图1所示的电路可为电信接口提供隔离的120V、60mA的电流源。恒流线路馈电不受馈电线路长度的影响,为后续电路提供直流电源和固有的短路保护。实现隔离电流源的关键,就是不必在变压器次级消耗过多电功率的情况下实现反馈和过压保护。IC_2、Q_1及相关的电路便可提供这两种功能。 The circuit shown in Figure 1 provides an isolated 120V, 60mA current source for the telecom interface. The constant current line feed is unaffected by the length of the feeder line, providing DC power and inherent short-circuit protection for subsequent circuits. The key to achieving an isolated current source is to eliminate the need for feedback and overvoltage protection at excessive transformer secondary power consumption. IC_2, Q_1 and related circuitry provide both functions.