This Instructable will show you how to build an adjsutable breadboard power supply entirely from Radioshack parts. It can provide multiple voltages directly to the power rails on a prototyping breadboard. This could be useful for people on a low budget, who don't like to order parts online, or who need a good weekend project.

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## Step 1: The LM317

The LM317, according to Wikipedia, is
an integrated three-terminal adjustable linear voltage regulator. It supports input voltage of 3V to 40V and output voltage between 1.25V and 37V. It has a current rating of at least 1.5A although lower current models are available. Its output voltage is controlled by a resistor or a potentiometer. The LM317 also has a built-in current limiter as a safety feature. LM317 is manufactured by many companies, including National Semiconductor and Fairchild Semiconductor. The LM317 will automatically reduce output current if it gets too hot under load. The use of a heatsink is recommended to extend the part's power-handling capability. LM317 is a positive voltage regulator. Its negative complement is the LM337

This will provide the Power in our Power Supply. It can also be found at a well-stocked Radioshack.

National Semiconductor's page

## Step 2: Calculating the Values

The following formula will allow you to calculate the resistor values to set the LM317 to any voltage that you need:

R2=R1((V/1.25)-1)

A standard R1 Value is 240 Ohms, so the final formula is:

R2=240((V/1.25)-1)

I chose the following power values for my power supply:
1.5
3
3.3
4.8
5
6
9
12

So my resistor values are the following(some have two for greater precision):
47
330
390
680
330 390
820 100
1500
1800 270

All of these resistor values can be found in the Radioshack 500 Piece Carbon Film Resistor Assortment.

## Step 3: The Parts

Barrel Jack--------------------------------Salvaged
Switch--------------------------------------275-409
Rectifying Diodes-----------------------276-1653
100uf cap----------------------------------272-1044
LM317T Voltage Reg.------------------276-1778
10uf cap-----------------------------------272-1025
.1uf cap------------------------------------272-135
Prototyping Board----------------------276-0149
500 Piece Resistor Assortment---271-312A
Heat Sink--------------------------------276-1363
8 Position DIP Switch----------------275-1301B
Scrap PCB------------------------------Salvaged

## Step 4: The Tools

These tools are common hobbiest items, most people should have:

Soldering Iron
Solder
Solder Wick
Wire (RS # 278-1221)
Multimeter
Various Pliers
Big Scissors
Duct Tape

## Step 5: The Schematic

This is your basic LM317 Schematic, with the DIP switch and the resistors added(Look at Notes!!):

## Step 6: Build It!

The Following steps will detail the construction of this power supply.
 1-40 of 65 Next »
Olivierh9 months ago

if you don't want to build it yourself, there is cheap power supplies on the internet and I think that would be cheaper

Awesome! Built this over the week end with a few additions, including a heat sink, wire terminals, and a 14 pin ic socket so that I could change the resistors. I'm hoping to add a trimmer potentiometer some project enclosure later as well.

BTW, the resistors in the image are only place holders until I find the ones I need.

alien99992 years ago
I have couple of questions. It's obvious that he used AC current at input, but how much voltage is on input ? I made this project with same resistor values but I power it with adjustable DC adapter (12V 1500 mA). So my problem is that I don't get the the voltages I suppose to get on output ( they are smaller). Also if I put smaller voltage on input (for example 9V) output will be even smaller. So final question is: how much voltage should power this circuit so I can get proper voltages on output? Help would be appreciated.
By the way, very practical project.
F-zero5 years ago
Great job on this! I made one for myself and it works great! I altered it a bit though.I made my own PCB board for it. Also, I added a fuse and a diode to be on the safe side and I replaced the 4 rectifying diodes with a bridge rectifier. I also added the little wire clip thing instead of placing it directly into the breadboard. I learned alot while making this. Thank you very much! One last note, when the switches on the DIP-8 aren't turned on, the output power 35 volts. I don't know if its supposed to do that or its my board. But, other than that, it works like a charm. Thanks!
3 years ago
I found the same with mine in regards to the output voltage when no switches are on. I think it's because you use a larger resistor for R2 to raise the output voltage, so when none of the switches are on, it effectively raises the value of R2 to infinite resistance, putting out the max voltage possible. Since your output in that situation is 35V, I would assume that your input is somewhere around 37VDC :)
oldskooldawgz3 years ago
y are there two 240 ohm resistors slot 22 n 23
ernie6663 years ago
why do u need capacitors?
beehard443 years ago
looks like the voltages are a little bit off. Why not use presets and calibrate so that you get the right voltages
jomac_uk3 years ago
I like the switch idea, once set up, its a simple matter of selecting the voltage, without having the hassle of connecting up your volt meter, all in all its a good instructable!
hokie884 years ago
Works great thanks man, I used a dc input source so i got rid of all the diodes and didnt bother with the switch, I wish they made a much larger 8 rocker switch
David_C5 years ago
There are 3 of us guys who tinker around doing electronics projects and we watch the youtube video by Kip Kay about getting Free Electricity from your phone line which is between 40~75 Volts ac and Kip showed useing a Bridge Rectifier as the input then the voltage goes to the Lm317 voltage regulator.

So why couldn't you use this input voltage to power your projects once you know that value that the phone line produces, as in this example by useing the method he memtioned and adapting it to be a varabile power source by useing a 5k Trimmer pot and adding a volt meter to the circuit so you could fine tune it to a voltage of 3v, 5v, 6v, 7.5v, 9v, 12v ect.

heres the link the the Jpeg image i came up with

http://i247.photobucket.com/albums/gg149/davidmann007/LM317withBridgeRectifierCircuit-1.jpg

Treasurehunterenterprizes@yahoo.com

Please Comment on this circuit if you think it would work
by E-mailing me.

Sincerely
Dave
5 years ago
I saw that earlier, on the make podcast, and I tried measuring the power from the phone line, but we ended up having to replace all of my phone modules due to them frieing from the energy draw that my multimeter created.
4 years ago
Also that is Illegal, and if the phone company notices what your doing they will shut off your phone and maybe sue you. If your want a cheap supply to power this circuit buy an old ATX supply from ebay they are about \$10 and work great. There are instructables that show how to convert them to work outside of a computer Or you could go to consignment stores and look around for an old wall-wart power supply that will meet your needs, You can get a whole printer at Goodwill for \$5 and their are lots of extra goodies inside
Minifig6665 years ago
Would a 12v 2000mA power supply be capable of powering this unit?
4 years ago
It gives a maximum voltage about 2 volts below what you put in, so yes it would. You would then have a 10 volt power supply.
geeklord5 years ago
i went to radioshack today, and they were all out of adjustable v-regs!!! I was a little upset....
4 years ago
grab a free sample from ti

I've made this and it works great, nice job. There is one thing, I think is weird though, the LM317 heats up very fast. Even when it is powering a standard low power LED (10mA) it gets hot enough to melt plastic bags.
6 years ago
seems like a short
6 years ago
It can't be, cause it works fine and I've checked the circuit board.
kersny (author)  Artificial Intelligence6 years ago
Make sure that your input voltage is not insanely higher than your output voltage(12v in for 3.3v out). Also, a heatsink helps if you don't already have one.
6 years ago
That could be the problem. I supply it with 24 volts.
5 years ago
yes, that would be it. voltage regulators regulate by turning the excess power into heat, and 24 volts to 3 volts would mean it would be dissipating 21 volts into heat. bad.
4 years ago
use a heatsink
i used the TO-92 package from Texas instruments. best of all, it was FREE!
Minifig6665 years ago
Can I ask what the diodes are for and why do you need two?
5 years ago
Sorry I meant 4. Are they for AC/DC Conversion
4 years ago
i think he was using ac, so he needed to convert it
the tape is a great idea
i always used to put in components and bend the wires down so they would stay still
Xellers5 years ago
An excellent project - but I would personally prefer to use a potentiometer to regulate the voltage coupled with an analog voltmeter.
reaman4ever5 years ago
how do you make connections from one point to another on a board like this (where none of the points are connected)? Do you drag the solder somehow? is there some kind of trick? I bought a whole bunch, but dont know how to use them. thanks
5 years ago
yeah, you creat solder bridges, use jumpers, and wires on the bottom as well.
MrNintendo6 years ago
Sweet instructable man. I've needed one of these for a good while, just now decided to see if anyone made these. One question though, on step 14, in the main pic, you said that 2 of the diodes were facing the wrong direction, but does it really make any difference? It might be a stupid question, but I'm still in high school, so I dont know much of this stuff, mind helpin me out?
5 years ago
hyperphysics.phy-astr.gsu.edu/Hbase/electronic/rectbr.html

That might help explain the current flow in a bridge rectifier for you.  Basically, it converts the AC signal to a pulsating DC signal (the capacitor on the bridge output smooths the pulses).
6 years ago
It does matter because diodes allow current to only flow in one direction. It comes out the end with the stripe and in the other. If you hook it up backwards it won't allow the current to flow.