The Study Of Flyback Switch Mode Power Supply Control Loop

The switch mode power supply (SMPS) plays a great role in the power familymembers, and with the development of power electronics technology, switch mode powersupply technology is also constantly innovative. As the power equipments are strict withswitch mode power supply increasingly and the electrical environment of switch modepower supply is more and more complex, the study of control loop design is of greatsignificance in designing a switch power supply module with good dynamic responseperformance.The mainly purpose and meaning of this paper is to analysis the control loopapproximately using scientific, rigorous way, research and summarize the idea and methodof loop design, and as a basis to guide the entire experiment debugging process to ensurethat meet the requirements of various performance indicators from customers (including:high-frequency, high reliability, low power consumption, etc.) with the best control effectin the required design period time.This article introduces some concepts concerning switch mode power supply and loopcontrol firstly, then analysis and compares the pros and cons of several loop designmethods, and determines the design methods and steps:(1) collecting system parameters.(2) modeling the transfer function of the entire system, draw a known portion of thefrequency response curve.(3) according to the actual requirements and restriction,determines the crossover frequency.(4) selecting a compensation and calculating theparameters. Based on those, discuss the flyback switch mode power supply’s workingprinciples, PWM control mode, the establishment of transfer function, and other key issues.Ultimately, gives a practical flyback power supply example with current mode, introducesthe loop design steps, the important parameters calculation method and PCB designproblems specifically. In the end, the design method is reliability proved by the powerprototype test meeting the requirements.In addition, found the significant impact of the capacitor ESR on loop stability from the analysis of loop stability, the calculation of parameters and relevant data from capacitormanufacturers proves that the metallized polypropylene capacitor has certain advantagesthan ordinary aluminum electrolytic capacitor as power’s output capacitor. At last, forecastthe trend of power’s output capacitor in the future, which has certain innovation.