When the voltage in the circuit exceeds the value set in the trimpot, the LED goes off and, if a low current buzzer is used, it rings. The circuit is from American documentation from 1999.
This circuit with 1W of output was found in a Mullard manual from 1960. The consumption is low and...
This circuit was found in an old documentation. It converts DC voltages and its maximum current...
In the figure we have the way to implement a 5 to 45 V zener diode with 50 mA of maximum current...