TTL capable laser diode driver, homemade

[Thomaskt]

Hello to all, even i dont write so often here, i do read a lot of stuff that u all discuss about
I see it's very hard to find good and simple TTL driver that you can use for most of diodes that people around this forum are often using so i decided to make my own driver that i can use in my projects or as replacement driver for laser projectors if i dont have any spare by my hand at that moment. To be able to do that, i was searching for a driver that i dont have to mess too much to change current limit to the diode and that TTL control works good. So, here it is. I've been using it now for like week or so with no problem at all. I'm using it at 25KHz and it works with no problem. Keep the voltage as low as possible on input so LM350 wont get too hot (or LM317, i had LM350 by my hand). I prefer to put 2V more then circuit needs (depending on the diode). If u use 12VDC as example, small aluminium cooler like 2x3cm or so will do the job.

Hope you can have use of it as i do

 

[Cyparagon]

There are a lot of problems here and/or things that don't make sense.

Are you sure you didn't wire your PNP backwards? Or is it supposed to be an NPN?

What are the 15k and the 8.2k doing?

Is this TTL active high or active low?

Is this TTL with respect to (+) or with respect to (-)?

Is the TTL net connected to the 15k and 8.2k? Because you've drawn it as if it isn't.

Why is there no base resistor on the PNP?

Are you aware this setup (if it does work, as you say), would have a minimum voltage dropout in the range of 5V?

This is a much better option: http://laserpointerforums.com/f51/simple-linear-mosfet-dimming-circuit-pwm-70812.html

 

[Benm]

^^ The circuit linked above by Cyparagon makes a lot more sense.

I'm not sure what the design idea about the OP's circuit is, but i doubt it will work. You could easily use the components to make it work though: Run the 1k resistor from the TTL input to the D882 base.

Remove the 15k, 8k2, pnp diode and 1n4007 on the bottom right (D882 emitter connects to ground), and you're in business...

Well, you are relying on the LM317 driver so it will require a fairly large voltage drop and may experience some instability running it a high speed, but as a concept it would make (some) sense.

The reverse-protection diode over the LD is not required either, but leaving it there doesn't do any harm.