PROJECT TITLE :

Asynchronous-Switching Map-Based Stability Effects of Circuit Parameters in Fixed Off-Time Controlled Buck Converter

ABSTRACT:

Each constant on-time (COT) and fastened off-time (FOT) control techniques are appropriate for various applications requiring quick transient response. But, the discrete-time model of COT controlled buck converter solely has 2 switched borderlines, whereas that of FOT controlled buck converter has four switched borderlines. Based on the derivations of those borderlines, an asynchronous-switching map of FOT controlled buck converter is established. With the decrease of equivalent series resistance (ESR) of output capacitor, instability and mode shifting from continuous conduction mode (CCM) to discontinuous conduction mode (DCM) are mentioned. Furthermore, with little ESR of output capacitor, stability effects of load resistance and inductance on dynamical behaviors are investigated, and also the approximate stability criteria and the corresponding normalized critical conditions are obtained. The theoretical analyses and experimental results show that the converter operates in DCM chaos via period-doubling and border-collision bifurcation routes, and its instability caused by tiny ESR can be removed by choosing appropriate load resistance, inductance, and voltage transfer ratio, which are terribly suitable for the circuit design of FOT controlled buck converter.