Fig. 1. CM noise model.
The low power (below several hundred watts) AC-DC converters have their unique common mode (CM) noise characteristics which cannot be predicted with the conventional simplified CM noise model for higher power converters. By identifying and characterizing the major noise sources and the propagation paths of the CM noise, a detailed CM noise model is derived to provide an insight into the CM noise generation and propagation of the low power AC-DC converters.
This CM noise model is not only able to predict the CM noise of the converter, but also yields some general converter design rules for minimization of the original CM noise of the converter. The effectiveness of the model is verified by CM noise measurements on two very different low power AC-DC converters.