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Why is it not popular using common mode chokes in differential mode configuration for differential mode noise filtering?

Mostly when using fly-wire type chokes with filters, where the chokes are simply kept inside the enclosure with its wires connected to X and Y capacitors placed on the PCB (due to its size which makes it costly to be placed on board), can't this kind of arrangement help avoid placing one common mode choke and two separate single winding chokes and go with one common mode choke for common mode filtering and another common mode choke connected in differential mode configuration as shown in attached schematicsenter image description here?

Could saturation be a problem for low current design? If yes, I dont understand why not if two separate chokes are used. I am assuming the core is properly sized to not go to saturation during normal operation.

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  • \$\begingroup\$ Try simulating the scenario you have drawn above and you will be in a better position to see why things are done the way they are done. \$\endgroup\$ – Andy aka Nov 13 '19 at 12:19
  • \$\begingroup\$ I've seen this done in higher power applications. The permeability of the core really matters when doing this. But as @Andyaka recommends, simulate it to see what the trade offs are. \$\endgroup\$ – Aaron Nov 13 '19 at 17:28
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Differential signals are often used where EMC is a concern, as interference is usually common mode and a differential signal on a close pair will radiate less. The EMC enemy is more often common mode noise or emissions. Your suggestion would be more useful in situations where you need multiple signal paths and want to do as much as possible to ensure they're all identical.

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  • \$\begingroup\$ Hi Cristobol, I believe you are talking about EMI induced on small signal lines. My primary goal is to mitigate lightning induced EMI affecting our SMPS power supply which, in my experience has high energy pulses of both common mode and differential mode nature. Do you find any reason why this wouldnt work? I will run a simulation and publish my results here.Thank! \$\endgroup\$ – Jaacs Pottas Nov 14 '19 at 3:35
  • \$\begingroup\$ @JaacsPottas LOL, I don't deal much with lightning, class 4 ESD is more my speed. I'll have to take your word on the requirements. \$\endgroup\$ – Cristobol Polychronopolis Nov 14 '19 at 13:37

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