EMI filter design


Joined Jul 18, 2011
I assume you're talking about a line filter for some type of product?

Did you try to Google "EMI filter"?

Usually, line filters are series LC filters scaled for high frequencies of interest.

You will want to filter common-mode RF and each line as well.

Does this need to meet CE/UL/CSA/... ?

Deleted member 115935

Joined Dec 31, 1969
EMI, like all 'filtering' in real life is a guessing game,

Sorry ,

there are great books on it, have look on your favourite web site, expect to pay USD 150 though.

there are lots of 'standard' ways of doing the filtering, and as many exceptions,

General , one designs in depth, with emc / esd / emi always in mind, and trying to retrofit is a long road of hardship.

If you need to meet a medical standard, then good luck retro fitting.


Joined Jun 26, 2012
Have you checked out Corcom? They probably already have what you need. If nothing else, you can read up on their application data. I've used a lot of their stuff and never failed any compliance tests. Download the Selector Chart to see what they have for various applications.

Good luck.


Joined Aug 1, 2013
I was going to describe why there is no guesswork in designing a power line filter, but the article in post #7 covers everything very well. The most difficult part is dealing with all of the safety agency requirements. The good news is that safety and EMI performance are not directly connected in filter design. For example, medical grade filters have lower leakage current, a safety issue, but the EMI performance is influenced by FCC rules (in the US), not the safety (UL) rules.