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Are commercially available common-mode chokes, such as one you'd pull out of a dead switching supply, suitable for DC service up to their rated current, or will they saturate/do other baleful things when subject to their rated current as DC instead of mains frequency AC? Do they need to be derated at all for DC service?

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  • \$\begingroup\$ The steady state for an inductor in DC is short circuit and fully deenergized. \$\endgroup\$ – Ignacio Vazquez-Abrams Jan 23 '16 at 8:00
  • \$\begingroup\$ @IgnacioVazquez-Abrams -- for that mythical ideal inductor, yes ;) but real CMCs are powdered-iron or ferrite core beasts with all sorts of quirks and nonidealities, and I wanted to sanity-check that I wasn't going to get bit on the rear by one if I just blindly grabbed/ordered a COTS part that's likely made for AC mains service. \$\endgroup\$ – ThreePhaseEel Jan 23 '16 at 8:06
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So long as you use them common mode they will be fine, but if the current becomes unbalanced they will quickly saturate and become less effective.

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