Optimization Design And Study On The EMI Filters Of A Switching Mode Power Supply

With the rapid development and wide application of switching power supply,electromagnetic compatibility design has become a vital part of the process ofswitching power supply. And switching power supply products must meetcorresponding electromagnetic compatibility standards. High-frequency switchingpower supply is a serious source of electromagnetic interference. The conductiondisturbances and electromagnetic radiation caused by high-frequency switching powersupply become more and more serious, and EMI filter is an extremely effective devicewhich can suppress that kind of conduction disturbances.In this paper, an EMI filter is designed, and structure selection and parameterscalculation of the filter circuit are studied. The influence of each parameter forfiltering performance is analyzed systematically through the simulation model.Furthermore, reasonable adjustments and optimizations of the structure andparameters of the filter are put forward to improve the filtering effect.The standards for common mode capacitor size have strict limits, since thecommon-mode capacitance values are related to personal safety. However, with thelimitations of common mode capacitance, insertion loss of common mode filtering isvery unsatisfactory, even less than the design goals or limits prescribed by standards,especially in the high-frequency. And the effect is still very limited, even thoughthere’s optimization of passive components, very sophisticated device fabricationprocess or devices which is used to decoupled cumbersome distribution parameters inhigh-frequency. In this case, the active devices will help optimize common modefiltering effect in high-frequency effectively.