LED driver doubles as fault monitor

摘要

LEDs find wide use as indicators and as light emitters in devices such as optocouplers. In some applications, the LED or the emitter maybe located remotely at some distance from the main unit. Typical examples are dashboard-mounted automotive indicators and industrial op-tosensors. In critical applications, you may require some means of monitoring the integrity of the LED. Using just four transistors and six resistors, this circuit provides switchable, constnt current drive for an LED and indicates both open- and short-circuit fault conditions (Figure 1). And there's a bonus, too.