A design of current balancing circuit for parallel connected LED strings using balancing transformers

This paper presents a design method of current-balancing circuits for parallel connected LED strings. Current LED error strings caused by characteristic deviations could not only reduce the life time of a particular point of LEDs by thermal spot but can also causes non-uniform luminance of the lighting device. Among the methods for solving this problem, a method using current-balancing transformers makes it easy to compensate for current errors and has simple circuitry. Generally, balancing transformers in lighting applications are applied to AC light sources. Applying these LED strings, which operate on a DC source, needs to verify performance and redesigned. In conventional deign methods, balancing transformers have equal inductance, but the transformer inductance could be smaller according to a cascaded level by worst-case impedance estimation. In this paper we designed a current-balancing circuit for an LED matrix and applied it to a 100-watt LED security light, consisting of an LLC inverter and balancing transformers. And experimental results are represented to verify the performance of designed driving circuits.