Research And Design Of Key Circuits Of Buck DC-DC Swiching Power Supply

With the development of integrated circuit technology and portable electronic products,the market places higher demands on the conversion efficiency and volume of power management chips.Based on the key sub-circuits of DC-DC converter,this thesis gives a kind of high efficiency Buck DC-DC converter.The main contents include:Firstly,according to the application scenario,a Buck peak current mode adaptive fixed off time(AFOT)control DC-DC converter is designed.For this Buck DC-DC converter,a small-signal circuit model is established,the description function method is used for modeling,and loop compensation is performed.Then the software Simplis is used to verify the loop stability.Secondly,based on the analysis of the loss sources of the Buck DC-DC converter,the influence of the system modulation mode on the conversion efficiency is studied.By calculating the conversion efficiency of different modulation modes,it is found that pulse frequency modulation can improve the conversion efficiency under light load.To improve the conversion efficiency under light load,these techniques are adopted including pulse frequency modulation,current zero-crossing detection technology and synchronous rectification technology.Finally,based on research of key sub-circuits,including bandgap voltage reference,high-side drive circuit,error amplifier,current detection circuit,comparator and AFOT generation circuit,a kind of AFOT buck DC-DC converter is proposed in this thesis.The simulation results show that when the load current is 500 m A and the input voltage varies from 10 V to 24 V,the output voltage change is less than 29 m V and the adjustment time is less than 193μs.When the load current changes within the range of 10 m A to 500 m A,the system output voltage change is less than 35 m V and the adjustment time is less than 178μs.The system conversion efficiency of the proposed Buck DC-DC converter is up to 93.8%.