Capacitive current balancing for parallel-connected LED strings with tight load-regulation by switch-controlled capacitor

This paper proposes a capacitive current balancing method for multistring LED lighting system driven by a LCC resonant converter. Different from conventional current balancing methods, this method replaces the capacitor in the resonant tank by a switch-controlled capacitor (SCC) with which the output voltage can be regulated by modulating the frequency of the resonant tank instead of the switching frequency of the converter. As a result, LED currents can be balanced and maintained to a desired value even for wide load and input voltage variations. A 70-W LCC resonant converter is built to validate the method.