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

Abstract

In this work high frequency SPICE models were developed to simulate the actual behavior of ferrite core inductors and transformers. The models include the nonlinear, multi-valued BH 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 dependent 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, while 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.