Modeling of Parasitic Inductive Couplings in a Pi-Shaped Common Mode EMI Filter

This paper analyzes the effects of parasitic inductive couplings among the filter components and printed circuit board traces in a pi-shaped common mode (CM) electromagnetic interference (EMI) filter. The result shows that some parasitic inductive couplings related with CM choke do not affect the CM EMI filter performance. And then, it proposes a high-frequency circuit model for filtration performance evaluation and prediction for pi-shaped CM EMI filter, in which the parasitic inductive coupling between input and output loops of the investigated filter is considered to be the crucial coupling parameter while other parasitic couplings are ignored. The model is simple because only one coupling parameter is involved. A procedure is introduced to extract the inductive coupling between input and output loops in pi-shaped CM EMI filter using Z parameters through virtual prototyping. Simulation and experiment finally validate the model.