Symmetric Current-Balancing Circuit for LED Backlight With Dimming

One of the key challenges in driving multiple light-emitting-diode (LED) strings for a liquid-crystal-display (LCD) backlight system is to ensure uniform current control. Unequal current sharing between the strings is due to manufacturing spread and temperature variations. In this paper, a novel current-balancing circuit for LED backlights is proposed. A smart combination of an inherent symmetry of circuit and capacitive balancing mechanism enables an efficient and cost-effective current balancing. The operating principle of the proposed method is analyzed, and an appealing generalization is made. The feasibility of the proposed scheme is verified by developing a hardware prototype with a dimming feature to drive a 100-W edge-type backlight system, having six LED strings for a large-scale LCD panel.