Study Of EMI Filter For Switch Mode Power Supply

Switch mode power supply provides a stable supply of power for the normaloperation of power electronic devices. However, because it is a noise source itself , EMIsource filter is needed to suppress conducted electromagnetic interference(EMI).As the three-terminal capacitors have good performance of suppressinghigh-frequency noise in switch mode power supply,in this paper, it is used to improvehigh-frequency performance based on typical EMI source filters of the general strcture.Firstly, the basic principles, circuit structure, design principles and the technicalparameters of EMI source filters are described.Then,a EMI source filter usingthree-terminal capacitors is designed,and its low-frequency model and high-frequencymodel are gived.The effects of C y and equivalent series inductance(ESL) on InsertionLoss (I.L.)of filter are analyzed in detail. The Insertion Loss is simulated by PSpice andthe simulation results are given.The characteristic of EMI filter is greatly influenced by the parasitic elements inthe high-frequency cases. In this paper, the typical methods of cancellation of parasiticparameters are summarized, which are used to eliminate parasitics in T-filters. Finally,we have a note of use and installation in filters.