Off-line buck LED driver for series connected LED segments

This paper proposes an offline light-emitting diode (LED) driver which is based on inverted buck topology. The proposed circuit consists of control circuit, bridge diode and inverted buck converter which has multiple switches connected to LED segments in parallel. While the conventional buck LED driver regulates fixed LED forward voltage, the proposed driver regulates variable LED forward voltage according to input voltage level. By the capability to adjust the LED forward voltage, it can reduce the current ripple while using same inductance. In addition, it enables to operate wide voltage range of LED lamp, simultaneously achieving high power factor. The basic operation principle and the control scheme are described. The proposed offline LED driver has been demonstrated in a 7 W, 110 V
_rms
experimental prototype, which provides high efficiency and low LED current ripple with high power factor.