Turn-Off Energy Minimization for Soft-Switching Power Converters with Wide Bandgap Devices

The advent of Silicon-Carbide and Gallium-Nitride MOSFETs offers potential to realize higher energy density power converters operating at increased switching frequencies. The maximum switching frequency in a power converter is limited by the ability of the switching device package to dissipate its switching and conduction losses. At a given value of drain-source voltage and current, the turn-on losses in a MOSFET are usually greater than the turn-off losses. This paper introduces a soft-switching technique for power converters using wide bandgap devices to replace the larger turn-on losses with smaller turn-off losses and thus reduce the power dissipation of the overall system. The turn-off losses are further reduced with use of additional capacitance across the MOSFET drain-source terminals. Results from an analytical model, LTSpice simulation and experimentation are shown to match closely, with a significant reduction in overall system losses.