Identification of Conducted Noise Causes through CWT in a Boost PFC

Limiting harmonics in the conducted noise of switch mode power supplies is very important, but finding the causes of harmonics to get the best solution to the electromagnetic interference (EMI) problem is often complex. A new tool for the search of conducted noise causes is presented: the more significant harmonics in the EMI receiver measurement are searched in the time evolution of the line impedance stabilization network (LISN) voltage by using the continuous wavelet transform (CWT). In the time frames where the harmonics are present, similar harmonic contents are searched for in the waveforms of the circuit, because these are the causes of the conducted noise. An example of application is described: signals of a boost PFC are processed in different ways to be compared to the EMI receiver measurements of LISN voltage spectrum. The CWT results match pretty well and give some further information than the Fourier transform does