On the nonlinearities of inductors using linear ferrite toroidal cores

The importance of magnetic device characterization as an engineering design tool for inductors and transformers using linear ferrites is emphasized. A piecewise linear model is given for the permeance of a toroidal core, to bring into evidence the role of core geometry on partial saturation under the assumption of an ideally linear core material with abrupt saturation. A variety of measurements are reported for two different inductors under extremes of signal that partially saturate the cores. Measurements and theory are found to agree well only for low-level signals where hysteretic effects are small. At high signal levels the lack of quantitative agreement is attributed to the fact that different features of the hysteresis are probed by the different classes of measurement signals.