T18.9 - FEA Prediction of Parasitic Capacitance and Common-Mode Current Performance in Planar Transformers

This study addresses the parasitic capacitance of planar transformers in high power density applications by proposing a fast prediction workflow based on the Finite Element Method (FEM). The approach not only accurately computes the six-capacitance model parameters but also visualizes the electric field and energy distribution across different winding structures. Simulation and experimental results show that while interleaved windings effectively enhance power density, they significantly increase common-mode capacitance, highlighting the trade-off between power density and EMI suppression. Furthermore, analysis of shielding layers indicates that incomplete dV/dt cancellation may cause additional interlayer capacitance to worsen EMI. Overall, experimental validation confirms that FEM predictions maintain parasitic capacitance errors within 10%, demonstrating the method’s high accuracy and reliability, and highlighting its potential as an early-stage design tool to help designers balance power density and EMI performance.