开关变换器提供了一种直接由标准电话线产生5V和18mA(最大为48V和5mA)的花钱不多的方法(图1)。由于输入电压高,可用的电流小,所以需要用一种独特的设计方法来实现高效率。图1 所示电路使用了LM2597HVM集成电路,它具有60V额定输入电压和节电功能。凡在输出高于4.4V时,它的VB_(IAS)引脚允许自举偏置功率这一功能至少能使偏置电流 Switching converters provide a cost-effective way to generate 5V and 18mA directly from standard phone lines (up to 48V and 5mA) (Figure 1). Due to the high input voltage, the available current is small, so a unique design approach is needed to achieve high efficiency. The circuit shown in Figure 1 uses the LM2597HVM integrated circuit with a 60V rated input voltage and power-saving features. Where the output is higher than 4.4V, its VB_ (IAS) pin allows the function of bootstrap bias power at least make the bias current