Investigation Of A Primary-Controlled High-PF Controller Deliver Constant Output Current

Due to the virtue of energy-saving, eco-friendly, long-life and small-size, LED was considered the most valuable illuminant of the 21st century. With the further development of lighting technology, LED is certainly going to replace bulbs in both general lighting and special lighting. The performance of LED depends on its driver, therefore, it is necessary to take a deep research into LED driver.Aiming at the low-cost, small size and high power factor requirements of the LED driver, a controller that integrated primary-side control and single-stage power factor correction was analyzed in this dissertation, and a novel strategy of secondary diode conduction period detection is proposed. The chip is designed for flyback topology. By adopting a novel primary side control technique, the output current can be well regulated without using an opto-coupler, which effectively reduces the cost and size. Besides, the chip works in quasi-resonant mode to improve efficiency and reduce EMI.The main work of this dissertation includes:Firstly, the principle of primary-side control was analyzed and a novel strategy of secondary diode conduction period detection is proposed. Then the current and power factor under quasi-resonant mode was analyzed.Secondly, a controller G7102 that implementing the technologies discussed above was designed, and overall simulation based on CSMC’s 0.35um technology is accomplished.At last, the design methods of LED drivers implementing G7102 is proposed, and then a prototype is made and tested. Experiment results have shown that the requirements of PF>0.9 and η>85%, as well as tight output regulation, were achieved through a wide range of input voltage, indicates that the topology is useful in LED lighting.