Design of High-Frequency, High-Power Class Φ₂ Inverter Through On-Resistance and Output Capacitance Loss Reduction in 650 V Parallel eGaN Transistors for Optimal Thermal Performance

This article presents a class Φ₂ inverters for high-power applications using multiple enhancement-mode gallium nitride (eGaN) switching devices operating at 13.56 MHz. The eGaN devices are beneficial in high-frequency, high-power applications such as plasma processing, thanks to the low switching and conduction losses. In addition, the small size of eGaN devices increases power density while reducing the impact of parasitic package components. However, their small package size makes it challenging to manage power dissipation, particularly at higher frequencies where additional conduction losses due to dynamic R_DS(on) and switching losses due to C_OSS can significantly increase power dissipation. To address these challenges, we investigate the individual contributions of dynamic R_DS(on) and C_OSS to power losses at high frequencies by paralleling multiple devices. We also propose criteria for selecting the optimum number of parallel eGaN devices to decrease power dissipation per device by reducing conduction losses greater than the addition in C_OSS losses. This approach helps to alleviate thermal stress in the devices. Finally, we demonstrate the effectiveness of our approach by designing a 1 kW single inverter and a 2 kW push-pull inverter at 13.56 MHz, which achieve over 90% drain efficiency while reducing thermal stress in the device.