When the voltage supplying the circuit falls below the zener value, the LED lights up, and if a low current buzzer is used, it is activated. The circuit is from a 1999 American publication.
September 2016 - can already be found at Mouser Electronics new integrated circuit from Texas...
Found in a 90s Popular Electronics, this circuit uses common components. The power transistors can be...
This circuit, suggested by Siemens, allows the activation of 24 V solenoids from TTL LSL signals,...