An Auxiliary Power Supply Utilizing Planar Winding Transformer with High Insulation and Low Coupling Capacitance Considerations

This paper proposes an auxiliary power supply (APS) for medium-voltage SiC MOSFETs with high insulation and low coupling capacitance. Firstly, the mathematical model of the LLC resonant topology is analyzed, and the overall framework of the APS is introduced. In terms of the isolated barrier design, the advantages of printed circuit board (PCB) planar windings are elaborated, and an equivalent capacitance model based on an air-gapped core structure is established, with results indicating a model accuracy exceeding 93%. Finally, a prototype is developed with a coupling capacitance of 1.23 pF. The APS delivers stable gate driver voltages and achieves a peak efficiency of 82.547%. High-voltage testing confirms a PDIV of 24.5 kV DC and a breakdown voltage of 31 kV DC, demonstrating the design’s excellent insulation performance and suitability for medium-voltage applications.