Design Of A High-Power,Off-line AC-DC Converter XD0798 With Accurate Primary-side Regulation

With the rapid development of power electronic technology, switching power supply technology has been more and more widely used, and has become an indispensable part in many fields. In switching power supply field, the Fly-back switching power supply has the characteristics of simple design, small size and high efficiency, which is widely used in the electronic equipment and system of small power. Under the trend of miniaturization and low cost of electronic equipment, the challenge of the Fly-back switching power supply is increasing, such as miniaturization, high reliability, high design flexibility, low cost and so on. These all drive the continuous innovation of Fly-back switching power supply.This paper is based on research project-“Design of A High-Power AC-DC Converter with Accurate Primary-Side Regulation”, which supplied by the Key Lab of High Speed Circuit Design and EMC Ministry of Education. Then, a high-power off-line AC-DC converter XD0798 with accurate PSR is designed.XD0798 is used in the fly-back switching power supply, which belongs to the off-line structure and use the transformer to achieve the electrical insulation between the input and output. XD0798 uses the Primary-Side Regulation technology, eliminating the need for the optocoupler and related circuits, and a 700 V high voltage MOSFET and controller are integrated in a package, and the auxiliary winding can be also used to feedback the output voltage and the input voltage, the 132 k Hz switching frequency using decreasing the volume of the transformer. In addition, XD0798 has comprehensive protection measures, to ensure that the chip and related peripheral components can be protected in a variety of fault conditions, and added a wealth of integrated functions, such as programmable current limited point, programmable auto-restart delay time, fast reset, remote on/off and so on, so that XD0798 can be flexibly designed according to specific application requirements. These features greatly reduce system volume and cost, and simplify the design of switching power supply, and improve the reliability of the system.XD0798 adopts the enhanced peak current mode PWM control scheme, which has the characteristics of multi-mode operation, and high-power PSR switching power supply in CCM can be designed the power supplies of which can up to 50 W. The control scheme uses the output signal voltage of the error amplifier to set the peak current and the switching frequency, to maintain the output voltage stability, and adds Safe Operating Area(SOA) Protection to eliminate the instability of the CCM mode with Primary-Side Regulation.In this paper, the development of switching power supply is summarized in the introduction, and then the basic theory of AC-DC converter is introduced. Its working mode and modulation mode are deduced in detail. After the system level functional design of XD0798, this paper analyzes the selection of the peripheral components in the typical Fly-back topology. Then, this paper introduces the design principle of the key sub module of XD0798, and gives the simulation results. At the end of this paper, the electrical properties simulation results of XD0798 with typical Fly-back type topology are presented.The design of XD0798 is based on 1μm 6V-700 V BCD process,and the Design and Simulation of this chip’s circuits is completed by Cadence and Hspice S, simulation results presenting that all the electrical characteristics of this chip have reached the design requirements, and have good performance in typical applications.