Instructables

Small-scale benchtop power supply

This is a short instructional for modifying a DC laptop brick to make an adjustable voltage output using the LM317 IC.

For schematics, please google "LM317 datasheet." I will only describe the build process in general terms.

 
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Step 1: Mini benchtop power supply

This instructional modifies a laptop DC brick to make a slick, breadboard-friendly power supply for all your low-powered projects.

It contains one thru-put, and two, independently adjustable voltage outputs. The circuit uses an LM317 for each of the adjustable outputs. Best of all, it outputs thru a breadboard power strip!

You will need a multimeter in order to accurately adjust the voltages. But you already have one, don't you? You can see my "pen" multimeter hanging in the back.

Step 2: What you need:

Some of the things you will need are

1) Laptop power supply, or any other suitable "power brick." The one I used is actually a regulated 12V 1.25A power supply that was originally for a VOIP phone.
2) A couple of LM317 IC's.
3) resistors, caps, and pots/trimmers to build the LM317 circuit. Because I had 500R trimmers handy, I used 50R for the fixed resistor. This provides for adjustment from 1.25V up to just above 12V. If you have any question, try Google.
4) A suitable enclosure.. such as this nifty case that used to house a travel alarm clock.

To do this MY way you will also need:
1) a glue gun!
2) some machined pin IC sockets and 26-27 awg solid core wire
3) a breadboard power bus strip.
agis689 months ago
nice presentation but for sure this is nothing! No schematic provided, no details nothing. Its like someone baking cookies, you will need sugar, flower, cinnamon butter and its baked!!!! hahahahahha no way mister isn't instructable!
i am just new here. could you provide a schematic of the design? thank you.
larams6 years ago
I don't see how this is an instructable. Don't get me wrong it's a nice idea and a useful one at that but I don't see how this instructed anyone on how to do anything.
klee27x (author)  larams6 years ago
This instructable provides the idea to adapt a common power brick into a multiple variable output powersupply with a universal breadboard output bus. If you take 5 minutes to read an lm317 datasheet, then you have all you need to know in this instructable. I believe I even added a link here, somewhere. But where does it end? Do I need to tell you how to solder, read, do simple mathematic calculations? I made this from spare parts... some of which I can't provide links or part numbers for. But the principle applies to a wide range of power supplies and applications.
A treat for those who asked for a LM317 datasheet data sheet :)

www.fairchildsemi.com/ds/LM%2FLM317.pdf if you can't use/see toe link above.
robonut6257 years ago
Good idea... I like how small it is. Heatsinks on those regulators would be a good idea though.
you can get away with out them they just use up space. unless your going to draw alot of current you dont really need them if the start getting hot i would go out and buy some though
LasVegas7 years ago
A link to the datasheet or schematic would help.
binnie LasVegas7 years ago
i agree howm i sposed to make it if he dosent even provide pin-pin diagram he better hurry up with it though... and what is a 'power brick' is it just a transformer 110/240 > 12
klee27x (author)  binnie7 years ago
Yes, a power brick, or "floor-wart" is just a rectified and filtered transformer, such as for a laptop power supply. The different between this and a "wall-wart" is that rather than plugging directly into the wall, it has a socket for a standard AC power cord. I have simply opened it up and removed the DC output wires. Then I routed power to two LM317 circuits. The final result is just a glorified transformer with it's original output, plus two adjustable outputs, and instead of a mess of output wires, posts, or jacks, I use a single, partitioned breadboard bus. This means I could theoretically hook up 20 small circuits up to it, at three different voltages with no special connectors. The strip also makes adjusting the outputs easier, since my multimeter's probes fit into a breadboard socket.
klee27x (author)  LasVegas7 years ago
Here's a link to an LM317 calculator. This will explain how to create a suitable circuit with the parts you have on hand.
http://www.cpemma.co.uk/317calc.html
I used RCA jacks for my power supply's outputs. They work rather well and are easy to connect/disconnect. I've got more then enough cables to hack if I ever need to use more power jacks :)
klee27x (author)  FrenchCrawler7 years ago
I considered that. I have a dozen-odd salvaged RCA connectors in the parts bin. But I decided that special cables or sockets were a part of the equation that I wanted to remove. Sometimes, you don't want to solder an RCA jack (or half an RCA cable) to a project, where you might just clip a couple wires, tin the ends, and plug it in. And anyways, there isn't any space on this thing for RCA jacks... although, with enough hot melt glue, I firmly believe that anything is possible! :)
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