要求恒流源产生1安培的恒定电流,其工作电压约30伏。此外,电子流方向必须从源到负载,如图1所示。这些要求可用一个加反馈到 PNP 功率管的电路来实现。图2是比较简单的办法,只用了一个 NPN 功率管和一个接在共基电路中的齐纳二极管。但是这种 NPN功率管相当贵而且很少,因此一般是不采用的。 The constant current source is required to generate a constant current of 1 amperes and its operating voltage is about 30 volts. In addition, the direction of electron flow must be from source to load, as shown in Figure 1. These requirements can be implemented with a circuit that feeds back to the PNP power tube. Figure 2 is a relatively simple solution, using only one NPN power transistor and a Zener diode connected to the common-base circuit. However, this kind of NPN power transistor is rather expensive and rarely used, so it is generally not used.