This paper examines parasitic capacitances in planar transformers in high-frequency isolated converters. Power magnetics with multi-layer printed circuit boards (PCBs) are advantageous for high-power density and frequency applications. Planar transformers are particularly useful in improving converter efficiency due to their thin-copper layers. However, the parasitic capacitances are added because of their configurations, and they resonate with the inductance at a specific frequency. It leads to a significant rise in the overall impedance. Impedance analysis is performed with a prototype planar transformer. Simple methods to increase the resonance frequency are also covered. Modified PCB stack-up and revised winding configuration have been proven to be effective.
