Electronic – How susceptive is an inductor to frequency and current


According to Coilcraft – Testing Inductors at Application Frequencies the inductance of a coil changes with frequency and current. Most datasheets don't give a frequency-inductance plot and current-inductance plot. Is there some rule/guideline to estimate the inductance at circuit frequency and circuit current given the test frequency and the max/saturation current?

Best Answer

In an air cored inductor this problems do not arise. It is the core material that introduces these seemingly bizarre dependencies. Take a look at 3C90 material: -

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Fig1 shows how the real part of permeability peaks at a frequency of about 700kHz. In fig4 as flux density increases (caused by more current for example) the permeability also peaks up. Temperature has also an effect for many ferrites and fig2 shows how permeability is affected.

It's the core that causes these problems and the only resort is to use the manufacturer's data sheets if you can get them.

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