The Impact of The Dead time on The Stability of 1.2kV SiC MOSFET Body Diode Under Hard Switching with synchronous Rectification

Abstract:
In this paper, the impact of the dead time on the performance and stability of 1.2 kV SiC MOSFET body diodes is characterised considering the variation of three factors (I) Gate turn-off voltage, (II) Junction temperature and (III) gate resistance. When synchronous rectification is used, experimental measurements show that decreasing the dead time reduces the peak reverse recovery current, reverse recovery charge, the turn-on losses and improves switching stability by reducing the dI/dt. In certain scenarios, utilising a dead time of 140 ns can reduce the turn-on losses of SiC MOSFET by 23.3% and enhance the switching stability due to a reduction in the dI/dt by more than 50%. Moreover, turning off the synchronous FET with a negative gate voltage leads to higher peak reverse recovery current, reverse recovery charge and switching losses relative to zero gate turn-off voltage. Utilising the short dead time with either zero gate turn-off voltage or negative gate turn-off voltage will reduce the aforementioned parameters, however, the reduction in the negative gate turn-off voltage case is more than the zero gate turn-off voltage. The impact of the junction temperature and gate resistance variation is extensively analysed. Increasing the former can increase the reduction in the losses and reverse recovery, while increasing the latter has the opposite effect. Moreover, the experimental results confirm that the thresh-old dead-time, at which a reduction begins to appear in the peak reverse recovery current, reverse recovery charge, and turn-on losses, depends on both temperature and gate resistance. This threshold time increases with higher temperature and with higher gate resistance and it can exceed 540 ns in some cases.