lemmyman

Fets will be better for voltage drop. But for high side switching in this design you definitely want p fets - they are basically a drop in replacement.

I don’t know if you need an lm317 replacement. Aside from the voltage drop issue, the only issue I’m aware of might be startup timing since you’re PWMing them. I could not find anything about this in a datasheet. Once you get the transistors figured out I would use an oscilloscope to probe your output and see if it is the waveform you want.

I do know there are multi-channel LED drivers that would work, and are definitely made for PWMing. So you have options if the lm317s are too slow.

My bad, thanks for the correction!

This is 100% the issue. OP should move to low side switching with NPN BJTs or N-fets for the simplest fix. The arduino IO is 3.3v so they won’t be able to fully turn off a pnp (without extra circuitry).

Also, I’ll just note: lm317 dropout voltage at 60 mA will be about 1.5 V. The adj pin will be another 1.25V. So there is only going to be about 2.25V available to drive the load. Minus whatever drops there are through the pdn and transistors. I don’t know what a typical Vf for a laser diode is, but I wouldn’t be surprised if OP isn’t getting the drive current they want.