Performance Comparison for A4WP Class-3 Wireless Power Compliance between eGaN® FET and MOSFET in a ZVS Class D Amplifier

Abstract:
eGaN FETs have repeatedly demonstrated higher efficiency than MOSFETs in wireless power transfer amplifiers when operated over a wide impedance range using a ZVS Class D amplifier [1, 2, 3, 4, 5, 6, 7, and 8]. In this article we examine a method to further improve the performance of eGaN FETs by replacing the bootstrap diode of the high side gate driver with an eGaN FET that is driven synchronously with the lower device gate. The integrated bootstrap diode of the gate driver has reverse recovery losses (PQRR), as it is very difficult to monolithically integrate a Schottky diode on the same wafer as the gate driver circuit. This limits high frequency performance of the amplifier because the frequency dependent reverse recovery losses are dissipated in the upper device. The technique that replaces the internal bootstrap diode of the gate driver will be implemented and evaluated using an eGaN FET based ZVS Class D amplifier and compared to an equivalent MOSFET version operated over a wide load impedance range of ±35j Ω to the A4WP Class-3 drive specifications [9]. The results show that the eGaN FET based amplifier losses were reduced between 15% and 48%, and it could operate over a wider load impedance range, by as much as 20j Ω, than the comparable best-in-class MOSFET amplifier.