Answer 3—The self-resonant frequency of an inductor is one way of expressing the amount of distributed capacitance that the coil exhibits among its turns. This capacitance is the inevitable result of having the turns located next to each other. It appears in parallel with the inductance, creating a parallel-resonant circuit.

As the operating frequency rises to the self-resonant frequency of an inductor, the impedance rises faster than it should for a pure inductance, and the voltage-current phase relationship changes. Above the self-resonant frequency, the inductor behaves more like a capacitor!

Contributor: David Tweed

Published December 2003