This circuit was found in an ancient American documentation. The power supply is not given, but we have the voltages used. The relay is sensitive type for high voltage.
This circuit, suggested by Signetics can be used as a shield. Modern operational can be employed...
In the figure we have a typical voltage follower. In a voltage follower the voltage gain is...
This 2001 circuit uses common transistors and can be used in an electronic lock. The relay trips...