The Design Of An AC/DC Power Supply Control Chip With Multiple Protection Features

Power Supply, as the power source of the electric equipments, has been applied inmany fields. And with years’ rapid developments, designers can use its basic structureand principle to design different supplies to meet the needs of users. And with theadvantages of switching power supply are more and more obvious, users prefer to theswitching power supply compared to the linear power supply. So, designers put moreand more energy into the switching power supply. But, with the technology moremature, the users’ requirements are higher. So, on the basis of completing basic function,how to design a safer and more efficient power supply, has become concerned by moreand more designers.Generally speaking, this paper can be divided into three parts:The first part is about the introduction of basic principle. Firstly, this part describesthe development of power industry, and the two mainstream DC power supplies: linearpower supply and switching power supply. And these two supplies have been discussedand compared in details. Then this part puts forward the work target of designing aswitching power supply with multiple protection functions. It introduces the basicworking principle of switching power supply and its classification and the workingmode of flyback converter used in this chip. At last, this part introduces the applicationcircuit and working principle of the chip.The second part is the design and simulation of every circuit module. This partmainly introduces the protection circuits, including the line voltage detection circuit, thecurrent limit setting circuit, the sampling circuit of high voltage power MOSFET andthe current limit comparator circuit. The line voltage detection circuit can achieve inputunder-voltage protection, input over-voltage protection, output over-voltage protectionand dual slope feed-forward etc. This circuit can provide effective protections when theinput DC bus voltage is abnormal. The current limit setting circuit allows users to setthe maximum current through the power MOSFET, and realize the flexible choice ofdevices and improve the efficiency of the chip. The sampling circuit of the high voltagepower MOSFET can be used in two ways. When the chip is on the power on stage, the drain voltage can be used as high voltage current source to get the power. When the chipis at the normal working condition, this circuit can use the on-resistance of the transistor,sampling the drain voltage to compare with the other voltage from the current limitsetting circuit. While, the current limit comparator circuit is to compare the currentflowing through the power MOSFET and the maximum current setting by the currentlimit setting circuit, and adjust the working mode of the chip. At last of this part, thewhole chip is discussed.The third part is about layout. This part introduces the basic technology ofintegrated circuit manufacturing and describes the basic device layout used in this chip.The layout design of each circuit and the whole chip is given at the end of this part.