Common mode EMI noise of AC-DC converters for low power applications

AC-DC converters for low power applications have their unique EMI characteristics compared to the converter for other applications. It has very high DM noise due to the DCM or CRM operation and results in a relatively high transformed CM noise caused by the unbalance of the noise propagation paths. This paper summarized the important unbalanced paths and proposed methods to limit the CM noise caused by these unbalances. They can be the guidelines for the converter and filter design process for achieving better EMI performance and smaller filter size of the converter at the very early design stage.