Turn-off overvoltage characterization and mitigation in wide bandgap power transistors

Turn-off ringing is a challenge caused by parasitic elements in power loop, resulting in switching losses, voltage breakdown and EMI issues. A worse case occurs while employing wide bandgap power transistors due to their fast turn-off. The conventional way to mitigate turn-off ringing is to reduce the commutation loop inductance or slow down transistors’ switching speed. However, slow turn-off speed is undesirable due to low switching loss. In this work, it is demonstrated that fast turn-off of wide bandgap(WBG) transistors can facilitate minimizing voltage overshoot with well-tuned parasitic loop inductance. Based on the characterization of the turn-off transition, an analytical model is derived that shows voltage overshoot can be reduced without sacrificing low turn-off loss and simple PCB layout while allowing high loop inductances. The proposed technology can fully exploit the potential of wide bandgap transistors in extremely fast switching conditions.