AMC7135 driver question

LuxorLasers147 · Oct 12, 2011

Hi!

Quality AMC7135 350mA Regulated Circuit Board for DIY Flashlights 20-Pack - Free Shipping - DealExtreme

I want to use some of this drivers in my LOC builds but i have to figure out a way to ajust the output properly.

The output of this driver can be changed by adding IC`s in parallel. To drive the 826 diode i need 500mA. So with the stock driver i get 350mA and with two IC´s i get 700mA.
What should i do to get 500mA?

Also, that driver seems poor in components. Should i use a capacitor across the diode?

thanks!

rhd · Oct 12, 2011

Short answer, you can't.

There's no way that I've come across to reasonable achieve current in between the 350mA increments.

They're also annoying drivers to use for LOC builds because they don't have a common (-), and LOCs are case (-).

LuxorLasers147 · Oct 12, 2011

That´s not what i want to hear xD

What if i used two IC`s to get 700mA and then add a res on the in or output to limit the current? would that work?

sorry what you mean by common - ?

What about this driver?

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rhd · Oct 12, 2011

LuxorLasers747 said:
That´s not what i want to hear xD

What if i used two IC`s to get 700mA and then add a res on the in or output to limit the current? would that work?

sorry what you mean by common - ?

What about this driver?

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1) Nope, that won't work.

2) By common, I meant continuous

3) Nope, the VIn can't be higher than the Vout for that driver. So no luck here either.

LuxorLasers147 · Oct 12, 2011

Could you tell me why not? i think i saw a guy on youtube doing that with a pot i guess xD (not the same driver though)

Oh so if its not continuos the diode would have to be insulated from the case right?

on your mosquito build did you use a AMC 7135 based driver?

I ran out of ideas. Could you point me a driver that can do 500mA from one li-on? the flex`s are on vacations..:thinking:

rhd · Oct 12, 2011

LuxorLasers747 said:
Could you tell me why not? i think i saw a guy on youtube doing that with a pot i guess xD (not the same driver though)

Oh so if its not continuos the diode would have to be insulated from the case right?

on your mosquito build did you use a AMC 7135 based driver?

I ran out of ideas. Could you point me a driver that can do 500mA from one li-on? the flex`s are on vacations..:thinking:

500mA is actually pretty tough on one cell without going buck driver. The challenge is that at 500mA, a LOC will require too much voltage for a DDL style driver to provide from one cell, once the 1.25V resistor drop is factored in, plus the IC's dropout voltage.

I don't have a solution for you I'm afraid. In fact, there was a whole thread about this tough current/voltage/battery combination. It's hard to DIY.

LuxorLasers147 · Oct 12, 2011

I see.. The only reason u maneged to build your mosquito was because the volage of the 635 is lower comparing to locs?

So the only way is to wait for the flex then (if i want to use one li-on). Why are they out of stock for soooo long?

rhd · Oct 12, 2011

LuxorLasers747 said:
I see.. The only reason u maneged to build your mosquito was because the volage of the 635 is lower comparing to locs?

So the only way is to wait for the flex then (if i want to use one li-on). Why are they out of stock for soooo long?

Nope, the Mosquito was luck, in the sense that it just so happened that the optimal current for a Mitsubishi 635 is 1050 (a perfect multiple of 350).

BShanahan14rulz · Oct 17, 2011

7135 are like little gates, only letting 350mA through. Caps are suggested, I've blown an LOC by driving it with a 7135 float-soldered between the wires. I don't have a scope, so I don't know if the 7135 was to blame or simply the very real possibility of static.

rhd · Oct 17, 2011

BShanahan14rulz said:
7135 are like little gates, only letting 350mA through. Caps are suggested, I've blown an LOC by driving it with a 7135 float-soldered between the wires. I don't have a scope, so I don't know if the 7135 was to blame or simply the very real possibility of static.

Agreed.

In fact, the early datasheets on the 7135 suggested one cap. If you look at the most recent revision, it actually recommends two.

That said, even the latter datasheet (and thus presumably most drivers based on the amc7135) doesn't place a cap in parallel with the LD.

There's a cap between V(+) and GND, and then between LD(-) and GND. But there's no cap between LD(-) and LD(+).

I'm admittedly not familiar enough with the regulator to know if a cap across LD(-) and GND accomplishes the same filtering objective as a cap across LD(-) and LD(+) would.

Blord · Oct 17, 2011

You could just use one amc7135 chip to drive 350mA current. That not shabby for a red laser.
or you could use a lineair driver like this,
http://laserpointerforums.com/f39/fs-jib-drivers-1-25a-1-8a-67623.html
it has a lower voltage drop than a standard LM317 driver. Setting current is the same as LM317, 1.25V=I.R
Remove both the soldered 1Ohm resistors and replace it by a 2.5Ohm resistor. That gives 500mA current.

Cyparagon · Oct 17, 2011

You could dump the extra 200mA over a resistor (~15Ω 1W I think) in parallel to the laser diode, but that wouldn't be very efficient

rhd · Oct 17, 2011

Cyparagon said:
You could dump the extra 200mA over a resistor (~15Ω 1W I think) in parallel to the laser diode, but that wouldn't be very efficient

That's interesting.

In theory, if I wanted a 600mA driver for a 405nm 12x, that would handle a source of 2x lithium ions, I could use 2x AMC7135s after all.

With a 60 ohm resistor parallel (perhaps right on the PCB) with the LD outputs, it would divert around 100mA from the 700mA output, and leave 600mA for the LD?

Of course, I'd need a 1W resistor (or 0.75 at least), but it should work.

chefla · Oct 18, 2011

Good idea to use a shunt resistor to route the current around the laser diode.
For 500mA drive current at 6V(?) the resistance of the laser diode would be 12 Ohm and require a 30 Ohm resistor with min 1.2W to shunt the not needed 200mA current from the 2x7135 driver. For 600mA current this would require a 60 Ohm resistor, as rhd has stated.
But, considering all the part tolerances and temperature effects I would in any case add some safety margin!

BShanahan14rulz · Oct 19, 2011

FYI, just because download used an LED to drop the Vin voltage down, doesn't mean that you can't use a regular diode. However, it would make a nifty AND functional "laser ON" indicator ;-)

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