Spice and Inductors

[sbench]

LTSpice has two different forms of nonlinear inductance, (or inductance that varies as a function of Flux. The most general form requires that you list the magnetic parameters (Bsat, Bresidual etc) and the geometry (magnetic circuit length, gap size etc).

Then, you can use the .param command and the .step command to see what happens as you change the air gap or whatever.

In the attached picture, I've given a simple example. I set up a linear current source (0 to 1 amp from 0 to 1 second) so that by plotting the voltage across the inductor, you are actually plotting inductance (di/dt constant) vs DC current.

Then I set up the STEP command to STEP through a number of different air gap sizes. This shows how inductance varies with current for the family of air gap sizes.

You'll note the similarity between this simulation and some of the plots that Dave has measured and placed in various sections of this site.

Steve