Design Of A Constant-current Control Chip For Driving High-power White LED

In recent years, semiconductor lighting 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 boom of high power white LED greatly promotes the development of integrated circuits for driving LED, which begins to play an important role in the market of power management and generates the enormous business opportunities. Currently in China, the development of integrated circuits for LED is at the initial stage. In order to seize the opportunity to closely follow the trend, the choice for my graduation topic is the design of an integrated circuit for high-power white LED.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.A chip which is used in the buck application to drive high-power white LED with a constant current is proposed and designed in this paper. Using 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 voltage regulator, a bandgap reference, a hysteresis-current control circuit, an output driving circuit and a power MOSFET. It is designed and fabricated with a 25V BCD process with input voltage ranged from 4.5V to 24V. The chip can provide a driving current of 350mA or 750mA for 1W LED or 3W LED, respectively. Test results show that the chip can work under power supply voltage of 24V, it can provide an average driving current more than 300mA through adjusting the outside current-sensing resistor and can drive several LEDs in series.