Design And Implementation Of High Voltage Off-line AC/DC Converter

With the rapid development of portable devices,switching power supply has become the most important application field of power electronics.Monolithic switching power supply has the advantages of monolithic integration,simplest peripheral circuit,optimal performance parameters,and being a power-free transformer switching power supply.At present,the low-power switching power supply without power frequency transformer on the market still mainly adopts the special integrated circuit of PWM and PFM modulation mode.They use power frequency transformer to realize voltage conversion and power grid isolation,thus saving the bulky and large loss power frequency transformer.This paper studies and designs AC / DC switching power supply with high voltage off-line,PWM control and no power frequency transformer.It can be widely used in various general switching power supply and standby power supply,such as LED,microwave oven,bread machine and other electrical equipment.In this paper,all functions of PWM control system and high-voltage MOSFET are integrated into a single chip.Its advantages are simple circuit structure,low cost,stable performance,low power consumption,self-protection and perfection.It is applicable to the requirements of modern society for energy saving and environmental protection of switching power supply.This paper mainly introduces the topological structure of optical coupling feedback and the control mode of current and voltage.Through theoretical research,simulation analysis and performance comparison,it focuses on the four modules of the designed high-voltage charging circuit,feedback loop circuit,reference circuit and oscillator circuit.It analyzes the different working conditions of the system in the working modes of DCM and CCM in detail,and carries out system modeling and loop comparison The small signal analysis of the circuit makes the working mode of the chip clearer and effectively guides the simulation of the whole circuit.After the overall circuit simulation reaches the designed target,the layout of the whole chip is also designed,from the overall chip layout to the layout of small modules,and finally the top-level wiring,and a comprehensive analysis of the layout design process for mismatch,noise,parasitic considerations and solutions.The correctness of chip layout design is ensured through various verifications.After the chip packaging,the performance of the chip is tested and analyzed to verify whether the chip meets the expected design targets.From the performance test and application test,the working condition of the chip in the extreme environment and the working condition of welding to the actual product are analyzed in detail.The chip has been tested for a long time to verify the stability of the chip.In this paper,through the whole system modeling analysis,various tolerance sub module circuit performance analysis,overall circuit performance simulation,combined with process parameters and practical experience,mask design,chip packaging test,product aging test and application test verify that the designed chip can work normally,and achieve the expected target of the design.