This circuit was found in the Electronics Experimenter Handbook from 1991. The sensor is a diode and the circuit has a relay according to the voltage used in the supply.
Found in a 1966 Electronics World, this circuit applies to the protection of any analog...
We found this circuit in an English documentation from the 80's. The circuit can make use of...
The power of this converter is not the greatest, it can only supply small fluorescent lamps,...