Active Power Device Selection in High- and Very-High-Frequency Power Converters

This paper aims to provide a road map for selecting power devices in soft-switched, MHz-frequency power converters. Minimizing C $_{\mathrm{OSS}}$ losses, which occur when charging and discharging the parasitic output capacitor of power semiconductors, is critical to efficient operation. These losses are excluded from manufacturer-provided information and measurements are either sparse or not reported at all in existing literature. We report the first high-frequency C $_{\mathrm{OSS}}$ loss data from Silicon Carbide (SiC) power MOSFETs, with a range of devices tested from 1-35 MHz and up to 800~V. In contrast to GaN HEMTs, C $_{\mathrm{OSS}}$ losses in SiC MOSFETs do not increase with dV/dt at these frequencies. 3-10% of the stored energy is dissipated in the measured SiC MOSFETs. We report new C $_{\mathrm{OSS}}$ loss measurements for vertical silicon MOSFETs and expand on existing measurements for superjunctions, finding high variance in C $_{\mathrm{OSS}}$ losses between devices for both constructions. High C $_{\mathrm{OSS}}$ losses preclude the tested silicon MOSFETs from efficient operation at MHz frequencies. Lastly, we compare devices in soft-switched applications using a loss calculation that includes these C $_{\mathrm{OSS}}$ losses, and demonstrate a 100 W, 17 MHz DC-RF inverter using a custom-packaged SiC MOSFET.