Design of CM Inductor Based on Core Loss for Radiated EMI Reduction in Power Converters

In power converters, common mode (CM) noise can radiate to cause radiated electromagnetic interference (EMI). Resistive, inductive and capacitive parts of the CM inductors can interact with the antenna to induce damping effect or additional resonance. The resistive component is desired for radiated EMI reduction with resonance avoided and noise energy dissipated. This paper researches on the equivalent core loss resistance and its application on CM inductors for radiated EMI reduction. This paper investigates the equivalent core loss resistance and quantifies its relation with core parameters and winding parameters. Critical factors for the equivalent core loss resistance include the ratio of core’s cross section area over core’s magnetic path length and winding’s turns number. Capacitive part of the CM inductor is also considered given its influence on impedance and on radiated EMI. Parasitic capacitances of both the winding and the core are analyzed. Experimental verification on the core loss based CM inductor design is performed on a flyback converter, with radiated EMI measured in a semi-anechoic chamber.