Hello Group, 

I have a "long-time" question, concerning the energy issues in a EMI powerline 
filter. 

I'll put a case, and ask the question after. 

This is the case: 

- When trying to minimize the conducted emissions from a electrical equipment / 
circuit, one of the things to do is to put a EMI filter at the power entrance. 
This filter can be from a manufacturer (ready filter) or you can make one (with 
common mode inductors, capacitors, inductors). 

This are the questions (they arearelated, i.e., complete each other): 

- What, physically speaking, happens to the EMI energy that leaves the 
equipment when I add a filter??? When there is no filter, I understand that the 
energy goes to the mains?? Does the filter reflect the EMI energy, keeping it 
"arrested" inside the equipment? 

- Thinking under the light of the principle of energy conservation, what 
happens to the EMI energy when I add a filter?? It cannot be lost... 

- ... And, supposing that the energy keeps arrested inside the equipment, isn't 
it worse for radiated emissions?? i.e., it can increase the level of radiated 
emissions?? 

Thanks in advance for your attention. 

Regards, 

Muriel Bittencourt de Liz 
Ph.D. Student 
Interest Areas: EMC for power electronics, RF measures, EM interference 
Federal University at Santa Catarina State 
Florianópolis, Santa Catarina, Brazil 



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