Design Of Constant-Current LED Backlight Driver For Portable Devices

With the successful development of white LED in 1998, white LED brought revolutionary change to display and lighting area. White LED has advantages of no pollution, long life, impact resistance, vibration resistance, power saving and low maintenance cost. LED is most widely used in portable lighting and display devices among all the LED applied electrical devices. Therefore research of LED backlit driver has become an increasingly important issue.Unlike traditional LED driver, this paper shows a LED constant current driver, which decreases the chip area and cost. In addition, the low voltage current mirror circuit designed in the paper makes it possible to achieve a very low dropout voltage according to the design targets, greatly reducing the energy consumption of the drive circuit and extending the usage time of lithium batteries of devices.In this thesis, system working theory and block diagram in PWM control mode are introduced firstly. Then it is elaborated that the working principle and circuit structure of each sub-module, especially the theory study and design realization of analog circuit modules-the current reference module and the current mirror circuit module. In the current reference module part, some typical voltage reference circuits are introduced firstly. Then a type of sub bandgap voltage reference circuits is chose and improved to achieve the design goal of reference current. In the current mirror circuit module, compared to conventional current mirror circuit the low voltage current mirror designed in the paper has a more simple structure and lower dropout. In the end of the paper, chip function and key performances are simulated and the results show that the design of LED driver meets the design requirement.