Predictive Shutoff Control Circuit Design For The CCM Synchronous Rectifier Of Flyback Switching Power Supply

With the development of electronic technology in recent years,the working voltage of circuit is becoming lower and the working current is becoming higher.Adopting metal oxide semiconductor field effect transistor,which has lower conduction resistance,in place of the rectifier diode to reduce the loss of rectifier has become mainstream.Among the applications of the low voltage and high current,synchronous rectifier in continuous conduction mode is more urgent,and it is also the hot spot of current research.This thesis will focus on research and design of continuous conduction mode synchronous rectification control circuit,which has the function of predictive shutoff MOSFET.Firstly,this thesis analyzes present development situation and main design method of synchronous rectification in flyback switching power supply.Considering switching process of the rectifier MOSFET and problem of traditional synchronous rectification circuit,a king of predictive control technology is designed,which can improve dead zone time management and deal variable frequency condition.And the efficiency of flyback switch power conversion is promoted.Then the core circuit model of predictive shutoff control circuit is established on the basis of the principle of volt-second balance,and the model is simulated.Predictive control scheme is studied under the condition of fixed frequency and variable frequency,Compatible with traditional discontinuous conduction mode by designing anti-resonant circuit.Correspondingly,the specific implementation circuit is design and the circuit simulation is verified.Finally,the thesis also design the layout of the predictive control circuit and complete post-simulation,which verifies the effectiveness of the designed circuit.The simulation results show:the predictive control circuit can achieve forecast shutoff rectification in a wide range of output voltage and high power.Output voltage range is from 5V to 28V,and power range is from 40W to 100W;Switching frequency range is from 65kHz to 140kHz;Predictive shutoff rectifier circuit can automatically track the dead zone time;Synchronous rectification conduction time is controlled based on the principle of volt-second balance,lower to 500ns,and synchronous rectification shutoff threshold has nothing to do with RDS(on)of MOSFET;The number of protection cycles is 15 switching cycles under abnormal conditions,during which the synchronous rectification is disabled;Predictive shutoff rectifier circuit can work compatible with discontinuous conduction mode,meeting design specification.