Reserch Of Low Loss Current Mode Buck DC-DC Converter

With the continuous improvement and rapid development of microelectronic technology, the requirements for micro power consumption, energy saving and intelligent electronic products are contiously growing. Power supply is the crucial part of electronic equipment. Its performance decides the technical indexes and stability of the electronic equipment. Compared with other switching power supply, DC- DC converter has the advantages of high efficiency, small volume, light weight, strong adaptability to the input voltage, flexibility and diversity in form, thus it has been developing rapidly. In conclusion, the research and design of Buck DC- DC converter have very important practical significance.A low loss current-mode Buck DC- DC converter is designed in this thesis.The chip responds quickly, has high precision of output voltage and high conversion efficiency. In the process of start, it has small overshoot voltage and surge current.First of all, the development and tendency of the development of switch power supply areintroduced. Secondly, this thesis analyzes tanvantages and disadvantages of each topology. And through the comparison, the current mode pluse width modulation technology is selected to control the converter. Thirdly, through the analysis of the power loss, some corresponding measures are taken to achieve the goal of low loss and high efficiency, such as synchronous rectifier technology, low loss of current amplifier, soft start circuit and zero crossing detection circuit. These measures not only reduce the power loss, at the same time, make the converter to avoid the overshoot voltage and surge current during the start-up stageand the happening of diacharge phenomenon during the discharge stage, which reduce the damage to the chip. In addition, the thesis also completed the design and simulation of main module in the converter, for example bandgap reference circuit, oscillator circuit, error amplifier circuit, PWM comparator circuit and slope compensation circuit.The chip uses 0.25?m BCD manufacturing process of CSMC. Circuit design uses Spectre of Candence for simulation. From the simulation results of the system, we can know that the output voltage ripple is less than 11 mv, linear regulation rate of input voltage is 0.923%, and load regulation rate is 3.32%. And the affectment of temperature to output voltage is very small, what stands for the converter has good temperature characteristic. In addition, the conversion efficiency of the system is more than 90%, filling the requirements of low loss, high efficiency. The chip can realize the prospective target.