不連續導通模式漣波調變定導通時間降壓型轉換電路之小訊號模型

Abstract

在傳統的直流對直流轉換器應用電路中，定頻式脈寬調變技術已被廣泛的採用。然而，近年來隨著節能與環保意識的崛起，直流轉換器的輕載效率比以前更加的受到重視。大多數的電子產品如可攜式電腦、隨身聽與手機…等，多數時間都運作在輕載狀況下。因此，針對提昇輕載效率的變頻式直流直流轉換器相關技術開始受到研究與重視。定開關導通時間型脈寬調變技術為變頻控制技術中的其中一種。此種調變技術本身就可使電路於輕載下降低切換頻率進而達到提升輕載效率的功能，然而，由於調變方式的不同，傳統的數學模型無法預測該電路在輕載時進入不連續導通模式下的運作情形。因此，本論文將研究重點著重在定開關導通時間型脈寬調變技術的小訊號模型上，提出了該電路兩種不同的非連續導通模式小訊號模型並加以驗證並分析該電路於非導通模式下的電路穩定性，希望幫助設計者針對此種新型電路做出最佳化設計。

A constant-frequency pulse-width-modulator controller is commonly employed in traditional DC-DC converters. In recent years, however, a constant on-time controller for DC converters is gaining popularity because of the new emphasis on the converter light-load efficiency in applications such as notebook computer and handheld consumer products. For such applications, the power converter is in standby or light-load conditions most of the time. The new mandate of high efficiency at light-load condition makes great sense because of overall energy concern. A constant on-time controller for the DC power converters naturally lends itself to lower frequency operation, and therefore, has higher energy efficiency at light load. Constant-frequency control of DC power converters can be accomplished in a variety of schemes. In this thesis, the work on the ripple-based constant on-time control scheme for buck converters will be reported. The focus is on the feedback control stability issue when the converter is operated in discontinuous mode. A control model is developed for investigating the stability issue of such a converter. Experimental and simulation results are given to verify the model.