The Study And Design Of Multi-mode High Efficiency Buck DC-DC Converter

With the development of science and technology,switching power supply chips are moving towards miniaturization and digitalization.At the same time,the chip is required to have a large load capacity,fast transient response and high conversion efficiency.This article designs a Buck DC-DC converter with multiple modulation modes and peak current feedback control.It mainly includes two parts: voltage control loop and current control loop.In this dissertation,the buck DC-DC converter is studied in depth from the aspects of the working principle,overall architecture,small signal model and circuit of the Buck switching power supply.The main work of the thesis is as follows:(1)Small-signal modeling of the Buck switching power supply system,combined with the switching network averaging method to derive the transfer functions of the voltage loop and current loop,respectively,and then use SIMPLIS software to simulate and verify them.(2)Designed three working modes,the system automatically switches the working mode according to the load: working in PWM modulation mode under heavy load;working in current limiting mode under overload,so that the system has higher efficiency in the full load range,will not be under overload Damage due to excessive current.(3)A piecewise linear slope compensation method is adopted to prevent over-compensation.At the same time,a slope recovery function is integrated to prevent the load capacity of the chip from decreasing under the condition of low step-down ratio.(4)The synchronous rectification technology is adopted to reduce the loss of the freewheeling diode,and a dead-time control circuit is also designed to prevent the system from short-time overshoot current.(5)A soft-start circuit without external capacitors is designed to prevent large inrush current when the system starts;the control circuit,power tube and compensation network of the system can be integrated in the chip,making the structure of the peripheral circuit very simple.This paper uses VIS 0.15 um BCD process to complete the design of the overall circuit,and uses the Spectre tool to simulate key circuits and systems.The simulation results show that when the input voltage is 12 V and the output voltage is 3.3V,the maximum ripple coefficient of the output voltage is 1.5%,the maximum load current can reach 3A,and the current is limited to less than 3.5A under overload.The linear adjustment rate of the system is 0.25%,and the load adjustment rate is 0.225%.The maximum conversion efficiency under heavy load can reach 92.1%,which meets the overall design index.