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I have sent out a PCB for manufacture and the manufacturer has suggested an alternative part.

The application is a mains powered (220V AC 50Hz) device. The common mode choke is being used to filter EMI on the power lines.

The original CMC is a 30mH min @1kHz with a DC resistance of 0.76ohms.

The suggested alternative is 25mH min @1kHz with a DC resistance of 3ohms.

I raised a concern that the DC resistance was larger than the original part so they suggested they change the wire from 0.25mm to 0.3mm.

My Question is - what will this do to the DC resistance of the CMC and will it bring it closer to the specification of the original part?

I am new to the use of common mode chokes and could not find resources that mention the wire thickness - happy to look over any resources you can suggest to understand this better.

jhorwood28
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  • what will this do to the DC resistance of the CMC and will it bring it closer to the specification of the original part? - it will lower it but only to about 2.1 ohm and nowhere near the 0.76 ohm of the original part. – Andy aka Jan 11 '22 at 11:55
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    What is the specification the CMC has to meet? That's the important question. 2 ohms or even 3 ohms may be OK, depending on what current you are drawing. – Neil_UK Jan 11 '22 at 12:24
  • The power of the device wont exceed 100W (a 480ohm load) – jhorwood28 Jan 11 '22 at 13:49
  • If you have already done your emissions (i.e. EMI) testing with the original part, changing this choke will effectively void the test and you have to re-do it. (Or risk shipping a non-compliant product) – Kyle B Jan 12 '22 at 01:28
  • Fortunately it hasnt gone through any EMI testing yet – jhorwood28 Jan 12 '22 at 09:02

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