The following picture shown a 3 to 30V power supply circuit diagram using L200 IC made by Anwar von Sroka.It is constructed for the use with 100W transceivers.
L200 IC which is known as virtually blow-out proof IC for voltage and
current programmable regulation, is able for regulating the voltage as
well as the current. It should be connected as close as possible to the
minus terminal. Here, if you need to see the L200 datasheet.
Download this application datasheet about 3 to 30V Power Supply using L200 IC Circuit by Anwar von Sroka, here: http://www.mydarc.de/dl5dbm/20a_e.pdf