I have an IGBT (with integrated anti-parallel diode; forgive the BJT symbol in the diagram) that is switching an inductive load with a ~300 Vdc supply. The threshold voltage is ~5V and I'm driving it with 0-10 V PWM pulses.
When I short the load to stress test, the PWM pulses the IGBT gate for a few cycles (before the micro catches the event). I see a large collector current spike for a few microseconds (~70 A for ~2 µs) that corresponds to the first PWM pulse after the load short event, followed by a few more similar pulses with much lower peak currents (~25 A for ~2 µs) before the micro turns off PWM.
Two questions: 1) Am I exceeding the IGBT current/SOA ratings? The IGBT has a short circuit rating of 10 µs at 360 Vcc, and a SOA max current (at any Vce) of 55 A. Is my 70 A spike going to damage the part? A load short isn't something I expect to happen very often, and I don't know if I need to be worried about this happening as a one-time thing.
2) After the load is shorted and the PWM is still firing for a few pulses, Vce stays at around 300 Vdc even though I'm seeing current flow with each of these PWM pulses; it's like the IGBT is on (passing high current) and off (Vce doesn't collapse) simultaneously. Even if this current was being delivered by the cap, shouldn't I see Vce collapse?
Thanks for your input.