Systematic power line EMI filter design for SMPS

Based on a two-probe measurement approach, noise source and noise termination impedances of a switched-mode power supply (SMPS) under its normal operating condition are measured. With the known information of the noise source and noise termination impedances, an electromagnetic interference (EMI) filter can be designed systematically with good confidence. An example to design a power line EMI filter for a SMPS to meet a regulatory conducted EMI limit using the proposed procedure is demonstrated.