Research On EMI Filter Of Power Supply

With the rapid development and wide application of the switching power supply, the electromagnetic leaks and the radiation problems caused by them are getting worse. The EMI filter as an auxiliary device of switching power supply can effectively suppress the conducted interference of switching power supply. Non-ideal high-frequency characteristics of passive components make high-frequency characteristics of passive EMI filter bad. The passive components also affect the high-frequency characteristics of the active EMI filters. So, the researches into the high-frequency characteristics of EMI filters have practical significance.For the passive EMI filter, several effective methods improving the self-parasitic parameters are studied, and the differences between the impact of the mutual coupling and impact of capacitor's self-parasitic parameters on theπtype common mode filter are compared. Then, a method is proposed to improve self-parasitic parameters of capacitor by using some mutual-parasitic parameters.For the active EMI filter, this paper discuss the insertion loss of a type of active EMI filter terminating pure resistance, inductive load and capacitive load, and analyze each module's role and influence on the feedback loop. At last, the high-frequency characteristics of this type of filter are improved by changing the structure of its capacitor in injection module.