A common mode choke suppresses common mode electromagnetic interference on power and signal lines. It presents high impedance to noise currents flowing in the same direction on both conductors while allowing the wanted differential current to pass almost unaffected. It is the standard fix for failing conducted emissions limits in an EMC test.

A common mode choke has both lines wound on one core so their fluxes cancel for the wanted current and add for noise, blocking only common mode interference. A differential mode choke is a single-winding inductor in series with one line, blocking noise that flows down one conductor and back the other. Most practical EMI filters use both, and a well-designed common mode choke with controlled leakage inductance can provide some differential mode attenuation as a bonus.

NG Electronics is an ISO 9001:2015 certified common mode choke manufacturer in Pune, supplying EMI filter chokes, ring core chokes and custom common mode filters to OEMs across India. All winding, testing and design work is done in-house at our Pune facility.

Start with the frequency band where you are exceeding the emission limit, your line current, and your voltage rating. From there the core material determines where the impedance peaks, the turns count sets the inductance, and the winding style sets the leakage. Send us your conducted emissions plot and schematic and we will specify the part for you.

Our standard range runs from 250mA on compact UU core PCB chokes up to 50A on high current ring core chokes. Custom builds beyond 50A are possible using heavier copper or foil windings — tell us your continuous and peak current and we will size the core.