This regulator can be controlled by a logic signal. The circuit is from an Electronics Now from the 90s. Note that the switching transistor is before the integrated circuit.
This circuit was found in Electronics Now. With it the dialing signals of a telephone are...
Found in American documentation, this simple circuit activates a buzzer with embedded oscillator. A...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...