A multi-string LED driver with constant-current output and automatic balancing

Soc. for Elec. Eng. The capacitive balancing scheme is widely used to mitigate current imbalance in driving multiple light-emitting- diode (LED) strings due to simplicity and reliability. To drive LEDs with the required current, variable frequency control will bring the high reactive power and increase VA ratings of the main switches. Fixed frequency control does not permit zero-voltage switching (ZVS) under load variations. To solve it, this paper proposed a multi-string LED driver with constant-current output and automatic balancing. The driver based on an LCLC resonant tank decouples the effect of load variation to output current, and has the resistive input impedance. So fixed frequency control can be implemented to avoid the reactive power. Also, it combines the existing capacitive balancing scheme to realize multi-string current balance with the smallest additional components. Moreover, it has short-circuit protection and the pulse-width modulation (PWM) dimming can be incorporated easily. The analysis, implementation and verification were detailed in this paper.