Analysis of the current distribution between paralleled capacitors in a chopper on printed circuit board

The current distribution between an electrolytic filtering capacitor and a ceramic decoupling capacitor is analyzed. A simple electrical equivalent circuit is developed that includes models of both capacitors and a lumped element model of the interconnects. Interconnect modeling is performed with CAD tool InCa, an implementation of the partial element equivalent circuit (PEEC) method. First, PSPICE simulation of a complete converter model with interconnects and semiconductors is performed. Next, the results are used to validate the simple electrical equivalent circuit. It is found that the lower part of the switching noise spectrum is filtered by the electrolytic capacitor, but that from 300 kHz on, the decoupling capacitor is the principal filtering device. The developed method can be generalized to the study of multiple paralleled capacitors.