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I came across this configuration in a schematic, and it makes no sense to me. I have to admit common-mode chokes are not my strong suit, but is this even going to act as an inductor?

schematic

simulate this circuit – Schematic created using CircuitLab

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2 Answers 2

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It'll act like an inductor with an inductance equivalent to one of the windings. Imagine both inductors as bifilar windings like this: -

enter image description here

Image from here. If you think about it, it might as well be one inductor with a wire of twice the cross-sectional area. And, of course, it gives you lower copper losses.

is this even going to act as an inductor?

If the winding dots were on different ends then, it won't particularly act as an inductor other than having an inductance that is very much smaller (defined by leakage inductance) and fairly tricky to predict in value.

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As @Andyaka notes, it's wired correctly.

The bigger problem is the unbalanced DC bias, which is only some 10s of mA for typical parts -- above which, the inductance drops precipitously.

CMCs are also often called "current compensated chokes", hinting at this feature. Normally, load current flows into, and out of, the windings respectively, canceling out their DC/mains frequency contributions, but leaving a high impedance in the common mode. This arrangement applies DC directly to the common mode.

Related: the same goes for ferrite beads, which are basically single-winding CMCs.

In general, for power supply filtering, one wants an "inductor" proper. Other magnetic components can be used only in certain cases (like ferrite beads in the 100s mA or below range).

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