Laser Driver Circuit Question

[Bryverine]

I need to drive a fiber coupled 50mW, 520nm diode from a 12V DC source. I'll probably only need 20mW out the end of the fiber but want the capability to go higher depending on further coupling losses.

For the driver, I have to drop voltage to 6.5V-7V and then want to regulate the current from 140mA (minimum threshold) to 350mA to control the power. The specifications sheet calls out a max of 7.5V at 400mA.

I originally made a quick breadboard with two LM317 in series to drop the voltage and then control the current. While the circuit worked well on the DC power supply I was using, both regulators rapidly became quite toasty (duh)!

I'm looking to now redesign it as a pcb with a LT8606 (switching regulator) to drop voltage and put out 350mA max followed by a LM317 to regulate current. I currently have it designed with space for a 5W heat sink attached to the LM317.
Without seeing the circuit, does this sound like a reasonable approach to drive this diode?

Diode: WSLP-520-050m

 

[diachi]

I'm looking to now redesign it as a pcb with a LT8606 (switching regulator) to drop voltage and put out 350mA max followed by a LM317 to regulate current. I currently have it designed with space for a 5W heat sink attached to the LM317.
Without seeing the circuit, does this sound like a reasonable approach to drive this diode?

That's one way to go about it, I've seen it done that way both in commercial products and in other applications. That said, if you can get a switching current regulator it's best just to just go that way and remove the linear stage entirely.

 

[Cyparagon]

I'd keep it simple and use a resistor and potentiometer. Assuming your 12V is relatively stable, all the silicon doesn't add much to the design.