ABSTRACT
One of the leading questions asked by people who have electromagnetic interference (EMI) issues or who are joining the EMI field is related to source impedance and how this affects the frequency magnitude response of the EMI filter. The wires used for inductors are selected to be sufficient to carry the power line current at the power line frequency. The DC power supply readings will be a smoother line, making it much easier to read directly off the spreadsheet graph. This higher output impedance could starve some circuits being powered by this supply. Skin effect also applies to the wire used for the inductors, the transformers, and the rest of the EMI filter wiring. Transmission line concepts may sound like a strange subject to introduce when discussing EMI filters, but the filter designer needs to have a basic understanding of this subject for several reasons.
