Sources, paths and traps of conducted EMI in switch mode circuits

Formal circuit analysis of the generation and propagation of conducted electromagnetic noise is very complicated due to the complicated nature of circuit parasitics. Not only are the parasitics caused by complicated three dimensional shapes, but the high frequency characteristics of components and materials are normally unknown to the designer. A structured approach to conducted EMI is presented whereby functional elements are defined, namely sources, paths and traps of EMI. A systematic testing method to trace the generation and propagation of conducted noise in switch mode converters is proposed and illustrated on an experimental boost converter. Lastly, some results are presented on the reduction of the noise source by employing soft switching.