Toroid vs ETD Ferrite Cores

[rentner]

In almost any Power supply with switching going on, you will have two type of cores:
Toroids - Used for removing noise.
ETD's - The standard Type of ferrite Transformers used in almost any Supply today and even back in the good old 20th century.

Why not use one of both types for the same purpose? Does this have advantages in price or efficiency?

[Neilm]

They generally have very different characteristics. It all depends on what they are being used for. For example a toroid will have a low leakage. A normal ETD core can have the leakage adjusted - either by grinding down the center leg or putting small shims on either side. If designing a flyback SMPS for instance, the energy you can transfer is down to the leakage in the transformer.

Neil