Design techniques for high efficiency LED drivers

Abstract

The increasing popularity of cellular phones with integrated cameras in the recent past has led to major improvements in its image quality. However, integration of new features, such as mobile email, video streaming, MP3 etc. tend to put the limitation on image quality as camera phone designers struggle to manage multiple features while maintaining healthy battery life time. In this research, a novel efficient power management scheme for camera phones with flash for better image/video quality is discussed. A prototype power management circuit comprising of a 2 MHz Buck-and-Boost DC-DC converter driving up to 1.2A flash light emitting diode (LED) in 500nm CMOS process is implemented. The converter achieves high efficiency over the entire Li-On battery voltage range of 3.0V to 5.2V by operating in buck, buck-and-boost and boost mode based on the input/output voltage and load current requirements. The proposed pulse width modulator (PWM) controller operates continuously over the entire Li-On battery range while providing constant LED current. The converter shows peak efficiencies of 87% and 83% for LED current of 0.6A and 1.2A, respectively.