Maximum Efficiency Point Tracking Based Synchronous Rectification for LLC Converter

Synchronous rectification (SR) is challenging for LLC resonant converter because of the difference between primary switches and secondary synchronous rectifier. Although numerous SR driving strategies have been proposed, they all have some disadvantages. A SR driving strategy is proposed based on the maximum efficiency tracking. The input current is sensed to find the maximum efficiency corresponded driving signals for SR. The proposed driving strategy has the following advantages: 1) it can applied to any LLC topologies; 2) the sampling circuit loss is small since the SR is normally used in low output voltage applications, where the input current is small; 3) the maximum efficiency operation for the converter can be ensured simultaneously. The operational principles, simulation and experiment verification are presented.