Design Of APFC Controller With THD Optimizer Circuit Based On BCD Process

In recent years, PFC (Power Factor Correction) technique has become the focus in the field of power electronics in that it is the primary way to increase the efficiency of SMPSs (Switch Mode Power Supplies) and reduce the pollution of Power Supply Network. APFC technology is widely used for its wide input range, small size, little weight and high power factor. The paper mainly studies the design and implementation of APFC (Active Power Factor Correction) controller. It comes from the project"Theoretical research and design of key technique for AC/DC IC based on BCD process".Firstly, this paper summarizes the principle and development of PFC technology. Secondly, several basic topology circuits of APFC controller have been introduced and two typical control modes have been analyzed and compared in detail. Based on analysis, through system design, circuit design, performance simulation, a design of peak current mode control, Boost type APFC controller XD9688 which operates in transition mode is presented. Considering that the bandwidth of error amplifier in the control loop is narrow, a two-step over voltage protection circuit is designed. It enables to handle over-voltages safely and betimes either changing abrupt or resulting from load disconnection for a long time. Furthermore, to improve the power factor, a novel design can considerably minimum THD of the AC input current by increasing the switch-on time near the zero-crossings of the line voltage.XD9688 is designed based on 0.6μm BCD process and verified by HSPICE program. According to the simulation results, the function and performance of XD9688 can realize power factor correction in transition mode by controlling the Boost pre-regulator.