Variable DC Power Supply for <$15




Introduction: 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!

Step 1: 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.

Start by making the variable voltage regulator. Refer to the schematics below.

Step 3: 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

Test it and have fun! Put it in an awesome enclosure like I did to impress your friends :)



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    70 Discussions

    Do this all for $5

    2 replies

    it will burn out after 3amps

    The power supply in this ible can only deliver 2.7A and the regulator can only handle 1.5A. Right?

    I'm no expert but I think the max of the lm317 is the max of the power supply witch is also the max of the whole thing

    1 reply

    The little leads that connect to the volt meter, what are they called?

    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?

    3 replies

    If you have a 3 pin pot, attach the wiper to the upper leg, the same leg that attaches to pin 1 of the LM317.

    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.

    I want to build the variable power supply. Can I build it with a 30 volt power supple? Will I have to change all the other parts? Thanks Dave

    Hi there,

    This is a very cool instructable! I already bought all the parts, except for the capacitors. I am quite a novice with electronics so please be patient… :)

    “0.1 uf Mylar Cap (~$0.10)” – Is this 0.1 uf Radial Electrolytic capacitor? In the pictures included in the pdf file it is a 0.47 uf 50v capacitor, will this also work?

    “1 Axial Electrolytic Cap (~$0.20)” – In one of the comments “silencekilla” said that is should be a radial capacitor, is this correct and what should the value be? 1 uf ?


    im sorry if i missed this but what voltage power supply is used?
    the links are broken so i cannot see :(
    and also would the resistors regulators and such change if i were to use a different voltage power supply?
    (sorry i do not know the purpose of these things and what they do)
    LM317 Voltage Regulator ($0.50)
    0.1 uf Mylar Cap (~$0.10)
    1 Axial Electrolytic Cap (~$0.20)
    220 Ohm Resistor (~$0.05)

    thanks in advanced

    How do you know what capacitors and resistors to use?

    While this will work well for small stuff, neither the "wall wart" nor the voltage regulator will provide much more than an amp, whereas bench supplies that cost $$$ generally provide upwards of 10, 20, or even 30 amps. Personally I like the idea of turning an old ATX switching power supply into a multi-voltage bench supply. You can find guides for it almost anywhere, and the power output is very nice. Granted, you're stuck with the standard +/- 5, +/- 12, and 3.3v levels. So for $15, not too bad, especially when you need an obscure voltage.

    2 replies

    Hmm. Don't forget you can mix them to get non-standard voltage, ie 3v + 5v or 12 + 3v or 12 + (-5v) or etc. etc.

    I agree. In fact, on my bench I've got a variable supply and a fixed supply. PC supplies need a dummy load of a few watts, eg a resistor or indeed, an old motherboard. My latest incarnation is to hack an old hard drive to get the 4 pin power plugs and the bit of printed circuit board round them and make a plug that fits into one of the 4 pin power sockets coming out of the supply of the computer that sits on my test bench. Then bring out the voltages to banana sockets on a face plate on the front. The module is thus self contained and can be moved to different PCs. 12V brake lamp from a car for the short circuit protection on the 12V and 6V 500mA torch globe for the 5V protection. I'm finding I use the fixed 12V/5V a lot more than the variable voltage power supply, though both are really useful.

    I built that exact circuit, and when i have no load, i get up to 15 volts ( i am supplying 20), but when i attach a small pager motor, the voltage becomes only 4 volts and i only get 12 milliamps of current. What is wrong?