Ac-dc Flyback Converter Secondary Side Synchronous Rectifier Control Chip Design

With the rapid development of the global electronics market, the demand of power management chip is continuously growing. With energy conservation, "green" power and electronic equipment must comply with the mandatory energy efficiency standards and multi-function portable device miniaturization trend. This requires higher power conversion efficiency, lower standby power consumption, good power factor correction, higher power density and reliability with low cost. Power management chips exhibit a good variety of topologies, the flyback converter is a commonly used topology in AC-DC converter. It has the advantages of fewer components and universal AC voltage range. For the power technology trends, it is quite important to improve the efficiency of the power supply (including efficiency at light-load), reduce standby power consumption and improve power factor to meet the emerging norms of energy efficiency standards, which are now advocated by the green switching power supply. In addition, miniaturization is also important to meet growing consumer demand for thin products. The development trend of power supply module is low voltage and high current. Power rectifier switching losses and voltage drop losses are major losses in AC/DC convertor. In the traditional secondary rectification circuit, Schottky diode is applied. For low-voltage high-current application, loss on the diode has become a bottleneck. In order to improve efficiency, the use of synchronous rectification has become an inevitable means. Synchronous rectification in the switching mode power supply is one of new technologies in recent years, thanks to the development of modern technology to make the power MOSFET on-resistance smaller and smaller. This makes the power loss significantly decreased. In conventional flyback synchronous rectification in the secondary side, the switch signal depends on the primary side of the switching signal, so the system is quite complex. In this research, secondary synchronous rectification is based on independent secondary side synchronous rectifier technology, enabling the chip to do the entire control in a simple and practical way, and the chip can be applied to a variety of switching power supply topology, greatly increasing the economic benefits. In this thesis, the design of a AC-DC flyback converter secondary side synchronous rectification control chip is described, using 1.2um high voltage BCD process. The system output voltage is 5V, with 1A maximum output current. The input voltage range is 85Vac to 265Vac. About 1-5% efficiency increase can be achieved compared with traditional rectifier diode.