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| Is this an acceptable way to drive a Laser Diode? |
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| wholder:
I bought a cheap laser "engraver" on eBay (the kind that uses a GRBL-based controller to drive two stepper mechanisms from salvaged DVD players to control the X and Y axes) and noticed that the beam power varies inconsistently even when drawing with the same PWM power level. So, I decided to reverse engineer the circuit that's used to driver the laser diode (see attached schematic.) I haven't worked with laser diodes before, but I do know that they require a constant current driver and the circuit I found seems to be nothing more than a 12 volt, high side switch. The laser diode and lens is in a small cylindrical tube which I can't seem to open, so it's possible that there might be some type of current limiting circuit inside it. Has anyone else seem something similar to this? And, if, so, can you explain how it functions? Or, is this just a shoddy design that will sort of work for awhile and then burn out? Wayne |
| NiHaoMike:
I think it was intended for a laser module with the driver integrated. |
| Psi:
Keep in mind that they are super static sensitive. And they will die instantly if you push too much current into them. (Unlike an LED which survives for a little while) For example, you can connect an LED up to a lab PSU set to 12V with 20mA current limit. The PSU limits the current to 20mA and that limits the voltage to ~3V for the LED. But if you connect a laser diode to a lab PSU set to 12V / 20mA the laser diode will die instantly. The psu is too slow to bring the voltage down from 12V, that small burst of current at 12V before the limit kicks in, or from the PSU output caps, is too much for the laser diode to handle. |
| ejeffrey:
I strongly suspect that the module has a constant current regulator in it, and the 12V is just the input power. Because of the ESD, overcurrent, and overvoltage sensitivity of laser diodes it is really preferable to put the driver as close to them as possible, Long leads from the diode are just more places to pick up ESD, extra inductance the driver needs to deal with, and potentially a way to pick up damaging EMI transients. |
| magic:
Are there 2 or 3 pins on the diode? |
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