Investigation of the Effects of Snubber Capacitors on Turn-on Overvoltage of SiC MOSFETs

Fast turn-on transition induced overvoltage between the drain and source of the opposite device in a SiC MOSFET phase-leg is investigated. A simplified but effective model considering the parasitic inductances, stray resistances, device's junction capacitances is proposed to study the turn-on transient of SiC MOSFETs. The factors that determine the turn-on overvoltage of the complementary device are then derived, which is the basis of designing the snubber circuit to suppress it. Moreover, a small signal model is proposed to investigate the effects of snubber capacitors on resonance based on the frequency-domain analysis. Furthermore, a guidance has been provided to select the snubber capacitor used to suppress the turn-on overvoltage. In last, experiments are conducted which shows that the performance of snubber capacitors in the turn-on overvoltage suppression is consistent with the small signal model analysis.