PWM控制器處理多個拓撲結構與負輸入電壓

　　傳統上，電信和數據通信設備提供負的直流輸出電壓，如48伏，為系統總線。原因很簡單：直流電壓保持低噪音，可以容易地產生從普通鉛酸電池，通常約12伏特。此外，負電源使電纜和銅線遠離腐蝕。通常情況下，在應用服務器和計算機，這不受管制的負直流輸出電壓倒正母線電壓驅動各種降壓轉換器，必須產生一個穩壓直流低電壓高電流輸出驅動一個范圍廣泛的系統主板上的電子負載。這種系統板還使用諸如放大器，運算放大器和傳感器的運作，調節，負電源或分裂的供應，以保持交流信號清潔。

　　將這種不受管制的負電源轉換成一個受規管的負降壓電源或一個調節的負升壓電壓，以及一個積極的調節電壓，是不平凡的。每個拓撲結構是復雜和耗時的分立元件。更重要的是，它不保證性能，可以花費更多，同時占用更多的電路板空間。

　　To make such a task easy for designers， Linear Technology has developed a novel synchronous multi-topology DC/DC controller， the LT8709， which can be easily configured in buck， boost， buck-boost， and inverting topologies with negative input， making it highly versatile for a wide range of power supply designs. In addition， its synchronous operation means that the output diode is replaced with a high efficiency P-channel MOSFET， thereby increasing efficiency and allowing for higher output currents up to 20 A. As a result， it eliminates the heatsink typically required in medium- to high-power applications， thus enabling a designer to generate a wide range of DC/DC conversion solutions with negative input voltage for a wide range of power supply designs.

　　This article investigates the architecture of this novel DC/DC controller to understand why it is so easy to generate buck， boost， and buck-boost， as well as inverting topologies with negative input voltages. Besides uncovering its unique features and functionalities， we will also present working examples of LT8709-based negative-to-negative and negative-to-positive DC/DC conversion solutions at a desired output load current. Measured performance results for a design example also will be discussed.