Light-Emitting Diodes (LEDs) have emerged as promising lighting devices for the future. LEDs are widely used in residential and commercial applications like indoor/outdoor lighting and television backlighting. Different from the traditional incandescent and fluorescent lighting sources, LEDs need constant current source to maintain the brightness and chromaticity. In some applications like street lighting or television backlighting, the multi-string structure is adopted because of the reliability and safety concern; therefore these applications need multi-channel constant current driver.
The current solution for the multi-channel constant current LED driver usually contains three stages: the PFC stage, front-end DC/DC stage and the constant current source stage. Each stage needs one or more controllers; therefore this structure is complicated and expensive. On the other hand, the price of LED driver is very sensitive to the market. Contrary to the requirements of LED market, the research and design of effective LED drivers is lagged behind.
The proposed multi-channel constant current LED driver combines the front-end DC/DC stage and the constant current source stage into one stage, and adopts very simple control strategy; hence only one common controller is needed and will greatly reduce the total cost and complexity. Furthermore, coupled inductor is implemented to further improve the output current accuracy. Therefore, this proposed innovation is very suitable for the street lighting and television backlighting applications.