Study On Digital Constant Current Control Strategy For PSR Flyback Converter

In recent years,the Fyback converter is popular in the design of driver circuit which requires high quality constant current input characteristics such as LED because of its flexible transformer inductance,synchronization of step-up and step-down voltage,and electrical isolation.In the process of highly intelligent and integrated development of electronic products,digital power supply is more in line with the design requirements of modern products because of its flexible programmability and simpler circuit design.Therefore,the digitization of switching power supply has gradually become an important branch of research in the field of power electronics.In this paper,a digital control strategy is presented based on the main circuit topology of the Flyback converter,and a digital control constant current drive circuit with original edge feedback is designed.The main work of this paper is as follows:(1)On the basis of analyzing the working principle of the Flyback converter,the working characteristics of the key components of the converter under CCM/DCM working mode are discussed at first,then the power level circuit design of the original edge feedback Flyback converter is carried out.Finally,the rationality and correctness of the power level circuit design of DCM are verified by MATLAB/Simulink software.(2)The control function for achieving constant current is derived,and the principle of soft-start and the controlling flow of constant current output are expatiated.Simultaneously,the internal structure of the proposed digital controller is constructed.The soft start/constant current switching module is responsible for suppressing surge current of the Flyback converter and brings the output current to enter constant state smoothly.Based on the principle of constant current control,the demagnetization time sampling module and counter modulation module are designed to work in coordination with the control signal generation module,which provides the automatically switching signal.(3)The code of each module is written by Verilog HDL in Quartus II,the logic function of each module is validated in Model Sim,and the HDL module of the digital controller is formed at the same time.The simulation model of the original feedback AC-DC flyback digital control constant current LED drive circuit is built by Simulink,and the joint simulation experimental platform is built by Model Sim and Simulink,and the designer is verified by Multi-software debugging.Feasibility of the case.The results show that the ratio of demagnetization time to switching period of the digital controller is constant when the drive circuit is running in constant current state.The output constant current 2A and ripple are about 2.3%,which meet the design criteria.The results show that the digital controller can keep the ratio of demagnetization time to switch period constant when the system is running in constant current state.The output constant current 2A and ripple are about 2.3%.The drive circuit can work stably and reliably,and the constant current precision can also meet the application requirements.