陶瓷電容等效串聯電阻之可調式差動零點補償技術的固定導通時間控制直流/直流降壓轉換器

Abstract

隨著可攜式產品的需求逐漸增加，用來提供可攜式產品系統電源並且具有小體積及高效能的電壓穩壓器變得越來越重要，在現實生活中，固定導通時間控制法的電壓穩壓器常被使用，因為具有幾項優點，如系統結構簡單、快速暫態反應，以及在輕負載時具有高效率的優點。然而，固定導通時間控制法將因為輸出電容與其等效串聯電阻之乘積所得的時間常數太小，致使系統遭遇到次諧波震盪的穩定性問題。雖然大的等效串聯電阻可以確保系統穩定性，卻也犧牲了輸出電壓在暫態反應的品質。 因此，本文中，我們提出一個新的差動零點補償器可以讓固定導通時間控制使用陶瓷的輸出電容或是很微小等效串聯電阻的輸出電容，另外，無論電容之等效串聯電阻值多寡，透過可調式動態零點補償技術，皆能有效地調整動態零點之位置，確保系統穩定。穩定條件的分析與模擬結果都說明了在2毫歐姆~30毫歐姆的等效串聯電阻的使用仍可以保持系統的穩定性。這個新的補償技術仍然會保留原有之固定導通時間快速暫態響應的優點，並且對於外部電容的選擇上，大大放寬了電容特性的限制條件。

With the increasing demand of portable products, it's more and more important to provide small size and high performance system power to portable electronics. Constant on-time control regulators are preferred in reality for several important advantages, such as simple system structure, fast transient response time, and high efficiency at light loads. However, the stability is often influenced by the sub-harmonic problem caused by small time constant, which is the product of the output capacitor and the Equivalent Series Resistance (ESR). Although, the output capacitor with a large ESR can ensure the system stability, it suffers from large transient voltage and cost issue. Thus, this paper proposes a new differential zero compensator stabilize constant on-time system through the use of a ceramic output capacitor with a very small ESR. Besides, without being affected by the variation of ESR, adjusted differential zero compensation technique effectively adjusts the position of the zero to ensure the system stability. Analysis of stability criteria and simulation results demonstrate that the stability can be ensured even if the ESR varies from 2 mΩ to 30 mΩ. This new compensation technique still retains conventional constant on-time advantages of fast transient response and highly enlarged the characteristic restrictions by selecting output capacitor.