A Medium-size Lcds Led Backlight Drive Circuit Design

Currently, Flat Panel Displays (FPD) on a global scale is rapidly replacing the traditional displays. In all types of FPD, Liquid Crystal Displays (LCD) holds a dominant position. Screen backlight as an important part of LCD are mainly using of Cold Cathode Fluorescent Lamp (CCFL). With the Light Emitting Diode (LED) development, it has been widely used in small and medium-size LCD backlight, and quickly infiltrating into large-size LCD backlight areas. The rapid development of market requirements of LED driver circuit has become increasingly urgent.This paper designed a medium-size LCD for the LED backlight driver IC. Its operating voltage range is 4.5V to 25V, and has the ability to driving a total of 96 white LED light array consisting of a total of eight current mirror channels (8×12), each with output current up to 30mA or more.The study in this paper is divided into three parts:first designed a high-to-low voltage conversion circuit. Instead of the traditional LDO structure, use a zener diode to form the regulator, simplifying the design of internal modules. Then designed a peak current controlled step-up dc-dc converter to driving the lamp array. Finally, the traditional current mirror structure has been improved, designed a high-precision high-matching 8-channel current mirror, the simulation showed that the error can be as low as 0.03%.Upon completion of the LED driver circuit design and simulation, finished the physical layout, post simulation and chip testing. This LED driver is manufactured with CSMC 0.5um HV BCD process. The chip area is 6.8mm2. The testing results show that it can stably drive 96 white LED when the input voltage is 12V. When the output current at 15mA/channel, its efficiency can be achieved to 91.2%, and the matching of 8-channel current mirror up to±1.3%.