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Old 10-03-2009, 05:22 PM   #2343 (permalink)
MPaulHolmes
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Jack: Right now, for an instant it's 12/22 amps, and then drops to 0 amps once the gate gets to 12v, because the gate resistors are 22 ohms. If you use 2 igbts in parallel, I would use maybe 2.4 ohm to 4 ohm, 1 watt gate resistors. That would bring the instantaneous current draw to about 6 or 10amps from the 12 amp driver. The RC time constant of the gate capacitance would be much shorter, so you could pile-drive through that miller knee where all that wasted heat is being generated.

Also, I believe it takes 2 times as long to turn the IGBT off as it takes to turn it on, so you could have a (say) 4 ohm gate resistor in parallel with "diode and 4 ohm gate resistor in series", so that when the current goes the other way, the gate resistance behaves like about 2 ohms, so it turns off in the same amount of time as turning on. Isn't that sneaky!? Fran suggested it to me.

You would have larger spikes from the lower gate resistors, but who gives a crap, you have TONS of room.
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