Design Of White LED Driver Based On BCD Technology

White LED is widely used and is gradually replacing the incandescent and fluorescent lighting due to its advantages over conventional lighting of high efficiency, low energy consumption, low pollution, long lifetime and high reliability. The development of integrated circuits for LED is introduced in this paper, which points out that it is better to drive LED with constant current other than constant voltage. Three kinds of methods for driving LED(linear regulation mode, capacitor switching mode, inductor switching mode)are discussed and some applications with these methods are exampled. Though the analysis of several modes of constant-current control, it is concluded that the hysteresis-current control mode is very suitable for driving LED due to its self-stability and simplicity.The paper designed a continuous current mode step-down constant LED driver based on CSMC 0.5um BCD technology with Cadence EDA integrated circuit design and simulation tools. The input voltage of the circuit is from 7V to 42V, and the output current is up to 1.5A. It can use DC voltage or PWM signal to control the brightness. The chip will be widely applied in LED/Display Back Light Driver, Lighting, Portable Communication Devices and Handheld Electronics etc.The chip use the scheme of high-side current sensing topology, it controls the driving current for LED to be averagely constant through hysteresis-current control technique. The chip is mainly composed of a power supply module, a bandgap reference, brightness control circuit, thermal shutdown protection circuit, ESD protection circuit, a hysteresis-current control circuit, an output logic driving circuit and a power MOSFET. The chip can provide a driving current of 350mA or 1A for 1 W LED or 4W LED, respectively. Test results show that the chip can provide an average driving current more than 350mA through adjusting the outside current-sensing resistor and can drive one or more LEDs in series. The efficiency can be up to 97%.