Systematic design of EMI-filters for power converters

EMI-filters are often designed by trial and error. To take guesswork out of filter design, a systematic approach is described in this paper. The design procedure is divided into three steps: (1) measurement of the impedance and amplitude spectrum of the noise source; (2) determination of the sink impedance; (3) calculation of the filter component values to fulfil a given limit curve with least costs for the overall filter. Using this design procedure, the filter topology, the filter order and the component values are determined to provide a lowest cost EMI-filter design.