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Old 10-30-2009, 12:31 AM   #2515 (permalink)
jyanof
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jack

here's a picture of my charger drain-source voltage before I minimized the parasitic inductance.



The ringing is much more severe than your results - it's as if you have more damping.

Nevertheless, if you haven't yet shortened the length of wire between cap/igbt/diode, you still have sections of wire where the current is going from output current to zero with every cycle. Large di/dt and any amount of inductance will create voltage spikes.

I recall advice from the members of the evtech list: Minimize the length (and thus inductance) of any wire/bus/trace that has large changes in current (large di/dt). Minimize the area (and thus capacitance) of any part of the circuit that has large changes in voltage (dv/dt).

When I changed the setup, the waveform looked like this:


Actually, that looks more like your output. In these photos, I was using fast turn-on/off times with a low value gate resistor. I think Paul's is set up to have longer turnoff times. Might be another thing to think about.
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