I have been very busy at the lab lately, too busy to update ublog regularly, and this set of formulas from Gamma Instruments has saved me a bit of trouble. Several air core inductor designs are outlined which allow you to make your own custom inductor, within reason, if you need to test something and you don’t have the part on hand. Typically, the inductance values will be modest, however, it is much easier to make an inductor yourself than a reasonable capacitor. Just think of all of the folding!

( pancakewheel )

I assume the pancake spiral formula would have to be altered if printed on FR4 (to take into account the µr of the substrate).

Hi Tom,

µr for FR4 is effectively 1 so no problems there. I mainly tested the solenoid designs which worked out pretty well. Since you are interested in putting a planar inductor on a PCB, I would refer to some RFID design literature as they have practical information for design and tuning of PCB antennas, which are effectively inductors. Hope this helps!

Thanks for your insight on those questions I asked earlier, it got me going in the right direction.

Working on a buck circuit lately and thought you might enjoy page 31 of AN35 from linear technology.

Heh, thanks Chris, this is almost as good as the write-only memory. I will have to make a separate post about that app note.

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Another great reference for inductance calculations is a book by Grover appropriately named Inductance Calculations. Old school text and largely based on look-up tables but it can be worth its weight in gold.