Ferrite cores found salvaged from cables.

[firewalker]

Are the ferrite core used as EMI filters suitable for inductors in DC-DC converter. What is the composition usually used?

Alexander.

[Kleinstein]

The EMI filter inductors usually are high loss materia - so not really suited for an efficient converter. It will work, but lossed are high.

An exception may be current compensated inductors - they may be just high permeability without extra going for high loss. So they might be ok in a forward DC/DC converter.

[firewalker]

Thanks you.

Alexander.

[MagicSmoker]

Ferrite cores for EMI suppression are usually made of the same material as "power" ferrites - Manganese-Zinc - so they could be used in a switchmode power supply. They really start looking lossy around 1MHz, so as long as you kept the switching frequency below, say, 100kHz you shouldn't have any problem with core loss.

They don't have an air gap (even the snap-on ones have very little gap when closed) so don't try to use them in applications where any DC bias is present (ie - chokes or flyback transformers). They also tend to have a very large core area to window area ratio, which helps with losses but hinders power transfer capacity (because you can't wind too many turns).

[T3sl4co1l]

Eh, MnZn and NiZn are both used.  Depends.  NiZn "wideband" I would say are the most common formulations (e.g., Fair-Rite #43, 44).

The loss isn't a problem at most power switching frequencies (< 500kHz).

What you do have to beware of is magnetization.  They saturate readily from DC, so they are only suitable in AC transformers and full wave converters.  You won't have good performance (or any at all), even from a quite oversized core, in any method that requires DC (half wave forward converter, flyback, etc.).

Tim