With the exception of air-core coils, all power inductors possess certain saturation characteristics. That means inductance decreases with increasing levels of current. This is due to the various core materials, which start to lose their permeability more or less strongly after a certain induction level B is reached and in extreme cases take on the characteristics of air. The saturation characteristics of an inductor can be influenced by
- the type of core material
- core geometry
- the number of turns
- and the air gap
However, deviations often exist between the calculated inductance at a certain current level (i.e. rated current) and the real inductance, because:
- production spread of the core is available
- the core’s spec sheet entries are inaccurate or incomplete
- the inductor geometry causes a non-homogenous field distribution
- manufacturing tolerances
- thermal influences
For this reason it is important to measure saturation characteristics during the development phase and quality inspection of power inductors.
On the following pages some sample applications will be presented.