This circuit was found in the Linear Applications Handbook of the National Semiconductor of 1994. Some of the components used are not easy to obtain, but equivalents can be used.
This circuit can be used to control loads up to 500 mA from the outputs of microcontrollers such...
This circuit with transistors in parallel was found in a Radio Electronics of August 1952....
This Linear Technology circuit can measure currents from 100 pA to 100 uA. The circuit is from the...