Development of high frequency SPICE models for ferrite core inductors and transformers

High-frequency SPICE models were developed to simulate the hysteresis and saturation effects of toroidal-ferrite-core inductors and transformers. The models include the nonlinear, multivalued B-H characteristic of the core material, leakage flux, stray capacitances, and core losses. The saturation effects were modeled using two-diode clamping arrangements in conjunction with nonlinear sources. Two possible controlling schemes were developed for the saturation switch. One of the arrangements used the current flowing through a series RC branch to control the switch, and the other used a NAND gate. The NAND-gate implementation of the switch proved to be simpler, and the parameters associated with it were easier to determine from the measurements and the B-H characteristics of the material. Lumped parameters were used to simulate the parasitic effects. Techniques for measuring these parasitics are described. The models were verified using manganese-zinc-ferrite-type toroidal cores, and they have general applicability to all circuit analysis codes provided that they contain nonlinear sources or equivalent function blocks such as multipliers, adders, and logic components.<
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