Research And Design Of A Single-stage Flyback Based LED Controller With Active Power Factor Correction

The global market of the lighting industry is becoming much larger than before,and the market share of LED lighting is also increasing sharply.The development of LED lighting promotes the growth of LED driver.It is predicted that the revenue of the global LED chip industry will be more than 80 billion US dollars by 2020.In this thesis,some research on improving the constant accuracy of output current and the power factor and efficiency of the flyback LED driver is studied according to the demand of the market and the research hotspots of LED driver circuits at home and abroad.A high-precision LED constant current driver controller has been designed based on the single-stage APFC flyback circuit.The flyback LED driver controller in this thesis introduces closed-loop constant-current control mode which has the advantages of simple structure and no complex compensation circuit.A high-precision peak current sampling compensation circuit and an inductor demagnetization time detection circuit are designed to improve the constant current accuracy of the output current.The adaptive-on-time control circuit is designed based on the constant-on-time control mode.The input current on the grid side is theoretically sinusoidal which realizes the sinusoidal follow-up of the input voltage and improves the power factor of the system.Through detecting the lowest point of the resonance voltage,the power MOSFET achieved resonance valley on which reduces the switching loss and improves the efficiency of the system.What’s more,a variety of protection mechanisms such as output over voltage protection and short circuit protection are also designed ensure the safety of the system.The circuit and layout design and simulation are completed with CSMC 1μm 40V BCD process.Under the condition of 85-265V AC input and the 30-48V output,simulation results show that the output current can be stabilized at about 350mA and the maximum power is close to 17W.More results indicate that the output current error is less than 0.5%and the power factor of the circuit is larger than 0.98.The layout is designed and the chip will be taped out in the near future.