High frequency characteristic analysis of EMI filter in switch mode power supply (SMPS)

In a switch mode power supply (SMPS), the EMI filter plays an important role in suppressing common mode (CM) and differential mode (DM) conducted emissions. In this paper, the high frequency characteristic of an input filter is analyzed. Its frequency characteristic measured by a network analyzer is compared with simulation results based on models with/without parasitic parameters respectively. The effect of the parasitic parameters of capacitors and CM inductors is analyzed and discussed using the parameter sensitivity analysis, which gives a reference to design the EMI filter and to deal with high frequency problems of filters.