Abstract: In order to further improve the working efficiency of switching power supply with light load,a novel hybrid modulation strategy based on variable topology half bridge LLC resonant converter is proposed in this paper,which makes the converter au achieve soft switching in heavy load and light load,and realizes high operating efficiency.In this paper,the working principle and working mode of the half bridge LLC resonant converter are analyzed in detail,and the maximum efficiency track of LLC topology converter is discussed.On this basis,a new hybrid modulation strategy based on the optimal state plane trajectory is designed,and the light load efficiency and control quality are further optimized.Simulation results confirm the feasibility and effectiveness of the proposed scheme.