We found this chopper circuit in a 1967 publication. The transistors are of the time, and current equivalents can be used.
This circuit is from a 1957 Raytheon transistor manual. The diode can be of general-purpose...
The circuit shown in the figure shuts off a load when the voltage drops below the value determined...
This circuit was obtained from an English magazine from 1976. The signal from the circuit should be...