My first experience of using Micrometals powdered iron toroids was in that power
supply I was working on a couple of years back. They aren't the easiest thing to
get hold of so I got some from RS components just to try.
They smoked very nicely. They were only -26 material though. When I got some in
-2 it was a very different story.
There is nothing wrong with iron powder cores from Micrometals or TSC-
Pyroferric provided you get the right balance between core losses and
winding losses in your design.
I've been a choke/inductor designer for winding companies for over 25
years, and have many thousands of my designs of iron powder cored EMI
filtering and storage chokes in use around the World.
The lower loss powder cores (MPP & Sendust/Kool-Mu) are OK for small
chokes, where labour costs are higher than material costs, but try
using cores of 3.06" diameter and upwards and see just what cost
penalty you pay.
Fortunately you would normally be into high power / low frequency
(c20kHz) switching here, so it's possible to succesfully use
Micrometals -34 grade for chokes like 6kW pfc chokes for applications
like film lighting ballasts, for instance.