Design Of A PWM Mode LED Driver Circuit With Multi-protection

As a new generation of lighting in the 21st century, semiconductor lighting is gradually replacing the incandescent and fluorescent lighting due to its advantages of high efficiency, low energy consumption, low pollution and long life. The boom of LED greatly promotes the development of LED driver IC, which is a part of LED lighting system. Nowadays, how to design a high-performance LED driver circuit becomes the research point.In this paper, several common constant current control modes is introduced by domestic and international popular LED driver chips. It mainly includes linear regulation mode and inductor switching mode. Through the analysis of these constant current control modes, it points out that by adding the voltage feedforward control loop in the voltage type PWM mode can effectively improve the system dynamic response speed of the power supply, and also can be carried out easily. It's suitable for constant current control mode of high power LED. In addition, several common protection circuits are introduced in this paper, which include thermal shutdown, overvoltage protection, under voltage lockout, overcurrent protection and ESD protection. It can improves the reliability of the chip by adding the protection circuits.A chip with multi-protection which uses voltage feedforward control PWM mode to drive high power LED with constant current is proposed and designed in this paper. It is mainly composed of voltage regulator, bandgap reference, error amplifier, integrator, PWM comparator, protection circuit, oscillator, D flip flop, output driving circuit and power MOSFET. It is fabricated with CSMC 0.5μm mixed CMOS process. Test results show that the chip can work at power supply voltage from 4.5V to 7.5V, and it can provide a driving current of 350mA for 1W LED. Its current accuracy can reach to 0.17% and power efficiency can reach to 95%.