Suggested by a 1968 documentation, this circuit limits the current of a regulator and can be adapted to other currents. The transistors are from the era.
This amplifier with very high input impedance was suggested by Texas Instruments in a manual of...
Using only a ULN5804 integrated circuit, stepper motors up to 500 mA can be controlled from TTL...
Constant current sources are used in applications such as battery chargers, electrolytic tanks, etc....