This circuit that appears in several versions in this section and on this website was found in documentation from the 1980s. The transistors can be of any general purpose NPN type like the BC548.
This circuit is interesting for experiments and can be part of the bench in the form of a module. The...
Constant currents from 10 mA to 1 A can supply the load, depending on the selection made by S1. Q1...
In the figure we have the transmitter and the receiver for an optical audio link via infrared. The...