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:

Components:

(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)

Comments

[alpe_97]

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

[ab_]

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

[ab_]

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

[vaati]

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

[drbill]

Nope !

Got Ya Last !

[Adri3l]

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.

[vaati]

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.

[Adri3l]

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).

[vaati]

(removed by author or community request)

[vaati]

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.

[drbill]

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

[stuuf]

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.

[vaati]

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

[Harry_W_Lewis]

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
http://www.national.com/ds/LM/LM117.pdf
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.

[vaati]

(removed by author or community request)

[ceemic]

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!

[vaati]

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!

[ceemic]

Tnx! No problem :)

[stuuf]

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 :)

[vaati]

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

Is that okay?

Thanks.

[stuuf]

You can use any software you want to make it, just export it to an image format that everyone can use (PNG, EPS, PDF, or even the obsolete, limited, and until-recently-potentially-illegal GIF).

[Gadget Gangster]

Here's the link straight to the project page, you might find it helpful.

[vaati]

Thanks for the quick feedback. I will post a schematic in Express Schematic/PCB (you can download that at http://www.expresspcb.com/ExpressPCBHtm/Download.htm) and it includes a great circuit simulator program.

Just a question directed to those of you who buy the kit from Gadget Gangster: Using this how-to, can you please post an approximate time span for assembling the project?
Thanks.

[inventorjack]

Good detail in this 'ible, but a couple more things you might add:

- You should document what the range of output voltages are, and point out that that range will be lower if using a 9V wallwart rather than a 12V one. Also, there is a minimum voltage output to this supply.

- A schematic would be helpful. If you don't have schematic capture software, download Cadsoft Eagle for free.

Other than those points, excellent work. I think everyone will appreciate the many fine-detail closeups you provided. Keep it up!

[lemonie]

Good job, and sharp pics! - can you add a circuit diagram? L