Sure, you could just as easily buy one, but where's the fun in that?

I present to you the first of three power supplies I'm designing and building. The ultimate goal is to design an ATX power supply with the following characteristics:

• Takes 12VDC input
• Input power can come from a car battery, UPS battery, or AC-to-DC converter
• Max 200 watts output

This first unit is a simple, unregulated 12V DC power supply. It can be used to test case mods, you could hook a cigarette lighter receptacle up to it, or any other purpose. Really, you could run the world off +12VDC.

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*WHOOSH!*

what was that?

oh, it was Wixx's enormous knowledge flying over my head.

I'm impressed. Before i had suspicion that you were some sort of engineer, but now im convinced. Are you an engineering student or something?

nice design, keep us posted on its functionality.

lol, you sure that isnt the diagram for a flux capacitor...

electonics noObies

ok, u say this i an unregulated 200w off a cig lighter??i thought cig lighter only prov 150w??

i believe he said the final goal is 200W, not that this one did it... he also said there were others to follow (2 to be precise)

im not a tech n00b clown, i can read stuff like that like its dr seuss...no offense or anything

EDIT: btw, what he has there is actually a good project, most of the parts could be purchased at radio shack for about...well...$25-30...but the experience alone will be worth it and there might be a cheaper solution to what i have here...

project case - $2-5
pcboard - about $2
diodes - $1-2
fuses- $2
115vAC to 12vAC step down transformer - about $10
rectifier (for making ac...dc) - forgot...used to get them from my dad for free...and im pretty sure you can get step down transformers/rectifiers but i havent done anything like this in a while so your mileage may vary)
cigarette lighter plug housing - $3-5....
gromets - ~$2
power cord - $2-3
thin guage wire - $3-5
maybee a couple of potentiometers and a pack of assorted resistors and capacitors...just for fine tuning and ensuring steady power in case you ever decide to add delicate electronics that are sensitive to power spikes or dips
LEDs for power indicator

this is a nice introduction to electronics for someone wanting the experience and already own a soldering iron, some solder, and a desolderer...and if you dont, the shack has them for like around $12 for the whole set i think...you might wanna get some flux (capacitor, lol, alright im over it) and some component cooler or canned air (takes the headache out of handling freshly soldered parts), and maybee a roll of desoldering braid...just because.

just remember to heat up the part that you are going to solder, and not the solder itself, for example, if you are soldering two wires together, rest the two wires...twisted together...on the tip of the iron, and gently rub the solder across the heated wire...letting it flow into the WIRE and not all over the iron...doing otherwise WILL result in very undesirable results...a messed up iron tip, and wasted solder that will just have to be sucked back up...doubling and tripling the amount of work you will have to do...so dont do it

and no, im not a electronics engineer, i just stayed at a Holiday Inn Express...

UPDATE: I've got a better design for the 110VAC-to-12VDC converter. This one is regulated and provides a max. of 30 amps which is way more than I need (200 watts / 12 volts = 16.66 amps needed for final design). When it comes to power, better to have too much than not enough I suppose. Sorry for the huge size.

Basically what's happening here is that the LM340A IC will provide about 500-600mA of power. After the current draw exceeds that the TIP2955 power transistors begin conducting electricity. Each transistor can handle 5 amps, so six of them wired in parallel should give 30 amps. The 1A fuse protects the IC in case of an overload, and the 30A fuse protects everything else. You can see the LEDs included which are visual indicators if the fuses blow.

The intended use, once I've designed the 12VDC ATX power supply, is to be put in a car. Therefore, this power supply allows me to simulate the car's electrical system (hence the reason for the switched ignition output) without actually having to hook anything up to the car.

And yes, I am an engineering student.

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that was a little bit more along the lines of what i was thinking of...cept id prolly have some sort of variable output or maybe a status indicator or something...maybe a way to adjust the voltages up to 32 volts...

Good design, but the switch should be connected after the 30A fuse(otherwise, you will get lots of blown transistors if you short the switched output to ground).
And have you considered switching technology?
It is much more compact(that is how PC power supplies are designed).

Quote: Originally posted by star882 Good design, but the switch should be connected after the 30A fuse(otherwise, you will get lots of blown transistors if you short the switched output to ground). And have you considered switching technology? It is much more compact(that is how PC power supplies are designed).

Oh, whoops, my bad, I wasn't paying attention to that part of the diagram. You are correct, the switch should be after the fuse.

The 12VDC ATX power supply I'm going to make will probably be switching, the schematic above is just to generate the +12VDC input the real power supply will need.

If anybody can do this............. it WIXX!!

Wixx,
you are amazing!

great idea wixx, i too was thinking of something along these lines but lost motivation, keep us posted with the final outcome. Maybe, hopefully it will light a fire under me

whooo do i feel dumber than dog sh i t. Man I gotta go back outside and start polishing the wheels on da trailer. HOLY BAT TURDS. I cant wait to show pa this. He may think i dun went and got some learnin. this wasnt taught in my "huKt on Foniks WerKt fer Me!!" books

Quick schematic question Wixx, do you draw those by hand? or do have a program for drawing the schematics(if so what is it, i could use it)

I had a program posted not to long ago but it was deemed unappropriate and I took the link out.. It was Electronic Workbench - Multisim 2001 ... Very good for building and testing your circuits on your pc

scapegoat--my normal schematic software (AutoCAD) is not working for some reason so I threw those schematics together with SmartDraw. I think you can download the trial version off of Cnet's download site (http://download.cnet.com).

Of course, the absolute, most important part of any case mod, electronics gadget, or doomsday device is to know exactly what you're doing before you pick up any tools at all. After spending most of this afternoon reviewing ATX power supply specifications and similar projects attempted by others, I have decided to design an ATX power supply that meets the following specifications:

• +12VDC @ 10 amps
• +5VDC @ 15 amps
• +3.3VDC @ 20 amps
• -12VDC @ 0.3 amps
• -5VDC @ 0.3 amps
• +5VDC standby @ 1.5 amps

You'll find similar information listed on the top of a normal ATX power supply. This is roughly the equivalent of what a normal 200 watt power supply can handle, which is enough to power all but the most extreme high-performance machines. I have also settled on the following design goals:

• The power supply will accept between 8 and 14 volts DC input to generate the appropriate outputs.
• The power supply will be directly powered off of a battery. Specifically, this battery.
• It will be capable of notifying the computer attached to it the status of input voltages, battery level, and ignition status.
• It will be ATX compliant, but not compatiable with Pentium 4 motherboards.

It looks like I can use the Maxim MAX787 voltage regulator to generate the +5V rail, and the MAX788 voltage regulator to generate the +3.3V rail with the fewest parts and highest efficiency. Keeping a stable +12V rail is going to be the hardest, I'm looking at possibly using the National Semiconductor LM2577 step-up regulator, or possibly the LM2578 flyback regulator. It all depends on how well those parts will interface with the part I've chosen for the -5 and -12 rails, the LM320L. If anyone has any suggestions on part substitutions or circuit designs, I'd love to hear it. In any case, I can tell you already this is going to be one bad mofo of a power supply, with some equally bad mofo'n heat sinks to cool the regulators. The idea here is to make things modular, so if I don't need as much power, I can leave parts of the circuit out for a smaller, cooler PSU.

Inclusion of a buffer battey and ignition sensing logic ensures that the power supply, if connected to a car, would neither cause noise in the car's electrical systems nor drain the main car battery when the car was off. Otherwise, the whole thing can be hooked up to a 110VAC-to-12VDC converter (schematic posted above) to simulate being in a car. At this point, the device becomes a direct UPS, completely eliminating things like expensive fancy filter circuits to get rid of spikes and noise since the source is a clean DC battery.

At the end of this project, I will have built a combination ATX power supply and UPS for cheaper than an industrial 12VDC PSU, UPS, and standard 110VAC PSU. Just goes to show you what a little bit of modding can accomplish .

Ok, I'm a little lost. Now, I'm an electronics technician (not an engineer however), so I know a thing or two (but thats about it) about DC circuits. What are the bases of those transistors connected to? Why do you have 120VAC input if you are getting this from a car? Are you hooking up an inverter to the cars 12VDC? This is where I get confused. Basically I see an AC input, a transformer, a bridge rectifier and some extra stuff on the output (where the bases of those transistors are connected to I don't know what). I read that you are making this so that you can basically have an ATX power supply that runs off of 12VDC, is that right? Where is the part where you have the 12VDC input? I'm not being an ass, i'm just a confused tech.

What I'm confused about is what is the advantage?
I can understand the "want" of doing it yourself, but why?