應用於陶瓷電容之差動零點補償器的固定導通時間控制直流直流降壓轉換器

Abstract

交換式同步降壓電源供應器具有輸出電流大、效率高的優點，因此應用在許多可攜電子產品上。在眾多的控制方法中，固定導通時間控制(Constant on time Control)在負載瞬間變化時具備快速反應的表現，透過迅速導通上橋的開關提供電流至輸出電容，提供良好的電源供應品質。如此一來，可以使用較小的輸出電容便可以提供穩定輸出電壓，也可以縮小電路所佔空間及降低電路元件成本… 等等的優點。但其穩定度卻是與輸出電容的大小與其等效串聯電阻有關係，其輸出電容的大小與其等效串聯電阻兩者的乘積必須足夠的大，才能使固定導通時間控制系統穩定。例如，如果固定導通時間控制的輸出電容使用陶瓷電容就會有穩定度上的問題，因為陶瓷電容的等效串聯電阻非常小，造成其輸出電壓落後電感電流接近九十度，如此系統會有穩定度的問題。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，這個新的補償方式仍然會保留原有的固定導通時間的快速暫態響應的優點，並且只有增加一點電路的複雜度與不需要使用任何的外部元件。

Synchronous buck switching power supply has high output current and high efficiency advantages, it is very suitable to application in the emphasis the efficiency of electronic products. In many control methods constant on-time control shows fast transient response at load step. The high-side switch quickly turns on to provide current into the output capacitor that can keep good quality of power supply. In this way we can use a smaller output capacitor to stabilize the output voltage. It also can reduce the circuit footprints and component costs ... etc. But its stability is related with equivalent series resistance of output capacitor and output capacitances. The both of their multiplication must be large enough to make the constant on-time control system stable. Such as, the constant on-time control using a ceramic capacitor in output stage will encounter stability issue. Because the equivalent series resistance of ceramic capacitor is very small to cause the output voltage phase lags behind the inductor current about 90 degrees, so the system will have stability problems. In this thesis we present a new differential zero compensator to make constant on-time system stable of using a ceramic output capacitor or using a very small equivalent series resistance output capacitor. This new compensation method still retain the conventional constant on-time advantages of the fast transient response …etc. and only increase a little circuits complexity and does not require any external components.