Research And Rmprovement On Crossover Characteristics Of Flyback Converter

With the continuous advancement of technology,modules in electronic systems often require different power supply voltages.If each module is powered by a power supply alone,it will increase the volume and unnecessary costs.As a result,multiple output power supplies came into being.You only need to add windings to the secondary of the transformer to achieve multiple output.However,this implementation method often only samples and feedbacks the output voltage of the main circuit,while the output voltage of the auxiliary circuit will follow its own The load and the main circuit load change,causing the cross regulation rate.Therefore,higher requirements are put forward for the cross regulation rate of the multi-output flyback converter.The main research contents of this paper are as follows:First,establish a simplified model of the multi-winding transformer,and use this model to establish a simplified circuit model of the three-output flyback converter.In continuous mode and discontinuous mode,observe the working mode of each time period of the circuit model in one cycle and perform quantitative calculations,and analyze the process of surge and sag caused by the output voltage of the auxiliary circuit.In this way,the cross regulation rate is derived.Through the actual measurement of the voltage data of the multiple output power supplies,the offset law of the cross regulation rate is summarized.At the same time,the cross regulation rate is mainly affected by the leakage inductance of the transformer and the voltage drop of the rectifier diode.Several methods to improve the crossover characteristics are introduced.Secondly,according to the influencing factors of the crossover characteristic,a control method based on the self-balance of synchronous rectification current is proposed.This control method not only fundamentally eliminates the influence of the voltage drop of the rectifier diode on the crossover characteristics,but also can use the synchronous rectifier to realize the transfer of the remaining power in the light-load circuit,restrain the voltage surge of the light-load circuit,and prevent the voltage sag of the heavy-load circuit.In order to obtain the driving signal of the synchronous rectifier,the topology of the basic three-output flyback converter is improved,and the windings that do not participate in the feedback are connected in series with the main winding,then the zero-crossing point of the leakage current of the main output winding is the secondary The time node where the current of the stage is fully distributed,as the switching signal of the synchronous rectifier,can realize the current self-balance between the output windings,thereby improving the cross regulation rate.Finally,use PSIM software to build a simulation circuit for the three-output flyback converter,and observe the leakage current waveforms in the three-output windings.The light-load output winding will always transfer the remaining power to the heavy-duty one through the synchronous rectifier..At the same time,the hardware circuit is built and the power-on test is performed to verify the correctness and feasibility of the control method,which can effectively improve the cross-adjustment rate.