Improved Small-Signal Model for Switching Converter With Ripple-Based Control

Abstract

Average small-signal model, known as a simple and powerful tool, is widely used to provide design guidance for switching converters. Due to the ignorance of high-frequency characteristics, conventional average small-signal model fails to reveal dynamics of switching converters with ripple-based control. Improved small-signal models for ripple-based controls, including peak and valley ripple-based controls, are proposed in this article, which can be accurate to half of the switching frequency. Specifically, as for peak or valley current control, the uniform gain representing sample-and-hold effect is derived and suitable for different averaging ways. With regard to V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> control, the improved small-signal model can predict subharmonic oscillation caused by duty cycle and reveal the influence of the equivalent series resistance of output capacitor. Moreover, by combining the improved small-signal models of ripple-based current-mode control and V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> control, small-signal model of V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C control can be analyzed. The relationship among these ripple-based control methods is revealed, and the stability analysis as well as the transient response is carried out. Finally, experimental results turn out to agree well with the theory analysis.