Analysis and Implementation of LLC Burst Mode for Light Load Efficiency Improvement

Burst mode control is applied to improve light load efficiency of LLC converter in this paper. Detailed analysis on characteristic and operation processes of LLC burst mode control with SR is presented. Based on the analysis, some important rules of LLC burst mode control are proposed, which is the key to achieve high light load efficiency. The rules include: the suitable primary and secondary driving timing, design guild line of output filter, reasonable control strategy etc. To verify the analysis, a prototype with 12 V/100 A output has been built. Thanks to the proposed control strategy and optimum design, light load efficiency of LLC converter can be improved significantly, such as efficiency at 10% load can be improved from 92.5% to 94.8%.