Prediction of Conducted Emissions in Switched Mode Power Supplies

The article discusses the generation and modeling of EMI in switched mode power supplies. Other authors have investigated the mechanism of generation of EMI in switched mode power supplies, but no model has been advanced to predict what the emanations will be. Discussion of common mode and differential mode noise is given, and a method for developing quick predictions in the frequency domain is given. Introduction The modeling of two of the predominate noise sources in Switched Mode Power Supplies (SMPS) is done in the frequency domain. To convert the time domain switching waveforms into the frequency domain, the envelope approximation to the Fourier transform of a trapezodial waveform HI (appendix A) is used. In the derivation of the noise models, the mathematical model is given first, then simplifying assumptions are made, and a graphical technique is developed.