Soft-Switching C O Hysteresis Losses in GaN HEMTs: A Resonant-Sawyer-Tower Measurement Method

The inherent dissipated energy losses ( E diss ) during the charging-discharging cycle of output capacitance ( C O ) in gallium nitride high-electron-mobility transistors (GaN HEMTs) limit their efficiency in soft-switching applications. Accurate characterization of E diss is important for power device selection and for understanding their origins. Existing measurement methods either fail to apply realistic voltage stress, or might include hard turn- off losses that can result in misleading conclusions. Here, we propose a resonant-Sawyer-Tower method, that only requires a simple resonant pulse generator and an ST branch to extract E diss under MHz operations, which was subsequently corroborated with a thermal method. Using the proposed method, we investigated the dependence of E diss on drain-source peak voltage ( V m ), resonant transient frequency ( f tr ), and switching frequency ( fs ) for six commercial GaN HEMTs, showing distinct power losses from the C O hysteresis, e.g., from 0.3 to 1.47 W at V m = 400 V, f tr = 10 MHz, and fs = 2 MHz. In particular, we discovered a strong dependence of E diss on f s for some devices, which had previously been overlooked. The proposed method and new findings in this article are essential for future designs of high-efficiency GaN power converters, especially operating at high switching frequencies.