@jens55 said in Duet 2 Mosfet switch off ringing:
Did you calibrate your probe (adjust probe capacitance) before you started your experimentation? Did you use a proper 10X probe or a straight wire hooked to your measuring point? If properly adjusted, the second trace should show a much cleaner signal.
thank you for your feedback and questions.
I'm using a diffential probe in 10x-mode.
Here is the same probe with same probe connectors, connected to a function generator providing a comparable 10V 50% duty cycle square puls:
Timebase is 50ns/div in zoom window, so the probe seems to be sufficient for the job above.
Besides that, switching an inductive load will always result in some ringing and can be reduced with a flyback diode as alankilian mentions but short of some major circuit design effort you will not get rid of the ringing.
I somehow was expecting this kind of answer, but was not shure due to lack of electronics experience.
I played with an external mosfet module on the desk some time ago. That module had an optocoupler between control and power circuit, and it works much cleaner.
But it would be difficult to change the gate side of the mosfet on a 3d printing main board.
Also, the hotend is not purely resistive .... it is a wire wound element so it experiences some (very small) inductive effects.
That would explain the sine ripple with the heater switch off, maybe together with the 1m wire from board to heater.
I wonder if this ringing would be present at all 3d printers, if I should just get used to it, or if there is anything in addition that might be considered.
Is it a good idea to add a capacitor to the fan like 100µF or 1000µF, or is there a risk that the initial current overloads the mosfet?