High-Frequency Planar Transformer Based on Low Parasite Capacotance Interleaved Serpentine Winding Method for High-Current Input LLC Resonant Converter

An LLC resonant converter must be designed for high efficiency and high power density, with a focus on reducing the volume and loss of the transformer, which plays a crucial role in insulation and voltage conversion between input and output. When using a planar core to achieve high power density, the size of parasitic components and transformer losses vary significantly depending on the winding configuration within the limited window area, necessitating careful consideration of various factors. This paper proposes an interleaved serpentine winding method that maximizes the use of the planar core’s window area, minimizes winding losses under high current input, and offers the advantages of low parasitic capacitance and improved assembly. This winding method utilizes litz wire to reduce DC losses and does not require additional space for winding placement compared to the conventional U-type winding method. To verify the effectiveness of the proposed winding method in reducing parasitic capacitance, we compare the capacitive energy distribution with the U-type winding method and derive formulas to calculate the effective capacitance of each winding configuration. Finally, we validate the proposed transformer’s effectiveness through Finite Element Analysis (FEA) simulations and a 7.5kW LLC resonant converter experiment.