Circuit UA79G Power Supply
A stable variable power supply with an adjustable output voltage from 5 volts to 30 volts can be easily constructed with the regulator ICs UA78G or UA79G.
These ICs differ from the common three-terminal regulator since their output
voltages are adjustable by a voltage level at their control inputs. The maximum current delivered by these ICs is 1 ampere.
The variable power
supply circuit presented here is designed to give maximum voltage level of 28 volts. If P1 is replaced with 25K potentiometer, the regulator can deliver up to a maximum of 30 volts. Capacitors C1 and C2 stabilize the IC and they must be connected as close as possible to the IC terminals.