AC LED driver with high power factor and balanced brightness for segmented LED strings

This paper proposes an AC LED driver with high power factor and balanced brightness. While conventional LED driver has some problems of large size and lifespan, the proposed driver overcomes those problems by elimination of inductors and electrolyte capacitors. The proposed circuit consists of bypass MOSFETs, digital logic controller and current regulator. The bypass MOSFETs, which are connected in parallel to segmented LED strings, are controlled to achieve high power factor and balance brightness of each LED and to minimize power loss, simultaneously. In this paper, the basic operating principle for balanced brightness and gate driving method are described. Experimental results with a 12 W LED strings verify the feasibility of the proposed LED driver.