Research Of Multiple Output Flyback Converter Based On Synchronous Rectification

The way of traditional diode rectifier，in the case of low-voltage and high-currentoutput,diode conduction voltage drop has become an important factor affecting the powerefficiency. In the structure of the multi-output，each channel requires a single diode to rectify.Therefore，the rectifier loss exponentially increase. The conduction voltage drop of outputdiode has become a bottleneck of improving efficiency.Synchronous rectification technique is to use a low-resistance and high-input impedanceMOSFET instead of a diode rectifier. In the case of low-voltage and high-current output cansignificantly reduce rectifier losses， improve the efficiency of the power supply. Ifsynchronous rectification technology combined with appropriate circuit topology, it can getlow-cost and high efficiency multi-output power. Flyback converter has the advantages ofsimple circuit structure，electrical isolation，easy to have multiple output and having a smallcross regulation. Therefore，it is widely used in multi-channel output of high-voltage andlower-power occasions，especially in power switching supply of5-150W.So,this articleconsider flyback as an example to introduce multi-output synchronous rectificationtechnology.The main content of this paper is synchronous rectification technology, multi-outputtechniques and their application. Firstly，we describe the scope of the principle and itsapplication of synchronous rectification. Analysis of the synchronous rectifier flybackconverter who works under different operating modes，dynamic process，as well as the transferof electromagnetic energy. In the same time，describe the process as well as the conditions ofthe conversion between various modes. Then，have a detailed analysis for the drive and lossmodel of the single output synchronous rectifier flyback converter. It introduces the multipleoutput synchronous rectification and the concept and its causes of cross regulation. At the endof the article describes in detail how to improve cross regulation of multiple output from therising edge of the secondary current waveform，the clamping voltage，weighted control， synchronous rectification and transformer.In order to validate the theory，apply synchronous rectification technology to design anflyback switch power whose input voltage is AC85-265V，two output are5V，5A and12V，0.5A respectively. Theoretical analysis and experimental verify synchronous rectificationhaving significantly improved to the efficiency and cross regulation of multiple output.Therefore synchronous rectification has a great practical value in the lower-voltage andhigh-current output of multiple power.