Comparative Analysis of Synchronous Rectifier Drive Methods in a High-Frequency Switching LLC Resonant Converter Using GaN FETs

This paper studies a method for generating gate drive signals to achieve synchronous rectification (SR) operation in a high-frequency switching LLC resonant converter using Gallium Nitride (GaN)-based power semiconductors. Through simulation, we compared the operation of four different approximation-based methods for generating synchronous rectifier drive signals, without the need for additional sensing circuits, across different operating frequency ranges. We identified operational zones that could lead to system failure, such as Early Turn-On and Late Turn-Off, and proposed suitable system specifications for each driving method. Experiments were conducted on a 1kW LLC resonant converter to test two methods capable of stable operation even below the resonant frequency. Among these, the method where &quotthe product of output voltage and duty ratio remains constant,&quot which compensates SR duty considering O-mode region oscillation, demonstrated superior overall performance compared to other methods, achieving a peak efficiency of 98.25%.