The effect of duty cycle on SMPS common mode emissions: theory and experiment

The theoretical time- and frequency-domain waveforms of common-mode conducted emissions for an arbitrary SMPS duty cycle is derived. It is shown that the magnitude of common-mode emissions is independent of collector voltage rise time. Experimental data is presented for model validation. Common mode emissions are shown to be independent of switching transistor rise time. The model predicts the variation of emissions with duty cycle, using Fourier analysis of the common-mode waveforms with the duty cycle as a parameter