A Simple and Accurate Method to Characterize Output Capacitance Losses of GaN HEMTs

Output capacitance (Coss) loss is produced when the Coss of a power device is charged and discharged in its OFF-state, and this information is not included in the manufacturer's datasheet. Large Coss losses compromise the benefits of GaN high-electron-mobility transistors (HEMTs) in high-frequency soft-switching converters. Prior Coss loss characterization methods cannot best mimic the device operation in steady-state power switching. This work proposes a new, easy-to-implement, accurate approach to characterize the Coss losses in a single pulse and under steady-state switching with tunable dv/dt, frequencies, and temperatures. For the first time, the Coss losses of four types of mainstream, similarly-rated commercial GaN power devices are comprehensively characterized in a single pulse and under steady-state switching. The Coss loss of all GaN devices is found to be identical in both conditions, and they increase with the peak resonant voltage. In addition, the physical origin of the Coss loss is found to be different from that of dynamic on-resistance. The comparison of the Coss losses of four types of GaN HEMTs is also presented. These results provide essential references for device users to guide the device selection and unveil new physical insights on the origin of Coss loss in GaN power devices.