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The LLC resonant converter with a full-bridge rectifier can achieve two balanced outputs with a simple balancing capacitor, which is quite attractive for LED driver application. To further improve the efficiency, synchronous rectification is an effective way to reduce the conduction loss of the rectifier. In this paper, a new hybrid driving scheme for full-bridge-type synchronous rectifier (SR) in LLC resonant dc/dc converter is proposed. The proposed hybrid driving scheme combines voltage-driving method and current-driving method to drive the SRs with simple circuit structure. The high-side SRs are driven by one auxiliary winding of the transformer and the low-side SRs are driven by a current transformer with only one secondary winding. Furthermore, the proposed method can be operated in discontinuous conduction mode and continuous conduction mode conditions. The detailed operation principles and design considerations are presented. Finally, the experimental results from a 200-kHz 100-W prototype verify the theoretical analysis.
Date of Publication: Nov. 2012