A 10-MHz Isolated Synchronous Class-Φ2 Resonant Converter

Abstract

Because of the forward recovery, the performance of the diodes degrades seriously at multimegahertz, causing extremely high power loss. So, the synchronous rectification (SR) is strongly desired in the multimegahertz resonant converters. This paper proposes a self-driven level-shifted resonant gate driver (RGD) for the SR FET in a 10-MHz isolated class-Φ2 resonant converter. The proposed RGD provides precise switching timing for the SR so that the body diode conduction loss can be minimized. A control stage is introduced to the proposed RGD to block the circulating current and the low-impedance path in the driver to realize ON–OFF control of the converter with high efficiency. The proposed RGD also generates a tunable dc bias to increase the peak gate voltage and extend the conduction time with the optimal $R_{{\rm DS}({\rm on})}$ so that the average $R_{{\rm DS}({\rm on})}$ and the associated conduction loss can be reduced significantly. A 10-MHz prototype with 18-V input and 5-V/2-A output was built. At full load of 2 A, the proposed RGD improves the efficiency from 80.2% using the conventional RGD to 82% (an improvement of 1.8%). Compared to the efficiency of 77.3% using the diode rectification, the efficiency improvement is 4.7% at full load.