Research And Design For Buck DC-DC Critical Circuits

In today’s consumer market, with its diverse performance, easy to carry, Portable electronic products’share is more and more big, and the power supply in the electronic products is a very important and indispensable component. The better the electronic products’performance, the higher requirements for power supply. Switching Mode Power Supplies (SMPS), for its unique advantages of high efficiency, high reliability, strong anti-interference ability and small volume, becomes the extensive research and discussed object of Power developers at home and abroad. Its highest efficiency can reach more than90%, the improved conversion efficiency can effectively avoid the waste of energy, complying with the trend of today’s energy conservation and emissions reduction. As the pivotal important circuit in the PWM system, Oscillator decides the switching frequency of the SMPS. The Over Temperature Protection circuit ensures the system works in a safe and reliable temperature environment. Therefore, it’s necessary for their study.This article first described the basic theory of DC-DC switching power supply, analyzed the circuit topology structures and working principle of several commonly used DC-DC SMPS, and emphatically discussed the BUCK topology; then their modulation mode and control mode are described in detail; finally explains the advantages and disadvantages of each type of modulation mode and control mode.In this paper, the Oscillator and the Over Temperature Protection circuit, which are used in a low power step-down SMPS, are detail analyzed and designed. Their working principle, the structure characteristics of transistor level circuits and small signal characteristics are analyzed in focus. Among them, the method of generation the ramp voltage and Over Temperature Protection circuit using the comparator mismatch characteristics to realize the function of temperature hysteresis is novel. In addition, based on the original Oscillator, this article also designed a synchronous Oscillator, with widely synchronous frequency range and strong portability.All circuits are designed using0.25um BCD process, Cadence and HSPICE simulation software are used to validation the circuit’s functions. Through subcircuit and the whole chip simulation, the designed circuit satisfied the design requirements and target, realized the function of the circuit.