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Sendust vs Ferrite for SMPS

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cupoftea

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Hi,
When we consider ferrite in general.
The law is pretty much as follows...
Ferrite starts to deeply saturate at just over 300mT
having 300mT pk2pk flux swing at above 60kHz is asking for too much core loss.

With Sendust, there is no such law making.
Sendust tends to saturate at 1T, though this is not a clear figure
The Bpkpk losses are not generalised anywhere.
 

Read more data on Sendust / KoolMu etc

the losses are there - you just have to dig for them - I have yet to see a Sendust core that can match ferrite for losses ( at sw frequencies ) under the same conditions.

They are used a lot for PFC chokes - as you ( luckily ) get fairly low ACR loss for a single layer winding - AND - best of all - you get heaps of area for cooling - of course the resultant is larger that a good litz/ferrite design - often by more than 2-3 times - but the toroids and standard wire are way cheaper ...
 
Thanks, yes i see that Saturation B is anywhere from 350mT to 1T, depending on the make of iron powder.
For some time now i have been trying to write a doc which calculates the CCM Boost PFC iron powder inductor for every different type, for a given inductance, for every different permeability torroid, and for every different type, and size, and for from 1 to 3 stacked torroids.........so as to see which solution is the cheapest and smallest, whilst still giving acceptable core losses and wind losses.
At the moment, i do an estimated guess at a torroid size in Sendust, then, after calculation, if its too small, i stack 2 and repeat, then if still too much loss i move to the next size up and repeat......quite a lot of calculations.
There is also something about micrometals "Bpk" actually meaning "Bpk/2"?....ie the "B" in the core loss equation of page 29 of the micrometals iron powder catalog is actually meaning Bpk/2?

Also, its a shame the "% of initial permeability" vs B doesnt graphs show below 90% for most of the iron powder types
 
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