Help needed implementing max current pot

Ill try to find a schematic for an op-amp driver I know that I can set the max current with R4, but I wanted a dynamic solution that can be modded when swapping to different lasers without having to change resistor values etc. Thanks for your post.

LaserAdct said:

Ill try to find a schematic for an op-amp driver I know that I can set the max current with R4, but I wanted a dynamic solution that can be modded when swapping to different lasers without having to change resistor values etc. Thanks for your post.

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Here is a pretty good shell for your current driver.

It can run off of most voltages above +9V. +12V will work.

R4 works as your "range" knob and R6 as your "% of range" knob.

With the given values, the current changes from 0-2A as you turn R6 if R4 is turned all the way down. If R4 is turned all the way up, it varies from 0-4A.

If you want a lower range you could half the 22kOhm resistor to 11kOhm and use a 11kOhm pot for R4. This will give you 0-1A range to 0-2A range.

I recommend testing your circuit in PSpice before you order the parts (although I have tested this one a few times so far and have one built so it should work.)

Thanks a lot If that schematic had a TTL it would have been perfect, I really need that for blanking the lasers. By any chance you have a schematic with TTL lying around?

Here is it updated for TTL. With the TTL input at 5V about 1mA will through the load. This is sufficiently low so that almost any laser diode will be "off".

Thanks a lot. I will try out the simulation soft and build this driver sometime in the near future

Is the schematic correct? Looking at LM324 and LM358A it seems one of these are missing? (I might just be reading it wrong)

No you're reading it correctly. You only use one of the op-amps on the chip.

LM358 pin 11 does not exist (it's an 8-pin case), the GND (negative) pin is the pin 8.

LM324 serie (124/224/324) is a quadruple op-amp, this one have the negative pin at pin 11.

Always remember to neutralize all the unused op-amps in the IC (not connecting both the inputs to GND, the better system is to connect the output to the -In, and the +In to GND)