Study Of A LED Backlight Driving And Controlling Circuit For Large Size LCD Panel

At present, the entire Flat Panel Display (FPD) industries are growing rapidly in the world. In all types of FPD, Liquid Crystal Display (LCD) occupies a dominant position. In a long time, as an important part of LCD, backlight mainly uses Cold Cathode Fluorescent Lamp. With the development of Light Emitting Diode (LED), LED has been widely used in small LCD backlight, and is entering large size LCD-TV backlight areas. In this paper, on the basis of LED driving and controlling technology, we study, design and produce a large-size LED backlighting module.First, according to the request for the size, brightness and uniformity of LCD, choosing, arranging and connecting LEDs are confirmed. Then we design and construct the optical parts of LED backlight, according to the structure of direct LCD backlight.Second, the I-V characteristics of LED is nonlinear and unilateral conductive. Small changes in voltage will cause larger changes in current and brightness. The life of LED will decay, if there is too large current. However, weak current will affect the LED luminous intensity. Therefore, LED drivers should maintain the current appropriate and constant as much as possible. HV9911 is used to design a constant current driver, which can guarantee the current of LED constant, and provides a LED protective circuit.Third, the brightness of the LED is affected by current and temperature. We design a color sensing circuit based on HDJD-S831-QT333 color sensor module, to monitor the chrominance changes in backlight module, and design a temperature monitoring circuit based on DS18B20, to monitor the work temperature of backlight module. On the basis of CIE 1931-XYZ color standards and red, green, blue color-mixture theory, using the FPGA chip EP2C8T144C8, we design the controlling and feedback circuit both in software and hardware, and test some parameters of it.