Abstract: A circuit for preventing switching voltage transients from damaging the IGBT during short circuit shut off, utilizing electronic gate control which decrease the rate of fall of the gate voltage of the IGBT only when a short circuit condition is sensed, thereby avoiding any losses during normal switching operation. In a first embodiment, a considerably higher value of gate resistor is switched-in in series with the gate resistor during a short circuit condition. In a second embodiment, a considerably higher value of external capacitor is switched-in in parallel with the IGBT gate input capacitance during a short circuit condition.

Abstract: A circuit for improving the short circuit withstand capability of an IGBT. The circuit utilizes a MOSFET which, when turned on, reduces the voltage applied to the gate of the IGBT during a short circuit condition, thereby lowering the short circuit current passing through the IGBT. A Zener diode is coupled between the MOSFET and the gate of the IGBT to clamp the voltage of the gate of the IGBT to a predetermined voltage when the MOS transistor is turned on during a short circuit condition. The circuit turns the MOSFET on when the voltage at the collector of the IGBT rises during a short circuit condition. If tile fault is of a short, transient type, the circuit advantageously restores the normal gate voltage. The circuit draws a small current from the gate driver and requires no separate DC source, making it feasible to insert the circuit in IGBT modules or connect the circuit as an interface between the gate driver and the gate.