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AMC7135 - Did some digging, still no definitive answers.

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cilegray

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Okay, so I've searched thru all the threads I could find about the AMC7135 chips on the forums, and google, and tho I've seen alot of mentions of people running these off two Li-Ions, with a total Vin 2.4V higher than 'recommended' max voltage, and 1.4V over absolute maximum input voltage.

From what I can gather, a few people have sucessfully done so with adequate heatsinking, but nobody has ever come back with definite results, run times, etc...

I want to know exactly what the limits of these things are, and am planning on torturing one...unless someone allready has the answers.

Basically I want to know if these cheap round chinese linears can be used at all with the 445s...either unmodified, or with diodes to drop somewhere around 1V down to the mid 7s? These would hypothetically be heatsinked properly.
 
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Benm

Benm

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It shouldn't be much of a problem, but i would recommend inserting 2 or 3 drop diodes between the batteries and the Vdd pin of the regulator. Diodes between the supply, LD and driver output aren't required since the 445s drop plenty of voltage to have the 7135 operating at a safe voltage.

As for power dissipation: Lets consider the worst case with 2 cells: 8 volt input, 5 volt diode drop = 3 volts at ~350 mA, or 1 watt. The chip can dissipate this amount of power as long as it is properly heatsinked. The best way to do that is probably to mount it on a metal core PCB that is thermally connected to the host - similar to how power LEDs are mounted in a flashlight.

You could (also) fit a heatsink to the 'top' of the package, but heat transfer is not as efficient as it is to the bottom.
 
Fiddy

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Ive used a 3x AMC7135 driver with a 445nm diode, as you would expect it isnt very powerful, it only made 270mW but it has 5 modes :)

I haven't experimented with pushing the voltage up, the chips are rated for 6V max Vin aren't they?
 
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cilegray

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From what I've read, they are rated 6V... one place said to run them up to 7V absolute max with heatsinking, and I've heard other people running them with full 8.4V

Actually, before I hit the post button, I found this datasheet, which specifies 7V as the absolute max : http://www.micro-bridge.com/data/ADD/AMC7135.pdf

Ben has suggested a way to drop the voltage supplied to the Vdd pin via diodes, letting the Laser diode drop around 5V resulting in a 'safe' 3.4V on the OUT pin. I've got some 1N4001s laying around, would those work ?
 
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benmwv

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I could do some tests for you later if you want, but I think Ben m's idea will work fine. The AMC chips regulate through the negative side and have one "gate" pin that needs a positive voltage to turn on the AMC. That max voltage is probably how much the "gate" can handle since it gets the full voltage of the battery.
 
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cilegray

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I was going to use the KD drivers that, according to what I've found on BLF, uses this www1.microchip.com/downloads/en/devicedoc/41190c.pdf for it's mode control.

The boards I am using are these : http://kaidomain.com/product/Details.S020075...

So really, the AMCs won't ever be seeing anywhere close to 7 or 8 volts, regardless... but I have to look into regulating pin1 on the controller... which has a Vdd max of 6.5v.

Should I just ditch the modes and the controller, rip those parts of the board off and just jump a bridge from the Vdd pin on the controller thru 3 dropdown diodes and to the 'output/enable' pad...
 
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Benm

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I'm not sure why the maximum voltage is only 6 volts, but i reckon it was designed that way because these chips are led drivers and should not see higher input voltages while still operating at a safe dissipation level - most white leds drop a lot less voltage then 445 diodes.
 
Jufran88

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You could use diodes or power resistors to drop the voltage down. It would be place inline between the battery and driver.

There have been people using these AMC7135 drivers to power triple XM-Ls with 3 batteries, so it should be fine.
 
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cilegray

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Yes, BShanahan, that's quite obviously right. Your name came up alot when I did some searching on these, you got any answers for me ?

In a case someone had wired a power indicator LED in series to the 7135's Vdd pins to lower the voltage the pin was seeing, correct ?
 
JLSE

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Not sure if it helps any, I have used 5 chips in parallel and 2x 16340's, the only
issue I had was tremendous heat from the excess voltage. Laser ran fine and reliably. :beer:
 
BShanahan14rulz

BShanahan14rulz

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cilegray said:
Yes, BShanahan, that's quite obviously right. Your name came up alot when I did some searching on these, you got any answers for me ?

In a case someone had wired a power indicator LED in series to the 7135's Vdd pins to lower the voltage the pin was seeing, correct ?
Click to expand...

That is certainly one way to do it. My simple remark was meant to inspire just that thought. As long as you are using a diode to drop extra voltage, might as well also make it an indicator. I learned this trick from CPF, where since it is a linear driver, ~350mA flows through the entire circuit. You can put an LED in line with the regulator on the positive side and it will also see 350mA, and it will drop whatever its Vf is at that current.

I've just been waiting for someone with a scope to see how these behave when you turn them on or turn them off with the recommended capacitors and without. After that, I think we'd officially be able to say "you can use these for laser drivers" or "you can't".
 
Benm

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Are you seriously considering running 350 mA through a led that is used as an indicator?!

I'm all for clearly visible indicator lights, but making them 100 lumen seems excessive :D
 
Wolfman29

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OR... you could use what these were built for, and stick the regulator AFTER the diode ;) Then you only have ~3.8V getting to the regulator and it's dropping it down to 0V.
 
benmwv

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^I was thinking about trying that with my red diode from lazeerer's group buy. The only thing I was worried about is if the Vdd pin would see enough voltage to turn on. Running 700ma the diode must drop about 3v (maybe more?) which means the Vdd pin would only see 1.2v at fresh battery, and get down to around 0.6v when the battery drains to 3.6v. Think that would be enough to turn on the chip?
 
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