Research And Implementation Of A High Reliability Synchronous Rectification Control Technology

The improvement of efficiency is a key research issue in the switching power supply.In recent years,the switching power supply gradually develops in the direction of low voltage and high current.The main loss of the switching power supply comes from the rectification loss.The power MOSFET with low on-state resistance and low forward voltage drop is used instead of the traditional Schottky diode or fast recovery diode for rectifier device,thus the loss of rectification can be greatly reduced,and the efficiency of the switching power supply can be improved.This paper designs a synchronous rectification control chip that can be applied to isolated switching power supply such as flyback,LLC resonance and other circuit topologies.The peripheral application circuit is simple in structure and requires less components.It’s more complex to drive the MOSFET for the difference between the operation principle of MOSFET and diode.The bidirectional conduction characteristic of MOSFET makes it necessary to apply the appropriate drive timing to the gate during the operation process,and has enough current drive capability.This paper uses a voltage self-driven method to drive the synchronous rectifier device(SR).Improve the efficiency of its application topology circuit by reasonable design the turning on or shutdown detection point and the internal sub-module circuits.the control chip can be used in both CCM and DCM operating modes.the open detection point is-150mV,the DCM shutdown detection point is-5mV,and the CCM mode uses the capacitive coupling to fast shutdown the SR.Based on the same type of chip,the anti-counterfeiting on/off judgment mechanism is added in this paper.The minimum on-time and minimum off-time circuits are used to blank the false triggering signals caused by Vds voltage disturbances for Parasitic inductance,capacitance,and transformer leakage inductance to ensure that the system can work efficiently and reliably.The blanking time can be adjusted by external resistors to meet the requirements of different application topology circuits.Further,the minimum on-time TON is compared with the on-time of the SR to judge whether the system enters a light load.In the light load mode,the SR is off and the body diode is turned on to optimize the efficiency of the topology circuit under light load.This article first introduced the working principle of the synchronous rectifier,its loss analysis and key technical parameters,and then compared the advantages and disadvantages of the several synchronous drive rectification methods,the application of common topology circuits.Finally,the working principle and system architecture analysis of the control chip designed in this paper,the key technical problems involved in the design of the synchronous rectifier circuit,the circuit design and simulation analysis of the internal sub-module are introduced.This paper based on the 0.5μm BCD process model to complete the sub-module circuit design simulation and chip simulation verification.The tapeout results show that the control chip achieves the desired design goals.