Electro-Thermal Circuit Modeling and Practical Evaluation of GaN Power Switches for Mega-Hertz Soft-Switching Operation

This paper investigates the switching performance and electro-thermal behavior of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) in megahertz (MHz) soft-switching operations, focusing on conversion efficiency, thermal stability, and electromagnetic interference (EMI). Contrary to the datasheets of GaN HEMTs manufacturers that highlight the reverse-conducting characteristics of the devices, this study finds that the performance of GaN HEMTs degrades significantly at MHz operations due to elevated reverse conduction losses, high-frequency oscillations, and thermal instability from self-heating. Toten-pole GaN inverters with and without antiparallel Schottky diodes are compared practically and with the help of an electro-thermal circuit model for operations at 1 MHz, 6.78 MHz and 13.56 MHz. Electro-thermal circuit modeling and experimental results demonstrate that GaN switches with antiparallel Schottky diodes can reduce dead-time switching power losses by 85% and improve overall converter efficiency by 2.7∼6.9% in prototypes of 24 W- 29 W. This approach also mitigates thermal runaway risks by lowering the junction temperature of GaN HEMTs, therefore increasing thermal stability. Furthermore, the junction capacitance of the diodes can dampen high-frequency dv/dt transients and reduce electromagnetic emission. The experimental results show reductions of 24.41 dBm in magnetic field emissions and 26.57 dBm in electric field emissions. These findings challenge the prevailing industry assumption that external antiparallel diodes are unnecessary for GaN HEMTs, providing a validated design framework for MHz-range applications.

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