Design and identification of an equivalent circuit for LCT component: inventory and representation of losses

A new kind of passive component, the LCT (integrated inductor (L), capacitor (C) and transformer (T)) is becoming very fashionable in power electronics. Starting from our knowledge in transformer characterization, we recently elaborated an equivalent circuit for this component. This equivalent circuit is fully deducible from impedance measurements, no dismounting of the component is needed and no information about its internal design is required. This paper aims mainly to present the new equivalent circuit and the method leading to its identification using a commercial impedance analyzer. A LCT intended to a 300 W power supply working at 200 kHz has been built and characterized between 100 Hz and 40 MHz. Analyzing the frequency dependence of the real part of serial and parallel impedances we identified several kind of losses rarely taken into account. Among these losses are those related to the capacitor insulator and those due to the dielectric constant of the Mn-Zn core material. Equivalent circuits are supplied to represent every type of losses and their accuracy is checked.