 CG IGBT failure
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DoS
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Mon Sept 12 2011, 07:33PM
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Registered Member #360
Joined: Sun Apr 02 2006, 12:13AM
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Posts: 12
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I have a board that contains both flyback driver for generating HV and IGBT for turning on the coil. The whole process is controlled by an AVR micro. Everything works fine most of the time (for example 100 shots, one every 5 seconds), but sometimes when switching on the 12V supply (linear, not switching one) for flyback and IGBT driving, the IGBT fails.
Before the supply stabilises, it rings quite heavily sometimes and most of the time it barely reaches the gate threshold voltage. Is it possible that when the capacitor is (half full) and I switch on the supply, a peak larger than the threshold will occur on the gate and the IGBT will turn on. Then the Miller effect kicks in and turns off the gate and then the whole process repeats and somehow that destroys the gate?
Currently I have reverse diode on the coil (no overvoltage on collector), 400V TVS between collector and emitter just in case, and 15V zener from emitter to gate? Should I add something to stop the spike and ringing?
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