Instructables

Variable Lab Power Supply

Picture of Variable Lab Power Supply
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I do a lot of work with low voltage electronics which often require various voltages. I was getting sick of constantly set up a series of batteries and then selecting the appropriate resistor just to test a single small part of a circuit. Ideally, I wanted to be able to dial in to a voltage simply and quickly and test. So that is what I made, a variable lab power supply for testing electronics. 

This variable power supply provides anywhere between 1V - 10.7V DC. It is really easy to make one slight adjustment to allow a range of AC voltages, but I never use AC, so I didn't bother. It is also really easy to provide 0V-36V, but I hardly ever need above 10V, so I left it with the smaller components that I had readily available. 

There are several other lines available off of the var psu including: 12V, -12V, 5V, -5V, 3.3V, GND, Variable (1-10.7V), and a mains-outlet extension (115V AC). The mimimum current limit on any of the lines is 2 amps, the max limit is 20 A on one of the lines. I forget the exact limits on each particular line. These limits will be based on the power supply unit (PSU) you choose to use in this project.

To all the comments I am sure will ensue, yes, I could have used a PSU and just installed binding posts, but I rather liked the geometry of this box. The size was right if I some day want to mount it to the workbench (when I get a real workbench) and there was plenty of space to install the fancy bells and whistles that I wanted (namely, the panel meters and the switch along with the variable line).

Anyways, this is a fantastic addition to your electronics workbench setup!
 
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one more question . why you connect 12 volts in put to the schematic ? when you was can connect 12v+ with 12v- and get variable 22-23v max

LostRite (author)  maxubergamer6 hours ago

While it is possible to do that, I think it is a better solution to use my way and here is why: 1) I rarely need a variable line above 12V but below 24V, 2) the -12V line has a much smaller limited current on it (I can't remember how low, but close to 300mA I think. Maybe you can spot the specs in an image somewhere) so a variable line up to ~24V wouldn't be able to source nearly as much current as the variable line I have shown. 3) finally, if you still want a variable line above 12V, just use the -12V line as ground and add 12 to whatever the variable meter reads :)
Hope this helps!

LostRite (author)  LostRite6 hours ago

Looks like I said minimum is 2A on any line but I don't think I can get that with the -12V line. So not sure about that. I guess what i said above would hold still though. Depends on your PSU specs.

paradise974024 months ago

This is one of the nicest units I have seen..this would be a GREAT addition to anyones bench, Thank you for sharing this.

does anyone see that the lm317 t is without heatsink and it's gonna be bad if it gonna heat to match or this not problem if you have in the case fan ? good instructables and sorry for my bad English I am Israeli 15 yers old boy :)
LostRite (author)  maxubergamer11 days ago

Hasn't been a problem so far and I use it regularly. I rarely run at higher current or for extended duration on the variable line though. I moved the temp probe one there to see what would change but nothing much changed. Either it isn't a problem with the fans on or I am not pushing the limits enough :)

LostRite (author)  paradise974024 months ago

Thanks!

Eternal668 months ago
Hi, that is a nice PS. But have a big problem: max voltage is 12 volt indeed have power full power supply. my suggestion is using a buck-boost inverters that is available all around the world!!
Cattmy11 months ago
How can I add current adjustment to this?
LostRite (author)  Cattmy10 months ago
That would be a lot more challenging and I don't think I would be the one to ask. I toyed around with the idea of current regulation when designing this but decided it was too complicated for what I needed and could understand properly. If you figure it out, post a link or description of how to do it on this page if you remember. I would like to know as well.
novosysta1 year ago
i cant understand how thermometr is working if without resistance it has 26 on the screen.Tell me please .
paul czech republic
LostRite (author)  novosysta1 year ago
The thermometer was kinda a random add-on for me. I didn't know how to use it when I put it on and assumed it is working correctly. According to the sensor and panel (which came connected, from adafruit) all I had to do was plug it in I believe. And 26 seems reasonable so I assume it is working. I don't know what you mean by "without resistance". I do know that the thermometer is accurate (within 1 degree) of the temperature here. But since the box does not heat very well, the highest I have ever seen the display is 28. I didn't test it much at all I'm afraid. I hope I gave some info that might help you out.
Bongmaster1 year ago
sonic screwdriver ;) vital tool
LostRite (author)  Bongmaster1 year ago
Always!
i got the one thats actually a screwdriver too x3
VERY NICE JOB !!!
vicsv1 year ago
I don't see the volt meter connections?
Wow this is complex.
LoL Yes sonic screwdriver.
Wait BONG Master? Jesuuuuus!