Apr 182012
 


Info This is an popular coil geometri used in todays wireless charger circuits.
The formula used in this calculation is based on the
Harold A. Wheeler approximations
for air core flat spiral coil inductor.

…where:

  • L = inductance in μH
  • Di = inner diameter in inches.
  • s = distance between windings in inches
  • w = wire diameter in inches
  • N = number of turns

1 inch = 0,0254m=2,54cm = 25,4mm.
This formula applies at ‘low’ frequencies (<30MHz)
using enameled copper wire. Some people call it "magnet
wire".

Click on image to enlarge

Flat spiral coil inductor example

Please note that the outer and inner diameter is measured from the center of the wire.
Flat spiral coil dimensions drawing

Dimensions

Coil inner diameter (Di):
Number of turns (N):
Wire Diameter (w):
Spacing between turns (s):
Inductance (L):
Outer diameter (Do):
Wire lenght (Wl):
      

image

More about spiral inductors..

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