The Research And Design Of The Driving Chip Of The High-power LED

Known as the21st century "Energy Star" LED has been rapidly developing in recent years. LED light source, as a green and environmental friendly light, has advantages of long life, high luminous efficiency, performance and stability, and multiple colors. Its scope of application also continue to expand in the fields of LED display, LED traffic lights, LED indoor illumination, street lights architectural illumination, as well as automotive lamps, etc. LED is a current driving device, which luminous intensity is determined by its forward current. Its performance stability is determined by the stability of its currents. Therefore, LED needs to have a special constant current chip and the constant current chip performance has a great influence on the LED promotional value. Especially in the field of high power LED lighting, there is more rigorous demand for the constant current chip.For meeting the requirements of over-temperature protection, overvoltage protection, long life, constant current output and low power requirements of LED drive circuits, this thesis researches a LED drive circuit as following.Firstly, the basic framework of the commonly used high-power LED driver chips was analyzed, as well as the problems in terms of constant-current, over-temperature, over-voltage be discussed in this section. Based on the existing circuit, the feasibility of improving the circuit feature was explored.Secondly, constant current module is determined by using the operational amplifier and CMOS tube. The current mirror is designed by controlling CMOS tube’s drain with the operational amplifier and operating in the linear region of the CMOS tube common-source, common-gate characteristics. It can achieve constant current module dual feedback, and the power CMOS module can achieve low power consumption and constant current output tube in the linear region.Finally, an automatically adjustable current structure was presented when the circuit temperature becomes higher. It makes over-temperature protection module into automatically adjust current mode. Through the PN junction voltage changes to sense the change in temperature of the chip, the changes of the PN junction voltage to control of the reference current, and achieve the chip output current automatically adjustable. The simulation results show that the driving circuit can realize stable when input voltage is change. The protection circuit will begin to work under high chip temperature, and so the expected protection performance can be achieved.