I would like to know how to select a common mode choke inductance value for EMC filter design for DC -DC power supply

The Specifications are :

Cutoff frequency : 20 Khz

Power suppply Maximum Current : 2A

Power suppply voltage : 24V

Required Impedence : Maximum Noise must be attenuated.

EMC test Environment immision : 450 Mhz

I am learning about power supplies , EMC Filters so kindly help me in this so that it would be a helpfull for my knowledge.


  • \$\begingroup\$ And where would you want to fit this CM choke in your target circuit. You need to identify the relevant part of the target circuit schematically. In other words, this cannot be answered within the limited constraints of this site without a circuit diagram of your power supply. \$\endgroup\$ – Andy aka Feb 3 at 12:40
  • \$\begingroup\$ I want to fit this CM Choke to the ON/OFF Switch which gives 24 V 2A when the switch is ON. and that power is siltered using Common mode choke and given to the display circuits \$\endgroup\$ – Muthu Feb 3 at 15:02
  • \$\begingroup\$ A switch "may give" 24 volts to a circuit but it certainly won't give 2 amps to a circuit. Show your schematic, \$\endgroup\$ – Andy aka Feb 3 at 15:06

You may want to read up on this Common Mode Filter Design Guide and also on the TDK site. I advise you decide on the filter you think may be required (if it is) then provide space on the PCB for the component(s) in case it is required. For EMC testing the results may surprise you, as you realise there is no requirement afterall, so you can leave the components out or replace them with 0-Ohm links ... Good luck !


Removing 450 MHz noise would need feedthrough capacitors screening etc A CM ferrite choke may have little attenuation at those frequencies.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.