The Design Of Digital Multi-mode Control Algorithm For High-frequency Flyback Quasi-resonant Converter

With the continuous development and progress of integrated circuits,flyback quasi-resonant converters have the advantages of low cost,small size,high power density and so on,and can achieve zero current switching(Zero Current Switching,ZCS)and quasi-zero voltage conduction(Quasi-Zero Voltage Switching,Quasi-ZVS).So it has broad development prospects.However,at present,the control mode of the flyback quasi-resonant converter is still relatively simple,which limits the improvement of the average efficiency in the full load range.In response to these problems,a digital multi-mode control algorithm for high-frequency flyback quasiresonant converter was designed by this thesis.Firstly,a DCM(discontinuous conduction mode)loss model was established,the optimal operating point of the DCM for the flyback quasi-resonant converter was determined,and a dynamic loss model was established based on different control methods,iteratively calculate multiple switching cycles to calculate the precise loss of different control methods under different load conditions.On this basis,a digital multi-mode control algorithm for the flyback quasi-resonant converter is designed.Using a new CCM(Continuous Conduction Mode)+ DCM combinated ON-OFF control mode and DCM+ "Tun off " combinated ON-OFF control mode improves the conversion efficiency of the converter in the full load range.And the Burst control mode is designed to salve the problem of audio noise in the light load range.After that,The circuit simulation model of the flyback quasi-resonant converter was built in Simulink of MATLAB,and the multi-mode control algorithm was simulated and verified by the joint simulation platform of MATLAB and Modelsim.Finally,a set of flyback quasi-resonant converter test prototypes were built,and the effectiveness of the loss model and multi-mode control algorithm was verified by board-level measurement.It can be seen from the simulation and actual measurement results that the calculation result of the loss model established in this paper is consistent with the overall trend of the actual measurement results.In the prototype 12 V / 4A flyback quasi-resonant converter prototype,stable control and fast switching of the digital multi-mode control algorithm are realized,light load efficiency increased from 81.1% to 85%,average efficiency increased from 86% to 88.96%,effectively improving the overall output efficiency of the converter.