Equivalent series and parallel equivalent circuits for metallized film capacitors

The most popular general purpose power and signal capacitor, the multilayer polypropylene (MPP) capacitor, exhibits virtually zero conductance losses and negligible distributed inductance. Self resonance is principally determined by lead and package inductance which can be modeled by a lumped equivalent inductor external to the capacitor. Inside the capacitor, the distributed resistance and capacitance represented by the metallization and the capacitance across the dielectric, correspond to an R-C transmission line with low pass characteristics. In this paper, distributed equivalent circuit modeling using numerical methods is used to derive empirical equations fitting the observed theoretical bode plots of equivalent capacitor parameters. The characterization of equivalent series and parallel components provides useful modeling tools for capacitor design and for predicting the effects of partial edge disconnection from the schooping due to corrosion or excessive current.