高输入电压下变频器的高频切换

　　高输入电压下变频器的高频切换

　　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，频率超过1 MHz的转换器对电源系统的影响不仅仅局限于它的尺寸和效率。因此，在设计高输入电压和低输出电压的高开关频率的DC/DC转换器时，存在着权衡取舍。本文探讨了一些设计实例，证明了在高频率下切换高输入电压降压型DC/DC转换器的优点和缺点。

　　为了解释这些权衡，德克萨斯仪器工程师们建造了三个独立的电源，分别在开关频率为100， 300和750千赫时运行。在设计高频应用笔记”描述的挑战，高输入电压的直流/直流转换器”，¹所有三直流/直流转换器设计的输入电压为48 V，而输出电压为5 V 1 A根据设计者的一个输出电流，这样的降压转换器通常用于供电5 V逻辑USB或作为中间总线转换器来驱动负载点（POL）在电路板上稳压器。

　　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.