We found this battery eliminator in a Radio Electronics magazine from August 1974. The transistor must be equipped with a heatsink and other voltages can be achieved by replacing the zener.
We find this circuit in an American 80's documentation. It makes use of IC sensor which is mounted...
This is a configuration obtained from an old manual, using an operational amplifier of the time....
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...