Suggested by General Electric this circuit has 3 control positions for one load. The diode is according to the controlled load current.
This configuration of PWM control with the LM317 was found in a Popular Electronics from the 90s....
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in Signetics documentation from the 90's. The circuit performance curve is...