Active clamping method for SiC MOSFET high power modules - Benefits and Limits

For high power applications, the SiC MOSFET switching speed is limited by the inductive overvoltage due to the high product of stray inductance and switched current [1]. The active clamping method properly designed for high power applications, allows the increase of the du/dt during the turn-off process without exceeding the MOSFET maximum blocking voltage. This paper investigates the active clamping method via scaled single chip measurements. This scheme includes scaling accordingly the commutation circuit stray inductance and the active clamping path, emulating the full module switching behavior with single chip measurements. In comparison to simple gate resistor controlled switching, the active clamping method allows a higher voltage gradient during the switching process while effectively limiting the overvoltage. Results show, that losses could be reduced in the range by 30% (for high current) and up to 70% (for low current). However, special focus has to be placed on the thermal design of the active clamping circuit. The temperature dependent breakthrough voltage of the transient voltage suppression diodes has to be considered for the correct implementation of the active clamping circuit.