV-adj (30v version)
IC2 LM350 (20v or 30v versions)
L1 200uH inductor, peak I=4 amps
Cin 6 x 1000uf (see also above output voltage selection)
Cout 3 x 1000uf (see also above output voltage selection)

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

5.0 amp output version parts

D10 SB550 or similar (5A, 50v Schottky)
R8 1.5k
R12 10k trim pot (adj for approx 2.2k)
R15 0.1 ohm, 5 watt
IC1 LM2678-adj (20v or 30v versions) with added C boost=0.01uf 50v ceramic cap
IC2 LM338 (20v or 30v versions)
L1 47uH inductor, peak I=6 amps
Cin 10 x 1000uf (see also above output voltage selection)
Cout 5 x 200uf (see also above output voltage selection)

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


----------



## PEU (Nov 3, 2004)

Edited: It's working again, take a look at the bottom of the Powersupply section /ubbthreads/images/graemlins/smile.gif

Al, working on it, I'll install a new version of the software that resolves this very problem.
Pablo


----------



## MrAl (Nov 3, 2004)

Hi Pablo,

Say hi to Tao for me /ubbthreads/images/graemlins/smile.gif

I tried the site and it's still not working.
Now, i can delete the old image but when posting
a new one with the same name (update) it uses the
old image not the new one.

Take care,
Al


----------



## PEU (Nov 4, 2004)

Hi Al, is Teo /ubbthreads/images/graemlins/smile.gif

I sent you a PM and wrote some lines at the bottom of the power supply page.

/ubbthreads/images/graemlins/popcorn.gif

Pablo


----------



## MrAl (Nov 4, 2004)

Hi Pablo,

Oh, Teo ok, sorry. That's a cool name! Is there any
translated equivalent into english by any chance?

Thanks for looking into the wiki problem.
I've sent PM too.

We're about done with this circuit now until the
breadboard gets up and running.
I've been looking into some replacements (even for lower
current versions) for the switcher ic, and found a few
interesting ones that may be even more efficient.
Im not looking for super great eff here, but i do want
to reduce heat as much as possible so i can put mine
in a small box without extraordinary cooling stuff
(like fans).


Take care,
Al


----------



## PEU (Nov 4, 2004)

Hi Al,

The exact translation of Teo is Theo /ubbthreads/images/graemlins/smile.gif

the circuit is now visible, I'll update the expressPCB schematic to reflect the changes and will post a pic for review.

/ubbthreads/images/graemlins/popcorn.gif

Thanks


Pablo


----------



## vicbin (Nov 4, 2004)

Great, more CPRer are joining the club ! /ubbthreads/images/graemlins/smile.gif

G'day Vince,

Wellcome ! /ubbthreads/images/graemlins/smile.gif
Thanks, yeah that comics was supposed to freshen that long serious discussion. I think it's time to make the new one here, before this thread going to heat up since Al is finalising the circuit ! /ubbthreads/images/graemlins/naughty.gif


Pablo,

I'm planning to use Eagle CadSoft since it is built in with trace autorouter ! /ubbthreads/images/graemlins/cool.gif 

A bit difficult to use compared to ExpressPCB but it will save me from trouble of wrong route or forgotten trace since I'll change abit from the original Al's design.

There is now a new version and a free and fully functional version with the only limitation of board size = 100 x 80 mm (4 x 3.2 inches) and max. 2 layers board. I think this limitation is more than enough for this PS project. /ubbthreads/images/graemlins/smile.gif
Btw, I'm from Indonesia, ever heard it before ? 
You'll have to dig across this earth to reach me ! /ubbthreads/images/graemlins/wink2.gif /ubbthreads/images/graemlins/poke2.gif


Hi Al,

What possible replacement for the switcher IC are you talking about ? Higher efficiency yet simple & affordable ? ....drool..... /ubbthreads/images/graemlins/drool.gif

Interesting issue, about the heat reduction, example from the thermal resistance value from datasheet :

LM317 - TO220
Junction to case = 3 Celcius/Watt
Junction to ambient (no heatsink) = 35 Celcius/Watt

LM338 - TO3 
Junction to case = 1 Celcius/Watt
Junction to ambient (no heatsink) = 35 Celcius/Watt (why same as LM317 ?) /ubbthreads/images/graemlins/thinking.gif

Let say with 3 Volt dropout across and with 1 Amp current (dissipation : 3 x 1 = 3 Watts), do we need a heatsink ? How to calculate this heat formula ?

Update:
Suggestion, you can use this free image hosting -> ImageShack <font color="red">just for temporary</font> and when problems is gone, you can re-edit the image URL back to Pablo's site. Just to remind you since it is free, no guarantee it will be there for a long time.

Regards,
Vic


----------



## PEU (Nov 4, 2004)

Hi Vic,

I downloaded eagle, but as you said is bit more difficult, autoroute is niiiiice, may be is worth the extra learning work..., I guess the netlist works for eagle too.

the server problem is IHP related, so I must wait for them to solve it... /ubbthreads/images/graemlins/frown.gif


Pablo
PS: IHP internet hosting provider


----------



## vicbin (Nov 4, 2004)

Hi Pablo,

Yep, that software is very powerful, it supports advanced management features like scripting, bill of material, cost, customized library, etc..etc ... tons of other features that I don't understand what are they for ? /ubbthreads/images/graemlins/grin.gif

The bad news for me is I just downloaded their "tutorial documents" few days ago ! /ubbthreads/images/graemlins/mpr.gif Time to squezee my brain ! /ubbthreads/images/graemlins/banghead.gif 

Oh, so its your IHP fault, you should demand a compensation for the downtime ! /ubbthreads/images/graemlins/whoopin.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif ..he..he..

Regards,
Vic

UPDATE :
Pablo, I think there are 2 mistakes at your converted schematic here -> Power Supply Schematic file for ExpressPCB 
Both voltage reference LM385-1.2 VR1 and VR2 should be reverse biased instead of forward biased (like ordinary diode). Just rotate 180 degrees for both of them ! /ubbthreads/images/graemlins/grin.gif


----------



## PEU (Nov 4, 2004)

Al: Well the IHP guys did their job, and the problem is solved (at least in my tests).

Vic: thanks, I connected them like diodes /ubbthreads/images/graemlins/smile.gif reading the spec sheet I see that they used a zener symbol but reversed ¿?¿? 

Updated both MrAl.sch and MrAl.jpg (use the same 1st links I posted above)
Did you found some other error?

BTW, expressPCB does not allow exporting the netlist /ubbthreads/images/graemlins/frown.gif so I'll route manually the whole board /ubbthreads/images/graemlins/smile.gif


Pablo


----------



## PEU (Nov 5, 2004)

Hi, I have some questions that popped up while placing components in the PCB:

for Vic:
-what are the Cap (Cin & Cout) dimensions?, I need the lead spacing of the 1000uF ones

for Al:
- Which parts need dissipation, and how big? 

I will update these three links while making the board: 

Schematics JPG / Schematics / PCB 

The switching part is already done, comments are welcome!


Pablo


----------



## MrAl (Nov 5, 2004)

Hi again,


Vic:
LM26xx types, with DMOS output transistor look interesting.
Maybe you mentioned these already?
Yeah, the LM317/x/x reg's will still require some heatsinking, but
i was thinking in the future go to low dropout so we can keep the
heat even lower. Hopefully find a 5 amp version with low dropout.

The heat formula is pretty simple. An approximation is one square
inch per watt per (approx) 60 deg C rise. Since i dont want my hs
hotter than 60 deg C above ambient, i need one square inch per watt.
This is min for me. At 3 amps and 3.6v drop (LM3xx linear) that means
at least 11 square inches surface area for heatsink, but the more the
better.

Pablo:
OH yes, the site seems to be working again, thanks.
On the new schematic there are diodes changed, D11, D7, D8.
Saw your pic of your son Teo ... cute! hee hee. How old is he now?
We're looking at different size heat sinks for the different output
current versions... would you like me to try to find some on the web?
or just specify the surface area?
Your schematic is coming along very nicely!


Take care,
Al

UPDATED:


----------



## vicbin (Nov 5, 2004)

Hi Pablo,

Thanks for the updates ! That is very nice of you ! /ubbthreads/images/graemlins/smile.gif

My 1000uF/100V cap dimensions :
Diameter : 18mm
Length : 41mm (lead not included, cap body only)
Lead size : 0.75 mm
Distance between two leads : 7 mm

Some suggestions and considerations on PCB design, and it is more applicable for "through hole" type only, for SMD it is h*ll a lot easier, since all nowday they're quite uniformed & standarized in size :

1. *Make sure you have the accurate dimension in hand *, download the datasheet first if you know exactly which type <font color="red">AND</font> brand of the component, for me I buy them first before PCB design cause some type of components can vary in sizes and also looking at my "supplier" conditions, I can not afford not to buy them first ! /ubbthreads/images/graemlins/frown.gif

2. Capasitor, different voltage rating will have different size and one thing I noted is sometimes even on same uF/volt rating, they're "slightly" variation among different brands. /ubbthreads/images/graemlins/frown.gif Oh yeah, to make thing worst, it is common that low ESR cap are bigger (some are taller or some are fatter) than ordinary one.

3. Inductor, was one of my nightmare in the past because I was winding them myself, since I can't be sure which correct inductor to use, sort of trial and error because I don't have a scope /ubbthreads/images/graemlins/frown.gif . Although finally it is working, the final result was a big mess ! Imagine what I've been through...... test, yuck, desolder, rewind, solder, test, yuck, desolder, change core, rewind, solder, test ,yuck, change core...and so on...and so on........ arrrghhh...... /ubbthreads/images/graemlins/mad.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif /ubbthreads/images/graemlins/xyxgun.gif I believe you can imagine how is the PCB looks like ? /ubbthreads/images/graemlins/grin.gif

4. Heatsink, I think you already know what I mean don't you ? /ubbthreads/images/graemlins/smile.gif For LM2576/TO220 especially you're planning for 3 Amps, it is a must, I used this types of heatsink pics below for most of my TO-220 components :







Remember, we're planning to use the TO3 sized LM338 at the linear part ! /ubbthreads/images/graemlins/crazy.gif That will be another beast to consider ! /ubbthreads/images/graemlins/grin.gif

Ok, now comments on your PCB design :

- The schottky diode, looks like it is way too small (like a 1N4148 to me ? /ubbthreads/images/graemlins/grin.gif ). Remember, I suggest you need at least a TO-220 sized one. Look at my component pic from previous post for B1045/MBR1045, I put a thin & small one, since "most of the time" schottky diode won't heat up too much , just barely warm.

- R1 & R2, why they're different in size ? For those voltage divider feedback, 1/4 watt is enough.

- Inductor, there is no way it is that small, looks like 1/2 watt resistor. /ubbthreads/images/graemlins/smile.gif 
Pics of my inductor with a 5mm led, the same type that I used for my 1st LM2576.




One is flying to Al and he will test it for me ! Thanks sensei ! /ubbthreads/images/graemlins/grin.gif

Pablo, again these are only suggestion and what I've been through. Other comments from other CPFer are wellcome. /ubbthreads/images/graemlins/smile.gif


Hi Al,

I've seen the new circuit with CC led, thank you ! /ubbthreads/images/graemlins/smile.gif

Now, question on how it works and why there are some other components added ?

What happened if that LED got disconnected by accident ? "Only" current regulation will be gone right ?
The reason I asked is because it is likely this LED will be placed on panel with some connector/wire instead of soldered steadily on the PCB. Again, just a thought and prolly nothing serious ? Am I too paranoid ? he..he...

Now I can imagine how the heatsink will looks like , thanks. /ubbthreads/images/graemlins/smile.gif

About the new regulator with DMOS, yes I've mentioned it in the past but I decided to skip it first since they're running on high frequency. "A lot" of PCB consideration needed, also read my experience above on core. /ubbthreads/images/graemlins/smile.gif

One of the LDO I'm looking at is LM1084, max 1.5 volt drop at 5 Amps. Is it suitable ?

Regards,
Vic


----------



## PEU (Nov 5, 2004)

you're right Vic, I'll purchase the components before wasting time in a pcb that will need to be redesigned. This will delay at least a week, but hey, there is no hurry /ubbthreads/images/graemlins/smile.gif

Thru hole PCB's are very expensive here, I just called a provider and they asked about $100 for a single board!!! 

So I'll try hard to use a single layer pcb or at least a double layer with no thru hole.


Thanks


Pablo


----------



## MrAl (Nov 6, 2004)

Hi again,

Yes Vic, the size is nice to know before making the PCB, but there are
a few parts that maybe a few different sizes could be used. For example,
the sense resistor could be 1/2 to 10 watt version if there are several
holes for short, medium, and long resistors.

The heaksinks could be mounted off board too. In one battery charger design
i did the power transistor was mounted on the alum case (with isolation 
hardware) and three leads run to the pcb.

The schottky diode changes with version too, as some of the other parts also do.

The CC Led turns on whenever the op amp detects overcurrent and
drives that transistor on. The LED get's current flow so it must
turn on. If you're worried about it coming disconnected and causing
a lack of current control (very good point) we can add one 2N4401 and a
resistor to allow it to be driven independently, if you like that idea
better. I tried to use min parts for the LED drive originally.
Voltage control isnt affected if LED becomes disconnected.
One idea for the mounting of this LED is to have it mounted on the very
edge of the pcb so it can protrude out through the front case. This means
shortest leads.

Yes, the DMOS switchers LM26xx are 260kHz. Advantage is also smaller
inductor. As you can see from the parts list i made, this results in
a smaller 47uH inductor.

Oh yes, LM1084, which i was looking at too  Looks like this would
reduce heat my 50% or so, which reduces heat sink to 1/2 size.

Extra parts? Do you mean the 100 ohm and 0.01uf cap? This was added
for extra stability with capacitive load, and keeping transient V overshoot
to almost zero with cap load.

Pablo:
Different sense resistor sizes are used with different versions, and
Schottky diode changes too. Review the parts list i posted to find
out what your version requires ok?


Take care,
Al


----------



## vicbin (Nov 6, 2004)

Hi Al,

Yes please, show me how to drive the LED independently. /ubbthreads/images/graemlins/smile.gif

From the LM317 datahsheet, there a note about protection diode across the Vin and Vout to avoid the damage when there is a short circuit, is it needed in this version ?

Also there is a note that a minimal load/output current required to maintain regulation, since the voltage loop is controlled by the external op-amp, do we still need it ? In my previous experience, the requirement for minimal load actually came from the switcher !

I'm thinking to do the PCB in 3 modules which are capasitors part(bunch of Cin), switcher part and linear part, and if possible, I'll make those 3 boards equal size so I stack them ! /ubbthreads/images/graemlins/smile.gif

I remember in the past you mentioned something like double inductors & capacitors for reducing ripple, how is that ?

Say if I want to place a LC filter, where is the suitable place for them ? Is it between the Cout and R2 (switcher out) or between R6 and C8 (linear input) ? Planning to reserve a space and pads for the "optional" LC filter. /ubbthreads/images/graemlins/grin.gif

On the DMOS switchers LM26xx, is it still possible to use the ordinary caps ? Since paralled big caps such like mine might have some distance from the switcher while from their appnote, it is clearly mentioned the power switching path must be very-very short, below 1 inch if I'm not mistaken. /ubbthreads/images/graemlins/frown.gif 
Is it possible for you to measure the ESR of the ordinary cap ? e.g.: 1000uF


Hi Pablo,

Ouch !!!! How come the board cost $100 there ? /ubbthreads/images/graemlins/mad.gif Are we talking about an un-etched copper clad board ? 

Here single sided copper clad board 20 X 10 cm cost $2 a piece, 2 double sided about $3.5 ! Your price there is way too much, want some help ? /ubbthreads/images/graemlins/smile.gif

Regards,
Vic


----------



## MrAl (Nov 6, 2004)

Hi Vic,

The LED drive is now on the new schematic (see below).

That's a good point about the protect diode, i think we should add it.
I'll put one on the next schematic update. That's for when the input
gets shorted right? We might have a condition similar to that in some
case, so maybe it's a good idea.
The minimal load for the LM317 (and similar) is already taken into
account with the control circuit. As soon as you hook a 100 ohm resistor
to the output (and control through this resistor) you've satisfied that
requirement just about. If the switcher or even the two circuits working
together need a small min load, i think the breadboard can tell us better.
Also the switcher might require a small min load if the inductor causes a
problem at low current output.
Yes, Double inductors and caps for a two pole filter instead of single pole,
but i havent had time to try this yet because i've been busy with the 
schematic and making sure everything is correct, like part numbers, and
other stuff that seems more important at the moment. In the past i did
some experiments that showed that a two pole filter might respond faster
than a single pole and that would be good for high voltage outputs, but
i havent gotten back to it yet. I'll eventually get to it but for now
it's sorta last because using the Simple Switcher the way it's shown
by National (single pole) at least we know already works, and the other
things like LED and just overall good operation were more important so
that took up my time.
Without looking closer, it does seem a small inductor/cap filter like
the data sheet shows should work without bothering too much. Just make
sure the resonate freq isnt close to the switcher's frequency (52kHz or
260kHz). The formula is fo=1/(2*pi*sqrt(L*C))
where sqrt() means to take the square root.
The best place is just before C8 on the schematic.
Break the line that leads from the switcher to C8 and insert there
(yes between R6 and C8).
It may be possible to use ordinary caps with the DMOS 260kHz switchers,
with perhaps a smaller low ESR cap close to the switcher with feedback
close too, then the remaining caps a bit farther away. I havent looked
at this too closely yet, but now that you mention it it should be looked
at carefully. Sometimes the low esr caps cause instability because they
make the LC tank look more underdamped.

You can measure the ESR of the cap(s), but usually you use a scope.
If you have high cap values on the output of the switcher, you'll see
the effect of the ESR by looking at the ripple voltage.
You can estimate the ESR by driving the cap with a square wave
of known voltage peak. The peak of the current wave shows the
ESR because the cap voltage doesnt change much. For example,
with a 1 volt peak square wave and 1 ohm series resistance you'll
see about 0.5 amps after the cap voltage ramps up to it's average
value of about 0.5 volts. This is because 0.5 volt divided by
1 ohm equals 0.5 amps. Pretty simple, and there's no reason why you
cant apply this technique once the switcher is operating by simply
measuring the peak output voltage with 50% duty cycle and measuring
the peak current through the cap.
Perhaps we can do the same by measuring the ripple voltage.
This might be possible using that 'Ripple Detect Network' i 
talked about before. If there is I average amps through the
cap and there is v volts of ripple, than Rs is probably something
like v/I/2. I'll double check this later today.
The ripple detect network isnt hard to build either, a few small
cheap resistors and caps.


Take care,
Al

MOST RECENT:





MOST RECENT PARTS LIST, PART 1:
All resistors 1/4 watt, 5 percent unless otherwise indicated.


Parts list, all versions

R1 1k
R4 100 ohms
R5 10k
R6 10k
R7 10k
R9 1k pot
R10 100 ohm trim pot
R11 47 ohm
R13 4.7k
R14 4.7k
R16 100 ohm pot
R17 100 ohm
R18 4.99k, 1%
R19 4.99k, 1%
R20 4.99k, 1%
R21 4.99k, 1%
R22 10k trim pot (adj for approx 5k and 5k)
R23 10k trim pot (adj for approx 1k and 9k)
R24 100 ohm
R25 8.2k
R26 1.5k


C4 0.1uf, 50v ceram disc
C5 0.1uf, 50v ceram disc
C6 100uf, 25v electro
C7 10uf, 15v electro
C8 0.1uf, 50v ceram disc
C9 10uf, 35v electro
C10 0.01uf, 50v ceram disc
C11 10uf, 35v electro
C12 10uf, 35v electro
C13 10uf, 35v electro

IC3 78L15 voltage regulator
IC4 79L15 voltage regulator
IC5 LF412
IC6 LF412

D1 1N5402
D2 1N5402
D3 1N5402
D4 1N5402
D5 1N4003
D6 1N4003
D9 1N4739A (9.1v zener)
D11 1N5225 (3v zener)
D12 1N4148
D13 1N4742 (12v zener)
D14 1N4148
D15 1N4148

VR1 LM385Z-1.2
VR2 LM385Z-1.2

Q1 2N4403 or similar
Q2 2N4401 or similar
Q3 2N4401 or similar
Q4 2N4401 or similar

LED1 20ma, any color LED


----------



## PEU (Nov 6, 2004)

Al: time to update my schematics /ubbthreads/images/graemlins/smile.gif
Vic: $100 is the cost of a fully etched double size, metalized thru hole board, not a simple bare one !!! /ubbthreads/images/graemlins/smile.gif

Pablo


----------



## MrAl (Nov 6, 2004)

Hi again,

Pablo:
Yes /ubbthreads/images/graemlins/smile.gif i find that im constantly updating the schematic too.

Vic:
I've verified that you can measure the ripple voltage peak
to peak and ripple current peak to peak and divide v/i
to get ohms ESR, at least in theory. How to measure
current, well, that's another story. It's got to be 
the ripple current and not the dc current. Maybe no
load, but still need something to catch the peaks if
no scope is available. Maybe modify the ripple
detect network to measure current peaks too.
Then a small resistor in series with the cap, but also
some kind of fast amplifier to amplify the peaks.
I dont think this would be too easy, and how accurate;
would have to be tried, tested and calibrated.
On the scope you can see the pp values and divide.

It's interesting that with high frequency and high value
cap, the cap looks like a short circuit to ac voltages,
but it has a series resistor (ESR) which drops voltage
and so a small but measureable ac voltage appears across
the cap in spite of it's high microfarad value.
Also, if it were really a short circuit an infinite ac 
current would flow but because of the series resistance (ESR)
the current is limited to some relatively small value,
but is also measureable.
Both ac voltage and ac current being measureable, it's
then possible to calculate the ESR.


Take care,
Al


----------



## NewBie (Nov 6, 2004)

Hey Al,

How much does the output voltage sag from no load to full load?


----------



## MrAl (Nov 6, 2004)

Hi there Newbie,

The spec's for that are about the same as the linear
regulator used. LM317 for example has typical 0.3 percent
load regulation. This works out to about 6mv at 20v out.
For comparison, two external leads of #16 gauge wire each 2 
feet long drop about 5mv total at 3 amps out.
I think Kelvin sensing is possible too with this ps.

Take care,
Al


----------



## vicbin (Nov 7, 2004)

Hi Al,

Sorry about the double caps & inductors question, didn't mean to distract you and I aware how busy you are ! And also I will concentrating on breadboarding the linear part very soon and will update you. 

[ QUOTE ]
Pretty simple, and there's no reason why you cant apply this technique once the switcher is operating by simply measuring the peak output voltage with 50% duty cycle and measuring the peak current through the cap. Perhaps we can do the same by measuring the ripple voltage. This might be possible using that 'Ripple Detect Network' i talked about before. If there is I average amps through the cap and there is v volts of ripple, than Rs is probably something like v/I/2. I'll double check this later today. The ripple detect network isnt hard to build either, a few small cheap resistors and caps.

[/ QUOTE ]

Great & thanks ! Will keep this in my high priority to do list ! /ubbthreads/images/graemlins/wink.gif

[ QUOTE ]

It's interesting that with high frequency and high value cap, the cap looks like a short circuit to ac voltages, but it has a series resistor (ESR) which drops voltage and so a small but measureable ac voltage appears across the cap in spite of it's high microfarad value. Also, if it were really a short circuit an infinite ac current would flow but because of the series resistance (ESR) the current is limited to some relatively small value, but is also measureable. Both ac voltage and ac current being measureable, it's then possible to calculate the ESR.

[/ QUOTE ]

Well, for sure I will definately looking into this, again noted into my todo list ! /ubbthreads/images/graemlins/smile.gif

Btw, a bit offtopic but related since you're talking bout high value & high freq cap, I bought some weird caps that I've never seen before and it looks like a firecracker or small dynamite with double fuses to me LOL ..he..he.. /ubbthreads/images/graemlins/grin.gif. 

It was my caps supplier that has a "very good" salesmen skill, they "persuaded" me to buy these caps below because they claimed that they're very good at high freq. and very low ESR, really ?

Although I don't believe it 100%, I just bought them anyway because they're dirt cheap, those 4 smaller one 1uF cost me only $0.2 a piece and the big one 10uF cost me "nothing" and as a sample since I purchased quite some electrolite caps for the switcher part from them. /ubbthreads/images/graemlins/grin.gif

Looking at the big one, it is labelled "Audiophiller" brand ? Geezz...is that only suitable for audio circuits ? Since it is non polarised and I didn't see any + & - sign, is it ok to subsitute it for the C2 capasitor in your circuit ? Yeah, don't worry, next time I'll ask again from him the 4.7uF one for free sample ! /ubbthreads/images/graemlins/wink.gif

Size compared with 5mm led.







About Newbie question, (Hi there Newbie ! /ubbthreads/images/graemlins/smile.gif ), is that depends on the load transient response od the switcher ? Linear part should be pretty fast aren't they ?

Kelvin sensing ? Is that the same as "remote sensing" ? That is great !!!! /ubbthreads/images/graemlins/clap.gif

Protection from "hard" short circuit at the output, CC loop mechanism also play the role of protecting the "overall" circuit right ?


Hi Pablo,

My mistake, I thought plain copper clad board. /ubbthreads/images/graemlins/wink.gif
But still expensive though, I can do for you for 3 LSs T series, and that's for 3 boards !! /ubbthreads/images/graemlins/grin.gif

What do you mean by "metalized" thru hole board ? Is that vias ?

Regards,
Vic


----------



## MrAl (Nov 8, 2004)

Hi Vic,

No that's ok, i would rather be reminded.
I'd like very much to hear about your linear once it's running.
Audiophiler? Well, if you find one 47uf i guess you can use it for C2.
Are they mylar caps there?
Yes, remote sensing would have two leads extra leads (sense leads) going
out to the load itself, but i think we shouldnt complicate this circuit
any more. It would require breaking a few connections and attaching
two leads for remote sensing.
For short circuit, CC loop plays a role yes, but so does the current limit
of the linear and switcher probably too.

Take care,
Al


----------



## koala (Nov 8, 2004)

I'll probably report back when dealer stocks his LF412 dual op amps. For now /ubbthreads/images/graemlins/popcorn.gif.


----------



## MrAl (Nov 8, 2004)

Hi (Vince right?),

Oh that's all you need? I think Digikey stocks them.

Take care,
Al


----------



## MrAl (Nov 9, 2004)

Hi again,

Here's the latest drawing, with the protection diode.






Oh, BTW, the load regulation is 0.3 percent which is 0.006 
volts at 2 volts output (full temp range), not at 20 volts 
output.
At 20 deg C the load regulation is typically 0.1 percent,
which is 2mv at 2v output.

Take care,
Al


----------



## vicbin (Nov 9, 2004)

Hi Al,

I don't know what kind or type of that caps, the seller was saying it is MKT type ? Is that Mylar ? If it is mylar, is it true they're low ESR & high freq cap ?

I need to find a polypropylene cap for the 4.5 dmm, since it needs a very low leak cap for accuracy and was goggling around and found out plastic caps poly-xxxxxx types are so confusing to identify. Any idea ? /ubbthreads/images/graemlins/icon3.gif

Please explain the underlying mechanism and the reason of the value of these resistors : R4=100, R3=2k or 2.5K, R17=100. 

Btw as you pointed out for 30V out, the R3 (Volt pot) is 2.5K ... this value also hard to find here ! Did you find a cheap 100Ohms pot yet ? /ubbthreads/images/graemlins/crazy.gif

Are those R24=100, C10=0.01uF sorta compensation for the voltage loop too ? 

Load regulation about 2mv for 2 Volts, I can live with that ! /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Nov 9, 2004)

Hi Vic,

MKT i think is polyester...better than electrolytic, but not as good
as low esr type. What would you like to use these for?

You need to find a polypropylene cap? Are you sure they didnt want
Polycarbonate or Polystyrene? Do you know what the dmm uses this for?

Probably the only way to make sure you get the right kind of cap
is to find one in a catalog and check the manufacturer's specs.
They'll have to state what kind it is and what it can (or cant) do.

The reason for R4 is because this sets the current for the resistor
network that sets the LM317 up for a certain output voltage while
conducting the minimum current required for all the regulator types
(LM317/x/x). It's a little high for the LM317 (12ma instead of 6ma)
but it's not a big deal and allows using the same network for all
the regulator types. The value of this resistor is chosen to satisfy
the minimum current requirement for all of the regulator types.

R3=2k or 2.5k is simply the adjustment pot for voltage adjustment (coarse).
When the resistance is increased, the output voltage goes up provided 
current regulation doesnt kick in. The value is set to provide full 
output with max resistance.

R17 has the same value as R4 and keeps at least some resistance between
pin 7 of IC5 and the ADJ pin of IC2 in case both pots R3 and R16 are
adjusted to minimum resistance, so that if the collector/emitter of Q3 
conducts heavily (current limit) it can pull down the ADJ pin without
sinking excess current from pin 7 of IC5. The value is somewhat arbitrary,
but 100 ohms conveniently allows exactly -2x the voltage of the reference diode
used in the current limit adjustment circuit to set the output voltage to
0.000v with min resistance of both R3 and R16 (and -2x is easy to obtain with
one op amp section).

R24 and C10 slow down the regulator slightly which damps an otherwise
overshot response for some values of load cap. I added 10uf on
the output to help swamp the low problematic value also instead of 1uf.

I tested my small 'configureable' power supply i built a short while ago
(LM317 regulator) and i found at 1.4 volts the output changes about 15mv
from no load to 1.2 amps load. This sounds a little higher than i wanted,
but i think it's because i didnt pay close attention to wiring the circuit,
using #24 gauge wire too /ubbthreads/images/graemlins/smile.gif
Interesting, the output INCREASES by 15mv!

BTW, i got your shipment today! Thanks very much.
You're very generous Vic!
More in a PM to you in a minute...


Take care,
Al


----------



## PEU (Nov 9, 2004)

Hi Al, please let us know when the project reaches FINAL status, I have all the samples arriving on monday, and I still have time to order some difficult parts from digikey, such as multiturn pots etc.

/ubbthreads/images/graemlins/popcorn.gif


Pablo


----------



## vicbin (Nov 9, 2004)

Hi Pablo,

I will try this coming weekend to breadboard the circuit on the linear part and post the result here. Wish me luck ! /ubbthreads/images/graemlins/smile.gif

Update:
How much do you pay for that multiturn pot ? Is that included the low 100 Ohm ? ...sigh...I still can't find it here ! /ubbthreads/images/graemlins/crazy.gif

Vic


----------



## MrAl (Nov 9, 2004)

Hello again,

Pablo:
We're really close now, and the pot values shouldnt
have to change anyway. Keep in mind however that this
circuit should be built up and tested at least once
to verify everything works completely as expected.
Normally before many circuits would be built and sold
at least one breadboard is built and tested completely.

Vic:
I cant wait to hear how you make out with the linear part.
Guess what else? Out of all the parts i have, i had
only three electrolytic caps of any significant uf values,
but i was lucky enough to find an assortment of them
at a local RS for about $4. There were a few 1000uf and
two 3300uf of at least 25v, so ill be able to test the
switcher part very soon, complete with your toroid core.
Too bad the esr is probably higher than the uf value /ubbthreads/images/graemlins/smile.gif
but perhaps they will work out good enough anyway.
Im wondering if we can use one of those smaller
toroids for the post switcher filter...it might
be possible. I noticed even 22uH and 100uf knocks the
ripple down quite a bit (simulation). The decrease has
a lot to do with the esr of that cap though.

Oh BTW, if you use 2k for the pot and 500 ohm for the
fine pot you'll get just what you need: 2.5k total !
No need for 2.5k for you then.


Notes on the adjustment pot's "turnage":

I currently use a high quality 10 turn Bournes pot
of 1k value on my simple LM317 ps, and that gives me about
1.23 volts to 7 volts adjustment range, but even with
the ten turn pot it's difficult to adjust right to the
millivolt...for example say i want to set it at 1.400
volts, it's kinda hard to adjust...might be 1.399 or 1.401
...although it is possible... but it would be nicer if a little
better than that. Because we'll be using 2k to adjust
for 0-20 volts, that will be a little harder to adjust
(right to the millivolt) even with a 10 turn pot.
If we want better, perhaps a 2k coarse pot, a 500 ohm
fine pot, and a 25 ohm super fine pot? It's up to you,
the third pot would be wired in series with the other
two.


Take care for now,
Al


----------



## PEU (Nov 14, 2004)

is this capacitor enough for Cin ? /ubbthreads/images/graemlins/crackup.gif






/ubbthreads/images/graemlins/popcorn.gif

Pablo


----------



## MrAl (Nov 15, 2004)

Hello again,

Pablo:
WOW! Where can i get a couple of those nice caps?
I need a good filter cap for my AAA flashlight /ubbthreads/images/graemlins/smile.gif

Vic:
Some less than good news...the diode you sent CSD04060
isnt a good idea for the simple switcher because it
has such a high forward voltage drop and probably will
keep the switch transistor (internal to the LM2576)
on during times when it's supposed to be off.
This probably would result in overheating of the LM2586.
With my app (1.5A) i might be able to get away with it,
but at 3 amps output i really wouldnt use this diode.
1N5822 would be better, or a little higher current rated
Schottky. This diode looks sorta like three 1N5822 diodes
in series, so the voltage drop is triple.

BTW, im getting ready to build up the switcher now so i can
run some tests on the big toroid you sent.
I've also looked at a few numbers and it looks like we
might even get away with a lower value inductor, maybe
around 100uH. I'll post more as soon as it's built,
and i've already got the little pc board drilled out
to fit the LM2576 with it's odd pin spacing (non 0.1 inch).
Im planning to try a ready made (and easily obtainable)
inductor also that i already have on hand for the lighter
current output apps.

I was also giving some thought to winding a special 
inductor. Heck, if we have a nice size toroid like
this to work with we can easily wind a secondary onto
the inductor and use it as a transformer to obtain
all sorts of interesting (and isolated) power supply 
outputs:
Negative of almost any voltage level
Positive double with half output current
Positive half with twice output current
Multiple windings for several outputs

Since they can all would be isolated, this would be
very useful for supplies that really have to be isolated
(like the panel meter dc supply).
And so few parts makes this look pretty attractive...
Two caps,
two 1/4 watt resistors,
one low cost Schottky,
one inductor (with or without secondary windings)
one LM2576 TO220-5 package.
All fits on one small pc board.

Sound interesting?


Take care,
Al


----------



## PEU (Nov 15, 2004)

My vote goes to build the PS and then start with this multiple windings toroid.

Look, I finally received all the samples/stuff I purchased in the previous 1 1/2 month !!!






/ubbthreads/images/graemlins/popcorn.gif


Pablo


----------



## MrAl (Nov 15, 2004)

Hi Pablo,

WOW, all them parts /ubbthreads/images/graemlins/smile.gif

Can i ask what you're planning for all those SCR's and
power transistors?
I see you're all ready to go to the LM1084 LDO too.
Plenty of LM2576's too i see  
How many power supplies do you plan on building?

I cant guess what that is because i cant quite see it.

Also, yes the multiple windings thing is just an idea
for the future. I agree let's get the main board going
first.

Take care,
Al


----------



## PEU (Nov 15, 2004)

Hi Al,

I only plan to build one PS, these power transistors & SCRs were fillers /ubbthreads/images/graemlins/smile.gif for the 33063/34063 samples I ordered from Onsemi, also not detailed (and free too) in the picture are 25x npn smd transistors and 25x 2A smd shottky diodes.

If you have some ideas on how they may be used, I'm all ears /ubbthreads/images/graemlins/smile.gif

Regarding the toroid I have, here is a picture:





Outside diameter is 27mm and inside diameter is 14.3mm. It seems to be standard for PC AT Power suplies (I checked 3 and all of them have this one)

Pablo


----------



## MrAl (Nov 15, 2004)

Hi there Pablo,

Fillers? What do you mean?
What are the 33063/34063 items?

Well, what are the part numbers of the npn smd transistors?
The 2A schottkys part numbers? Maybe for approx 2A switcher supplies...
such as running an LS or other LEDs on a 12v automobile electrical 
system...ideal.
Any other kinds of regulator circuits you need?

Regarding the switcher for the PSw/SPR (this thread)...
Im going to have to use a lower current diode (1A) to
start if the big diode Vic sent keeps the switch transistor
'on' (transistor in the LM2576 package), at least until i get
my other parts (very soon now) for this thing.
I'd like to be able to test up to the full 3 amps at least however,
so one diode or the other will have to work. The 1N5822 diodes are
really cheap, luckily /ubbthreads/images/graemlins/smile.gif Just a matter of getting some.
Maybe i could check the NTE site too, as there is a shop near here
that carries some of their parts. Heck, even 1$ for one diode would
be ok since i only really need one for now.

Is that the toroid you plan to use with this ps? If so, what is the
height of the toroid? You already said 27mm OD, 14mm ID, right?
Do you have any idea what kind of material it is made out of?

Take care,
Al

ADDED A FEW MINUTES LATER:
Called the shop, they have the diodes but they are
$1.85 each !! He he, geeze. I guess they're in a 
high rent district /ubbthreads/images/graemlins/smile.gif I only need one for now 
anyway though...


----------



## PEU (Nov 15, 2004)

Hi Al,

The 33063/33064 are MC33063 and MC33064 regulators (smd), the schotkys are smd 40v 2A (onsemi ss24t3), the npns are smd 30v 2a switching (onsemi mmbt489lt1), when I said filler I mean, they charge you $11 for 10 sample items, so I "filled" the order with these. All the smd regs are for building lambda ill-pill regulators, the npn&schotkys are for unregulated step-ups.

Back on the main track: The height of the toroid is 11.3mm, I don't know the specs for the core, but they are pretty common in PC-AT power supplies.


Pablo


----------



## MrAl (Nov 15, 2004)

Hi again Pablo,

Oh ok, thanks for letting me know.

Where did you obtain this toroid? Online 
anywhere? Just wondering...

The toroid Vic sent has the same dimensions...
27x14x11H, so i asked if you know the material
because if i test this one i can forward you the data
too, so you, i, and Vic will have the exact same cores
and know very well what to expect from an inductor made
from this one. Mine's kinda bright yellow though...

Take care,
Al


----------



## PEU (Nov 15, 2004)

I ripped the toroid out of a non working PC-AT power supply. 

I'm sure if you look inside a PC-AT of yours, you will find a similar toroid.


Pablo


----------



## MrAl (Nov 16, 2004)

Hi Pablo,

Oh yes ok. Well, you should be aware that some cores
have high permeability and some have low, so the number
of turns that will be required for an inductance of
at least 100uH will vary greatly from core to core,
depending on the material.
Since this came from a high current power supply,
there's a good chance it's got high enough u to work
as an inductor for our power supply.
Ideally, you'd wind some turns and connect it up with
low input and look at the waveforms on a scope.
From the waveforms you could deduct what type of
material it was and if it would be suitable for
our power supply. My guess is that it will be
useful because of where it came from, but i cant be
sure without some measurements as mentioned.

Take care,
Al


----------



## MrAl (Nov 16, 2004)

Just a little update:

I've measured the esr of some of the random caps i obtained
from RS a few days back. The caps are from various manufacturers,
yet there is a relationship between their esr and their
value. That is, the higher the microfarad value, the
lower the esr is.

For example,
22uf measured about 2 or 3 ohms,
100uf measured about 1.25 ohms
1000uf measured about 0.1,
another 1000uf measured about 0.2 ohms,
a 3300uf measured about 0.05 ohms.

Interesting i thought, and these caps are all from different
manufacturers.

I was dissapointed with the 100uf above, because of
it's 1.25 ohm esr, but i was very surprized to see
the lower esr's of the higher valued caps, and quite
happy. Unfortunately, there are a couple things here
i didnt count on... the 100uf is higher than i wanted,
and the 1000uf's are LOWER than i wanted.

I wanted to check these before i assembled the circuit
so i would know what im dealing with (wont have to break
connections later to test this stuff maybe).
Im glad i did, and maybe i'll use a 1000uf cap as the 
input cap on my circuit because of the lower esr.
The other 1000uf cap i'll use on the output and hope
that the esr doesnt cause instability or (hee hee) i'll
have to add a resistor in series with it (geeze!).

Take care for now,
Al


----------



## vicbin (Nov 17, 2004)

Hi Pablo,

Wow, what a cool stuffs you got there and LM1084 too, congratulations ! /ubbthreads/images/graemlins/grin.gif

hmm..looking at your dino size orange Cin picture /ubbthreads/images/graemlins/grin.gif , is that your stepdown transformer at lower right ? Geez.. those caps will eat it and it'll melt into a nice iron core scuplture once you power up.... he..he.. just j/k /ubbthreads/images/graemlins/yellowlaugh.gif

Your core looks like mine and Al's too, I guest it will suitable too since you said it came from switching PS. But ours are bright yellow and your are a bit greenish one, was that the camera ? Or maybe the epoxy coating yellow color got a bit washed out since it is used ? 

Ok, I gave up, what is that stuff you're asking us to guest ? Looks like a wounded toroid to me, isn't it ?


Hi Al,

Sorry , wasn't updating you on the linear part since I'm catching a realy bad cold and almost impossible to concentrate on translating it to breadboard ! /ubbthreads/images/graemlins/sick.gif
And I don't want to short circuit the breadboard and components from my dripping nose ! /ubbthreads/images/graemlins/crackup.gif

About that diode I sent you, it is ok if it doesn't work quite well. Anyway, maybe it will be usefull in the future project on very high to low stepdown (no big transformer ?) /ubbthreads/images/graemlins/grin.gif It is just my curiosity how it is performing on the "zero recovery" feature. Please just test and see the result it if you got spare time and doesn't bother you too much. /ubbthreads/images/graemlins/smile.gif

Don't worry, I'm not planning to use that on this circuit either, already got couple high rating 16A/45V TO-220 schottky diodes.

[ QUOTE ]

I was also giving some thought to winding a special inductor. Heck, if we have a nice size toroid like this to work with we can easily wind a secondary onto the inductor and use it as a transformer to obtain all sorts of interesting (and isolated) power supply outputs:

Negative of almost any voltage level
Positive double with half output current
Positive half with twice output current
Multiple windings for several outputs

Since they can all would be isolated, this would be very useful for supplies that really have to be isolated (like the panel meter dc supply). And so few parts makes this look pretty attractive...

Two caps, two 1/4 watt resistors, one low cost Schottky,one inductor (with or without secondary windings) one LM2576 TO220-5 package. 

All fits on one small pc board.

<font color="red">Sound interesting?</font>

[/ QUOTE ]

YESSSS !! !! /ubbthreads/images/graemlins/buttrock.gif

I'm totally ear for this one, of course I agree to proceed with the basic main configuration first, then go with this option later. 

The inductor value change to 100uH ? Any particular reason ?

My core (same as yours) is already wounded with 263uH with 2 strands (see close up pic below) to keep the wire resistance low, and its measured approx. 0.04 Ohm DCR. Is this practice of multiple strands ok ?

Measured : 263 uH






Close up, any suggestion on improving the winding technique ?





Looks like I need to reduce the winding down to 100uH and about your question on how many turns, really sorry I lost the note, and it is difficult to count how many turns in it now. /ubbthreads/images/graemlins/frown.gif Will update you how much uH per turn when I got a chance.


Thanks a lot for the cap's ESR info. /ubbthreads/images/graemlins/smile.gif

Since I bought a lot of 1000uF/100V for switcher Cin and Cout and assuming they're 0.1 ohm as yours, is there any concern their ESR in parallel will be too low ? /ubbthreads/images/graemlins/confused.gif

How low is low anyway ?

My Cin will be 0.01 Ohm (10 X 0.1) and Cout will be 0.02 Ohm, is this ok for 50Khz (3 Amp) or above 100Khz (5 Amp) switcher ?

About C1, as you said 100uF ESR is quite high, which will be placed close to the switcher, replacing C1 with the 1000uF should ok right ? 

My plan to separate the Cin (bunch of those 1000uF caps) from the main swicther board, but the C1 still close to the IC.

Just curious, have you measured the ESR between two caps which have same capacity but different voltage rating ? Just wondering how much different ?

Vic


----------



## PEU (Nov 17, 2004)

Hi Vic/Al,

its part of the motor of a 5 1/4 floppy drive I dismantled for parts /ubbthreads/images/graemlins/smile.gif
While I was waiting for the samples/parts to arrive and the PS to be finished /ubbthreads/images/graemlins/popcorn.gif I began building a propeller clock. 
I finished and tested the moving part, now I'm messing with the mechanicals (powering the moving circuit is a royal pain)

Back on track:

Regarding the toroid, mine is bright yellow also, but it seems that the auto balance of my PDA camera (TH55) corrected it wrong ... 


Pablo


----------



## MrAl (Nov 18, 2004)

Hello again,

Pablo:
Wow neat! I was going to build an oscilloscope once 
using a rotating column of LEDs (forms a cylindar instead
of a circle that way).
Oh perhaps you have the same toroid then. I just did
some measurments on that one (see below).

Vic:
Oh, a cold, that's nasty...hope you get better soon.
I'll certainly test the diode first, because im going to
start the circuit by using that diode first. Since there is
no recovery, i probably wont see any current spike on my scope,
but when i get a 'normal' schottky i should so we can compare.
I think that diode would be very beneficial for very high voltage
switchers, probably even running off rectified 120vac directly.

The inductor change to 100uH only to make it smaller. 200uH
means less ripple voltage, so if you have 200uH keep it; 200uH
is actually better. 100uH means less turns on the core if using
a bare core (like we are with the yellow one), and less turns means
less series R, but then we dont get much with this anyway.
BTW, i estimate you have approx 45 turns on your toroid in that
pic...how many turns actually?
Using multi strands is ok yes and reduces skin effect.

Yes, im concerned about 0.1 ohm ESR in the output caps being perhaps
too low for the LM2576 ic, but i'll know more a little later today
or tomorrow morning. When i did simulations with 1 ohm esr i didnt see
much ringing at all, but with 0.1 ringing, so we'll see once i get my
switcher up and running. I guess worse case we'd have to add a small
resistor in series.

Replacing the 100uf with a 1000uf should be a good idea yes, and im 
going to do that myself. The low esr is good on the input side.

I dont know yet if very low esr (less than 0.5 ohms) will be a problem
with the simple switcher ic's. I'll know within a day or so now.
See, the block diagram given by National isnt that good, so breadboarding
seems to be the only way to tell...which im presently building.

I did measure the ESR of two caps both 1000uf, one 35v and one 16v rating,
and the 35v had the lower esr, which was 0.1 and the 16v had the 0.2 ohm,
so yes, the higher voltage rating cap had the lower esr as originally 
guessed. Good point to bring up 

Now i have some measurements of your core too:

The material doesnt look like "J" material (high 5000u type)
but rather low 115u or something around there.
With 10 turns i only get 16uH, which would be much higher than
that with J material and no dc bias. With J material about
4 turns would get to roughly 100uH (low dc bias).
The good news is that with approx 25 turns i should get close to
100uH, which is what i was thinking of starting with, and i dont
care if the dc resistance is higher because im not that interested
in high efficiency for this 'bench' power supply.
One other thing worth mentioning is that this core is wayyy too NICE
for this small power supply /ubbthreads/images/graemlins/smile.gif A smaller core would work also.
On the other hand, if we ever get around to adding secondary windings
(sometime in the future) we'll have plenty of core window space left
(hee hee).

Remember to let me know how many turns you have on your core ok?
Thanks.

Take care,
Al


----------



## MrAl (Nov 19, 2004)

Hi again,

I've got my switcher built up now!
I have to say, it is pretty simple.
Thanks to Vic for sending the chip so i could get one
built up without spending much.

So far the ripple is very good and im only using
68uH to start with!

Zero Recovery Diode
The 'zero recovery' diode looks like it is truely
a problem...although i'll be more sure very soon.
This diode has about 1.4v across it during switch
turn off periods, so what looks like is happening
is that because this puts -1.4v at the Vout pin on the
LM2576, it turns the switch transistor back on,
then the voltage rises a little, then turns back off,
then back on, then back off, etc. This works out as
high frequency ringing at the Vout pin, which is not good
for the Pd of the switch transistor. The ringing is quite
pronounced too especially at low load current, but it
doesnt get to the output because of the low w0 of the
filter (inductor and output cap) and the high freq of
the sine part of the ringing (about 500kHz to 1MHz).
This high freq ringing is not good, so i'll have to 
try another lower Vf Schottky.
It did work, however, for the short time i ran the circuit,
and the output ripple voltage is pretty low...at 1.2 amps
out it was only 50mv, but i'll have to test at other
output voltage levels also.

The other concern is that with the low esr of the output
cap im also seeing a low freq ring as expected, but it manifests
itself as a very high overshoot mostly, that at low output
current can mean the output will jump up two times as high
as programmed by the feedback resistors. At some point 
as the output current is increased this goes away luckily,
but i havent established just how low we can get away with
yet. Also, because we have the linear regulator this might
not affect our main output anyway.
This should be a great concern however, to anyone using
the LM2576 for very light loads, as the load will see
2x voltage for as long as a second (1000uf output cap).
This most likely occurs because the internal feedback 
circuit has some measureable slew, which takes time
to adjust the output when the output voltage first begins
to appear.

As soon as i get another diode i'll get the big core
going and see how well it works in this circuit.
I expect good results.

Overall, the LM2576 "Simple Switcher" is looking like
a very good choice for step down applications, and
i'd bet the next generation models (higher freq)
would be even better.

Take care,
Al


----------



## MrAl (Nov 21, 2004)

Hello again,

UPDATE

I've found the minimum current to keep overshoot down
is about 10ma, which is pretty low so it's not too much
of a problem. The linear circuit that follows the switcher
for this ps should draw at least that much even no load.

I've also found that the high freq ringing was not caused
by the diode, but by the inductor going into discontinuous
operation (normal) for a short time period the length of
which depends on load current.
When the inductor does this, the capacitance of the diode
(whatever diode is used) resonates with the inductor,
which causes a high frequency (~800kHz) ringing on the
Vout pin of the LM2576 ic. This doesnt seem like too
much of a problem at low voltage output, but because the
ringing rides on top of the dc output level it will
have to be checked at higher output voltages as well
as low output voltages to see if the peak of the ring
goes above the ic max voltage rating or the max voltage
rating of the diode. I hope we dont have to add a
snubber circuit just for this alone!

One thing that really improved by changing to the 
recommened 1N5822 diode was of course the forward 
voltage drop. Since the 'zero recovery' diode's 
forward drop was about three times higher than the
1N5822, it was getting very warm at 1.2 amps out.
With the 1N5822 diodes installed, it's hardly above
room temperature (maybe 1 deg C).

Vic:
Hope your doing better with that cold!


Take care,
Al


----------



## vicbin (Nov 21, 2004)

Hello,

Hi Pablo,

Hey, nice project you're playing at , thanks for the link ! /ubbthreads/images/graemlins/smile.gif

This make me thing to try it too since I got tons of old hardware back to early IBM PC-XT era ! /ubbthreads/images/graemlins/grin.gif


Hi Al, /ubbthreads/images/graemlins/smile.gif

Really sorry cause I haven't start breadboarding the linear part since I'm not fully recovered yet. The best I thing I could do was counting the core's winding and did some simple measurements on various cores. (see below on the detail)

[ QUOTE ]
I was going to build an oscilloscope once using a rotating column of LEDs (forms a cylindar instead of a circle that way)

[/ QUOTE ]

Huh ? Round scope ? Was that for fun or serious ? Talking bout leds scope, I remember I was trying years ago the circuit from Forrest Mims Eng. Notebook using two LM3914s with lot of leds in matrix 10x10 and it looks funny. /ubbthreads/images/graemlins/grin.gif

Zero recovery diode, looks like you will have to save it for other high volts future project ! /ubbthreads/images/graemlins/icon3.gif
Just curious, was it really "zero recovery" or recovered very-very fast ?


Capacitor :

Looks like I need to build again your ripple detector, yes the 1st one (back in very old Zetex thread) is lost somewhere. /ubbthreads/images/graemlins/frown.gif

Talking about ripple detector, is it possible to couple it with simple voltage peak detector circuit using fast op-amp to detect the peaks ? Just my another "wild" (prolly stupid) idea. /ubbthreads/images/graemlins/icon3.gif

Good thing and information from you is for input, low ESR doesn't matter, infact the lower the better right ? /ubbthreads/images/graemlins/smile.gif

[ QUOTE ]
The other concern is that with the low esr of the output cap im also seeing a low freq ring as expected, but it manifests itself as a very high overshoot mostly, that at low output current can mean the output will jump up two times as high as programmed by the feedback resistors. At some point as the output current is increased this goes away luckily, but i havent established just how low we can get away with yet. Also, because we have the linear regulator this might not affect our main output anyway.

[/ QUOTE ]

Please update us on how low is the lowest one for LM2576, gezz... never thought it will be this complex, and I haven't touch the 5 Amps swicther yet (higher freq.). /ubbthreads/images/graemlins/icon23.gif
Correct me if I'm wrong, the switcher "overshoot" should be taken care or some how got suppressed by the front end linear part right ? or I'm wrong ?

[ QUOTE ]
This should be a great concern however, to anyone using the LM2576 for very light loads, as the load will see 2x voltage for as long as a second (1000uf output cap). This most likely occurs because the internal feedback circuit has some measureable slew, which takes time to adjust the output when the output voltage first begins to appear.

[/ QUOTE ]

No wonder, remember my 1st PS project ? I had to use a constant dummy load (100-200ma) for a light load output cause the regulation was fluctuated like crazy. Is it related to your above explanation ?

If we have to use a dummy load to take care the low load problem, should it be placed between switcher and linear "or" at final linear (of course not in the regulation loop) ?

Now, about the CORE : /ubbthreads/images/graemlins/grin.gif

You almost correct on estimating my core turns, yes, mine are 53 turns = 263 uH measured with my el-cheapo LCR meter. /ubbthreads/images/graemlins/blush.gif

I did measure few cores and you also have some of them in hand. 

Some homework pic





Ok, now looking at the pic, starting a 1st row (bare cores) from left to right, I believe you got number 1 (that ours, yellow one with 4 turns of red wire), 3 (black thin one), 4 (white), 6 (black) and last one 7 (tiny black). Too bad I got no 2 (grey) and 5 (thick black one) after I sent the package, otherwise I'll send em anyway for you to test, these are high mu cores. /ubbthreads/images/graemlins/frown.gif

Now these below are the measured uH per turn using my cheap LCR meter, please be reminded the meter lowest resolution in only at 1uH, so I believe for low uH value are not very accurate. /ubbthreads/images/graemlins/icon3.gif

Format -> Core number. (front row left to right) = turns:measured uH value,turns:uH,......stopped until my fingers numb ..he..he.. /ubbthreads/images/graemlins/grin.gif

1 (yellow big core) = 2:1,3:2,4:2,5:4,6:6,7:7,8:8,9:11,10:13,11:14,12:16,13:18,14:20,15:23,16:26,17:29,18:32...and mine 53:263 (is this same with your finding ?, so its not type J then, have to complain to the vendor)

2 (grey) = 1:14,2:32,3:56,4:89,4.5:128...(this is a high mu core)

3 (black) = 1:9,2:13,3:24,4:54,5:74,6:107,7:140,8:177,9:215 ...(please try this first since it needs only 9 turns for 200uH, hope it won't get saturated easily)

4 (white) = 1:1,2:1,3:1,4:2,5:2,6:2,7:2.5,9:4,10:5,11:6,12:7,13:8,14:9,15:10,16:11....(low mu, should be suitable for LC filter maybe ?)

5 (fat black) = 1:14,2:33,3:58,4:90,5:130,6:177,7:230,8:291,9:359,10:427....(almost the same type as core number 2 grey one right ?)

6 (black) = 1:8,2:19,3:23,4:56,5:80,6:105,7:140,8:178,9:228,10:275,11:320....(used to be one of the best core for single or double transistors boost circuits) /ubbthreads/images/graemlins/smile.gif

7 (smallest one) , sorry, lost my dexterity cause by this nasty cold and I'm too tired for this tinee thingy ! /ubbthreads/images/graemlins/frown.gif


One thing interesting, look at the one behind core number 2 (grey). That is a combination of one big grey (no.2) with 2 cores (no.5) inside it, with only 4 turns I got 251uH ! (1:41,2:91,3:161) !!! Those black two cores fit nicely (not too loose and need just abit push) to get into the big one ! /ubbthreads/images/graemlins/grin.gif

Btw, what do you mean the yellow core is "way too nice" for this kinda circuit ? Overkill ?

Great news also from your 1st testing on the LM2576, and the 50mv ripple at 1.2 Amps is nice !! What was the Vout and Vin ?

If the ripple is that small, once it passed the linear, how small will it be ? 

Please, test with low Amp load and see how this beast react, how about powering single LED ? he..he.. of course I don't mean using your LS or Nichia leds. /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Nov 22, 2004)

Hi Vic,

This turned out to be a rather long post, so i 
started it yesterday and finished it today.

[Zero recovery diode update at end of this post]

Take your time with the linear part. We're not in a big
hurry here are we?

The oscilloscope 'screen' is made by rotating a column of LED's around in 
a circle so that the column forms a cylindar of light as it rotates.
The part not visible to the user would be blanked, or just left showing
some part of the wave too. The part that faces the user would show
the main part of the wave. The led's would then sweep around back and
when they return the wave would be shown again. It saves on LED's, but
you'd have to get it rotating fast enough to be useable. I dont know for
sure if it would work because i never actually tried it, and then computers
got pretty decent so if you need a display you could tie the circuit into
the port and view onscreen as many scopes do these days.

Yes, i'll certainly have a nice fast diode with very high Voltage rating,
for an 'off-line' converter at some point, thanks to you!
I didnt check the actual recovery yet, so i'll do that next thing.
I have to insert a resistor in series with the diode in order to see
this, and i was afraid too do that until i looked at the effect in
a simulator. That's been done, and it looks ok so i'll be able to do this.
I'll set it up tomorrow morning as the first test.

If you'd like to build the ripple detector (probably a good idea) i can
post the schematic if you like.
We can use a fast op amp if you want to do that, that's actually a good
idea to make the peak detector work even better. There's some very nice 
op amps out there these days that would make good preamps for this.
It would be easy to use two 9v batteries for the power supply to
power the op amp since a measurement wouldnt take very long.

Yes, for the input cap esr the lower the better. I've measured the ripple
riding on the input wave (looks like tiny hairs on the screen /ubbthreads/images/graemlins/smile.gif )
and the lower esr keeps this down low, but the lower the better.
Keeps the internal circuitry of the LM2576 working correctly.

The low freq 'overshoot' looks ok with only 10ma load, so i think our linear
circuit will draw that much so everything should be ok.
The high freq overshoot im not sure about yet, but i should know by
tomorrow afternoon. Im going to install a pot so i can change the
voltage level. So far only tested at one voltage level.
Yes, this might have something to do with your other ps needing a 100ma 
minimum load, because this overshoot could certainly cause instability.
With the load, the overshoot goes away, so the stability would come 
back. I'll certainly test this once i get my linear built up.
I'll probably start with a simplified linear circuit just to get
going.

CORE(S)
Oh ok, 53 turns so yeah i was close. It's very hard to count turns
from looking at a picture i can tell you /ubbthreads/images/graemlins/smile.gif

Oh that pic is cool! Showing all the cores there together /ubbthreads/images/graemlins/smile.gif

I see you did plenty of tests on all your cores. I've tested the big
yellow one because we're going to use that one for the main inductor,
but i'll test the others you sent too and compare numbers.
I can see already that we got close to the same number for the big yellow
one (you got 13uH and i got 16uH) and i used a completely different
method (not exactly precise but it's close enough).
The main idea with the core test is to determine approximately what
the initial u of the core is, by measuring the L and then using a
formula for inductance with u in it.

That muli-cored one looks interesting. The two cores inside mean the
area is increased about 2x, which is quite a bit. The thing i would
like to add is that if the mu of the two cores is about the same
the area is increased by about 2x, but if one is very much lower
it wont help much except maybe at different frequency.
I see that the grey core is [4:89] and the two black cores are
[4:90] and [4:90] so if you add them all up you get [4:269]
which is sorta close to your measurement of 251uH. Pretty cool!

I was just saying that the yellow core is 'way too nice' only because
it's so large and we're only making a small power supply, but then
on the other hand you're going to 5 amps which means you can use larger
wire without any problem and probably not have to worry about 
saturation (i'll check this out further). For my own 1.5 amp version
i can probably get away with a smaller core, but i'll still use this
one for lots of testing.


Vin and Vout with 1.2amps out and 50mv ripple:
Vin 10v
Vout 1.24v
The reason Vout was only 1.24 was because i ran the output directly
to the FB pin in order to get this circuit fired up as quick as 
possible. I already have the 1k FB resistor in place so all i have
to do now is add a trimpot to get other outputs (higher).
I realize also that at some point i have to get a 20v or 24v transformer
because i have none right now. What i do have is a HUGE 12v sealed LA 
battery i can use but that's only 12v. I'd like to get up to 20v or
at least say 18v and i'd like to go up to 3 amps just to see how the
core reacts and diode and stuff like that.
Since the ripple is going to be fairly low, the output ripple will
be even lower. The LM317 ic rejects high freq ripple fairly well
so i think we're looking good on the HF ripple!

I tested with low amp load and it looks like a 20ma LED could be
run from this thing. I wouldnt try to run it at 5ma however, unless
a parallel resistor is used for at least 10ma minimum.
I guess this circuit would be an overkill for a 20ma LED anyway,
but for a Luxeon 1 or 3 watt JUST RIGHT! Unfortunately, we'd
have to connect a 2 ohm (approx) resistor in series with the LED
and maybe adjust Vout for each particular LED, but it should work.
National does make these switchers with current limit too, so 
perhaps that would be a better choice for a Luxeon.

Once i saw that the low freq overshoot was down with min load i 
dont mind connecting a Luxeon to mine.

ZERO RECOVERY DIODE
I've done some more testing to see the difference between the 1N5822 diode
and the 'Zero Recovery diode'. On my scope i cant see the pulse width,
but i can still get an idea what the recovery pulse looks like.
Running at 1.2 amps output, using the 1N5822 diode causes a 6 amp recovery 
pulse, while the ZR diode shows only 2 amps, and that 2 amps might really
not be caused by the recovery, but rather caused by the high freq ringing
(peak) that i was talking about earlier. Even at 2 amps though it's three
times better than the 1N5822, and this is only at low voltage of 10v.
At 500v there should be even more difference. As soon as i get a transformer
that can provide 20v or more dc voltage i'll check again. I have the
breadboard set up so it's not too hard to switch diodes.
Remember though that the forward voltage drop of the ZR diode is quite 
high -- being 1.4v or higher -- so it gets very warm even at 1.2 amps out
(and low voltage output). The 1N5822 does not get warm. This means 
the ZR diode is eating power...just something to keep in mind.

Also, the high frequency overshoot (caused by the diode's capacitance resonating
with the inductor's inductance) probably goes down with increased Vout, and up
with increasing Vin, so we should be ok. Of course i'll check this first thing
as soon as i get the pot installed. I cant see this being too much of a problem
however, because the success of National's Simple Switcher line of ic's would
depend partly on not using a snubber, which none of their reference designs
currently use. Of course one measurement is worth 1000 reference schematics /ubbthreads/images/graemlins/smile.gif


Thanks again for the nice pic's of your cores!

Take care,
Al


----------



## MrAl (Nov 24, 2004)

Hi again,

Minor Update

Vic, your flat black core (#3) saturates very easily.
With enough turns (varied 4 to 6 turns) to get the
required inductance, the core saturates badly at only
240ma output! It works at 120ma if that's any help /ubbthreads/images/graemlins/smile.gif
but who wants only 120ma output from a 3 amp switcher ic?
<hee hee>
The effect is quite dramatic: current shoots up to maybe
10 amps and the ripple increases to 0.3v or around there.
At 120ma this doesnt happen.

For what it's worth, this core looks like J material
with high mu (5000) so a few turns gets high inductance,
but the AL is also very high so it saturates easily with
dc current.

The big Yellow core is amazing...I was able to get output
current up to 3.5 amps and could have probably gotten
more, with no saturation. I hope Pablo has this kind of
core too, but that would require a lot of luck.
Perhaps Pablo should get something to measure his
inductor with.
BTW, the n turns was 25 which gave about 110uH (tested),
and 110uH worked just fine with the sorta low esr cap.

Hopefully more testing today sometime.

Take care,
Al


----------



## PEU (Nov 24, 2004)

Hi Al,

I don't have a mH meter nor a scope, is there an easy way to check it?

Again, I guess is a good quality one coming from a PC AT supply, since the currents there are at least 5A

/ubbthreads/images/graemlins/popcorn.gif


Pablo


----------



## MrAl (Nov 24, 2004)

Hi Pablo,

The inductor is a rather important part for the switcher,
so it has to be right. 25 turns works fine on a core
that has the right mu, but saturates badly with one that
doesnt have the right mu.

Since there's no easy way to test it without some
special equipment, i have several solutions for you:

1. Send me the core via your friend and i'll test it
and send it back...dont worry about the mailing cost.
Maybe i could send it back to your friend, and he
can forward it to you?
2. I can look for a new core on the web that fits the
bill.
3. I can look for a ready-made inductor on the web
(prob Digikey) that will work without winding etc.

Anything here sound good to you?


Take care,
Al


----------



## PEU (Nov 24, 2004)

Hi Al,

I'm short of friends traveling to USA this days /ubbthreads/images/graemlins/smile.gif

When all else is ready I can ask some friend here to test the inductor I guess, or I can go to a shop and ask for a LC meter demo /ubbthreads/images/graemlins/grin.gif, if a meter can test it, I guess this is the easiest solution!!! /ubbthreads/images/graemlins/grin.gif

Thanks for caring!!

Pablo


----------



## NewBie (Nov 24, 2004)

If a fella wants to buy them, the Panasonic FC series is pretty decent.

http://rocky.digikey.com/WebLib/Panasonic/Web%20data/EEA-FC,%20EEU-FC%20(Series%20FC,%20Type%20A).pdf


----------



## MrAl (Nov 24, 2004)

Hi again,

NewBie:
Thanks for the link for the caps.
If you feel like looking for some nice
high current inductors too, that would be cool /ubbthreads/images/graemlins/smile.gif
The three versions we would need would be:
1.5 amps (so inductor has to work up to say 2 amps)
3 amps (so inductor has to work up to say 3.5 amps)
5 amps (so inductor has to work up to say 5.5 amps)
Of course the lower the cost the better.

Pablo:
Hey no problem!!
If you can get one tested there, then first wind 25 turns on the
core then test it. It should read around 100uH to maybe 120uH
or something like that.


Take care,
Al


----------



## PEU (Nov 25, 2004)

Al, how can I be sure if I test the toroid that all features needed are correct, the saturation problem comes to mind. I never saw a LH meter, so I don't know the common features /ubbthreads/images/graemlins/smile.gif


Pablo


----------



## MrAl (Nov 25, 2004)

Hi there Pablo,

Wow, you're up early too this morning /ubbthreads/images/graemlins/smile.gif

Well, without a scope, i dont think it's possible to
check all of the features of the inductor. If the
number of turns is 25 and the inductance reads somewhere
around 100uH then i was going to assume it was made
from the same material as the one Vic and I have so the
other spec's should be about the same too. Of course
this isnt absolutely guaranteed, but what else can we 
do?
If the turns/inductance comes out right, the other thing
that can be done is to measure input current while running
the ps up and check to see it doesnt go too high (which
would cause very gross bad efficiency). Also, the
switcher ic would get very hot very quickly.

If you built up the Ripple Detect Network (Zetex thread)
you would see the ripple voltage shoot up too when the
load is increased to a level which causes the inductor
to saturate. For an example, i was testing Vic's other
small core recently and at 120ma output the ripple was 
pretty normal, around 50mv or something like that.
When the load was increased to 240ma (still not much 
current for a supply like ours) the ripple shot up to
something around 0.3 volts, which is 6 times higher!
With the inductor that doesnt saturate, the ripple goes
up only a little bit; maybe 20mv or something, but nowhere
near the amount with the bad inductor.

Does this seem to help?

I can post the Ripple Detect Network if you cant find it.
It's made from a few 1/4 watt resistors and two caps
and a 1N5817 Schottky...very simple...takes about
15 mins to solder the parts together.

I wish you and your family a very Happy Thanksgiving!

Take care
Al


----------



## PEU (Nov 25, 2004)

My son woke me up asking for Yogurt at 8AM (local) /ubbthreads/images/graemlins/smile.gif

We don't celebrate Thanksgiving here, but thanks!!!

I'll build the toroid inductor & try it Al. I'll let you know

Thanks

Pablo


----------



## NewBie (Nov 25, 2004)

Not sure what you term low cost.

How about something like these?

http://www.jwmiller.com/pdf2/2300LL.pdf
http://www.jwmiller.com/pdf2/2300HT.pdf
http://www.jwmiller.com/pdf2/2200LL.pdf
http://www.jwmiller.com/pdf2/2100LL.pdf

Suppliers (non-stocked)
http://www.mouser.com/index.cfm?&handler=data.listcategory&D=*2300HT121V*&terms=2300HT-121-V&Ntt=*2300HT121V*&Dk=1&Ns=MfgrPartNumber%7c%7cSField&N=0&crc=true
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=44604&Row=39239&Site=US

I don't have any frequency data on these parts though, and with different ferrites, it makes a difference as far as losses, as well as does the ripple current.

If you don't mind Surface Mount, these are stocked, 
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=45251&Row=317145&Site=US
and a group buy will get you into the 2 dollar range.

These will get you into the 1.84 range in a group buy,
PM2110-101K, and meet your 5A need, with 0.032 DCR, and 5.4A.

Unfortunately, with most torriods, their inductance drops to around 50% under load.


----------



## MrAl (Nov 26, 2004)

Hi again,

Pablo:
Oh geeze, hee hee. Wonder what made him want
that so early in the morning /ubbthreads/images/graemlins/smile.gif

Yes, i realized it's mostly a US holiday, so
many other countries wont celebrate that...sorry.

Ok, im also looking for other inductor solutions,
and Newbie has posted some finds i looked at.

Newbie:
Thanks much! I've looked at some of these and they
look pretty nice. Some of the prices arent too bad
either. I guess im looking for a price around $2.00
or so, but realize sometimes this cant be found for
a high current model.
Now i guess the only thing left to do is get a few
and try them out at some point 
Oh yeah, BTW, the digikey 'search' links dont work because
they say the search has "expired". All the other links
worked fine however.


Take care,
Al


----------



## MrAl (Nov 29, 2004)

Hi again,

Just a few notes for anyone interested...

I've tested the small flat black core Vic sent, and
it does saturate with as little as 240ma dc, but
i've gone over a few calculations that show that
the core might be useable up to 1.5 amps or more
if there is an air gap cut into the core.
Now if i can cut this core with the dremel, i'll
get the gap although it will be larger then desired
so i'll have to add turns.
With the lower current (1.5 amps) i can probably get
away with #24 AWG wire. At 4 amps dc, quite a large
gap and many turns are required -- so many turns that
#24 gauge wire is the largest that will fit that many
turns on the core, and that eats lots of power (like 4 
watts, which will heat up fast) so i dont think it's a 
practical choice at more than about an amp or so.

Now im just trying to decide if i want to cut up this
nice little core, or break it into four pieces to get
the required air gap...or not. Maybe save it for the
extra filter that will follow the switcher.
If it's broken into 4 pieces (easy to do) i'll want to
glue it back together with the required gap(s) but
i'll have to find a decent glue that can handle at least
some temperature rise (say 30 deg C) without melting.


Take care,
Al


----------



## PEU (Dec 2, 2004)

Pablo


----------



## MrAl (Dec 3, 2004)

Hi there Pablo,

Eating a lot of potcorn lately? /ubbthreads/images/graemlins/smile.gif

I've been doing some more tests with the switcher, but
the circuit should be 'buildable' now.

I found a few other cores i had laying around and a
small one might work for my lower current demands (1.5A)
so i might use that. It's going to require a gap,
however, so im preparing to crack the core and glue
it back together. I've found an epoxy called "PC11"
that seems to be pretty good stuff, working up to
about 90 deg C.

I've also found a small pot core i had around and did
a simple experiment and some calculations and found that
without a gap the core saturates at as little as 1 amp,
but even with a mere 0.0025 gap the core works!
It's amazing that a little gap like that turns a small 
core that doesnt work into a core that works!
I wish it was easier to gap toroids though.

Take care,
Al


----------



## vicbin (Dec 4, 2004)

GREETINGS FOLKS ! /ubbthreads/images/graemlins/smile.gif

Really sorry guys, maybe you're wandering where the heck am I recently, again, just back from offisite/job assigment and back home just yesterday ! /ubbthreads/images/graemlins/mpr.gif Goosh, wished I had the energy level like a teenager ! /ubbthreads/images/graemlins/grin.gif

Wow, "A LOT" of updates ! But anyway , I think I will skip the tons of questions especially to MrAl ! /ubbthreads/images/graemlins/wink2.gif

Now, back to our baby, just finished "part" of the breadboarding level, man ... it was really hard. Infact I couldn't continue to finish it since my back and my neck were hurting me. Will update once I got fully recovered !

Pics of work is in progress on the linear part only.

That bright color marking on every insertion ! /ubbthreads/images/graemlins/smile.gif





The RAT NEST !!! he..he..., please if any, tips or kungfu in better breadboarding.





Close up.






Heya Pablo,

Sorry, its me to blame, because of the waiting, now you suffered "popcornoholic" syndrome ! /ubbthreads/images/graemlins/crackup.gif


Hi Newbie,

Thanks for the update and links, really appreciate your efforts ! /ubbthreads/images/graemlins/smile.gif

Looking at the datasheets, its true, those toroids drops 50%. Does it mean I need to increase the value 100% when I wind the toroid core ?


Hello Al,

Again, sorry for late update on the linear part, I will try once I get them all wire up and fully recovered from my last journey.

Although I got tons of questions regarding your recent updates (lot of updates on switching /ubbthreads/images/graemlins/smile.gif ), I think I'll take some rest first ! 

Questions while I'm breadboarding :

- I forgot to buy the D9 1N4739A (Zener 9Volt), is it ok to replace it with other lower one ? or maybe other options.

Wow, 3.5 Amps output ! Was that on breadboarding or PCB ? what's the Vin , Vout ? and ripple ? ... please... /ubbthreads/images/graemlins/grin.gif hmmm... did you use the IC I sent you or your's other one ?.... See !!! I can't help it not to ask you more questions ! /ubbthreads/images/graemlins/grin.gif

Regards,
Vic


----------



## MrAl (Dec 5, 2004)

Hi Vic,

Nice to see you're back. Thought maybe you got lost somewhere /ubbthreads/images/graemlins/smile.gif

It's nice to see you're going to try the linear part of the circuit,
so we can get some assurance this is going to work as planned.
All the simulations looked good, so it should work well.

You can try a 12v zener in place of the one you asked about.

3.5 amps, with the switcher right? That was at 1.25v output and
10v input. I now have it set for 5v output though, which is more
realistic. My wall wart isnt able to put out as much power
with the switcher set to 5v output, so i might move to using a
huge 12v battery, then later to 12v battery in series with 10v
wall wart.
As i had mentioned, the Vin=10v and Vout=5v, and the ripple varied
with the inductor, but with the big yellow one you sent and 25 turns
it was around 50mv even at 1.5 amps output, and this is happening
even with only a single 1000uf, 35v output (electrolytic) cap!
I also got good results with the 'store bought' inductor, but
it cant handle as much dc current.
I also started looking into using a very small core about
0.5 inch diameter for currents up to 1.5 amps. Originally,
the core couldnt handle even 0.5 amps dc properly due to some
rather high current spikes but after cracking the core (see other
thread here on CPF) and gluing back together and then adding more
turns the inductor worked very well up to what i could test up to:
1.5 amps dc. Pretty interesting i think. I'll put more details
about this in the other thread as soon as i can.
I've also done a few calculations which indicate that the big
yellow core you sent should be able to handle around 5 amps dc
but i dont think i would run it any higher without a gap. Im
not sure if i would want to take a chance cracking this core 
though. Keep in mind, however, that this is using 25 turns...
...any more turns and the core will saturate sooner. Perhaps
ill run over the numbers again just to make sure. I wish i
could test all the way up to 5 amps, but the switcher only puts
out 3 amps (which isnt bad really).

Oh yes, it's the switcher ic you sent! It's working nicely as
a dc converter and makes testing the cores pretty easy too.
Now i'd like to come up with a test that people can do without
requiring a scope to see if the inductor is starting to saturate.
I think the best would be using the Ripple Detect Network i talked
about before, because the sure sign of saturation is the output
voltage ripple peaks go up quick.

Thanks for the nice pic's too! Looks like you dont have much
farther to go with the quick breadboard.

BTW im using a pc board with only single hole copper patterns
with all the parts soldered to it. I'll try to get a pic
or two of it so you can see what it looks like. It's pretty 
small really, with the caps sticking up from the board (pc mount
types). Only had to drill one hole for one pin on the switcher
ic because it didnt line up with 0.1 inch hole spacing which the
board has. The other pins were bent at various distances from
the ic chip body so they could be inserted into holes.


Take care,
Al


----------



## PEU (Dec 9, 2004)

updates?

/ubbthreads/images/graemlins/popcorn.gif 






/ubbthreads/images/graemlins/smile.gif (actually I'm drinking mate ) 


Pablo


----------



## MrAl (Dec 9, 2004)

Hi there Pablo,

Hey, that's a cool cup there. Where'd you get that cup?

I've read the story about the indians...pretty cool!

No updates recently because everything still looks good.
Vic is almost ready to test the linear part so we'll know
more then.

What i might do is write something about how the ps
should be run up for the first time and tested as
it's run up. Of course i'll post it here.

Take care for now,
Al


----------



## vicbin (Dec 11, 2004)

Greetings !!!! /ubbthreads/images/graemlins/smile.gif

Hi Al,

Good news on the linear part, .... IT WORKS !!!! /ubbthreads/images/graemlins/happy14.gif

Now, "brief report" :

- Vin to LM317 = 25V with 2 Amps capable source

- Op-amp supply +15 and -15 Volt was supplied by batteries with 7815 and 7915. Don't worry, it was closely monitored all the time. /ubbthreads/images/graemlins/grin.gif

- Bypassed the R16 100 Ohms (fine voltage adj), R3 change to 1K since I plan to test low votage load in breadboarding phase.

- Bypassed R10 100 Ohm for fine current adj

Measurement with 3 el-cheapo DMMs at :

- Vout at 20 Volt resolution
- Vin at 200 Volt resolution
- Iout by voltage drop across R15 (0.1 Ohm) sense resistor at 200mv resolution

Tested load so far :

- 5V volt mini DC fan at 250ma, voltage loop control is good and from open circuit (unloaded) to loaded with only 10-25 mv changes ! Probably its the breadboard or the cable. /ubbthreads/images/graemlins/grin.gif

- 5 mm Red and Blue led, CC loop is proven capable of 2-3 ma resolution and that was only with R9 (1K pot) and no R100 (fine tune trimmer) ! CC mode LED1 = ON ! /ubbthreads/images/graemlins/buttrock.gif

- LS 1 Watt /ubbthreads/images/graemlins/grin.gif , yes, its Luxeon Star running at 150ma CC mode and ... while holding my breath....tested by turning the R3 pot (voltage adjusment) to max and the CC loop still in control (+/- 2-3ma) with Vout stayed at 3.15 V. When the LS was unplugged the CC mode LED1 light was gone, and the Vout jump to 7.5 Volts !!! he..he...phheww....

- With CC adjusment to minimum, shorted the Vout and only 1-2 ma measured at 0.1 sense resistor, again, CC led1 on.

This is only early testing, planning to do further with higher current (500ma to 1 Amps) and voltage (above 10 Volts)when I find a suitable load for it.


Findings:

- I think my pot is noisy (dirty prolly ?), at fine adjusment the voltage or current is a bit jumpy but still at acceptable range.

- CC mode LED was not stable (sometimes it was blinking 2 - 3 times) especially when turning the R9 1K pot, again, I think may be it is the pot problem, will find the replacement.

Since this is your design, please if anything else that you need me to verify.

Too bad I can't take a snapshot, my camera is gone with my nephew for her end of year vacation for about a month. /ubbthreads/images/graemlins/icon23.gif

Al, as you said, please write down some early adjusment or important start up procedures. In my case when I powered it up for the 1st time with volt adjustment to minimum, the Vout was -0.1 V (minus) and but it was corrected by adjusting R22 for Vout down to 0.01 Volt at Vout. 

About the switcher, did you try the pregulator mechanism (Q1+D11) with simple LM317 configuration as the front end ? Just curious how it looks at the scope when the mechanism kicks in at loading time.


Pablo,

Looking at this early result, I recommened that you can start to do the "delayed" PCB work ! /ubbthreads/images/graemlins/smile.gif

Vic


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## PEU (Dec 11, 2004)

Hi Vic, good to read you again!

It seems the design is about to go final in a few days!! /ubbthreads/images/graemlins/smile.gif then I'll put all my energies to draw a nice ONE SIDE board

I can't wait ! (no more popcorns /ubbthreads/images/graemlins/grin.gif )


Pablo


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## MrAl (Dec 12, 2004)

Hi Vic and Pablo!

Nice to hear from you Vic, and you too Pablo.

Pablo:
Yes, the design is close to final now, as the linear part looks good
according to Vic and im running out of popcorn too /ubbthreads/images/graemlins/smile.gif

Vic:
That's great to hear! I cant wait to try mine too. I guess i'll 
have to break down and order the parts now. I've been holding off
waiting until we know for sure, but i guess it's time to try it.

You can try measuring voltage right at the output from the breadboard for
possibly better voltage readings under load, but beware the plugboard creates
little voltage drops sometimes that interfere with good performance.
I've noticed that i got better performance once i soldered all my parts
together rather than use the plugboard for various power circuits, but
it still works somewhat so it's still good results.
Also, the changes in output voltage might not increase with load current.

Not sure what you meant by "Red and Blue led", did you use red or blue or try
both?

Im very happy to hear you had the Lux Star running, but with a new ps
it's best to test first with cheap resistors, like 10 ohms or whatever.
If you measure the voltage across, you know if it's putting out the right
current (current loop mode). No need to risk a nice Luxeon just to test.
Remember also that there is 10uf output capacitance, so connecting
a Luxeon while the circuit is not current limiting (like say 7.5v out)
means the Lux has to DISCHARGE the output capacitance BEFORE it can go
into current regulation (activate current loop). This means the Lux would
get a huge current spike before current limit takes place, although it
wouldnt last for long. I have a feeling it wont hurt, but i cant say
it's a good idea either. Rather, turn the volt pot down then connect
the Lux, then turn up the volt pot until current limit takes over.
That's what i would do.
Now that you mention it, a few words on using the power supply to
test various components would be nice too right?

Nice to hear short circuit test worked too, and you know, i ended up
testing the switcher part (alone) for short circuit by accident.
Luckily, it works too /ubbthreads/images/graemlins/smile.gif

I'd like to hear about more of your higher current testing too
when you get to do it. Dont rush though, take your time.

Noisy pot? Maybe a cap across arm to one leg. Say, 0.01uf.
I was thinking about this issue recently too. I know some older
pots are already noisy, and some new ones become noisy at some 
point and require a spray of contact cleaner.

CC mode LED not stable...
This does sound like the pot, but if not it could be the LED draws
current and that changes the circuit to a small degree and that
turns it off. This would mean when the output current gets very close
to the actual current setting (current limit set point) the LED might
blink instead of turning fully on or off. I wouldnt think this to
be a problem really, unless something else is happening.
Measure the current at the point where the LED blinks.
If it only blinks while turning the pot, it's not a problem
If it blinks while the pot is not being turned, try to measure
the output current very carefully in order to ascertain if the
current is varying wildly or just a little. Keep in mind
that the op amp responds to very small changes, so it
could turn out that we just need a little hysteresis on the
LED comparator (op amp).
It could be that when the level is close to the set point,
the op amp turns on, then off, then on, etc.

Tests:
1.
Set output load to some available resistance value.
adjust current limit until LED blinks.
Measure output current change as LED blinks.
Record result.
With a SLIGHTLY HIGHER setting, see if LED blinks.
With a SLIGHTLY LOWER setting, see if LED blinks.


I'll try to do the run-up procedure as soon as possible.

I'll also look at your adjustment of R22 for zero output volts to 
see if it's a good idea. Originally, R22 would be adjusted for 
twice the reference voltage out of the op amp.
I'll try to think of some more tests also.

BTW, would a small minus voltage (like -0.1 volts) be a problem
for you if it ended up being that way?

I didnt do the test with the Q1+D11 yet, as i got sorta side tracked
by looking at creating the smallest inductor for a given current level
I'll have to do that this week then, and should have results by say
Friday.

Ive had some unusual problem come up this past week too, as i've had
some complicated dental surgery and it's still being a problem.
After the surgery, you could actually see the little bone in
the jaw! Pretty strange. It's starting to heal, but hurts
quite a bit. Kinda puts a damper on doing things.
I go back on Monday, so hopefully it will be solved.
In the mean time im taking Motrin.

BTW, i'll probably build a PCB at some point too instead of wiring
point to point like i did with the switcher.


Take care,
Al


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## MrAl (Dec 17, 2004)

Hi again,

Quick little update...

I've simulated applying a load to the power supply and
found only about a 20us dip in output voltage with very
minor ringing until stabilization. In short, it looks
very good.
I havent yet wired up the switcher to my existing LM317
based ps for a test with the transistor/zener feedback
arrangement but i hope to be able to do that very soon.

Take care for now,
Al


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## PEU (Dec 27, 2004)

updates?


Pablo


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## MrAl (Dec 27, 2004)

Hi there Pablo,

None yet, but im hoping to get to test the switcher with
my LM317 linear (the transistor/diode section as Vic
asked about) very soon. I dont have any real doubts 
about it, but it's always good to test something.

If you want to start designing a board for this you might
as well start, because any changes (if any at all) would
be small now anyway.

Take care for now,
Al


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