This circuit was found in an Electronics Now of the 80s applying to NiCad batteries of the time. The circuit is powered by a 12 VAC source, for example, the secondary of a transformer.
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....