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The question derives from my last question.

When the power circuit is powered up, there is surge because of the input capacitor. The surge is a differential mode signal. So to reduce the surge, why not use a differential mode inductance? Why is a common mode inductance often used?

I used LTspice to check the effect. The waveforms are as follows. It thinks that the common mode inductance is better because the current peak is smaller and there isn't a oscillation.

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JRE
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T L
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  • Both circuits can be reduced to a single L and C in series. The CM version has less equivalent inductance so is better damped with respect to whatever ESR you've set in the circuit (please show them on all V, C, L). – Tim Williams Jan 01 '23 at 05:20
  • Where is the difference between common mode and differential source "voltages" ? See this ? https://electronics.stackexchange.com/questions/586646/is-this-explanation-of-a-common-mode-choke-correct/645911#645911 you need at least 3 points. – Antonio51 Jan 01 '23 at 11:34
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    The input capacitor current surge IS NOT common mode. – Andy aka Jan 01 '23 at 12:11
  • @Andy Sorry, I've made a typo. I will edit it. – T L Jan 02 '23 at 01:20

1 Answers1

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Perhaps, this can help ... See also this.

Behavior of coupled inductors (CMode & DMode, just change coupling from 1 to -1).

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Antonio51
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