High-Frequency Planar Transformer Based on Interleaved Serpentine Winding Method with Low Parasitic Capacitance for High-Current Input LLC Resonant Converter

An LLC resonant converter should have high efficiency and power density. Further, it is important to reduce the volume and loss of the transformer, which provides insulation and voltage conversion between the input and output. When a planar core is used to achieve high power density, the magnitude of the parasitic components and the transformer loss considerably depend on the winding arrangement within the limited window area. Therefore, analyzing the various winding arrangements is necessary. To this end, an interleaved serpentine winding method that reduces the winding loss attributed to the high current by maximizing the window area of the planar core and has advantages of low parasitic capacitance and excellent assembly is proposed. The proposed winding method uses a Litz wire to reduce the DC copper loss, and it does not require additional space for the winding arrangement compared to that required by the U-type winding method. The capacitive energy distribution of the proposed winding method is compared with that of the existing U-type winding method to confirm the parasitic capacitance reduction effect of the proposed winding method. The formulae for calculating the effective capacitance of each winding method are derived for accurately estimating the parasitic capacitance. Finally, the effectiveness of the proposed analysis method and prototype are verified through finite element analysis simulation and experiments and it shows improvement of current waveforms and the overall efficiency increases about 0.5%.