Design Of A High Performance Off-line 700V AC-DC Converter

In recent years,the rapid development and rapid change of electronic information industry has been dominating the civilization and progress of human society.With the increasingly stringent requirements for parameters such as input and output range,volume,power consumption and output accuracy for devices related to smart home,industrial electronics and automotive electronics,power management chips,which provide power for devices,have been undergoing technical innovation time and again to meet many working requirements.At present,among the multi-category power supply chips,AC-DC power converters play an important role as the main product to achieve AC-DC conversion.In this paper,we study the system knowledge theory of AC-DC converter and design a low cost and high performance low power offline AC-DC converter by combining with the application requirements.The converter can provide an output voltage of not less than 2V and a load current of not more than 80mA.An integrated high-voltage BCD(UHVBCD)process is used to build in a 700 V high-voltage MOSFET,while a combined JFET tube is used to design a high-voltage start-up circuit to provide a stable operating voltage for the internal modules of the system.This structure improves the system withstand capability while achieving a high degree of chip integration,reducing the number of peripheral devices and making the peripheral circuit structure simpler to build.In order to ensure the load regulation rate and energy conversion efficiency of the chip,the loop adopts multi-mode control technology and designs a frequency regulation function related to the load state,so that the system switching state is automatically adjusted according to the load change.In the design of reducing power consumption,the system adopts a bandgap reference structure without op-amp and a combined over-temperature protection structure to reduce the consumption of quiescent current;the design of an under voltage latching structure without comparator to avoid the loss of energy caused by the early operation of some modules during system startup;the design of internal peak detection threshold can be automatically adjusted with the actual load condition to limit the quiescent operating current of the system and effectively reduce the standby power consumption under no-load condition.The design of the internal peak detection threshold can be automatically adjusted with the actual load to limit the system quiescent operating current,effectively reducing the standby power consumption under no-load conditions.The overall circuit design is based on the 0.8um?700V?BCD process.The simulation results show that the converter can work stably under different input voltages and different load conditions under the operating environment of-40-135?,and all the performance parameters meet the design specifications.