# A question concerning 7135 chips



## tx101 (Oct 5, 2009)

With the SST-90 and SST-50 emitters becoming available
I am looking for a low cost board/s to drive them.
Since I have a draw full of 7135 boards, my question is,
is there any limit to how many 7135 chips wired in parallel 
to drive a SST-90/SST-50

Example, I have the following, 1 x 8 7135 (2.8A), 1 x 3 7135 (1A)
and 1 x 3 7135 (1A) with multi levels. Can these all be wired up together
to drive a SST-50 at 4.8A ?


Thanks


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## jar3ds (Oct 5, 2009)

i think so as long as you only give the boards 4.5v max... i have plans to do something like this too... so i'd love to hear more input!


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## bshanahan14rulz (Oct 5, 2009)

I think you can hook as many up as you want. If your battery can't provide the amps via DD, though, they won't be able to with a 7135. I think of it as a current limiter device. At least, that's my understanding.


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## Mettee (Oct 5, 2009)

I have seen a picture from download or netkids where they have 9 amc boards stacked up. they did confirm that it worked, and it was an experiment because another driver did not exist at the time they created it that would do the job.


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## csshih (Oct 5, 2009)

there shouldn't be an issue, I'd suspect.
though.. what are you running it on? (gonna guess it's going to fall out of regulation very early on)

edit  ssts are pretty low Vf.. it's gonna be nice and regulated for a long time.


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## jar3ds (Oct 5, 2009)

Mettee said:


> I have seen a picture from download or netkids where they have 9 amc boards stacked up. they did confirm that it worked, and it was an experiment because another driver did not exist at the time they created it that would do the job.



:twothumbs


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## tx101 (Oct 5, 2009)

csshih said:


> there shouldn't be an issue, I'd suspect.
> though.. _*what are you running it on?*_ (gonna guess it's going to fall out of regulation very early on)
> 
> edit  ssts are pretty low Vf.. it's gonna be nice and regulated for a long time.



IMR 26500


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## darkzero (Oct 5, 2009)

Yes it will work. bshanahan14rulz is right, if your battery can not deliver the target current it won't with the 7135s hooked up. 

I made a few a while back & put them up for sale. I made some with 10x AMC7135s. Problem is with only 1 li-ion it would not deliver even 2.8A with a single li-ion cause of the voltage drop. with 4 NiMhs it did but the chips got very hot cause thet were over spec. Not sure how they perform with IMRs though since IMRs were not available then & I haven't used any since then.

8x 71235s & 10x 7135s


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## csshih (Oct 5, 2009)

tx101 said:


> IMR 26500


sounds like it's gonna be a kickass light.


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## Al Combs (Oct 5, 2009)

One thing I was wondering about. I found out from this thread the DX.6190 uses an ATtiny13V-10SSU RISC processor. I guess the others are using a similar type processor if that's not the board you had in mind. I have no idea how this controls the output from a bunch of 7135's. But since the LED+ output is picked up from the Atmel chip and not the Vdd lead of the 7135 chip, doesn't that mean the 4.8 amps is going through the trace of the multi-mode board? Even if the chip can handle that much power, the traces on those 17 mm boards are really tiny. A stack of single mode boards would definitely work. There you have the choice to pick up the power from the wire you use to make the parallel connections. Since DX is selling those multi-mode boards for $3.19, it seems like an acceptable risk.

I think the battery will be fine. I use a single IMR26650 in a P7 Mag2C. I bought a DSVNI P7 from PhotonFanatic. With a pair of 1,400 ma 7135 boards I got from DX, it delivers 2.82 amps just like I was hoping. The voltage across the LED was only 3.28 volts. It is almost an H bin. I'm sure that's a big help as far as staying in regulation. I also removed the reverse polarity diodes from the DX boards. When it seemed to be ever so slightly dimmer I measured tailcap current as ≈ 2.5 amps. The battery voltage at that point was about 3.6 volts. One of the things I like about an unprotected battery in this setup is you would easily notice it dropping below 3 volts.

I think the SST-50 take a little more voltage to reach full power. Guesstimating from the current vs voltage graph on page 9 of the Luminus docs on the SST-50, it takes 3.53 volts to reach 4.8 amps. So its Vf is a little higher than my P7's. Then again that same graph in the P7 docs say I need 3.61 volts to reach 2.8 amps. They haven't changed that graph since the J bins. I guess it really depends on the luck of the draw with the LED you get. 

I used your idea DZ of drilling through the board from the sales thread I first saw that picture in. I used a #60 drill hole to run a 20 gauge resistor lead to make the parallel connection. It looks so much neater than a wire looping around the edge of the board. Thanks for the idea!:wave:


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## tx101 (Oct 6, 2009)

Thanks for all the input guys lovecpf

I was already thinking that using 7135s at such a high current
could cause issues with heat. I guess I will mount the boards
on a couple of Sharksinks (component side down)

To be on the safe side, I will take your advice Al Combs and
do away with the multi-output board and replace it with a
plain-Jane 7135 board .... Yes, I known $3.19 is cheap BUT
they take forever to ship 

BTW, I received a Britelumens SST-90 HS this morning 
all I need now is to cannibalize one of my Mag builds to get 
the host


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## jar3ds (Oct 6, 2009)

use the d2Flex for your dimmer... use the 7135 to limit current


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## tx101 (Oct 6, 2009)

jar3ds said:


> use the d2Flex for your dimmer... use the 7135 to limit current



Hmm ... thats a good idea, now if only I had a spare one 
Do you know if this combination will actually work ?

To be honest, this build is more of an experiment to see if it will
work. If it does then I was planing to get the more manageable 
SST-50 and build a light with a Fivemeg blood red 1C that is on the
way to me


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## Mettee (Oct 6, 2009)

_I used your idea DZ of drilling through the board from the sales thread I first saw that picture in. I used a #60 drill hole to run a 20 gauge resistor lead to make the parallel connection. It looks so much neater than a wire looping around the edge of the board. Thanks for the idea!:wave:_

I wondered if I could do that the other night, glad to see the drill idea works well.


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## Al Combs (Oct 6, 2009)

jar3ds said:


> use the d2Flex for your dimmer... use the 7135 to limit current


From the TaskLED site, "Maximum drive current 3.4A (70C ambient) or 4.5A (25C ambient)". Here is a post from George himself in a cmacclel thread that there is apparently a new version D2Flex that can handle 10 amps. If you want to get a D2Flex, maybe you should email TaskLED first to make sure you get the right one. If you look at the top of this thread, cmacclel says he used a D2Flex with no regulator on an SST-50 with a BatterSpace 26650. I'm not sure if these are IMR's as they have a max discharge of 10 amps. It might behave differently with the AW IMR26500's. Here's a post from moviles using a pwm (unregulated) dimmer from an MTE SF-15. He says the FET handles 71 amp. I guess that should be enough.


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## Al Combs (Oct 6, 2009)

Mettee said:


> _I used your idea DZ of drilling through the board from the sales thread I first saw that picture in. I used a #60 drill hole to run a 20 gauge resistor lead to make the parallel connection. It looks so much neater than a wire looping around the edge of the board. Thanks for the idea!:wave:_
> 
> I wondered if I could do that the other night, glad to see the drill idea works well.


I got a little close to the ground ring on one of the boards. It was easy to trim away some of the copper with a #11 X-Acto blade.


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## Justin Case (Oct 6, 2009)

Right. You want to use a very small drill bit that fits in-between the outer ground trace and the center anode pad. I've also used a #60 (0.040") bit. I wouldn't use any drill bit size larger than that.


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## darkzero (Oct 6, 2009)

Al Combs said:


> I used your idea DZ of drilling through the board from the sales thread I first saw that picture in. I used a #60 drill hole to run a 20 gauge resistor lead to make the parallel connection. It looks so much neater than a wire looping around the edge of the board. Thanks for the idea!:wave:





Al Combs said:


> I got a little close to the ground ring on one of the boards. It was easy to trim away some of the copper with a #11 X-Acto blade.


 
:twothumbs



Carbide drill bits for use on PCBs work best for this. You can get the resharpened ones on ebay or Harbor Freight for cheap.


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## Al Combs (Oct 6, 2009)

Hmm, carbide makes sense drilling through glass. I had a regular HSS #60 handy at the time. But even if I had thought of carbide, I don't think I would have had enough patience to wait for the mail.

Thanks again Will.:wave:


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## StefanFS (Oct 7, 2009)

tx101 said:


> Thanks for all the input guys lovecpf
> 
> I was already thinking that using 7135s at such a high current
> could cause issues with heat. I guess I will mount the boards
> ...


 
The ATMEL chip used for multimode on the 7135 boards get less than a few mA (much less if I remember correctly). Well within specs. The ATMEL on my two level 7135 boards survive in my 3xP7 Mags powered by 3 x D-size LiION. I've also been overdriving a 4x CREE R2 setup running it at 5A for a long time without problems.


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## tx101 (Oct 7, 2009)

StefanFS said:


> The ATMEL chip used for multimode on the 7135 boards get less than a few mA (much less if I remember correctly). Well within specs. The ATMEL on my two level 7135 boards survive in my 3xP7 Mags powered by 3 x D-size LiION. I've also been overdriving a 4x CREE R2 setup running it at 5A for a long time without problems.



Now that is a handy piece of information, Thanks Stefan :thumbsup:

Is 5A the highest you have pushed the ATMEL chip ?


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## Al Combs (Oct 7, 2009)

StefanFS said:


> The ATMEL chip used for multimode on the 7135 boards get less than a few mA (much less if I remember correctly). Well within specs. The ATMEL on my two level 7135 boards survive in my 3xP7 Mags powered by 3 x D-size LiION. I've also been overdriving a 4x CREE R2 setup running it at 5A for a long time without problems.


Thanks for the info Stefan.:wave:


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## jar3ds (Oct 7, 2009)

Mettee said:


> _I used your idea DZ of drilling through the board from the sales thread I first saw that picture in. I used a #60 drill hole to run a 20 gauge resistor lead to make the parallel connection. It looks so much neater than a wire looping around the edge of the board. Thanks for the idea!:wave:_
> 
> I wondered if I could do that the other night, glad to see the drill idea works well.



can't find this sales thread... can someone link it? :candle:


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## Al Combs (Oct 7, 2009)

jar3ds said:


> can't find this sales thread... can someone link it? :candle:


There really wasn't anything else in that thread besides the same picture he posted here. The picture caught my eye though. I only mentioned it to thank DZ for the idea.


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## Justin Case (Oct 7, 2009)

KD ProductID=1770 also uses a hole drilled through one of the boards to make a 2-board, 8xAMC7135 sandwich (the photos on their web site, which show an external wire connecting LED- to LED-, don't match the actual product). The boards are oriented with the non-component sides touching, so KD1770 is probably better suited for something like a Mag mod than a P60 pill.


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## Der Wichtel (Oct 7, 2009)

tx101 said:


> Now that is a handy piece of information, Thanks Stefan :thumbsup:
> 
> Is 5A the highest you have pushed the ATMEL chip ?



The 5A is not going through the Atmel chip. The AMC chips have an enable pin which can be seen on this pic ( from the link above):







The red connection is the enable pin of the AMC chip. If that pin senses a high level then the chip will "turn on" otherwise it disconnects the circuit.

So what the Atmel does is just turning the chips on and off very quickly, not noticable for usual human eyes .
if the on-time is equal off-time then you'll see 50% brightness. That's called pwm . Therefore the brightness is controlled by the ratio of on-time and off-time.


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## Mettee (Oct 7, 2009)

great post yitao


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## Der Wichtel (Oct 7, 2009)

Mettee said:


> great post yitao



thanks, thought I could clear a few things up.



Al Combs said:


> From the TaskLED site, "Maximum drive current 3.4A (70C ambient) or 4.5A (25C ambient)". Here is a post from George himself in a cmacclel thread that there is apparently a new version D2Flex that can handle 10 amps. If you want to get a D2Flex, maybe you should email TaskLED first to make sure you get the right one. If you look at the top of this thread, cmacclel says he used a D2Flex with no regulator on an SST-50 with a BatterSpace 26650. I'm not sure if these are IMR's as they have a max discharge of 10 amps. It might behave differently with the AW IMR26500's. Here's a post from moviles using a pwm (unregulated) dimmer from an MTE SF-15. He says the FET handles 71 amp. I guess that should be enough.



If the Attiny13V or whatever µC is used on the amc is desoldered and the pwm output of the D2Flex is soldered on the red connection then you won't have the maximum drive current problem of the D2flex.
A low esr capacitor paralleled with the batteries will reduce input ripples --> more runtime, since batteries are "more efficient" with lower currents


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## tx101 (Oct 7, 2009)

Der Wichtel said:


> The 5A is not going through the Atmel chip. The AMC chips have an enable pin which can be seen on this pic ( from the link above):
> 
> 
> 
> ...




Thanks for the explanation Der Wichtel


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## Al Combs (Oct 7, 2009)

Der Wichtel said:


> The 5A is not going through the Atmel chip. The AMC chips have an enable pin which can be seen on this pic ( from the link above):
> 
> The red connection is the enable pin of the AMC chip. If that pin senses a high level then the chip will "turn on" otherwise it disconnects the circuit.
> 
> ...


Yes, thanks for the explanation. It also helps explains the debate about removing the protection diodes from the 7135 boards. The pdf on the AMC7135 says the minimum Vdd voltage is 2.7 volts. But the output can still be more than that. There was a good post about the 7135 from Drewfus2101. In post 30 of this thread he gave the results in a graph after removing the reverse polarity diodes. There was no difference. But he only went down to 3.4 volts supply. Which is still 0.7 volts above the trigger threshold. I get it now, thanks.:thumbsup:


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## Justin Case (Oct 7, 2009)

Al Combs said:


> Yes, thanks for the explanation. It also helps explains the debate about removing the protection diodes from the 7135 boards. The pdf on the AMC7135 says the minimum Vdd voltage is 2.7 volts. But the output can still be more than that. There was a good post about the 7135 from Drewfus2101. In post 30 of this thread he gave the results in a graph after removing the reverse polarity diodes. There was no difference. But he only went down to 3.4 volts supply. Which is still 0.7 volts above the trigger threshold. I get it now, thanks.:thumbsup:



Yes, Drewfus2101's measurements didn't show any difference even after removing the diodes. But #1, his measurements didn't go low enough in input voltage as you say, and #2, it isn't a "trigger threshold" issue. It is being able to still run in full regulation even with a low Vf LED and relatively low Vin. See my explanation in Post #44 of that thread.


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## Packhorse (Nov 27, 2009)

As Der Wichtel points out the control chip does not see the total output current. BUT it does have to control all AMC 7135 chips and there will be a point where it will not be able to control any more chips. Where this point is I have no idea.

Anyway who has hooked up the most AMC's? What battery pack did you drive it off? What problems did you have?
I am wanting to run 20 of them off a 20ah Li Ion 3.7v pack.


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## darkzero (Nov 27, 2009)

Packhorse said:


> As Der Wichtel points out the control chip does not see the total output current. BUT it does have to control all AMC 7135 chips and there will be a point where it will not be able to control any more chips. Where this point is I have no idea.
> 
> Anyway who has hooked up the most AMC's? What battery pack did you drive it off? What problems did you have?
> I am wanting to run 20 of them off a 20ah Li Ion 3.7v pack.


 
Most I have ever done is 10 but only because there was no sense in going higher for the P7. There were no SSTs around back then but I'd be willing to try.

Like the "AMC" boards that uses the Atmel MCU to control the ADDtek regulators, the FLuPIC is similar which uses a Microchip MCU to control Texas Instruments regulators. I built a Tri-FLuPIC running 15 regulators (5 per channel wired in parallel) to power a SST-50 & the PIC did not like that. Aside from the UI acting funny, at times it would trip out & push 9.5 - 10A to the poor SST-50.


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## Linger (Nov 28, 2009)

your work is art


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## tx101 (Nov 28, 2009)

:bow: DZ :bow:, if only my soldering was half as neat as yours :sigh:


=========================================


I still have not gotten around to "slapping" a couple of 7135 boards together 
I keep getting distracted by another project


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## StefanFS (Nov 28, 2009)

Packhorse said:


> As Der Wichtel points out the control chip does not see the total output current. BUT it does have to control all AMC 7135 chips and there will be a point where it will not be able to control any more chips. Where this point is I have no idea.
> 
> Anyway who has hooked up the most AMC's? What battery pack did you drive it off? What problems did you have?
> I am wanting to run 20 of them off a 20ah Li Ion 3.7v pack.


 
I did run a total of nineteen AMC7135 chips controlled by a Atmel Tiny chip (the "new?" two level 1A board from KD). Three on the 1A controller board and four 1.4A boards with four schips on each. Three IMR about 18650? size/three D LiION, both setups in parallell. One SSTx0. No problems that I could observe. The low level is still ~10%. 10% of a lot more 100% level, but that is also true of my P7 and MC E lights with AMC7135 based drivers. It's a simple design, as Yitao explained the Atmel chip just switches the string of AMC chips, it doesn't seem to matter if it's one or fifteen. I stepped it down to ~5A to control heat from the emitter in a Mag D size package before I took it apart permanently.


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## Der Wichtel (Nov 28, 2009)

Well the Atmel µC can only deliver 20mA max per pin. The more AMC boards are added to the setup the higher the capacity on that pin will be.

If the capacity is too high on that pin the edge between on and off state of the AMC boards will be too long which will cause some problems.

Furthermore the switching current will rise up and can destroy the output of the Atmel µC if there is no internal protection.

So we need to find out the enable pin's capacity of the amc board and the pwm frequency of the µC in order to estimate how many boards can be connected in parallel.


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## Packhorse (Nov 28, 2009)

For my application 10% is too low for low mode. I really want about 30-50%.

The way I figure it is get the control chip to control 70% of the AMC's and run the remaining 30% as single mode.
This way hi is 100% and low is 30% + (10% of 70%) or 37% of high.
I can then also run a thermal switch connected up to the dual mode driven AMC's and if /when it over heats it will shut down to 30%.
It also means the Atmel chip is driving less AMC's.


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## saabluster (Nov 30, 2009)

Packhorse said:


> As Der Wichtel points out the control chip does not see the total output current. BUT it does have to control all AMC 7135 chips and there will be a point where it will not be able to control any more chips. Where this point is I have no idea.
> 
> Anyway who has hooked up the most AMC's? What battery pack did you drive it off? What problems did you have?
> I am wanting to run 20 of them off a 20ah Li Ion 3.7v pack.



Wouldn't it be possible to have the Atmel run one AMC which then in turn switches the remaining AMCs? That way the current load on the Atmel pin is reduced. I'm no electronics expert so don't roast me if I'm way off.


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## Packhorse (Nov 30, 2009)

No I dont think that would work. You could use a pair of transistors though. ( I guess). I not think it is required though.


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## Fulgeo (Dec 23, 2009)

StefanFS said:


> I did run a total of nineteen AMC7135 chips controlled by a Atmel Tiny chip (the "new?" two level 1A board from KD). Three on the 1A controller board and four 1.4A boards with four schips on each. Three IMR about 18650? size/three D LiION, both setups in parallell. One SSTx0. No problems that I could observe. The low level is still ~10%. 10% of a lot more 100% level, but that is also true of my P7 and MC E lights with AMC7135 based drivers. It's a simple design, as Yitao explained the Atmel chip just switches the string of AMC chips, it doesn't seem to matter if it's one or fifteen. I stepped it down to ~5A to control heat from the emitter in a Mag D size package before I took it apart permanently.



StefanFS in your thread https://www.candlepowerforums.com/threads/195358 you fashioned a 3.0 amp driver for a P7 build and ran it for 30 minutes. You measured 39.1 degrees Celsius on the flashlight head. I was wondering if you ran any similar tests on the SST-50 using a string of AMC chips and if you did what temperature readings did you get at different amp settings. Forgive me for being ever so slightly off topic.


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## TorchBoy (Feb 19, 2010)

Der Wichtel said:


> Well the Atmel µC can only deliver 20mA max per pin. The more AMC boards are added to the setup the higher the *capacity* on that pin will be.
> 
> If the *capacity* is too high on that pin the edge between on and off state of the AMC boards will be too long which will cause some problems.


I think that should be "capacitance". Without that issue you could potentially run about 100 AMC7135s.



saabluster said:


> Wouldn't it be possible to have the Atmel run one AMC which then in turn switches the remaining AMCs? That way the current load on the Atmel pin is reduced. I'm no electronics expert so don't roast me if I'm way off.


You would need an extra 2.7 V, the Atmel might not like the extra voltage, and it's not needed anyway. (You wouldn't actually need to run the first AMC7135 in regulation because you wouldn't need the full 330-350 mA, so you could get by with less than 2.7 V.)


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## vestureofblood (Feb 19, 2010)

Der Wichtel said:


> The 5A is not going through the Atmel chip. The AMC chips have an enable pin which can be seen on this pic ( from the link above):
> 
> 
> 
> ...


 
Hi,

Could someone please tell me if I understand how current flows through this driver?

From batter NEG. To the outside of the board (or ground).
From the edge of the board to the center pin of the 7135 chips.
From the center pin of 7135s to the NEG pin on the right side of the chip.
From pin on the right to the led NEG.
From Led POS back to the left pin of the 7135 chip and the PWM control (where the circuit is quickly broken and restarted for dimming) 
From Left 7135 pin and PWM out the bottom of the board back to the battery positive?

Is this correct? Even Close?
Thanks.


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## TorchBoy (Feb 19, 2010)

That doesn't sound right. The LED neg pin will be on the left if the large ground pin is at the top with the lettering right side up. Batt pos/LED pos is separated from the PWM controller by a diode. The right pin of the AMC7135 (the Vdd pin) is connected to the PWM controller output pin.

Have you had a look at the circuit diagram in the AMC7135 datasheet?


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## ti-force (Feb 19, 2010)

Datasheet:

http://www.micro-bridge.com/data/ADD/AMC7135.pdf


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## vestureofblood (Feb 20, 2010)

TorchBoy said:


> That doesn't sound right. The LED neg pin will be on the left if the large ground pin is at the top with the lettering right side up. Batt pos/LED pos is separated from the PWM controller by a diode. The right pin of the AMC7135 (the Vdd pin) is connected to the PWM controller output pin.
> 
> Have you had a look at the circuit diagram in the AMC7135 datasheet?


 
Ok, sorry when I wrote that I was thinking of the chip upside down, with the large ground facing down and the 3 small pins sticking up.

So the last part then is 
Led POS to the VDD leg of the 7135 chip 
Then to the controller board
Then to the diode and out to battery pos?

I looked at the data sheet just now and it helps a bit, but mostly for me to get a clear idea of what is taking place, the pictures that others have drawn over the board seem to be best for me.


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## TorchBoy (Feb 20, 2010)

Still not right. LED pos *is* battery pos, and the Vdd pin of the AMC7135 is controlled by the Atmel chip, which has a diode between it and LED/batt pos.


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## eebowler (Jul 10, 2012)

NEW QUESTION GUYS. Does the 7135 chip (350mA) limit the output current of the driver or its input current? I have one of the 1050mA (3x 7135), 5 mode drivers in a Streamlight ProPoly, 4AA light and on high, it produced too much heat for the plastic body so, I broke off one of the 7135 chips to reduce current. Using 4 alkaline cells, I measure approximately 730mA draw from the battery. Using 4 NiMH cells (5.2V,) current draw is 700mA. Power consumption with NiMH is approximately 5x0.7=3.5W and assuming an effeciency of 90%, (3.5x0.9)=3.15W goes to the LED resulting in an approximate current of 3.15/3.2=0.98A. With the higher voltage of alkaline cells, LED current would be a little higher. Is my math correct? Why is the LED still getting close to 1A of current instead of closer to 700mA? (YES, there was a reduction of heat produced by the module after the chip was removed.)

Also, can I do something (change a resistor) for the low voltage warning to kick in at a higher or lower(LiFePO4) voltage than what is set on board? Thanks!


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## yazovyet (Jul 10, 2012)

So a normal resistor has a set resistance, the 7135 acts like a variable resistor. When the voltage applied is lower than that needed to run the LED and it can't get the current above the 350mA the 7135 has a very low resistance. Once the voltage applied is enough to get the current over 350mA then the 7135 will start acting as a larger and larger resistance so that only 350 mA get through it. Having 2 or 3 in parrallel lets 700mA or 1050mA through.

A simple way to think of it is that if you have too low voltage then the 7135 acts as if it isnt there (well nearly, it will always burn off some voltage), if you have too much voltage then it allows the right amount to get to the LED and burns off the extra voltage as heat. 

You may be getting a higher voltage with the alkilines because the higher input voltage is pressing the 7135 to give a hihgher output current. teh data sheet I am looking at only goes up to 4 or so volts. 

data sheet:
http://illuminationsupply.com/AMC7135.pdf


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## wquiles (Jul 10, 2012)

eebowler said:


> NEW QUESTION GUYS. Does the 7135 chip (350mA) limit the output current of the driver or its input current? I have one of the 1050mA (3x 7135), 5 mode drivers in a Streamlight ProPoly, 4AA light and on high, it produced too much heat for the plastic body so, I broke off one of the 7135 chips to reduce current. Using 4 alkaline cells, I measure approximately 730mA draw from the battery. Using 4 NiMH cells (5.2V,) current draw is 700mA. Power consumption with NiMH is approximately 5x0.7=3.5W and assuming an effeciency of 90%, (3.5x0.9)=3.15W goes to the LED resulting in an approximate current of 3.15/3.2=0.98A. With the higher voltage of alkaline cells, LED current would be a little higher. Is my math correct? Why is the LED still getting close to 1A of current instead of closer to 700mA? (YES, there was a reduction of heat produced by the module after the chip was removed.)
> 
> Also, can I do something (change a resistor) for the low voltage warning to kick in at a higher or lower(LiFePO4) voltage than what is set on board? Thanks!



I just finished design of my own 3x 7135 LED driver board for a custom project that I am doing for a customer of mine, so I can give you some hands-on feedback:
http://atdms.com/linear_led_driver.html


















- The 7135 controls and regulates the the output current that is sinking on the output pin. BUT, since it is a linear regulator, by definition, that is ALSO the input current.
- The higher the Vin to the 7135 above the vf of the LED at that rated current, the higher the heat loses are - again, in a linear driver the extra power (V * current) is dissipated as heat
- The efficiency of a linear driver is not 90%. It is variable, depending on the amount of voltage above the vf AND the output current. So if the voltage is really high, the efficiency could be 50-60%, but when close to the vf, it is in the 90%.

For a linear regulator: 
Input power = Power loss at regulator + Power delivered to the LED

Since the current is the same in/out, and Power = Voltage * current:
Voltage in * current = Voltage across the 7135 * current + Voltage across LED * current


Here in this older post, page 2, post #41, a forum member tested efficiency with the input voltage varied from 3.4 up to 6 (max for the 7135):
http://www.candlepowerforums.com/vb/showthread.php?192925-AMC7135-Specs-Inside-**UPDATE**/page2


Will


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## eebowler (Jul 10, 2012)

A lot to absorb here. I get it that higher input voltage results in higher power losses so, 4 alkaline cells is not the best battery. If linear regulators dissipate extra power as heat, what happens when med and low modes are selected?


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## wquiles (Jul 10, 2012)

eebowler said:


> If linear regulators dissipate extra power as heat, what happens when med and low modes are selected?



At high level the 7135's are on 100% of the time, so brightness (and power loss) is at maximum. As we discussed above this gets worst the higher the difference in voltage from the LED's vf.

In the lower power modes, the 7135's are being pulsed ON/OFF at less than 100% duty cycle, so they are ON less of the time, so the LED is less bright, but also the power goes down as well. Note that the PEAK current is still the same as in the high brightness mode, but on average, the energy send to the LED's is lower.

Will


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## yazovyet (Jul 10, 2012)

Usually for med and low modes the microprocessor will turn the 7135s on and off really fast, so for medium (30% power) you might have it on for 3 ms then off for 7 ms and repeat, for low power (5%) it might be on for 0.5ms then off for 9.5ms (depending on the chip it might be slower or faster but thats the idea). Our eyes don't work that fast so we just see it as being dimmer than full blast. *Now I am not sure if the LED actually works that fast and is full on/full off or if it is like an incandecent light in that it takes a small amount of time to turn on and off and thus it sees the input pulses as an average (or I suppose there might be a capacitor there to average it out). So it is like having it on for only 30% of the time and thus only around 30% of the heat is generated.

edit:
* what will said above would indicate that the LED does operate that fast and our eyes are what make it appear dim instead of a fast strobe. 
apperently it took me 8+ min ot type that up, damn i'm slow.


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## eebowler (Jul 21, 2012)

If I understand correctly, at 35% output, the energy dissipated by the chips will be approximately 35% of the energy dissipated at max ouput?


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## wquiles (Jul 22, 2012)

eebowler said:


> If I understand correctly, at 35% output, the energy dissipated by the chips will be approximately 35% of the energy dissipated at max ouput?



Not necesarily. At 35% output, if the Vin and the vf of the LED are the same, the chips would dissipate almost zero energy as heat.

Power lost as heat depends on two factors:
- difference between LED vf and Vin
- current being delivered 

Power lost = (Vin - vf) * current


Will


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## DIWdiver (Jul 23, 2012)

eebowler said:


> If I understand correctly, at 35% output, the energy dissipated by the chips will be approximately 35% of the energy dissipated at max ouput?



Yes, very close. There could be slight differences because the battery droop may be slightly less (but remember you are drawing full power on and off, so the droop will be pretty similar), and the LED temperature will be less, which changes its forward voltage. But you would have to make careful measurements to notice these differences.


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