This circuit was obtained in a 1967 General Electric manual. The circuit applies to other triacs. The other components are common today. The load is inductive.
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....