Critical Considerations for EMI Filter Design in Switch Mode Power Supply

Offline switching power supplies have high voltage and high current switching waveforms that generate electromagnetic interference (EMI) in the form of both conducted and radiated emissions. Consequently, all offline power supplies must be designed to attenuate or suppress EMI emissions below acceptable limits. EMI filters are actually simple combinations of inductors or chokes and capacitors but many key parameters need extra care and attention while designing the optimum EMI filter. This paper addresses this subject and presents a conceptual view of some critical design considerations for EMI filter optimization. Some important guidelines for the selection of EMI filter components are suggested to provide an efficient helping tool for the designers.