EMC Question of the Week: November 1, 2021

Three inductors on a printed circuit board

A dot on an inductor package indicates the location of the

  1. input current terminal
  2. external winding terminal
  3. shield connection terminal
  4. core


The best answer is “b.” When inductors have several layers of wire turns, it is sometimes important to know which terminal connects to the outer-most layer. This is because electric-field coupling from the outer turns is much greater than that from the inner turns.  

In power converter applications, it is generally recommended that the terminal with the dot be connected to the switching node to minimize noise coupled to the non-switching side of the inductor. However this advice can be application dependent, so it is best to evaluate the parasitic coupling on a case by case basis. 

Note that the term "shielded inductor" generally refers to a magnetically shielded inductor, so there is no electrical connection to the shield. 

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