Nonideal Smoothing Transformer for Effective Differential Mode Noise Reduction in an SMPS

An effective way of reducing differential mode (dm) noise of switching converters is still an open issue. Here, a thorough investigation of the filtering technique with integrated magnetics, taking nonideal effects into account is presented. Parasitic components and component variations due to tolerances are considered, and the obtainable attenuation is calculated. This paper also gives an analysis of the optimized coupling factor, as well as the distribution of the capacitance between the two capacitors involved. The entire analysis is done in the frequency domain. Therefore, a proper model is given. In order to show the relevance of this paper, a practical validation is presented. Finally, a dm noise comparison between the regular boost converter and the boost converter with an incorporated smoothing transformer in a real hardware prototype for the input stage of a laptop adapter shows the dm filtering effectiveness of the smoothing transformer.