Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
This circuit is the conventional use of the 7805 as a constant current source up to 1 A. The...
The integrated circuit used in this application is not currently common. The circuit is from an...
This circuit is from a Radio Electronics from February 1966. The circuit is of a type that was...