Dead economical (and easy) +/-12V regulated power supply.

[MapacheRaper]

I had the idea the past month while designing my first modular and I thought it could be uselful for some people around.

You know that LM2596 Buck Step-down converters that are at 1USD in ebay:



The idea is simple. Feed two with a power supply that is at least 15V and have quite juice. A spare laptop adapter, around 18-19V is ideal.

Regulate both outs to get 12V in each converter. Join one positive out with the negative of the other. This is our GND. The free positive is the +12 and the free negative is the -12.

You can regulate them for +/-15V +/-9V if it´s what you need.

Put a bank of electrolitic capacitors on both outs. Two 3300uF of at least 16V should work.

Quirks

The LM2596´s works in the 150KHz range, but this ones shows ripples in the 50KHz area. Obviously they are fakes, I suspect they are discarded or fakes LM2576 witch operates precisely in the 50KHz area.

After some tests normally you can load it until 2A. They get warm/hot, but keep working nicely. That should be the absolute maximum. You may not use more than 750mA per rail to be in the safe side and mostly using homemade/cheap modules. You don´t want to fry an expensive one in case the converter blows and let the 19v flow intact. Be ultra careful with that. This is an experimental idea from a newbie hobbist-me- that could not work properly.

Also, remember to put heatsinks if the converters get warm/hot

The ripple is there, but it´s usable and filtrable. To filter it you need an oscilloscope- that I hadn´t yet- some ceramic caps and ferrite tubes. A homemade ferrite with 7 loops of transformer wire can do the trick.


This guy get stellar results filtering LM2596´s with this technique:

https://www.youtube.com/watch?v=h9xU1K2bqrI&t=0s&list=LLayLziN5aF2KjyYGsomq0Iw&index=31

(the filtering magic starts at around 4min of the video)

If someone has a good oscilloscope and wants to try it would be fantastic.

Remember to load the circuit to test it!

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[LFLab]

Not being familiar with that regulator, does that have floating or isolated outputs? If so, that yeah that will work.

[MapacheRaper]

Not really sure what you mean. The negative input and output are directly connected, if it´s what you mean. The regulation happens in the positive rail.

Does it means it´s floating type?. Should this be a problem?

[blue hell]

[MapacheRaper]

Damn!

So it was too good to be true. Now Im guessing if you can put some diodes (not sure if before the output or after) to isolate the circuit.

Any ideas on how to isolate it and render it usable would be most welcome.

Thanks for pointing at the error!

[AlanP]

TANSTAAFL, I guess.

You could try using two regulators, and TWO dc power supplies.

But by then, you may as well just use two decent 12VDC wallwart power supplies, some filtering, and not bother with these modules.

[blue hell]

Yeah well .. or use a transformer with a mid tap, four diodes in a bridge and two fat caps.

Can not find an example with one bridge, but basically it would be a combination of :

http://www.circuitstoday.com/wp-content/uploads/2011/03/dual-supply-for-tone-control-circuit.png

and

https://i.stack.imgur.com/EUq8D.png

where the LM350's are replaced by your switching regulators.

[MapacheRaper]

Yeah, I have spent some good hours trying to find some loophole to feed it from only one DC source, but seems like it´s contranatura. Diodes don´t work and there seems to not exist a negative counterparty to the LM2575 that insulates the negative rail.

In fact I have a centertapped transformer coming home, that I will adjust with LM317 and LM337, the typical suspects. This is for my main and first Euro setup and I want it as clean as possible.

The idea of this thread was to recycle a laptop brickwall- that all people has some spare- and use the LM2595 chinese modules to get the most cheap possible power supply. (And playing with the filtering stage to tame decently)

In fact after crunching some offers in ebay, is way more cheap to buy 2x 15v 2A brickwalls than a CT transformer, but this is more elegant, for sure.

Thank you so much for taking the time to help and to solve the puzzle

[LFLab]

The alternative is a DC/DC converter, those can be used with a laptop PSU, if you choose the right one. They usually also have isolated outputs (but not all!) and can be had with two pairs of outputs. Think about 40 euros in a 30watt version.

[JovianPyx]

[LFLab]

[MapacheRaper]

I read somewhere in muffwligger´s that the simple AC current produces more ripple, noise and is less eficient. Tons of pages of obsesivecompulsiviness minutia and details about the topic. So I thoght, fuck, lets go the "pro" route.

After that I have see tons of people recomending and happy with the single AC regulators and for sure will be my next power supply.

That way I can even switch between supplies and ear it by myself.

By the way, today I have received the center tapped transformer. 15/-15V, 1 A in every rail. The thing is MASSIVE. I was expection something more reasonably sized and lightweight. So big that probably doesn´t enter in the eurorack case, or left very little depth for some number of modules

I don´t recomment it for starters at all. Whatever, lets see how it works!

[blue hell]

[AlanP]

The Meanwell RT-65B is popular on MW -- you need a load on the 5V rail, however, so a power resistor for that may be needed.

[gabbagabi]

Does anyone has experience with computer power supplys ?
They have a lot of power, they are ready made, no-one use them,
is there a why?

[AlanP]

Computer PSU's are not known for low ripple current, they are known for a lot of power on tap.

Actually... what is the minimum load for a typical computer PSU? I know that minimum load is a factor for switching PSU's

[gabbagabi]

in all those "instrutables" they talk about 10Ohm 5Watt or better 10Watt-Resistor at the 5V Output.

that should be 0,5Amp.

edit: i had a little read in the hardest elektonik form of the world (of course it is german) "microcontroller.net" they where mostly not so happy about them,
because of bad behaveiour when load changes and that u have like 20A on the point where one had produced a short circuit.


the one happy guy is using a 21Watt/6V car lightbulb on the 5V rail as a load, so he can take always a good load out of the 12V rail, there seems to be a dependence between the 5V and 12V rail.

and we sdiy-honks are not producing a lot of load changes

stays the argument with the shortcircuit

[MapacheRaper]

[blue hell]

[MapacheRaper]

[MapacheRaper]

So it seems somebody has build a design like this and its working... I don´t understand how, it should be shorting the power brick...

Magic? Magic smoke? Tons of magic smoke??

http://nozoid.com/diy-eurorack-power-supply/

[PHOBoS]

that setup makes my brain hurt a bit
The positive side is wired as usual but the negative side is rather odd. It's actually pretty much as you draw it in the first post,
which would work with 2 seperate supplies for the input, but the GND is unconnected and still becomes the -12V.

[MapacheRaper]

Yeah, probably nozoid used a digital LFO that was only feeding from the +12 and GND, so it worked. It´s the only logical explanation

[blue hell]

Hah, of course .. just redraw it a bit .. and it will make sense .. the negative regulator regulates ground to be 12V above -12V .. and the positive one has GND as a reference to regulate its output to 12V above that.

Actually .. I once had a PSU built like that .. with two positive regulators to make a dual supply ...and had forgotten about it..

[elektrouwe]

sorry, but I see many false statements in this thread and the nice looking
noizoid page is full of "alternative facts"
I tried to discuss it here ( with no response from the author):
https://www.muffwiggler.com/forum/topic-212318.html