I've been looking at FET switching performance on the current board. I am switching the D8 output with a 50% duty cycle and a 1kHz frequency. My heatbed is 5 aluminium clad resistors, 6.8 ohm in parallel. Nominal current draw at 12V is 8.8A, but I haven't measured it. That's a bit less than a Mk2 PCB heatbed. The MOSFET has no heatsink, and gets slightly warm.
I'm measuring the voltage at the gate and drain of Q201, D8 mosfet. Ch1 is the gate (orange), and Ch2 is the drain (blue).
Here are some scope traces:
[attachment 23434 DS0000.png]
[attachment 23435 DS0001.png]
[attachment 23436 DS0002.png]
The turn on time seem to take about 12us, which doesn't seem too bad.
Switch off is fast of course due to the small FET, but there is a big spike and ringing on the switch off, which might be expected for wire wound resistors.
The results seem better than I was expecting, although I am not entirely sure I am measuring this the right way.
I'm measuring the voltage at the gate and drain of Q201, D8 mosfet. Ch1 is the gate (orange), and Ch2 is the drain (blue).
Here are some scope traces:
[attachment 23434 DS0000.png]
[attachment 23435 DS0001.png]
[attachment 23436 DS0002.png]
The turn on time seem to take about 12us, which doesn't seem too bad.
Switch off is fast of course due to the small FET, but there is a big spike and ringing on the switch off, which might be expected for wire wound resistors.
The results seem better than I was expecting, although I am not entirely sure I am measuring this the right way.