This circuit was found in an Electronics World of 1968. It can be applied to any modern triac and the diac can be any type. The load depends on the triac.
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....