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# Designing iron powder chokes

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#### Easy peasy

Designing chokes with iron powder cores:

Designing with iron powder cores is a somewhat iterative process ( unless you are very experienced in such design ) the basic steps are:

1) Take the AL of the core and use this to calc the turns for the desired L.

2) Congrat's you now have an L that is correct at zero current and L will fall with increasing current ( the nature of Fe-powder )

3) See if the turns will fit on the core - for the current intended - higher current = thicker wire = more wdg space needed

4) If they don't, keep going to bigger cores until they do with 50-70 % fill factor

5) Now work out the ampere turns and see how the AL falls at max current - work out the L at this point and decide if acceptable or not.

6) If not go to a bigger core, and/or a lower mu core that is also bigger - now go to step 1) ....

you can see below the ampere-turns/mag-path-length for Kool Mu iron powder

you can see the curve for the least dropping off of Ui ( also L ) is for the low mu material -26u.

For -26u material;

at 100 ampere-turns/cm the L will be reduced to 78% of the zero current value.

If we desire 100uH at 100 A-t/cm, the L at zero current will be 100/0.78 = 128.2uH. If the AL at zero current is 27 nH / T^2, then the turns are 69.

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#### Attachments

• Fe powder.jpg
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• Kool mu.jpg
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