| In recent years, switch mode power supply has been widely applied because of its high efficiency and low cost. However, as the traditional switch mode power supply has a low power factor, a distortion is introduced in the input current with a high harmonic component, leading to a harmonic pollution to the electricity network and a decrease in the power efficiency. By adopting active power factor correction (APFC), the power factor can be improved to nearly 1, not only getting rid of the harmonic pollution but also improving the efficiency of the switch mode power supply. Therefore, APFC plays a very important role for the development of electronic industry.Firstly, the concept of power factor is proposed in the paper, and the principle of APFC is also described in detail. Next, based on the principle above, a boost APFC controller is designed. Both the voltage and the current loops are introduced in the design, so that the input current can vary with the input voltage, which makes a high power factor and improves the power efficiency. Furthermore, the output voltage can be stabilized by the feedback loop so as to make the input of switch converter pre-stable.The controller designed in the paper is based on 0.6μm 30V BCD process, and works on the critical-conduction mode by peak-current mode controlling, so it has the characteristics of simple structure, small size and high power factor. The simulation results by HSPICE show that the chip realizes the function of PFC perfectly, and all the simulation data meet the specification well. |
