Research On Synchronous Rectification And Multi-output Flyback Switching Power Supply

With the rapid development of electronic information technology,miniaturized and integrated electronic devices emerge in endlessly,and the power supply requirements are becoming more and more low-voltage and high-current.In addition,these devices often integrate multiple electronic modules,and the power supply requirements of each module are not all the same,this requires the power supply equipment not only to meet the requirements of low voltage and high current,but also to achieve output of multiple voltage levels.Flyback converter has many advantages such as simple structure,low cost and large input and output dynamic range.It is currently the most widely used switching power supply topology.Due to the existence of the isolation transformer,it can not only achieve electrical isolation between input and output,but also easily achieve multiple outputs.However,only the output winding is added,and the feedback control only strictly regulates the main output path,and other output paths cannot be effectively adjusted,which leads to the emergence of the cross-regulation rate problem.Moreover,in the scene of low voltage and high current,the traditional diode rectifier conduction voltage drop is large,and the rectification loss becomes the key factor restricting the efficiency improvement.This article aims at the problems of low diode rectification efficiency and cross regulation rate in the multi-output flyback switching power supply,researches on synchronous rectification technology and multiple output technology and realizes their comprehensive application.First,the synchronous rectification flyback converter is studied,the basic principles and working process of the flyback converter and synchronous rectification are introduced,and the rectification loss during the synchronous rectification of the flyback converter is analyzed.Introduce in detail the technical points of different synchronous rectification drive methods and their respective advantages and disadvantages.Then research the multi-output flyback converter,put forward the concept of multi-output cross-regulation,build a two-output flyback converter model,model and analyze the causes of cross-regulation,and put forward the influence factors of cross-regulation Three methods to improve the cross-regulation rate,including transformer optimization,RCD clamping circuit and weighted voltage feedback regulation,and the design points are discussed.In order to verify the theoretical research,a prototype of a 3.3V4.5A/5V3A/12V1 A three-output flyback switching power supply was made.The design of the main control circuit,synchronous rectifier circuit,RCD clamp circuit,weighted voltage feedback loop and planar transformer in the prototype production are explained in detail.Finally,the performance of the experimental prototype was tested,and compared with the prototype of the diode rectification method,the weighted voltage weight was changed to compare the cross-regulation rate of each output under different weights.The experimental results show that the output performance of the prototype is good,and the full-load efficiency is increased by 7.6% compared with the diode rectifier prototype.Also,the synchronous rectification technology greatly improves the output voltage accuracy of the prototype and improves the multi-output cross-regulation characteristics.