This is an interesting configuration of the LM317 voltage regulator found in an EDN from the 90s. The circuit uses an optical coupler and is intended to supply constant current to a sensor resistor.
This circuit was found in a 1987 edition of the United States' Hands-On Electronics magazine. The...
We found this circuit in an old English publication. The resistor not indicated can be 2k2 and the...
This circuit was found in a Popular Electronics from the 90s. It uses a LASCR which is a photo-SCR...