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What is a Common Mode Choke

Date: Dec 1st, 2022
Common mode choke also known as Common Mode Choke Coil is commonly used to filter Common mode EMI signals in switching power supplies of computers. A common mode choke is an electrical filter that blocks high frequency noise common to two or more data or power lines while allowing the desired DC or low-frequency signal to pass.  

Common mode (CM) noise current is typically radiated from sources such as unwanted radio signals, unshielded electronics, inverters and motors. Left unfiltered, this noise presents interference problems in electronics and electrical circuits. In board card design, common-mode inductor also plays the role of EMI filter, which is used to suppress the electromagnetic wave emitted by high-speed signal line

How do I Choose a Common Mode Choke?

The main criteria for selecting a common mode choke are:

Required impedance: How much attenuation of noise is needed?
Required frequency range: Over what frequency bandwidth is the noise?
​Required current-handling: How much differential mode current must it handle?