使用定導通時間電流模式控制電壓調節器在不連續導通模式之穩定度分析

Abstract

近年來，採用定導通時間(COT)控制之電壓調節器(VR)受到相當程度的重視，因為此架構在輕載時擁有較高的轉換效率之特性。在定導通時間控制的種類中，本論文將著重研究於電流模式結合輸出電壓直流準位校正(OC)電路之型態。在過去，轉換器操作在不連續導通模式的分析較少，而且在一般情況下也不會產生穩定度的問題。但是觀察實際電路，在某些條件下不穩定的情形確實會發生。因此嚴謹地對此架構在不連續導通模式下做穩定度分析是一個非常重要的課題。 描述函數(DF)經常被用來分析以回授漣波資訊來調變責任週期的控制架構之穩定度，但是此方法在不連續導通模式下太複雜而無法用上。本論文將提出一個不同的方法：時域波形分析，以用來建立系統穩定度準則。這準則之建立對實際電路之穩定度設計大有幫助，也可作為減少控制晶片面積之依據。

In recent years, constant on-time (COT) controllers for voltage regulators (VR) have received much attention because of their characteristics of high conversion efficiency under light-load conditions. Among the varieties of COT controllers, the current-mode version in combination with a DC output voltage offset correction (OC) circuit is considered in this thesis. In the past, discontinuous-conduction mode (DCM) operation has been considered trivial and there was no stability problem under such a condition. However, it was observed, in practice, instability can occur under such a condition. Therefore, it is critically important to have a rigorous stability analysis because the converter is usually in DCM operation under light-load condition. Describing function (DF) approach was usually used to obtain the stability behavior of the converter in which the duty cycle modulator is ripple-based, but it is infeasible under DCM operation. In this thesis, a different approach, a time domain analysis, is used to establish the stability criterion. The criterion is verified and proven to be useful for minimizing the controller chip area of the RC filter in the OC circuit.