A fast transient LED driver with adaptive frequency control according to load variation for large-sized LCD backlights

Abstract

A fast transient light-emitting diode (LED) driver is proposed for large-sized liquid crystal display TV backlights in attempt to shorten the recovery time and to reduce the voltage fluctuation, while maintaining a high power efficiency. The direct current-direct current (DC-DC) converter in the proposed LED driver accurately detects the load variation using the dimming data and then adjusts the slew rate and operating frequency according to the detected load variation. Thus, it rapidly controls the turn-on time of the power switch and then controls the inductor current so that the output of the proposed LED driver can be accurately regulated during the load transient time. To verify the performance of the proposed LED driver, a DC-DC converter and an expandable LED current controller were fabricated using a 0.35-m bipolar-complementary metal-oxide-semiconductor (CMOS)-double-diffused metal-oxide-semiconductor (DMOS) process technology and assembled with 48 LED channels for measurement. The measurement results show that the proposed LED driver improves the recovery time and voltage fluctuation by 45.1% and 45.6%, respectively. In addition, it achieves a maximum power of 115.2W and a maximum power efficiency of 89.2%. Therefore, the proposed LED driver is suitable for high-end applications such as large-sized LED TV backlight modules.