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IGBT Short circuit withstand time

Question asked by vega.marco_antonio on Mar 10, 2016


I'm using 6 IGBT's part no. STGF10NC60KD in a typical three-phase inverter application and I have designed a short circuit protection to prevent IGBT damage when 2 phases of the motor becomes accidentally shorted. 

Base on the IGBT datasheet "Short circuit withstand time" is 10us. My designed protection acts in less than 5us, disabling PWM. However, I've done several short-circuit tests where the IGBT becomes damaged in less than 5us. Enclosed you can find an oscilloscope capture of the current pulse that flows by the damaged IGBT when it becomes shorted (channel 2 - green color). The current is scaled 20A/V. 

The oscilloscope capture shows an initial current pulse of 80A, followed by a 2nd current pulse of 140A at 1,5us and also a 3th current pulse of 120A at 2,5us. Finally at 3,2us the PWMs are disabled and current goes to 0A. The 2nd and 3th current pulses appears since we are short-circuiting 2 phases of the motor, it means short between 2 branches of 2 IGBTs.

Could you give me more details of how to interpret the "Short circuit withstand time" parameter given at the datasheet of IGBT? Why is it not able to support such short-circuit of total time 3,2us? Moreover, in case of IGBT short-circuit detected and successfully protected, which should be the minimum time that I've to wait for next IGBT driving signal retrial without damaging it?