Quote:
Originally Posted by MazdaMatt
jyanof, i believe that your wiring solved the problem because a charger has no output inductance... we're driving a motor here, not a battery pack, so we are guaranteed to have inductance. (and by guaranteed, i mean "i think"... care to speculate?)
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Actually, the charger has inductors in the output loop. In fact, what I have in there is several times more inductance than these large series motors (300uH vs ~80uH, i think?). It's primary purpose is to supply the current when the mosfets are off so that the battery sees a more constant current, but I think they also serve the purpose of slowing di/dt so that the current doesn't rise too high during a single pulse.
At first I thought the output inductance were the culprit of all the ringing too! I asked the evtech list about it and they pointed out the drain-source ringing is actually caused by the inductance in the input loop (caps/flyback diode/mosfet).
That's why Paul's layout is so great - the caps/flyback diodes/mosfets are are all very close to each other and reduce the intrinsic inductance of the pcb traces by making the paths short. At first I thought it was just nifty packaging to make the whole thing smaller, but I'd say the electrical reason is far more important.