The Magnetized Capacitance, First Resonant Frequency, and Electromagnetic Analysis of Inductors With Ferrite Cores

The parasitic capacitance of magnetic components, i.e., inductors and transformers, are crucial, because it dominates the high-frequency impedance, causes voltage / current spikes, and arouses electromagnetic interference issues. The existing methods characterize capacitance from all five parts (turn-to-turn, layer-to-layer, winding-to-magnetic core, winding-to-electrostatic screen, and interwinding). However, the calculated results are always less than the measured capacitance, especially for the inductors with few winding turns. This article discovers another mechanism of the parasitic capacitance caused by dB/dt. It points out that a time-varying magnetic field also generates an electric field, which leads to parasitic capacitance, and proves that this capacitance dominates the first resonant frequency (denoted by f(R)) of the inductors with few winding turns. The factors related to the capacitance and the f(R) are analyzed. The proposed theoretical analysis is validated by numerous simulations and experimental results. All the simulations are included in the multimedia folder.