#015 EMI Suppression ~ What is common mode and normal mode? ~

In noise suppression, you’re sure to see and hear the terms “common mode” and “normal mode”. In taking EMI suppression measures, it is important to understand these factors correctly and take them into account.

First, normal mode means when an electrical signal flows through a certain line and its return current flows through a counterpart line. (The relationship between the sending and the return is clear.)




The common mode, on the other hand, refers to a case where a portion of the return current flows back through an earth, enclosure, etc., and the sending and return are asymmetrical.



This common-mode current loop is difficult to manage and has a significant effect on noise emission. Therefore, it is important to properly manage the current path and suppress the common-mode noise in order to take EMI suppression measures.


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