具直流校正功能之漣波調變定導通時間電壓調節器之穩定度分析

Abstract

近年來，漣波調變定導通時間之控制架構因其在輕載與重載皆具高效率的特性，使其廣泛被運用於電壓調節器等應用。然而漣波調變定導通時間之控制架構通常伴隨輸出電壓準位的誤差，因此在需要精準輸出電壓之應用上極需加直流準位誤差校正電路至漣波調變定導通時間之控制架構。本篇論文主要探討準位校正漣波調變定導通時間之控制架構的穩定度分析。 在漣波調變定導通時間控制機制下，由於輸出電壓之切換頻率漣波會影響脈衝寬度調變之操作過程，因此無法使用傳統小訊號模型加以分析，然而描述函數的方式可成功應用於漣波調變定導通時間之控制架構。但若將準位校正漣波調變定導通時間之控制架構完全以描述函數來進行建模且不具有調變訊號須為直流無漣波的假設，會使數學分析變得相對複雜。本論文不僅運用具有基本假設之描述函數方法進行分析，論文中也使用分析時域波形伴隨實驗觀察之方法來對此議題進行研究，並以此建立穩定度準則。 此論文中穩定度準則的建立，能有效解決準位校正漣波調變定導通時間之控制架構的穩定度議題，並以模擬及實驗結果來作為驗證。且此穩定度準則的建立，不僅有助於實際電路的穩定度，也能做為有效減少控制晶片面積之依據。

In recent years, the ripple-based constant on-time (RBCOT) control scheme for voltage regulators has been adopted in many applications because of its high efficiency feature under both the heavy-load and the light-load conditions. However, the basic RBCOT control suffers from output-voltage offset problem. Therefore, an offset correcting circuit (OC) is sometimes added to the basic RBCOT scheme to correct the problem for the applications in which output voltage precision is critical. This control scheme is abbreviated as OCRBCOT in this thesis. The main focus of this thesis is on the stability issue of a buck converter regulator using the OCRBCOT control scheme. Traditional low-frequency small-signal average models cannot be applied to the basic RBCOT due to inaccuracy [1]. A describing function approach was proposed and applied to model the behavior of a buck converter regulator employing the basic RBCOT scheme [2]. To model the conventional regulator using describing function approach is mathematically too complicated to be feasible. In this thesis, a time-domain analysis approach with a semi-empirical observation is used to address this issue. Experimental and simulation results are given to verify the stability criterion derived. The result obtained in the thesis, while not analytically proved, provides a useful tool for addressing the stability issue of a buck regulator with OCRBCOT control scheme. It also provides a way to eliminate the proper RC value of the offset correcting circuit to minimize the chip area of the OCRBCOT controller integrated circuit.