I read in sci.electronics.design that Paul Keinanen
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:
On Sun, 7 Dec 2003 19:13:36 +0000, John Woodgate
wrote:

Low-frequency iron-cored coils are quite another matter; the
inductance varies with frequency, voltage, temperature, previous history
and the state of the tide on Europa.

I assume that you are referring to DC biased iron cores (without an
air gap) or some high permeability ferrites with a strong DC bias
current. These do indeed show a variation of inductance depending on
the DC bias current.

Not only that, the inductance can vary with the AC voltage applied, most
notably when saturation is approached, but it can also happen with
silicon iron at very low inductions. Nickel-iron alloys don't normally
show this 'bottom bend' effect.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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