High-Efficiency,High-Speed Synchronous Rectification Driver Technology Research And Chip Design On The Secondary Side

Integrated circuits continue to develop rapidly under the impetus of Moore's Law,which requires the external voltage of the chip to be reduced and the size to be continuously reduced.Switching power supplies use diodes for rectification,and the forward voltage drop is needed to make it turn on.This voltage drop increases the rectification loss of the system.When the system works under high current and low voltage conditions,its efficiency will be greatly reduced.Therefore,it is necessary to reduce the forward voltage drop.At present,the most effective method is to use power MOSFETs instead of diodes.The low on-resistance characteristics of MOSFETs can reduce the rectification loss of the circuit,and the system efficiency can be improved.This technology is called synchronous rectification(SR)technology.The MOSFET is a bidirectional active device,and the diode is a unidirectional passive device.Therefore,the synchronous rectification technology needs to set a suitable driver and a large current drive capability.To control the normal operation of the power MOSFET.The thesis designs a synchronous rectification drive chip,which is suitable for flyback converter(Flyback Converter),the chip performs real-time negative voltage sampling on the drain-source voltage of the SR tube Compared with similar functional chips,this paper improves the synchronous rectification driver.Mechanism,increase the SR tube gate voltage pull-down early control,by reducing the SR tube gate voltage to increase the on-resistance,extend the SR tube on-time,so the corresponding body diode freewheeling time is eliminated,the efficiency of synchronous rectification is improved.This function is also suitable for light load conditions to prevent the SR tube from turning off prematurely.In addition,in Continuous Conduction Mode(CCM),the gate voltage has been reduced when the SR tube is turned off,so it can be turned off quickly.Turn off the SR tube to slow down the pass-through of the primary and secondary side of the flyback converter in CCM mode,and improve the efficiency of synchronous rectification.At the same time,a SR Slew-rate Detection scheme was designed.By detecting the change in the slope of the drain terminal voltage of the SR tube,the resonance and parasitic inductance of the drain terminal voltage in the discontinuous conduction mode(DCM)were shielded.The Vds disturbance caused by the capacitor ensures the reliability of the synchronous rectification drive circuit.In addition,the voltage slope can be adjusted or enabled through an external resistor to meet the needs of different circuit applications.The thesis first introduces the working principle of synchronous rectification technology,analyzes the difference between SR tube loss and diode,and considers the parameters when selecting SR,compares and introduces the advantages and disadvantages of high and low side connection,and introduce the mainstream light-load detection mode of driver.Then,the architecture of the synchronous rectification driver chip designed in this thesis.The circuit is based on the BCD process model with a minimum line width of 0.35?m.The circuit design,simulation and layout drawing are completed,and similar chips designed in the laboratory are taped out and mounted in the Flyback converter system for testing.The comparison of the two chips proves that the performance of the chip designed in this thesis has been improved,and the understanding of synchronous rectification technology has been deepened,and the problems encountered in the test process have been analyzed.