The Design Of LLC Synchronous Rectifier Circuit With Parasitic Inductance Compensation

LLC resonant converter has the advantages of low switching loss,high efficiency and high power density.And the primary side switch ZVS(Zero Voltage Switching)and secondary side rectifier ZCS(Zero Current Switching)can be realized in a wide load range.Therefore,it is widely used in communication power supply,server power supply and lighting and other high power fields.Due to the existence of packaged parasitic inductance in the MOSFET(MetalOxide Semiconductor Field-Effect Transistor),the synchronous rectifier MOS will shut off in advance,which significantly affects the efficiency of the LLC resonant converter.Therefore,it is of great significance to study the synchronous rectifier circuit for compensating parasitic inductors in LLC topology.The influence of packaged parasitic inductance on LLC resonant converter is studied in the first,and then a compensation scheme of parasitic inductance is proposed.On the basis of this scheme,a circuit combining parasitic inductance compensation and voltage detection is designed,which not only solves the problem of not generating negative voltage,but also has the advantages of high precision and fast speed.Then,a minimum turn-off/turn-on time circuit with external resistance adjustment is designed,which not only solves the problem that the minimum turn-off/turn-on time is not easy to adjust,but also has the advantage of high linearity.In addition,in order to improve the driving ability and reliability of the synchronous rectifier circuit,the driving circuit and the reliability circuit are designed.Then,the function and performance of each circuit module are simulated and verified through Cadence,and the layout design is completed.Finally,the synchronous rectifier circuit of the convection plate is tested in practice.The test results show that the functions and parameters of the synchronous rectifier circuit meet the design requirements.The designed synchronous rectifier circuit has a maximum working voltage of 24 V and a maximum compensation voltage of 35 m V.When the load capacitance is 10 n F,the rise time and fall time of the output signal are 85 ns and 30.6ns respectively,and the maximum transmission delay is 51.8ns.The minimum turn-off and turnon times can be adjusted according to the resistance value of the external resistor.In the case of no external resistor,the minimum turn-off and turn-on times are 620 ns and 311 ns,respectively.Compared with industrial devices,the drive delay time of the circuit is reduced by 15%,and it also has the function of minimum turn-on/turn-on time and inductance compensation.