Based On PFM Primary Side Feedback Synchronous Rectifier AC/DC Controller

With the application of switching power is getting more and more popularizing,So the performance of the switching power supply is demanded rigorous.We want to make witching power supply just like this :smaller size,higher conversion efficiency,lower standby power consumption.The primary side feedback uses the auxiliary winding to sample the output voltage in order to isolate the output voltage.The pulse frequency Modulation regulates the operating frequency of the power MOSFET according to the output voltage so that the system has higher conversion efficiency and lower standby power consumption.The study on the switching power supply of this paper is based on the PFM regulation mode,and the output load is divided into several different sections.The controller regulates the output voltage and current in the primary side by piece-wise Pulse Frequency Modulation in discontinuous conduction mode.The system operating frequency reduces linearly from heavy load to light load in each interval of the piece-wise Pulse Frequency Modulation.Dynamic response eliminates the need of loop compensation circuitry while maintaining stability.The change of the output voltage is detected when the system is in the standby mode,and the dynamic response is used to maintain the stability of the output voltage.In the internal structure of the chip,the situation of the load will be divided into a number of different models in constant voltage mode(CV)in order to regulate the operating frequency.The power MOSFET switching on time reference voltage will be set according to the different output load,changing the turn-on time of the power MOSFET by changing the output load.Line compensation can weaken the influence of power MOSFET delay off.Constant current(CC)module limits the maximum output current.In order to improve the reliability of the system,the maximum switch on time limit electricity to prevent circuit from burning out because the power is too large.Short circuit protection(SCP)and over-voltage protection(OVP)protect the system from abnormal working state.At the same time,the periodic variation of the reference voltage of the frequency jitter can improve the electromagnetic interference caused by the pulse frequency regulation.