Developing parasitic cancellation technologies to improve EMI filter performance for switching mode power supplies

Electromagnetic interference (EMI) filters have been used for power electronics converters to attenuate switching noise and meet EMI standards for a long time. However, because of the parasitics in the filters, filters cannot attenuate high-frequency noises efficiently. In this paper, critical parasitics, which include both mutual and self-parasitics, are first identified in both differential and common mode filters. Three techniques are then developed to cancel the adverse effects of mutual parasitics. These techniques can effectively cancel the inductive couplings between an inductor and capacitors, between an inductor and trace loops, and between two capacitors. Two additional techniques are further developed to cancel the self-parasitics of components, such as the equivalent series inductance of capacitors and the equivalent parallel capacitance of inductors. Experiments are carried out to verify these developed techniques. It is shown that the high-frequency performance of EMI filters is drastically improved.