| Synchronous rectifier uses MOSFET instead of diode because of its low resistance on state. Due to the advantage of low rectifier loss, in recent years, synchronous rectifier circuit is also a hot topic of research. But current technology research confines to the field of small power of computers and portable devices. And technical research has not been developed yet in high power occasions. The technical problems involved: difficult and complex design of sync drive circuit, poor current-sharing in parallel tubes, low efficiency of light load and reverse current in parallel modules. Therefore, the topic research to solve these technical problems are studied, the main work includes the following aspects:1. This article discusses in detail and compares the difference of MOSFET conduction time under the three kinds of synchronous control mode, and selects the optimal way of synchronization control by quantitative calculation of rectifier losses in a period.2. In order to overcome time delay and complexity of traditional external drive in synchronous rectifier, an improved synchronous control drive circuit is proposed, basing on the direct detection of MOSFET rectifier drain-source voltage. It needs no detection device and has strong anti-interference ability and high control precision.3. The multi-tube parallel technology is applied in the large current output occasion. This article makes a research and simulation analysis of the impact on current distribution by the parameters of MOSFET and drive circuit, and provides the improvement measures to realize the current uniform distribution such as selecting the reasonable driving resistance, reducing the line inductance of source and keeping the temperature of the tube shell in balance.4. A simplified parallel model is built to analyze the cause of reverse current, and the formula of the duties of parallel modules is given. Thus, a novel digital control system is designed with the functions of preventing reverse current and achieving current sharing.5. Based on the above research and analysis, a high-power synchronous rectifier power supply prototype is developed. The novel synchronous control circuit, the technical measures to improve the multi-tube parallel module and the digital control program for current sharing is tested. Test data shows that the efficiency of power supply prototype can reach 93% and the power factor is 0.92. The accuracy of current sharing in parallel modules is within 1%. |
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