This circuit was found in a Popular Electronics from April 1993. It is a voltage regulator circuit for solar battery. R3 and R4 determine the output voltage as a function of the number of cells. This circuit is a regulator for 125 mA output with a voltage of 2.4 V, with given component values. A larger current can be adjusted using the BD136. In this case, the maximum current is limited to 500 mA, and the transistor must be equipped with a heat radiator.
