Modelling iron-powder inductors at high frequencies

A high-frequency model of iron-powder core inductors is studied. The skin and proximity effects that cause the winding parasitic resistance to increase with the operating frequency are considered. The inductor self-resonance due to the parasitic capacitances is also taken into account. The frequency response of the inductor model is compared to that of an experimentally tested iron-powder core inductor. The first self-resonant frequency is determined from the plot of the measured reactance and allows for the calculation of the parasitic capacitance. Equations for the inductor parasitic resistance are derived in a closed form. Expressions giving the AC resistance as a function of the operating frequency are given. These expressions allow for an accurate prediction of the inductor power loss over a wide frequency range. The measured and calculated values of the inductor impedance magnitude end phase, the real and imaginary parts of the inductor impedance, the inductance, and the inductor quality factor are plotted versus frequency and compared. Theoretical results were in good agreement with those experimentally measured. Therefore, it is demonstrated that the discussed equivalent circuit has a frequency response matching that of the real inductor. Moreover, the circuit model is simple, it allows for an immediate understanding of iron-powder core inductor behavior and can be easily used in computer simulations of electronic circuits