Electronic – How to wind a toroid for 170 uH Inductor


I am planning on buying a toroid core from Digi-Key. I want to be sure that this is the right type and that I can achieve 170 uh inductance with 22-18 AWG wire. How can I wind this and what is the formula so I can calculate this myself in the future. If this doesn't work which one can I buy from Digi-Key to get the right inductance. (my budget is 4 dollars or under for the toroid core) Last, I want this to handle up to 10 amps of current so tell me if I can't use 18 AWG wire.

edit-fixed broken link, i guess it was just because it was linked directly to my shopping cart

From a comment It said to buy my own I can't find any already pre-wound 10 amp 170 uH toroid and the only thing close was like 10 dollars so I would like to wind it myself!!!

Best Answer

The next step after MMGM's excellent answer is to put a few numbers from his datasheet into the calculator from Mark B's answer at

Averaging the inside and outside diameter (6mm and 10mm) we get radius 0.4cm and MMGM's 10 turns. Datasheet has "Ae=7.83mm^2" so enter 0.0783 (cm^2) in the "Area" box and it will calculate a coil radius. Enter 4300 for relative permeability (datasheet calls it ui, calc calls it k, these things happen!) and the calculator confirms inductance 0.168mh, pretty close... So far so good.

Now the crucial question : will the coil take 10 amps?

There is another calculator to answer that on the same site... Enter the radius (0.004m this time!) 10 turns, k=4300 again. And new, the "Flux density near saturation" from the N30 data sheet - B = 380mT = 0.38T, and click the link to "current" above.

For this core size and material, with these turns, and this saturation flux density, the calculator says "0.177 amps".

So, no...

As an experiment, try a 4cm radius, 1cm^2 area, 9 turns, same material. The first calculator says 0.174mh, again pretty close. The second now says 1.96 amperes which is heading in the right direction, but a MUCH bigger coil...

So, as MMGM says, magnetics design is hard.

But that was a first step. Now try some different core materials (lower ui=k, larger cores, lower inductances, and see where you get.

(Also bear in mind that 10A DC may translate to 20A or more at AC. Try designing for 1A,5V until you have something working)