Extraction of parasitic capacitance for toroidal ferrite core inductor

In the higher frequency range, an inductor can be considered an equivalent circuit model, which is formed of a series branch of a resistance and an inductance paralleling a parasitic capacitance (PC). The capacitance gives a large contribution to the high performance of the inductor. This paper presents a 2D parallel plane field and 3D electrostatic finite element model for the toroidal ferrite core inductor and the stray capacitances (SC) between every two turns are calculated. The equivalent capacitances network can be built and the equivalent lumped capacitance, i.e., PS can be calculated. Moreover, the PS can be obtained using the measured resonant frequency and the calculating inductance and resistance at this frequency. Contrasting calculated results with the measured one, it was demonstrated that the fringe effect of an inductor is crucial to build its electrostatic model. If only considering the SC between the three neighboring turns, the value of equivalent PC will reach above 95% of the total value of which all turns of the coil are considered. The PC has a linear relationship with permittivity of the ferrite magnetic core and the insulating coats of conductor, which is more obviously influenced by the insulating coats.