Analytical Model to Study Hard Turn-off Switching Dynamics of SiC mosfet and Schottky Diode Pair

Fast switching transient of SiC mosfet may lead to prolonged oscillations, spurious turn on, large device stress, and high amount of electromagnetic interference generation. For an optimal layout and gate driver design, study of switching dynamics is important. This article presents an analytical model that captures the turn-off switching dynamics of SiC mosfet and SiC Schottky barrier diode (SBD) pair using parameters obtained from device and gate driver datasheets and the values of external circuit parasitics. Unlike linear approximation, a detailed model of channel current is considered that captures the gradual transition from ohmic to saturation region and the transverse electric field effect. A comprehensive model of the transfer capacitance is used and the effect of external gate-drain capacitance is considered. This results in a better estimation of switching transition time, actual loss incurred, (dv/dt), (di/dt), and transient overvoltage. The behavioral simulation and experimental results confirm the accuracy of the presented analytical model over a range of operating conditions for two 1.2-kV discrete SiC mosfet and SBD pairs of different current ratings.

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