高輸入電壓下變頻器的高頻切換

　　In an effort to reduce the size of the output capacitor and inductor to save printed-circuit board （PCB） space， more and more high-input-voltageDC/DC converters are being operated at higher switching frequencies. However， as the output voltage drops to 5 V and lower， designing faster switching high-input-voltage step-down DC/DC converters is becoming difficult for several reasons. Key among them is lower duty cycle.

　　因此，頻率超過1 MHz的轉換器對電源系統的影響不僅僅局限于它的尺寸和效率。因此，在設計高輸入電壓和低輸出電壓的高開關頻率的DC/DC轉換器時，存在著權衡取舍。本文探討了一些設計實例，證明了在高頻率下切換高輸入電壓降壓型DC/DC轉換器的優點和缺點。

　　為了解釋這些權衡，德克薩斯儀器工程師們建造了三個獨立的電源，分別在開關頻率為100， 300和750千赫時運行。在設計高頻應用筆記”描述的挑戰，高輸入電壓的直流/直流轉換器”，1所有三直流/直流轉換器設計的輸入電壓為48 V，而輸出電壓為5 V 1 A根據設計者的一個輸出電流，這樣的降壓轉換器通常用于供電5 V邏輯USB或作為中間總線轉換器來驅動負載點（POL）在電路板上穩壓器。

　　Before building the supplies， the engineers established a few design constraints. For instance， the acceptable ripple voltage was set to 1 percent of the output voltage， which in this case amounted to 50 mV. In addition， peak-to-peak inductor current selected was 0.5 A. Each design， which was based on the circuit in Figure 1， incorporates TI’s TPS54160， a 2.5 MHz， 60 V， 1.5 A step-down DC/DC converter with an integrated MOSFET.