Abstract：In the higher frequency range, the ferrite core inductor can be considered as an equivalent circuit model, which is formed of a series branch of a resistance and an inductance paralleling a parasitic capacitance, and the capacitance can play an important role in the high performance of the inductor. The models of 2D parallel plane field and 3D electrostatic finite element (FE) for the toroidal ferrite core inductor are presented, and the stray capacitances between every two turns are calculated. Then, the equivalent network of capacitances can be obtained. If a unitary current is applied between the input and output turns of the inductor, the capacitive lumped parameter, i.e., the parasitic capacitance can be calculated using the node-voltage equation method. The stray capacitance can be measured using resonant frequency method on the assumption that the capacitance is independent of frequency. Contrasting calculated results with the measured one, it is shown that the fringe effect of inductor is very crucial to build electrostatic model, i.e., the problems of the electrostatic field must be analyzed using 3D model as well as calculating the stray capacitance of turn to turn for inductor. If only considering the stray capacitance between the adjacent three turns, the value of equivalent parasitic capacitance can reach to above 95% of the total value of which all turns of the coil are considered. The parasitic capacitance has a linear relationship with permittivity of the ferrite magnetic core and the insulating coats of conductor, in which it is more obviously influenced by the insulating coats.
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2009, Vol. 24 
