Shared External Driver for VHF Converter With a Synchronous Rectifier Based on Matching Network Parameters Optimization

Abstract

In order to reduce the conduction loss of diode, synchronous rectification is usually adopted in very-high-frequency (VHF) converters, in which the rectifier diode is replaced by a MOSFET with very low on-state resistance. And to ensure normal operation of the synchronous rectifier switch, it is necessary to design a suitable driver with accurate timing. The widely used self-oscillating resonant drive circuit has a limited range of duty cycle adjustment, and the body diode of synchronous rectifier switch has long on-state time and a large conduction loss. Therefore, based on the analysis and parameters optimization of matching network, a shared external drive circuit is put forward. That is, the drive signals of the inverter switch and the synchronous rectifier switch come from the same external oscillation signal. On the premise of ensuring accurate drive timing, it can improve the drive signal's duty cycle of synchronous rectifier switch, reduce the conduction loss of body diode, and improve the efficiency of converter. Then on the basis of the proposed drive circuit, a VHF converter prototype with operating frequency of 10 MHz, 13 V input and 8 V/10 W output is designed, and the feasibility of the proposed drive circuit is verified by simulations together with experiments.