Here is a circuit idea to provide a variable voltage PWM drive from a 3v3 PWM source, this has not been tried yet. I have been thinking of a way to incorporate a front panel laser current control with the pwm from a controller board. The pot would be able to be used to set the maximum current and the PWM m/s ration would then give proportional control up to that maximum. The circuit would depend on the power supply integrating the pwm voltage to produce the laser driving current.
FYI: I have been doing quite a bit of research on driving the laser power supply. I have concluded that a level shifter is not necessary. Depending on your supply TL,TH, or -L on the supply can be used for the PWM input using an open drain configuration, while leaving the current control pot in the machine. I am in the process of testing and characterizing this approach all the way out to the lasers output.
Don, I look forward to hear your test results. I would be happier to have the open drain FET separate from the microprocessor output to offer some protection in case of a mis-configuration allowing 5v to be applied to an output pin. Otherwise sounds like a good idea. David.
Update, perhaps I misunderstood and you are meaning to use one of the high current driver FETs and not an open drain microprocessor output. In this case it should be just fine.
@Mircea_Russu it’s no point to be HV<LV, at 3.3V you are under the max mA ceilling and your tube is safe. (main goal)
now I get your point if you move inadvertantly the pot, but it’s true both way.
