Single-Stage Buck-Derived LED Driver With Improved Efficiency and Power Factor Using Current Path Control Switches

This paper proposes a single-stage lightemitting diode (LED) driver based on an inverted buck topology, using current path control switches. The proposed circuit consists of a control circuit, a bridge diode, and an inverted buck converter with multiple switches connected to the LED segments in parallel. Whereas the typical buck LED driver operates with a fixed LED forward voltage, the proposed driver operates with a variable LED forward voltage, according to the input voltage level. Because of this capability to adjust the LED forward voltage, it can reduce the current ripple and the switching frequency with a small inductance value. In addition, it enables operation with LED lamps of a wide voltage range, while simultaneously achieving small dead-angles. The detailed operation principles are described, and the design considerations for the proposed driver are discussed. The proposed driver circuit and control operation are verified experimentally using a 7 W hardware prototype with four LED segments. The obtained experimental results show that under a 110 Vrms input voltage, the proposed driver achieves a power factor of 0.94 with a small dead-angle and an efficiency of 94%.