The Design Of An AC/DC Converter With Low Standby Power Consumption Based On Exponent Compensation

Serious environment problems such as haze drive the rapid development of green energy and environmental protection. With the development of electronics industry, the need for small power off-line AC/DC power supplies has been growing dramatically due to the users of portable electronic products increasing sharply. Therefore, it is an important development direction to continuously expand a lower cost and more efficient small power AC/DC power supplyin line with the national energy saving and emission reduction requirements.The main work of this thesis is to design a flyback converter with low standby power consumption based on exponent compensation, mainly focus on the analysis and design of exponent compensation circuit. This paper first outlines the circuit structure and basic working principle of AC/DC converter, and gives the design parametersand analysis of the sources of power dissipation of primary side flyback converter. Secondly, this paper has carried on the summary analysis to standby power consumption reducing technique. The traditional primary side flyback converter usually adopts frequency conversion to reduce standby power consumption. But the system frequency can not be unrestricted reduced, since the system has the minimum switch frequency, which limits the further reduction of the standby power consumption. In order to further reduce the system standby power consumption in the lowest switch frequency, this paper presents a flyback converter based on the two-stage exponent compensation circuit. The preceding-stage exponent compensation circuit is achieved by RC integral circuit, and the generated waveform have a large slope at the beginning to close the power switch fastly, then the minimum conduction time of the system is no longer limited by the LEB circuit under no-load or light load output condition, finally obtaining a smaller conduction time. The second-stage exponent compensation circuit is used to mitigate the rising trend of exponent waveform, making the exponent circuit unable influence the normal operation state of the system under heavy load output condition. The principle of the whole frame structure and index compensation circuit are given, and using SIMetrix/SIMPLIS software to carry on the modeling and verification of the system and exponent compensation circuit.Based on the principle analysis of the improved circuit and design of the key sub-block circuits, the whole circuit simulation are done by Cadence tool. The proposed control IC has been fabricated in TSMC0.35μm 5V/600V CMOS/LDMOS process, and the chip layout area is 1580× 1350μm2. The prototype circuit is tested when AC input voltage is within the range of 90V-260V. The test results indicate that output voltage range is 5 V and the constant voltage precision within ±4%, the average efficiency of the system is 86.6%, the system standby power is only 29mW at 220V input voltage, meeting the standby power requirements of the latest energy star on the AC/DC converter.