Here they exist two regulator circuits, that use the IC L200, as regulator of voltage and current, the company SGS-Thomson, which give these circuits. In circuit Fig.1, we can regulate the output voltage, with the RV1, while in the Fig.2, we can regulate also output voltage current, with the TR2 and TR1, respectively. More information on characteristics for L200, you can see in list datasheets. Shortly will be added also certain other useful circuits with L200.