As just about all of us who deal with switching power supplies know, flyback converter designs use an air-gapped coupled inductor instead of a transformer. Typically, this gap is an explicit gap in an E-I type core.
Nick Alexeev points out in a comment, though, that:
Transformer cores are usually not gapped. Inductor cores tend to be gapped. Toroid cores of power inductors have what's called "distributed gap", which you can't see.
Can a "distributed gap" toroid core yield satisfactory results when used for a flyback converter's coupled inductor, or will it cause undesirable effects when used instead of an E-I core with an explicit gap?
Best Answer
I believe the type of "distributed gap" that Nick Alexeev comment refers to in This question , is regarding a "Powder Core" material.
Powder Iron Core material is, loosely speaking, granules of Iron emulsified in a binder (the stuff that holds the material together), similar to an epoxy. So the iron granules literally have a physical separation from each other by virtue of the binder material. This is the "distributed gap". Literally a large number of small gaps.
With laminated iron cores, the gap is explicit and at one section of the core.
Ferrite cores for the most part do not have a distributed gap.
Providing a gap is a technique to avoid saturation of the core material.
Since the "distributed gap" of a powdered iron core material is literally a gap, yes, a powdered iron core can be used as if the core were literally gapped.
Powder Iron cores are lossy, and that should definitely be a consideration. In most cases the core loss will be too high to use in most high frequency transformer applications. But the distributed gap is still valid as a gap. The losses in powdered iron core material may make it an unsuitable candidate, but that would depend upon the application.