A very simple variable power supply circuit can be constructed using this electronic circuit diagram . This Circuit is use common components and is very simple to design . This variable regulator circuit will provide an variable regulated output voltage , between 0 and 50 volts . The CA3140 operational amplifier compares the regulator output to a reference voltage , that depends on the R9 value . The output voltage will be nominally twice the voltage between the positive input ( noninverting ) of the CA3140 and ground . The unregulated input voltage must be around 60 volts . The output voltage can be set between 0 an 50 volts using R9 potentiometer . The 2N3055 transistors must be mounted on a heatsink , to prevent the overheating of transistors .