This constant current source from a 1980 publication can be used on a battery charger. Transistor Q1 may be BC548 and the input voltage must be higher than that of the battery being charged. Rc is found by dividing 1,500 by the mA current that is desired at the output. For example, for 300 mA, we have 1,500/300 = 5 ohm. Transistor Q2 must be equipped with a heatsink. The maximum recommended current is of the order of 2 A.
