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When designing this power supply, my objective was to have it as portable as possible, so you can take it almost anywhere. One of the reasons I want it to be so portable is because every time I go to visit my family and friends abroad, they always have something for me to fix (or at least “try to fix” ) They have a soldering iron, but that’s about it. That’s why I made the voltpen, this mini power supply, and a mini usb sound card oscilloscope (Instructable to follow soon).

I made other power supplies, but none of them had current regulator. This time I decided to use the LM2596 instead of the normally used LM317 or LM350, so I could also adjust the current.

The beauty of this unit is that you can connect it to any DC source from 7.5V to 28V. So I can just take it with me and connect it to a laptop power supply for example. The output voltage will be very close to the input voltage, maybe about half a volt less. It can also be use as a voltmeter without being powered for voltages from 2.5V to 30V and as an ammeter from 5V. And It’s great for charging batteries.

Enough talking, lets cut to the chase..

Step 1: Materials and Tools

I organized the materials into two categories, necessary and optional components. The prices are based on what I paid or the lowest price I could find on ebay. Normally I buy components from HK. With most of the electronic components you can buy about 10 units for the price of one in the UK. The links to ebay are the cheapest I could find.

Necessary components:

  • Project enclosure Box £2.15, 72 X 50 X 41MM (Drawing) (link)
  • LM2596 £1.67 (Datasheet) (It’s best to buy this little circuit (link) with all the components already there, makes it easier) Make sure you buy the version that adjusts current also, it’s easy to tell because it should have 3 trimmers on the board.
  • Ammeter £2.05 (link) Please read step 5 before even trying the ammeter.
  • Voltmeter £1.49 (link) Make sure you buy the one with 3 wires (black, red, white). You could use the one with only two wires, but you won’t be able to read voltages lower than 2.5V or 3V.
  • BNC connector £0.20 (link)
  • Heat sink for the IC £0.12 (link) Or if you want to buy the one that fits on the IC (link I thought that is just too much for the heat-sink. Maybe you could use a raspberry pi heat sink)
  • Aluminium plate (reuse any aluminium you can find anywhere)
  • x2 10k potentiometers £0.17 (link) (I recommend getting 10 turns wirewound potentiometers to have more precise adjustment. Although the box will have to be a bit bigger.)
  • x2 Potentiometer Knob £0.18 (link)
  • Switch £0.12 (link)
  • Bread box, or some sort of plastic plate. £0.24 (link)
  • Heat paste. £1 if you don’t have any. (link)
  • DC connector £0.27 (link) I use a different model, but the one on the link was the cheapest I could find.

Total so far £9.66


Optional components:

  • x3 5mm LEDs £0.10
  • X3 LED’s Mounting clip for 5mm LEDs £0.05
  • x2 Servo extension cable £0.20 (link)
  • Heat shrink £0.50
  • PCB headers £0.06 (link)
  • BNC to Alligators cable £1.05 (link)

Grand total of only £12.12


Tools:

  • Dremel and cutting disk (you could use something else to cut the holes in the box if you don't have a dremel)
  • Hot glue gun
  • Soldering iron
  • Drill and drill bits (6mm,7mm,10mm)
  • Helping hands (optional)

Step 2: Regulator Circuit Modification

This little circuit is great, but it has been designed to be adjusted just once, so it needs to be modified.

  • The first thing you need to do is desolder the trimmer potentiometers and solder the headers instead, they fit just right in the holes. You can skip this step if you'd rather solder the wires straight to the board.

The other modification is really optional, as you don’t really need to see the LEDs but I thought they will look good.

  • Bend some of the header to match the solders on the PCB and solder it on. Some hot glue will add strength.

When charging batteries, the green LED will light when the current is less than 0.1 of the adjusted current. This can be adjusted with the middle trimmer, the one left on the board. This is not really necessary as you can see the milliamps going down as the battery charges.

Step 3: Heat Dissipation

This little circuit is rated “3A”. But I think that is more like 2A and 3A max with heat sink. I decided to make my own heat sink so it will fit inside the box, but If you don’t mind too much about the side of the box, you may be better off buying a unit with the heat sink attached to the back of the unit (link), and skip this step. Although it will add £7.50 to this project. I don't think it's worth it just for the heat sink, so I made my own.

  • The heat sink I had was too big for the space where the regulator is on the board. So I cut the heat sink. I used a saw to cut it, but the dremel with a cutting disk will do just fine.
  • Make the necessary holes on the breadboard. In my case I made holes for the back of the soldered headers and for extra heat dissipation for the regulator.
  • Cut the aluminium plate to the size of the box, and also cut a corner where the input connector will be. That piece will be used to level things out (see pics) The plate is held with some cable ties, so additional holes will need to be drilled to the board and aluminium plate.


    Before fixing everything together with the cable ties, use some heat paste to help transmit the heat to the aluminium heat sink.

Step 4: Enclosure Box

It is good idea to cover the box with decorator's tape before you start working with it. This will protect the box from scratches and make it a lot easier marking the box. Please double check the measurements, as I'm giving the measurements of the components I used.

  • Use the dremel with a cutting disk for the holes for the meters and the switch.
    • Meters 22.5mm x 14mm
    • Switch20mm x 12mm
  • The LEDs, potentiometers, input connector and BNC connector holes can be made with the drill. The holes for the LEDs are made with a 6mm drill bit if you are using the LED's mounting clips.
    • LED's mounting clips 6mm
  • The potentiometers I used came from an old CCTV monitor.
    • Regular potentiometers have a shaft of 6mm, but the thread is a big bigger, so a 7mmor 8mm drill bit will do.

  • For the BNC connector it is best to measure it as there may be different models.
    • My BNC connector fit with a 10mm hole.
  • The 5.5mm input connector can be also drilled and the size will vary depending on the connector to be fitted. For mine I just needed a hole of 7mm. To align the input connector with the hole, I plugged a connector while I glued it with hot glue (see pics).

Step 5: ​The Ammeter

You may wonder why I dedicate a whole step just for the ammeter. There are two reasons:

  1. I could not find any decent info on how to connect the ammeter, so I blew up the ammeter and had to wait for weeks for another one from HK.
  2. The ammeter needs modification so it can be fitted to the box.

Let's explain further:

  1. This ammeter is very sensitive and it will fry instantly if wrongly connected. The ammeter has 4 wires, 2 thin and 2 thick wires. The two thin wires (black and red) are power input, black = negative, red= positive, nothing too complicated. This is the bit where you need to be careful: The 2 thick cables (black and white) are black= negative in to ammeter, white= negative out of ammeter. Make sure you connect the cables right. It may be a good idea to try the accuracy of the ammeter before mounting it to the box.
  2. The ammeter has a resistor shunt (or at least that’s what I think it is), on the front of the PCB, this shunt is coming out even more than the 7 Segment LEDs, making it impossible to mount on the box. To solve the issue what I did is desolder the resistor shunt and resolder it to the back of the PCB.

Do not connect the small black wire if you are powering the ammeter from the same source to be read like I did. Otherwise it will give you a wrong reading.

Step 6: Schematic and Soldering

Here is the schematic, it’s very simple really.

  • Use servo wires for the potentiometers, and with electrical tape or some heat shrink cover the solders. The same is done with the LEDs. See the photo for the “polarity” of the LEDs on the PCB I used.
  • After soldering everything, it’s time to fix the meters to the box. Secure them with hot glue, but not too much just in case you need to replace them in the future.

Step 7: Finish!

Everything just about fits in the box. I hope you enjoy reading this Instructable, I'll be happy to answer any questions.

See my other Instructables for cool projects like this one :)

If you like this Instructable please vote for it in the contest. Thank you very much! :)

<p>Hey! Can this circuit step-up voltage too? lets say im powering it with 12V, and on the outup I want 15 V is that possible, or it can only step down the voltage?</p>
<p>Very nicely done!</p>
hello there, I really want to build this PSU. how to remove the blue potensio without breaking the solder pad and track? I've tried desolder it and pull with plier, but the pads and tracks are being pulled too :(
<p>Hi there! If you are not planing on reusing them, use some cutters to cut the top, bit by bit remove it leaving only the three pins, that way you can remove one pin at a time.</p><p>I hope that helps. :)</p>
finally, i successfully made it. i add 2A fuse for protection. thank you very much.
Thank you very much for the answer. I'll try it again. Wish me luck :)
<p>give me circut digram with pcb layout</p>
<p>how to purchase <a href="https://www.instructables.com/id/Mini-adjustable-power-supply/" rel="nofollow">Mini adjustable power supply</a></p><p>send me price </p>
<p>how to add usb module</p>
Thanks newtonn2 very easy to follow ,<br>I did the blue and red meters , didn't use the board or Led's because I will cut a side and add a glass to be able to see the led's on my circuit &amp; will have to replace my potentiometer when I get the 10turn on the mail
<p>Ammazing! Thank you.</p>
<p>I did it too, just a little smaller with no meters. :-)</p>
Love the project and I added a few thing extra like 2 USB ports and 4 negative and 4 positive GPIO outs
<p>can you tell me how to connect correctly ? <br><br>i get reading from volt meter... <br>amp meter no reading....</p>
<p>Hi there, sorry for late reply. </p><p>You have the negative of the voltmeter connected to the output. Do not connect that negative. Only the amp meter should be connected to the negative.</p>
<p>like this? sorry my English not that good</p>
Hi newton,<br>the three wires from the voltmeter where do they go? Do we connect the thin black wire but where does it get connected?
<p>Hi! </p><p>Instead of the LM2596,</p><p>Will this module work: </p><p><a href="http://www.elecdesignworks.com/index.php/shop-layout/power-supplies-regulators/xl4015-detail" rel="nofollow">http://www.elecdesignworks.com/index.php/shop-layo...</a></p><br>
Any idea what the 6 pin header is for next to the output current pot?
NM. I found it. It's a solder matrix kinda thing. Looks VERY similar to my LCD driver's address block: Solder 1 pair, get some option, &amp; so on
<p>I wasn't able to limit current under 300mA with 10K pot, should I increase its value?</p>
What's the hottest it's gotten during normal/heavy use ?
<p>Do you agree with that for Current control a logarithmic potmeter is more useful for low current stuff?</p>
Hi again,<br><br>What do you think about displaying the max current set, with a pushbutton shortcircuiting the output trhough a 0,1-1 ohm 5W resistor?<br>
<p>Give it a try, that most probably works.</p>
<p>Hi newtonn2,<br><br>For me it is not clear when is it in CC or CV mode.<br>E.g. I set const 3V, but on your video when you turned up the current pot the voltage went up!<br>That would kill my MCUs.<br><br>Is there a hack to make it CC+CV mode, so voltage won't rise?<br><br>Thanks,<br>Great project! </p>
<p>It will be fine. If you adjust the voltage fist at 3V, it will not go higher than 3V. If you adjust the current, it will not go higher than the adjusted current. In the video I didn't stop moving the knob after it got to the maximum, that why it appears that the current knob its afecting the voltage.</p><p>I hope that makes sense</p>
<p>I want to make power supply board. can you take me schimatic power supply board?</p>
<p>Hi Newtonn2,</p><p>whilst i have not made the circuit like you have i am using the boards to give me current/voltage control as i like to play with electronics/arduino but seldom get to make anything permanent I had never heard of these devices i have a low priced computer psu and use the circuit to give me the current/voltage control as in the past when testing circuits i would get the magic blue smoke on several components when i got it wrong.</p><p>i have been using these meters:-</p><p>eBay item number:141197770442 from china at &pound;1.39</p><p>eBay item number: 390799784629 from UK at &pound;3.79</p><p> which have both voltage and current in the one device which would make fitting into a box a little easier due to only having one hole to cut.</p><p>good luck with the competition.</p><p>regards Poppy Ann</p>
<p>Hi Poppy Ann.</p><p>That is a very good idea, using the PSU along side the voltage regulator.</p><p>I used one of those meters for my small bench power supply, you can see it here:</p><p><a href="https://www.instructables.com/id/Small-DIY-Bench-Power-Supply/" rel="nofollow">https://www.instructables.com/id/Small-DIY-Bench-Po...</a></p><p>I'm very happy with the performance of those meters. </p><p>About the contest... I won second place !! :) I'm already using the tools Instructable so kindly sent me! </p><p>Thank you very much</p><p>Regards, Newtonn2</p>
<p>Hi Again,</p><p>i just came across this item and gave it a try it works great and the nice thing is there is nothing to do to get it working i just hot glued it to one of my breadboards and connected the power and for &pound;7.62 including shipping is well worth it.</p><p><a href="http://www.banggood.com/DC-LED-Digital-Controlled-Step-Down-Driver-Power-Module-p-910096.html" rel="nofollow">http://www.banggood.com/DC-LED-Digital-Controlled-...</a></p><p>the output current limit can be set in 1mA increments and the output voltage in 0.01V increments, down to 0V. It remembers the last settings for voltage/current when it's disconnected from power, and the output is off by default </p><p>, this saves messing with the little ten turn pots to set it.</p>
<p>That is very cool! I will defenitely get one of those.</p>
The amp meter wire the thin black n red go to input n the thick white is output out same as thick black is that right n the volt meter white n red go to input too yes .is that right newtonn2
Hi acetaz,<br><br>The amp meter connect the thin red wire to input, don't connect the thin black one to anything if you are reading from the same source. <br>The thick black wire is negative reading input, the thick white is negative reading output. <br><br>The volt meter, read and black are input, white is positive measurement voltage.<br><br>I hope that enuf for you to get it working, please post some photos once you have it done.<br>
Where does the white wire on the volt metre go .n do we leave both black wire out form the amp n volt metre thank it a good project to do it look cool man
<p>Hi acetaz, The schematic and all the info you need are in steps 5 and 6. What extra information do you need?</p>
Newton can u please change the wire colour to exactly wat on the volt n amp metre so it easier I keep trying but can't get the volt n amp to move I m new to this thank u
Can some1send me a proper volt n amp wiring thank
<p>So everything seems to be working pretty good..kind of. I'm getting a reading on the ammeter, but I'm not sure what it correlates to as it doesn't adjust either. Any thoughts?</p>
<p>Cool!</p>
Hello Newtonn2, <br>I was just curious if you were close to finishing the instructables for the Small DIY bench power supply.<br>Just wondering;)<br>Thanks.
<p>i made one like yours But mine is just a big bigger and its enclosed in a nice wooden case.</p><p>But all the Schematics are just like yours Same Materials. Cheers</p>
<p>thanks bro.. nice to hear from you. how are you?</p>
That looks cool! I love it!
I don't know why I just can't figure out the ammeter. everything else is built and working fine, but the more I think about the ammeter wiring the more I second guess myself. I just need help with the thick wires. can someone tell me exactly where to hook them?
<p>Almost finished! :)</p><p>Just missing display filters for the almost-too-bright 7-seg displays and descriptions in the LED window.</p><p>Strange thing: I had to use only the tiny black wire on the amps meter, to get it to measure correctly. A bit odd, so I probably have to check that some time.</p>
That looks awesome!!!<br><br>Did you try just with the thick wire? That is what I had to do to get a good reading, the thin wire may be not strong enuf to handle the power.<br><br>Thank you very much for sharing photos of your power suppy!
<p>Yes, I did try using it, since you had that in your description, but I only got a 0.00 reading.</p><p>The thin wire will handle the kind of current I plan on using this for, so that should not be a problem. I did not mount a heath sink either, as while testing this the chip did not get warm at all.. :)</p><p>Some other strange thing: I had mounted a faulty CC/CV LED and while it was mounted the current readout was maxed out to 10A. Soldered in a new LED and the problem was gone.. </p>
Would this be suitable for a bench power supply or should I make one from an atx psu
<p>ATX power supplies does not allow you to regulate the current consumption (as far as I know), so if you short circuit something there it will probably give you max current and then power down - or burn up. (They usually have no fuses you can change) And maybe burn your experiment in the process (and let the magic blue smoke out).</p><p>If you short circuit this (and normal Lab PSUs) it will give you the current you chose, but not more. Often that is sufficient to save your ICs, transistors or whatever you are working with, sometimes even if you connect the VCC/GND the wrong way.</p><p>There are no guarantees if you connect something wrong, but this circuit can save you some problems at least.</p><p>And if you sometimes want 4.5 instead of 3.3, 5 og 12V, you have to regulate the ATX PSU output in some way anyway.</p>

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Bio: Always loved electronics. I like to reuse parts or componets and I Love to be part of the Instructable community.
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