A new current-balancing method for paralleled LED strings

This paper presents a current balancing and dimming scheme for paralleled light-emitting-diode (LED) strings directly powered by a dc source. The current balancing is achieved using current-balancing transformers. To make the operation of the balancing transformers possible and provide equal driving currents for the paralleled LED strings, a series-connected switch is turned on or off by a high-frequency signal. The brightness of the LED strings can be adjusted by varying the duty cycle of the control switch in addition to achieving current balancing. The proposed current-balancing and dimming method was verified experimentally.