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# Finding inductance and core loss for a powered iron torroid inductor in an "2TFC" SMPS

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#### zenerbjt

##### Guest
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Hi,
Would you agree that the following PFC application note calculates the wrong value for core loss?

PFC Application note:

It concerns the equation for calculating B at the top of page 7.
The values for a,b,c,d,e, and x are wrong?

They should be as at page 72 of this below, or am I missing something?

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#### FvM

##### Super Moderator
Staff member
As mentioned before fitting parameters in Magnetics catalogs are often changed between issues. A different parameter set isn't necessarily wrong, as long as it results in a similar loss order of magnitude.

zenerbjt

Z
Points: 2
Z

#### zenerbjt

##### Guest
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Thanks, What is the maximum flux density use-able with "Kool Mu" inductors?

Page 9 of the following Mag-Inc powder core catalog says that “kool mu” material has a saturation flux density of 1 Tesla.
So why does the "Kool Mu" B vs H graph on page 48 only show flux densitys up to 550mT?

Mag-Inc powder core catalog
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#### Easy peasy

Maximum "useable" flux density depends on: ability of ckt to handle the lowered Ur, the flux ripple at or about that peak flux, temperature, and the cooling available ...
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Notice the saturation B = 1.0 Tesla, you may have read the 550 mW/cc @ 100kHz, 1000 Gauss ( 0.1 Tesla ac peak )
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You can see from the graph, p48 that 1T requires likely more than 1000 A-t / cm - so getting up to high levels of applied H.
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you can see above for Kool mu at H = 1000 Oe = 79600 A-t / m = 796 A-t/cm, the residual permeability is very low for all grades and the thing is tending towards being an air cored magnetic ...

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zenerbjt

Z
Points: 2
Z

#### zenerbjt

##### Guest
Thanks, i see what you mean, from that, i believe we would not want to operate kool mu at much above 100 A.t/cm