Picture of Variable DC Power Supply for <$15
Variable DC power supplies are critical to many electronics projects. You'll never have to go out and buy dozens of different single-voltage power supplies or battery configurations with this new unit. Professional units can cost hundreds of dollars, but now you can make one for less than $15!

Remove these adsRemove these ads by Signing Up

Step 1: The Parts

Picture of The Parts
These are the parts you will need:
  • LM317 Voltage Regulator ($0.50)
  • 0.1 uf Mylar Cap (~$0.10)
  • 1 Axial Electrolytic Cap (~$0.20)
  • 220 Ohm Resistor (~$0.05)
  • 5K Potentiometer ($1.00)
  • Cheap Voltmeter ($7.95)
  • Enclosure ($1.65)
  • Power Supply ($2.85)

Total Cost: $14.30
Not bad for a homemade variable DC power supply!

Step 2: The Variable Voltage Regulator.

Picture of The Variable Voltage Regulator.
Start by making the variable voltage regulator. Refer to the schematics below.

Step 3: Adding the Digital Readout

Picture of Adding the Digital Readout
Adding the digital readout is really simple! Just open up your multimeter and solder your output to the test leads. Add a switch to the battery. And that's it! You're done :D

Step 4: You're Done

Picture of You're Done
Test it and have fun! Put it in an awesome enclosure like I did to impress your friends :)
stewie00564 years ago
correct me if i am wrong but in the schematic you drawn the pot is just going to be a 5k resistor because you didnt attach the wiper to anything.

would you care to explain that for me?

one more thing. would a tl780-05c voltage regulator work?
I'm pretty sure that's just a standard symbol for variable resistor.
In comparison to some other similar instructables, I'd say the wiper terminal just needs to be connected to ground (ie. connect the wiper terminal to the bottom (in terms of the circuit diagram) terminal of the 5k variable resistor.
How do you know what capacitors and resistors to use?
hitachi85 years ago
how much power can i draw from this little thing ? what if i put a big heatsink on the transistor ?
I dont know much about this , but is a LM317t good enough ? What is the difference ?
It will work.
neardood6 years ago
what schematics?