The Design Of White LED Driver With PWM And Programmable Digital Mixing Control

As one of the most promising light sources with many advantages, such as high luminous efficiency, high luminous intensity, long life period etc, White LED has been widely applied to portable electronic appliances, such as mobile phone, digital camera, MP3, digital TV and so on. An excellent power driver for high performance White LED is essential. The main function of White LED driver is to provide constant current, and now it has become the star of power management field. Using step-up DC/DC converter to drive White LED is a major method for portable applications. The design of a step-up synchronous rectification DC/DC converter Chip, with PWM and programmable digital signal dimming control, is introduced in this thesis.In the main part of this thesis, firstly, some key techniques to reduce power waste and to enhance performance for boost DC/DC are analyzed, and in the same time, the required feature of White LED driver is deduced from the White LED feature. Based on the design requirements of the objective IC and the key technologies which analyzed and studied before, the whole chip's architecture is constructed and the sub-circuits'function are defined. And then, some sub-circuits such as error amplifier, digital dimming control unit, PWM dimming control module, over voltage protection circuit, current limit circuit and thermal shutdown circuit are then studied in details. Finally, the whole chip simulation results by HSPICE are given: the start-up delay attains 200μs, the output voltage ripple coefficient is only 0.5%, the efficiency is above 80% under moderate load, and the over-voltage protection and PWM luminance modulation are effective.