A digital detecting method for synchronous rectification based on dual-verification for LLC resonant converter

GaN HEMT has a higher voltage drop than conventional silicon based power MOSFETs during the time of reverse conduction, which is an unneglectable interval in LLC converter with synchronous rectification (SR). To further improve the efficiency of the LLC resonant converter, this paper presents a SR detecting scheme base on an adaptive drain-source voltage sensing strategy to eliminate both the body diode conduction and reverse current from the load to the source. Compared to the current SR detecting methods, the turning off time of the SR can be stabilized by the proposed dual-verification technique instead of switching between the body diode conduction and the reverse current from the load to the source. The principle and the algorithm are discussed and optimized based on the operating modes and the turning off transition of the SR. A prototype based on GaN HEMT is built and tested to verify the proposed method. The experimental results show that the proposed SR detecting scheme eliminates the current from the load to the power source, thus, the reliability of the converter can be improved. Moreover, compared to the current best technique, the efficiency of the converter is further improved by 0.2 %.