Study of EMI filter performance without LISN based on noise impedances

Abstract

The performance of the electromagnetic interference (EMI) filter under the condition without the Une impedance stabilization network (LISN) are revealed and analyzed from the perspective of the common mode (CM) and differential mode (DM) impedances of the switched-mode power supply (SMPS), AC mains, and LISN. The in-circuit CM and DM impedances of the SMPS, AC mains, and LISN are extracted with an inductive coupling approach based on the theory of the two-port ABCD network and the EMI filter is designed according to the extracted CM and DM impedances. By installing the designed EMI filter on the SMPS and measuring the conducted emissions with and without LISN, the performance of the EMI filter operating under the actual condition without LISN is revealed.