A Flyback Switch Power Converter Design

As for ac input, especially in low power applications, the flyback converter is widely used because of its high security, high reliability, and the circuit is simple, easy to design and low cost. However, there are many challenges to design a good performance of flyback converters. Such as how to achieve good EMI characteristics, how to maintain a small output voltage ripple, and how to choose parameters of various components of the converter in order to achieve low cost and high efficiency, also, reasonable compensation circuit should be designed so that the converter can have a good stability under different input voltage or different load.In this paper, the knowledge of switching power supply and analog integrated circuit design are used. The frequency jitter of oscillator is used to improve EMI characteristics. Reasonable system parameters are designed to reduce output voltage ripple, to achieve high performance and low cost of the converter. And average model of switching power supply are used to design compensation circuit to achieve good stability under different input voltage or different load. This paper presents a converter, it has a input of AC85-265V, maximum output power is30W, the typical output voltage is12V. When under heavy load, the converter works in PWM state, and in PSM state when it has a light load. It has a high efficiency under different loads.This paper focuses on analysis and design of the system parameters of the converter, the power supply module, the current detection module, the mode switching module, overload current protection module. Simulation results show that the converter has a high efficiency and stability under different input voltage, different load. It has a small output voltage ripple and good load step transient characteristics. The results of the simulation show that the rationality of the design of the converter.