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

In this paper, we extend recent work on COSS losses, which have a significant impact on high- and very-high-frequency resonant converters, from GaN HEMTs to the remainder of the core active power devices used in medium- and highvoltage power conversion. Here, we characterize COSS losses in Silicon MOSFETs - including superjunctions and traditional constructions - and Silicon Carbide MOSFETs. The measured COSS losses in SiC MOSFETs do not increase with dV/dt at frequencies from 1-35 MHz and applied voltages up to 900 V. Across the tested SiC MOSFETs, 3-10% of the energy stored in the output capacitor is dissipated. In Si MOSFETs, COSS losses make the tested devices non-competitive with wide-bandgap devices for MHz-frequency, soft-switched applications. In superjunctions, COSS losses are much higher than those in comparable GaN and SiC devices. In planar MOSFETs, COSS losses are similar to the wide-bandgap devices but the on-resistance is an order-of-magnitude higher in the Si MOSFETs.