eugeneo
Joined: 05 Feb 2006
Posts: 6
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 Posted:
Sun Feb 05, 2006 6:16 am Post subject:
IGBT fails |
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I have a charge system that charges 4 x 350v 22uf caps and then discharges them to 1kv aircraft igniter tip (This app is not for an aircraft but it's designed to work under water).
Operation:
Once the voltage is at 1kv, I have a Pic triggering a optoisolator. The optical isolator has a max rise and fall time of 20 us (detector side).
That output is triggering the gate of a completely isolated IGBT at 15 volts. The IGBT rise is 60 ns and fall of 230 ns.
Problem:
The system functions the way it is supposed to. Except once in a while during my tests, the IGBT will completely latch up, and must be replaced.
I've checked the safe operating zone for the IGBT and everything is in check. The temperature of the IGBT is only warm after several minutes of operation. The IGBT is good for 70 A continuous at 1200V, 230A pulsed, short circuit of 10us.
My thoughts:
Is it possible that my optoisolator is triggering too slow and causing a high inrush of current when the collector/emitter has not completely reached a turn-on state, causing excesive power dissapation on the IGBT?
The igniter tip kind of acts like a metal oxide varister and triac at the same time. when the voltage applied to the tip is 1000volts, it will discharge the caps between 5 to 10 us. If the voltage is lower than 400, the tip discharges the caps within 3 seconds.
Any and I mean any suggestions would be appreciated. Thanks in advance.
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