LM317T Adjustable Power Supply





Introduction: LM317T Adjustable Power Supply

NOTE: As this is my very first Instructable, I hope all of the "Instructables veterans" aren't too harsh when it comes to rating this how-to. Also, if anything at all isn't clarified by this how-to, please comment with your constructive criticism so I will know if there is something I left out. Thank you.

This is an Instructable that tells you how to make an adjustable voltage regulator, which has endless applications. It can be used to test your LED's and other low voltage loads, and there is another terminal for higher voltage applications. All of the parts as well as the circuit board can be purchased here.

Now, this requires a 9-12 volt "wall-wart," or wall adapter. You can take one from something you already have (as long as it fits the 2mm barrel plug) or you can buy one. If you don't want to buy a cheap-o one that will break or damage your circuits once you plug it in, you can get Gadget Gangster's 9 volt adapter, which will also work. You can find all the tools needed at their tools and equipment page. One other note is that if you have a 9 volt adapter, the voltage will not be able to exceed 9 volts. The same applies with any other input voltage; you cannot get a greater output voltage than what you have as the input. Just wanted to clarify that point.

If you already have the tools and parts, I believe it is possible to buy just the board. Check out the Gadget Gangster website for more details.

Step 1: Step 1: Getting Everything Together

Now, you should have the following parts in your kit when you get it, or you can just make this gadget from components you already have:


(1) Radial electrolytic capacitor (10 uF)
(1) Axial ceramic capacitor (0.1 uF)
(1) 2mm barrel power plug
(2) 1N4001 rectifier diodes (the '02s work as well)
(1) TO-220 heatsink
(1) 560 ohm resistor (grn-blue-brn-gold)
(1) 470 ohm resistor (yel-vio-brn-gold)
(1) 10k ohm potentiometer (trim)
(1) green LED (2.1v, 3mm)
(3) 2-port terminal block
(1) Gadget Gangster PCB (you can only get this from Gadget Gangster)
(1) LM317T voltage regulator

Also, you need a nut and a bolt so you can attach the heatsink to the regulator. It uses a very common size, so just grab a handful and see which ones fit.

Jumper wires:

(3) .1" wire (no insulation)
(2) .2" wire (red insulation)
(2) .3" wire (orange insulation)
(1) .5" wire (green insulation)
(2) .6" wire (blue insulation)
(1) .7" wire (violet insulation)
(2) 1" wire (brown insulation)

Step 2: Warm Up Your Soldering Iron!

There is quite a bit of soldering for you to do in the next 30-45 minutes. After warming up your soldering iron and tinning the tip, you need to get the circuit board and the components and parts out on a workbench or desk where you solder. The image below has notes on where to place the parts.

Just a little note to you who are first-timers when it comes to soldering. In order for the jumper wires to stay in place when the board is flipped over, slightly bend the leads outward so it is stable. Note the bolded word: slightly. Do not bend them too much, or else it is difficult to trim the leads, causing a risk of a short.

Step 3: Flip the Board Over and Solder Some More Stuff

Once you've soldered down the power plug and the orange jumper, flip the board over. As shown in the picture, insert a red jumper from Q13 to O13. Be sure to bend the jumper slightly around P13 for the potentiometer later on.
With that red jumper down, solder another orange jumper from K21 to K18. Once those two are down, flip the board over again.

Now with the board flipped over, you need to bend excess leads to span two hles in the circuit board. Once you have three of those little jumpers, insert them as shown at G21 to G20, another one from I18 to H18, and the last goes from J17 to I17. Solder those down and trim off the excess bits sticking out on the back.

Once again, flip the board over.

As shown in the picture, solder down a green jumper and a brown jumper; the green goes from P17 to L21, and the brown jumper is from Q23 to H19. Trim the excess and, you guessed it! Flip the board over once more.

In the next picture, the jumpers you need to solder are shown with an explaination of where they go. There are only two to place for this subsection, so take heart. Soon, you will be soldering components instead of boring little jumpers everywhere. Trust me, components are a LOT more fun to solder than a bunch of tiny bits of wire.

Once you have the red and violet jumpers soldered down nicely, trim the leads and grab the 10 uF capacitor. stick that in the circuit board from I14 to H14. Be sure to have the lead on the striped side in H14, or else it won't work. with that soldered down, you have one jumper to go until the halfway mark!

Almost at a stopping point!

Okay, this is a difficult jumper to solder down. BE VERY CAREFUL! You need to put in the brown jumper wire from G14 to Q14. The tricky part is that when you heat up the wire, the insulation shrinks, as shown in the picture. You need to solder this down quickly but carefully, or else the jumper will short out the capacitor and ruin your circuit. It would probably be best to bend the brown jumper a bit so there isn't as much of a risk.

You are halfway there! Take a break if you aren't having the best of luck so far. If you are doing great and getting everything exactly as shown in the pictures, continue to the next step.

Step 4: Keep It Up!

Okay, this is the easy and fun part now. The first thing to place after the halfway point in this project is the potentiometer. If the leads of the potentiometer seem bent, which they usually are, straighten them out with a pair of flat pliers so it will go in more easily on the circuit board. The single lead on the narrower side of the potentiometer goes in P13, right where the red wire was bent slightly to make room for it. The other leads go in as shown in the image notes. Solder that down good and tight. There isn't really a need to trim it's leads, as they are fairly short already.

Shown in the image notes are the descriptions of what needs to go where. Follow those notes, and you will be about 75% done!

Once you completed all shown in the notes, go on to the next step.

Step 5: The Final Few

Now is the big moment for your circuit: find the little piece of silicon with three leads and a metal tag. This semiconductor is what powers the whole circuit. (no pun intended) Look at the image below for notes on setup.
Once you have the regulator set up as shown, it's time to stick it in the circuit. It's fairly easy to guess where it goes, but if you aren't in the mood for 20 questions, it should be placed with the label away from the edge of the board. Once again, consult the pictures below to see the placement of the regulator. Solder it down. You might have to slightly bend the resistor out of the way to get it in there, but if you need to bend anything else, that probably isn't a great sign....

Okay, you now only have a few parts left that you got in the kit, right? Well, of those parts, there should be a 470 ohm resistor, which in case you didn't know is marked with a yellow, violet, and then a brown stripe, plus a gold one for tolerance. This resistor goes from I16 to A16. Solder it down and trim off the excess.

Next up is the little green LED. If you look at the two leads, one should be shorter than the other one. That lead is the negative one. With that in mind, stick the LED in the circuit board with the negative lead in B14. The other lead goes in A14. For optimum photon emission rates, have the very top of the LED about 1/2 to 3/4 inches from the circuit board. Once you have it placed, solder it down.

After that, there are the terminal blocks to place. One of them goes in the far bottom left corner of the board with the "G" of Gadget Gangster upside down. If you want specific points, one of the two leads goes at 1, while the other goes in Q3. Solder that block down with the actual terminal openings facing away from the very edge of the board, pointing towards the empty section of the PCB. Directly across from the terminal block you just soldered, place another terminal block. As shown in the picture, the terminals should mirror eachother: both facing in and on the far edges of their respective sides. If you didn't understand any part of what I just said, then place a second terminal block facing inwards with one of the leads at A1 and the other lead at A3. Solder it.

You're almost there! Only a few more things to solder down! Alas, there are two jumper wires that seemed to slip my mind while placing all the others. They should both be a sort of bluish color. One of them goes from I2 to F7, while the other wire goes from L7 to I12. Both of them need to be on the back of the circuit board. Once those are down, consult the picture to ensure that your PCB looks just like the one shown.

One final part! The last part should be a third terminal block. this one goes at H7 and J7 with the openings facing away from the rest of the circuit. Solder it down and give yourself a pat on the back, because you're done! the image notes give info on which terminal is which. Also, the potentiometer changes the output voltage. When the potentiometer is turned so the small flat part on the clear section is facing the voltage regulator, the LED power light is off, but a bit of voltage still goes through. If you have a multimeter, you can just play around with this for a bit to see what output voltage you get at certain points of rotation of the potentiometer. This has endless applications, so it is a very handy thing to have around when building circuits. Good luck!

As a final note, I hope I made a satisfactory first Instructable. If you have any questions, comments, or constructive criticism, please post a comment about it.



    • Creative Misuse Contest

      Creative Misuse Contest
    • Water Contest

      Water Contest
    • Oil Contest

      Oil Contest

    25 Discussions

    Great instructable! Just was wondering, does it matter the mA for the adapter? Should I use a 700mA or a 2A adapter?

    1 reply

    what is the point of the led tester
    a)The voltage reg. can be used to get that voltage
    b) The voltage of it will depend on the current of the led of low voltage curcut

    I am going to make the circuit on stripboard later. Also, to improve it don't say to use a gadget gangster PCB: stripboard is a lot more common

    Very good looking. I have not done it but i may make one. if you want to improve this i would:
    1) Provide a circuit diagram.
    similar things to the board you specify can be bought elsewhere

    1 reply

    There is a schematic -- you can see it by selecting the thumbnail below the first image on the introductory step.

    I know the last comment here is one year old, but I had to say this:
    Very good instructable in my opinion. I like how you started by placing the jumpers first. I use the same LM317T for my bench lab source and exactly the same schematic for the regulator, only diference is I used a 1k pot, since it was lying around, and i had to change the value of R2 acordingly. I also like to use the entire frame for the circuit as it is easier to bolt it. All in all great job on the circuit and the instructable.

    2 replies

    Thanks!  This was my very first project that I actually built and documented, so I'm kind of surprised that it was used by someone else...
    Right now, I am in the process of making a much more powerful and better power supply, which will include the transformer, bridge rectifier, and a front panel with manually adjustable current and voltage which will be displayed on an LCD.  I'll be sure to post an instructable on that as well once I finish it.

    If I may suggest using the LM350T (which is impossible to find in my city) for double the amps on the variable regulator. The LM317T can handle only 1.5 amps. And if you mention it however, I am very curious what volt/amp meter you are planning to use(and if it's diy).

    Oh, and one more thing-- I'm not sure how I can put this into words, but I'm not the greatest schematic maker Instructables has. i.e.; I did my best with the schematic, which might not be up to scratch with reality... Be ready to prod your circuit with a multimeter and post a bit of feedback on it's functionality. Thanks again.

    3 replies

    TinyCad.com has a free CAD program for schematic drawing. Free.

    two points: your title frame is way too large for the size of the circuit itself, so when it's scaled down you can't read anything, and the full version is a BMP image so instead of being able to view it directly in my browser i have to open a separate program. Try a smaller title frame and save it as a PNG.

    Okay, I'll do that in a moment--I'm about to eat dinner. :d

    This type of circuit is very handy to have for your lab bench.

    The schematic has an error as drawn. I don't know what the actual circuit would be if the wiring instructions are followed but the 1N4001 diode between R1 and R2 should be across R2. R1 and R2 should be connected directly together.
    The data sheet is available at
    See figure 3 on page 10 to clarify.

    The minimum output voltage would equal the reference voltage which is about 1.25 volts. With the pot (R1) at maximum the maximum voltage out would be roughly 1.25V * (1+ 10,000/560) = 23.5 volts. That would make much of the pot range unusable with a 12 volt input supply. Perhaps a 5 K pot for R1 would be better for this input range.

    The maximum voltage is also limited by the input voltage - the dropout voltage. The dropout voltage depends on the output current but it can be anywhere from 1.5 to 2.5 volts - see the graph on page 6 of the datasheet.

    Another thing to note is that most DC "wall wart" power packs have higher voltage out than the normal output ratings. The ratings are for full load current so the output voltage for a 12 volt can go to 17 volts with no load.

    If You look that schematic, You'll notice there's a "bridge" between LM317's Out and Adj. Just right before 560ohm resistor. The pic on the "first step" page doesn't have that bridge!

    2 replies

    Oh--I forgot to fix the pic in this post... I did fix it in the actual instructable, though... There is NOT supposed to be a bridge, just so you know. Sorry!

    As jack says, it's best to post an image of the schematic instead of just a list of "solder a jumper from $PAD to $PAD" instructions, especially if people are using a different type of perfboard or want to etch their own board or something. Images are usually better than the original schematic format your editor uses, mostly because you can read them right from your browser, and also because there are at least half a dozen different popular editors and not everyone wants to install the one you use, or even has the money/operating system/etc required. Gschem/gEDA is another schematic program if you prefer open source :)

    1 reply

    Eh... I will just do the schematic in paint. =) Then, even those who are still using Win 98 can see it.

    Is that okay?