Design of LLC Resonant Converter Based on Planar Transformer

LLC resonant converter has low switching loss and high operating frequency. It can meet the requirement of high power density and high efficiency, thus is suitable for vehicle- mounted DC-DC converter. However, under the heavy load condition of low voltage and high current, LLC resonant converter fails to achieve zero voltage switching (ZVS), resulting in efficiency decrease and deteriorating EMC performance. To solve this problem, this paper analyzes the working mode in the dead time of LLC resonant converter in time domain and proposes a design method of resonant parameters for optimizing ZVS implementation. A planar transformer with integrated synchronous rectification is utilized to reduce the leakage inductance and satisfy the design requirements. Finally, simulation and experimental results verify the rationality of parameter design and the effectiveness of ZVS implementation.