Circuit by Ron J
Variable Voltage Regulation
Text by ANC
As Ron suggests, controlling the output voltage from a regulator can be made variable in three ways:-
1. Using a fixed reference zener diode to increase the output by the value of the zener
2. A variable resistor for variable output, note that a voltage less than the nominal regulator is not possible
3. A chain of diode such as 1N4001, this increases the output by +0.7 V for every diode used.