EMI RFI filters eliminate any unwanted signals (noise) or disturbance that affects an electrical circuit due to electromagnetic radiations. The disturbance may interrupt, obstruct, degrade or limit the effective performance of the circuit. EMI RFI filters use electromagnetic interference (EMI) also known as radio frequency interference principles.

An EMI filter or a RFI filter consists of a circuit or a device containing series inductive and parallel capacitive components, which provide a low impedance path around the protected circuit for high frequency noise. EMI filters can run on alternating current (single phase or three phase) or direct current (DC) power supply.

You can use an EMI power filter to eliminate noise in high frequency power lines. To protect electrical equipment subject to variable load and power supply conditions such as motors, you can use variable EMI filters.

Some important parameters you must consider before buying an EMI filter or RFI filter:

1. Rated voltage and current of the filter
2. Specifications related to frequency band such as passband and stopband
3. Rated insertion loss of the filter

Action Steps
The best contacts and resources to help you get it done

Buy EMI/RFI filters from reputable manufacturers

Once you understand your requirements, check out different standard EMI/RFI filters available in the market.

I recommend: Tyco Electronics, a reputable manufacturer, supplies a wide range of products such as an EMI noise filter, a RFI line filter, an AC RFI line filter and a DC EMI filter. If you need an EMI noise filter and a RFI noise filter, check out products offered by Genisco Filter Corp.. You can also buy EMI/RFI filters at Captor Corp., another reputable manufacturer.

Buy EMI/RFI filters from reputable suppliers and distributors

You can compare different EMI/RFI filters based on their features and prices at distributors or retailers' websites.

I recommend: DJM Electronics is a reputable distributor that can supply various filters including an EMI power filter, an AC RFI filter, an EMI noise filter and a DC EMI filter. Nu-Way Electronics is another reputable distributor of EMI RFI filters and related accessories.

Buy specialty EMI/RFI filters from custom manufacturers

If standard EMI/RFI filters available in the market do not meet your requirements, you can opt for the custom manufacturers to supply suitable EMI/RFI filters.

I recommend: Pacific Aerospace & Electronic manufactures custom EMI RFI filters for defense, aerospace and medical industries. Capcon International is a reputable manufacturer of miniature EMI filters.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  For better understanding of the product, check EMI filter schematic available on the manufacturer's website.
• •  When you are searching for EMI RFI filters consider operating temperature range of the equipment.
• •  Important accreditations for an EMI filter design or RFI filter design include Canadian Standards Association (CSA) mark, Underwriters Laboratories (UL) listing mark, UL recognized component mark, VDE component mark and Mil Spec or military standards.