Research And Design Of High Power Factor Driver With Variation On Color Temperature

With decades of development,LED lighting has become a mature and vigorous technique due to its low power consumption,long life and environmental friendliness.More requirement have been put forward such as low cost,high power factor and color variation.For example,power factors demanded to be above 0.7 for residential and above 0.9 for commercial according to Energy Star.Color temperature of LED lighting has been gradually concerned in recent years because appropriate color temperature greatly improves user experience.This thesis proposes a LED driver chip which achieves high power factor and provides variable color temperatures.A cool light LED string and a warm light LED string are applied,and each LED string is divide into four parts.The proposed chip contains four current channels in order to control the four parts of LED string.The conduction of each part of LED is controlled by the chip.The output current is adjusted according to the input voltage to achieve high power factor.If the wall switch is closed and turned on in a short time,color of LED lighting changes to the next state because of an on-chip ring counter.An off-chip capacitor supplies for the counter to store the color temperature status during the power cut,so that the color temperature can be easily changed in sequence by manually switching the power switch.This system has the advantages of small size,low cost and high reliability because no magnetic components is used.The IC is designed by using lum 700V CMOS process.The simulation results show the proposed driver has a power factor of 97.80%and an efficiency of 90.22%.The color temperature switching function is also verified by the simulation.