Variable DC Power Supply

Voltage range: 0.7 - 24V
Current limiting range: 50mA - 2A

Parts:

P1:  500ohm Linear Potentiometer
P2: 10Kohm Log. Potentiometer

R1,R2: 2Kohm  1/2W Resistors
R3:  330ohm  1/4W Resistor
R4: 150ohm 1/4W Resistor
R5: 1ohm 5W Resistor

C1:  4700µF, 35V Electrolytic Capacitor
C2:  4700µF,  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:  120V Primary, 36V Center-tapped Secondary 50VA Mains transformer

PL1: Male Mains plug
SW1: SPST Mains switch

Notes:

P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.
P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.

You can choose the Transformer on the grounds of maximum voltage and current output needed.  Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.

Capacitor C1 can be 2200 to 6800µF, 35 to 50V.

Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit. In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.

The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type.

Schematic diagram is embedded within the Word Document, but here it is separately.

Sorry, the web server encoded the "Ohm" symbol as "&#8486"

Has any one built this? Has any one had any difficulty with its operation?
mailto:dbowlin@elmwood.k12.ar.us

i've built it and it works fine. make sure you use alarge heatsink on the 2N3055 if u want it to sustain short ciruit loads.

To Andrew:

Do you think yhat it is possible to use 48vac as input

best regards,

I am having some difficulty with local suppliers not being
able to come up with a polyester capacitor. Can a sub.
be made? Thanks