EMI Filter

[terrym]

I need to know how to select AC Line EMI Filters. What type of filter is recommended for Common Mode and/or Differential Mode?

Thank You.

 

[melone]

For what purpose?

 

[Lewish]

What problem are you trying solve with your filter?

Or is this a what does each type of filter do, question?

 

[geezer]

Unfortunately, trial and error is the only reliable way. Everytime I think I have a handle on the problem, the very next project throws everything I've ever learned about EMC out the window. The EMC test house should have a large variety of EMC line filters on hand to help the selection. Do a baseline first to find out what frequencies are a problem. This should also give you an idea of how much filtering at what frequency is needed. Look for inductive coupling paths on the PCB's - eg. the use of rod cores vs. torroid cores for inductors. Don't forget about leakage current creating shock hazards! There is a trade-off between leakage current and common-mode filtering. The EU allows non-lethal shock hazards to meet the EMC emission requirements. Good luck and count on several late nights!

 

[terrym]

Thank you for the responses.

I will be getting involved in a filter project very soon. I just wanted basic info on EMI filters. I have been looking in to Corcom (TYCO) & Power Dynamics catalog and also Filter Concepts website for EMI filters. Has anyone used any of these suppliers. Basically, I’m trying to understand the filter selection process. Given a schematics how do I
determine which schematic is recommended for Switching power supplies, or Linear power supplies. Which schematic is recommended for low impedance loads or high impedance loads?

T.

 

[geezer]

Corcom is good and is readily available through distribution. Delta and Schaffner have lower priced units, but you get what you pay for. TRI-MAG in Visalia, CA, has a good line, but you have to deal with them direct, they may not have it in stock, and you will need a charge card.

In sizing the filter, make sure that peak currents do not saturate the magnetics.

 

[jbartos]

Suggestion: Visit

http://www.coilcraft.com/prod_emi.cfm

http://www.coilws.com/emi.html

http://www.mdipower.com/content/ApplicationNotes/html/dcpower06.htm

etc. for more info