Design Of A Primary Side Regulation Flyback Conventer

With the development of science and technology,the Internet of Things era is getting closer and closer to us,and all kinds of electronic products are in our lives.All electronic products are inextricably linked to the stable and continuous power supply,so power management has likewise become an important research direction for various electronic product manufacturers.In all power management products,the flyback converter has the potential to multiple output,and can both constant current output and constant voltage output,and it can both step up and step down during constant voltage output.In addition,there are multiple input and output channels.Electrical isolation between the outputs can be achieved.Therefore,in the field of low-power AC-DCs,such as adapters for laptops,chargers,and chargers for smart phones,LED drivers have been extensively used.In this context,this thesis presents a primary side regulation flyback converter.First,the working principle and common control methods of the primary side regulation flyback converter are introduced.In order to improve the efficiency,under light load,this paper adopts PWM and PFM dual-mode modulation.Second,the loop of the primary side regulation flyback converter under PWM modulation and PFM modulation is modeled and analyzed,and the compensation scheme is established.Then,in order to increase the accuracy of the output voltage,the voltage sampling module is mainly designed.The principle is used by a three-way sampling to obtain three sampling values.Using DCM and CCM,different judgment algorithms are utilized to select select the sampling value closest to the true value.Then the system's mode switching strategy is established.When the system is in the PWM mode and the output voltage of the error amplifier EA is detected to be less than 0.6V for five consecutive cycles,it is judged that the load is lighter at this time and it needs to be switched to the PFM mode;When the system is in the PFM mode and the output voltage of the error amplifier EA is detected to be greater than 0.6V for five consecutive cycles,it is judged that the load is heavy at this time and it is necessary to switch to the PWM mode.In addition,the error amplifier module,the PWM comparator module,and the drive LDO module are introduced from the principal analysis to the circuit simulation results.Finally,the overall simulation results of this chip are introduced.Based on the 0.18?m BCD(Biplor CMOS DMOS)process,this thesis simulates the primary flyback converter designed.The input voltage range of the converter is 25~35V,the output voltage is required to be 30 V,the error is within 5%,and the load current range is 0~1A.The simulation results show that the chip can be normally soft-started,and can maintain the output voltage error less than ± 5% when dealing with unexpected conditions such as input voltage steps and load steps,and at the same time using PFM modulation under light load,under heavy load The strategy of using PWM modulation satisfies the design requirements.