Two-Input Floating Buck Converter With Variable OFF-Time Control Scheme for High-Efficiency and -Accuracy LED Lighting

A two-input floating buck (TIFB) converter is proposed to decrease voltage stress dramatically, while achieving high power efficiency for LED lighting systems. Its power transistors can also be low voltage and on chip to reduce cost with small chip area. A proposed variable off-time (VOT) control with an on-chip current sensor would detect the peak inductor current and adjust the off-time period dynamically depending on the number of series lighting-emitting diodes (LEDs) and its input voltage. High-accuracy LED current can thus be realized with little additional power. The TIFB converter's operating principle and the VOT control scheme are described in detail. Experimental results of a prototype in 0.25-μm 5-V CMOS process are shown to verify the theoretical analysis of a proposed LED driver.