Design and Implementation of a Single-Stage Flyback Converter with High Power Factor and High Efficiency for LED Drivers

• Main Authors: Chun-Wei Huang, 黃俊偉
• Other Authors: Shun-chung Wang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/89273859736188173029

碩士 === 龍華科技大學 === 電機工程系碩士班 === 100 === The electrical consumption of global lighting is over twenty percent of the total annual energy consumption. The light emitting diodes (LEDs) have the advantages of energy saving, high luminous efficiency, small size, long life, and fast response etc. In response to the coming of the LED lighting era, an isolated single-stage flyback converter with optimization efficiency control for LED drivers is presented in this thesis. The LED driver consists of a flyback converter with power factor correction (PFC) and a constant-current drive circuit with functionalities of dimming control and efficiency optimization. The single-stage topology can obtain high power factor benefit in low-cost outlay, the lineal dimming mechanism cooperating with the constant-current control circuit complete the LED dimming control. In order to reduce the power losses of the LED strings, a dynamic voltage regulation method (DVRM) is proposed to minimize the LED supply voltage by means of the sensing of the LED forward voltage drop. The dynamic voltage regulation technique can decrease the current of the lineal constant-current circuit and enhance the drive system efficiency further. The proposed voltage optimization control features the following characteristics: 1. The flyback converter can dynamically regulate the optimum voltage supplied to the LED string according to the variation of the LED string forward drop induced by the operating temperature change. 2. Without additional feedback loop and phase compensator design, the proposed method can automatically adjust the supply voltage of the LED string in stable condition. 3. The proposed DVRM can memorize the best LED supply voltages under different operating conditions, this helps the LED getting better brightness and higher drive efficiency. A 30W white LED driver has been implemented. The experimental results verify the effectiveness and performance of the proposed method.