Compact Quasi-reasonant Flyback Synchronous Rectifier Converter and Control Method

Traditional flyback converters has been widely used because of their simple structure. However, the development trend of high efficiency and miniaturization still needs to be improved. To solve this problem, a compact quasi-resonant flyback converter with synchronous rectification and its control method are proposed in this paper. Based on the traditional flyback converter, synchronous rectifier technology and quasi-resonant soft switching technology are added to the converter, and integrated isolation communication scheme is adopted. In this scheme, the volume is reduced and the primary power tensistor and secondary synchronous rectifier transistor are not be switched on simultaneously. The fully integrated control of the primary and secondary side can ensure that the primary power transistor will not be switched on until the secondary synchronous rectifier transitor is switched off. Consequently, it is not necessary to set the maximum switch-on time of the secondary synchronous rectifier transistor, which can maximize its effect and further improve the working efficiency of the flyback converter. Under the condition that the input voltage of the primary side is unchanged, the converter can be divided into three operating modes according to the load from light to heavy: deep discontinuous conduction mode (DDCM), discontinuous conduction mode (DCM) and continuous conduction mode (CCM). By detecting the peak of the secondary winding (corresponding to the valley of the drain-source voltage of the primary power transistor) and the feedback voltage of the reaction load, the secondary controller sends the request signal to the primary controller to realize the quasi-resonant soft switching operation and improve the efficiency. In this paper, simulation results on Candence platform based on smic 0.18μm BCD process show that the proposed converter and control method can effectively improve the efficiency, and the peak efficiency can reach 93.20%.