Simple 12V power supply build

[mth5044]

Anybody know any schematics and/or layouts that will put out 12v DC and do all the filtering I need? I'm in the U.S., so 110/120V is good.

[JKowalski]

Transformer -> Rectifier - > Filtering Capacitor -> LM78XX Regulator -> Bypass Capacitor = Basic general purpose power supply! The LM78XX is a three pin regulator IC that you can get for different voltages, the XX is the voltage. For example, LM7809, LM7812. (I think you knew that but w/e)

http://www.generalguitargadgets.com/pdf/ggg_reg_power_supply.pdf

Make sure you get the right transformer, a 12V transformer does not mean 12VDC after filtering but 12VAC RMS, usually.

[mth5044]

Thanks JKowalski 

I'm going to try to make a schematic and layout and I'll post it here to make sure I got it right 

Power scares me 

[mth5044]

Hey wait.. why can't I just use the GGG one you posted w/o the 9v regulator? I'll need 6v too, so instead of diving the voltage, can't I just tap those... secondaries (I think that is what they are called)...

[petemoore]

  Looks like no leads showing here.
  http://www.smallbearelec.com/Detail.bok?no=339
  On the GGG page^, it looks like the secondary center-tap, maybe could be used to get 6vdc, but you'd have to Rectify and filter and regulate again.
  Instead, a 6vdc regulator could take an existing voltage and convert it to DC.
  Never tried it.
  Looks like a tap could be at the diode regulator, or at the 9vdc regulator output.
  Tapping the 6v circuit at the same place the 9v circuit taps means you get as much current as the 6v regulator can handle [or the transformer], after means the 9v regulator gets the current of both the outlet taps and running the 6v regulator.
  I'd test for need of a heat sink for sure on the 6vdc, it's got to drop more voltage, so more heat sinking might be needed.

[mth5044]

Well forgetting that last comment, how about thes

Transfomer:
http://mouser.com/ProductDetail/Hammond/164G16/?qs=JhldWgE%2f6bt%252bWrzyJ9IHwg%3d%3d

Diodes (4x):
http://www.fairchildsemi.com/ds/1N/1N4001.pdf

7812:
http://www.fairchildsemi.com/ds/LM%2FLM7812A.pdf

With corresponding caps.

[compuwade]

Well forgetting that last comment, how about thes

Transfomer:
http://mouser.com/ProductDetail/Hammond/164G16/?qs=JhldWgE%2f6bt%252bWrzyJ9IHwg%3d%3d

Diodes (4x):
http://www.fairchildsemi.com/ds/1N/1N4001.pdf

7812:
http://www.fairchildsemi.com/ds/LM%2FLM7812A.pdf

With corresponding caps.

Everything there looks good. However, the transformer is a little overkill (overpriced). I'm not sure what your gonna use the P/S for, but if you only need an amp or less current you can use any wallwart transformer 12-24 volts @ 1amp to power the regulator. You can buy one at the local thrift store, crack it open, and mount it to a perfboard along with the rest of the circuit. For the 6v tap, you can use a voltage divider (ie: 2 100k resistors across the 12v and ground, tap the middle for 6v) as long as you don't need much current for the 6v tap. If you need more current for the 6v tap, you can connect a 7805 regulator, use resistors to adjust the regulator to 6v and you're done. Or...use a LM317T adjustable regulator for the 6V tap if adjusting the 7805 introduces noise. As you can see there are many ways to get what you need. Search google for DIY power supplies and you'll find many good designs.

Hope this helps!

[R.G.]

Have you read "Power Supplies Basics" at geofex yet?

It covers a whole lot of the ground for you, and is relatively easy to digest.

[mth5044]

Have you read "Power Supplies Basics" at geofex yet?

This is like when you go to the dentist and they ask if you've been flossing 

You know you haven't, they know you haven't, but you usually tell them you did 

Off to GEOFEX. 

[JKowalski]

You know you haven't, they know you haven't, but you usually tell them you did 

Ahahahaha, I love that analogy 

[mth5044]

Ahahahaha, I love that analogy 

Everything there looks good. However, the transformer is a little overkill (overpriced). I'm not sure what your gonna use the P/S for, but if you only need an amp or less current you can use any wallwart transformer 12-24 volts @ 1amp to power the regulator. You can buy one at the local thrift store, crack it open, and mount it to a perfboard along with the rest of the circuit. For the 6v tap, you can use a voltage divider (ie: 2 100k resistors across the 12v and ground, tap the middle for 6v) as long as you don't need much current for the 6v tap. If you need more current for the 6v tap, you can connect a 7805 regulator, use resistors to adjust the regulator to 6v and you're done. Or...use a LM317T adjustable regulator for the 6V tap if adjusting the 7805 introduces noise. As you can see there are many ways to get what you need. Search google for DIY power supplies and you'll find many good designs.

Hope this helps!

That is a good idea, to just crack one open and use the circuit. If I weren't so dead set on making it myself, I would definitely do that.

As for the overkill transformer, how about this one?

http://mouser.com/ProductDetail/Hammond/161G16/?qs=sGAEpiMZZMv4oUrzpPKU3L2j9JyvMp7Oviud9IttgSU%3d

A couple bucks cheaper.

  Looks like no leads showing here.
  http://www.smallbearelec.com/Detail.bok?no=339
  On the GGG page^, it looks like the secondary center-tap, maybe could be used to get 6vdc, but you'd have to Rectify and filter and regulate again.
  Instead, a 6vdc regulator could take an existing voltage and convert it to DC.
  Never tried it.
  Looks like a tap could be at the diode regulator, or at the 9vdc regulator output.
  Tapping the 6v circuit at the same place the 9v circuit taps means you get as much current as the 6v regulator can handle [or the transformer], after means the 9v regulator gets the current of both the outlet taps and running the 6v regulator.
  I'd test for need of a heat sink for sure on the 6vdc, it's got to drop more voltage, so more heat sinking might be needed.

So taping the center for 9 and 6v would be a bad idea? I forgot about the heat sink thing too, so I'll have to keep that in consideration, thanks! I don't know how I missed this post earlier.




So hopefully one final question that I don't think I saw in the geofex article. The primary voltage rating... Is that like the max power the transformer can take? There seems to be 115V and 230V. I know 230V is for some European settings, but I thought the U.S. had 120V coming out of the wall? Is 115V ok?

[compuwade]

It looks like that's the best priced transformer at mouser for what you need. It'll work just fine. Some transformers have primary taps for Europe and the US (ie: 220,230,240 for international, 110,115,120 for US). When you recieve the transformer it will come with a wiring diagram for 230 and 115. Just use the 115 tap and you're good to go. I assume that the 115 rating is in case your wall voltage is slightly higher than 110 volts. Which most are. Mine is actually around 117v. But I don't have any issues with anything I use.

[petemoore]

  Doesn't get any much simpler than this:
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-534
  I just recieved it.
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-536
  ~16 buxx gets you ~1 amp of 12vdc.

[mth5044]

It looks like that's the best priced transformer at mouser for what you need. It'll work just fine. Some transformers have primary taps for Europe and the US (ie: 220,230,240 for international, 110,115,120 for US). When you recieve the transformer it will come with a wiring diagram for 230 and 115. Just use the 115 tap and you're good to go. I assume that the 115 rating is in case your wall voltage is slightly higher than 110 volts. Which most are. Mine is actually around 117v. But I don't have any issues with anything I use.

Good to know!

  Doesn't get any much simpler than this:
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-534
  I just recieved it.
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-536
  ~16 buxx gets you ~1 amp of 12vdc.

Woah I thought desk power units were more expensive than that. In any case, I'll be putting this power in an effect, so unless I take the power out of the enclosure, it may be easier just to build one. I'll keep these in mind though when I need a desk unit!

[mth5044]

Okay here we go!



Transformer: http://mouser.com/ProductDetail/Hammond/161G16/?qs=sGAEpiMZZMv4oUrzpPKU3L2j9JyvMp7Oviud9IttgSU%3d

Not sure if i'll need the heatsinks on the regulators.. I made these in hopes that I wouldn't  

[mth5044]

Bah, just realized I have the regulators messed up. I'll put up the fixed ones in a few minutes.

EDIT: ok, the layout is fixed from the problem I saw.. unfortuantly it meant I had to put in the dreaded jumper overtop the 7805. Oh well.

[compuwade]

It looks like you have the 5 and 6 volt outputs backwards.
As far as heatsinks...It depends on your input voltage. 16v rectified could be as much as 20v after the 1st filter or even more. If this is the case the diferences in input voltages to the regulator output voltages will result in heat. You should be good with the 12v regulator but the 5v regulator could get hot if your application requires any real current.

[mth5044]

It looks like you have the 5 and 6 volt outputs backwards.
As far as heatsinks...It depends on your input voltage. 16v rectified could be as much as 20v after the 1st filter or even more. If this is the case the diferences in input voltages to the regulator output voltages will result in heat. You should be good with the 12v regulator but the 5v regulator could get hot if your application requires any real current.

I fixed that on the second one too, thanks for pointing it out though.

I'm not sure if the circuit is going to require any real current.. it'll be be a bunch of stuff thrown together. What would be a real current? The only thing the 5v will be feeding is 4 pt2399 chips and I can't find a current draw for them in the datasheet.. I may be missing it though

PT2399: http://www.datasheetcatalog.org/datasheet/PrincetonTechnologyCorporation/mXyzsyzt.pdf
7805 : http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Just out of curiosity, why wouldn't i need a fuse for this circuit?

[sean k]

You want 100n caps to ground on either side of all the regulators to help quieten them down and you can also use an opamp for the 6V supply to get a low impedance output or use a 5V regulator with resistors to lift it to 6V. Maybe even make your first 220uf 2 x 100uf with a 100 ohm resitor between them as a low pass to get rid of a little ripple.

[Brymus]

And a fuse on the mains couldnt hurt anything...