Design Of Synchronous Rectifier For Flyback Converter

PSR flyback converters has been widely used in chargers, adapters and LED drivers for its low cost and simple topology and electrical isolation. In order to satisty the increasing demand of larger output current and higher efficiency standard, synchronous rectification has been introduced into the design of PSR flyback converters. The difficulty of this application is how to acquire the proper driving signal for the synchronous rectifier MOSFET. A kind of synchronous rectification is proposed in this thesis, including an IC to drive the rectifier MOSFET for DCM PSR flyback converters.Based on real-time tracking proposal suggested by MPS and linear prediction proposal suggested by Fairchild, an optimized framework is given for the target application system which is a 5V/3A DCM PSR flyback converters. To avoiding the spurious triggering of the self-driven signal, spurious trigger detection and protection module is designed in this framework. The functional modules in the framework have been designed and simulated with EDA tools. Finally, after the synchronous rectification IC having been taped out, it has been verified in the target application system, and synchronous rectification function has been achieved, system efficiency has been measured in different load conditions.According to the results of simulation and test, the system efficiency is improved by 7% comparing to the rectifier with schottkey diode in the same application system. And the spurious trigger detection and protection module is verified to contribute to the stablility and reliability of this synchronous rectification proposal. In conclusion, the test result meet the requirement of the design index, and can be applied in universal AC input DCM PSR flyback converters.