Variable DC Power Supply

Voltage range: 0.7 - 24V

Current limiting range: 50mA - 2A

Circuit diagram:

Variable Power Supply


P1____________500R   Linear Potentiometer
P2_____________10K   Log. Potentiometer

R1,R2___________2K2  1/2W Resistors
R3____________330R   1/4W Resistor
R4____________150R   1/4W Resistor
R5______________1R     5W Resistor

C1___________3300µF   35V Electrolytic Capacitor (see Notes)
C2______________1µF   63V Polyester Capacitor

D1,D2________1N5402 200V 3A Diodes
D3_____________5mm. Red LED

Q1____________BC182  50V 100mA NPN Transistor
Q2____________BD139  80V 1.5A  NPN Transistor
Q3____________BC212  50V 100mA PNP Transistor
Q4 __________2N3055  60V 15A   NPN Transistor

T1_____________220V Primary, 36V Center-tapped Secondary
               50VA Mains transformer (see Notes)

PL1____________Male Mains plug

SW1____________SPST Mains switch

Device purpose:

A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. Well suited to supply the circuits shown in this website. You can adapt it to your own requirements as explained in the notes below.