High-Efficiency Direct AC LED Driver with Adaptive Constant-Power Architecture

This paper presents a high-efficiency direct-AC LED driver integrating a 14-stage voltage-segmented architecture, digitally coordinated stage selection, and adaptive current-reference regulation. The proposed driver provides finer matching between the rectified bus voltage and the cumulative LED voltage, thereby reducing the residual voltage and power dissipation of the linear regulating devices. Unlike conventional constant-current segmented drivers, the current reference is adjusted according to the selected operating state and the corresponding active LED voltage. A valley-filler circuit is employed to extend the conduction interval of the LED driver and reduce the low-voltage dead zone. A prototype operated at an input voltage of 112.92 V AC and a rated power of approximately 12 W was experimentally evaluated. The measured input power, total LED active power, conversion efficiency, and power factor were 12.12 W, 11.54 W, 95.18%, and 0.9, respectively. The results demonstrate that finer voltage segmentation can reduce voltage-mismatch loss, although the increased number of stages introduces additional component and control complexity.