In the figure we have the way to obtain an adjustable 1 to 10 mAconstant current source. The transistor may be the BC558 for currents up to 10 mA, but the circuit can provide larger currents by reducing the resistor from 470R to 100R and using the transistor BD136 in a small heat sink. The circuit is from a 1991 documentation. Other current ranges can be programmed by changing values of the components.
