Hello everyone, We have a problem with a circuit we built. The circuit seems to work properly with a green laser diode (130mA, lower voltage). With the red laser (higher voltage) on the other hand, the circuit delivers only 60mA max of the 130mA it should be giving the laser.
The problem seems to be the transistor's resistance because it works properly if we bypass the transitor and give +5V to the LM317.
Is it this assumption correct?
We tried a few transistors (BC241, BC236, TIP41C and TIP41) but with no luck. Is there a way to find a drop-in replacement for the transistor? MOSFET seem to have lower resistance but require an external driver with Arduino.
We need to use the Arduino PWM with these drivers, so at least 980hz switching frequency is needed.
Thanks in advance
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.