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 Post subject: PC PSU.. Why?
PostPosted: Fri Sep 24, 2010 10:14 am 
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I was just thinking. Do PC's really need all the different voltages for the motherboard to be created in a seperate box - then have the power transferred through 20+ individual wires to the motherboard?

Would it not be cleaner and more efficient to have the PSU just produce +5V and +12V, then have the other voltages converted either on the motherboard, or via a plug in module (which needen't be much larger than the current ATX connector). After all, the power has to be PWM converted again on modern motherboard to supply the specific voltages for the CPU e.t.c - it seems wasteful converting the voltage twice.

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PostPosted: Fri Sep 24, 2010 11:09 am 
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its all down to design considerations, its much easier to do all the different voltages in the PSU, than do it on the motherboard. it was done on the motherboard, this would increase the size of the motherboard by upto 50% in size. as the copper tracks would need to be thicker and wider

Also to get better stablized voltages, then the voltages need star grounded/earthed, which is very difficult on a motherboard, star grounding/earthing, prevents stray eddie currants moving around the motherboard which can blow a motherboard to kingdom come and back again.

so why dont they do this with laptops. simple the above applies to high ampage, which are present in a desktop( 15 amps or more) , and not in a laptop(less than 6 amps)

i hope that helps, as ive tried to keep the answer simple, without going into PHD stuff

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PostPosted: Fri Sep 24, 2010 12:13 pm 
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You're pretty much right on. The part you left out is cost. A good PSU that will last years costs $150 or less. Start adding all that tech into a complete motherboard, you'd wind up with a $500 part to replace if part of the power supply wound up blowing, along with a strong likelihood of the entire system being taken out with it. Now you're looking at $1000 to replace something that could have cost $100. Doesn't make a whole lot of sense, does it?

Power always, always needs to be seperated and isolated from the components to avoid catastrophe.

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PostPosted: Fri Sep 24, 2010 2:38 pm 
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The PSU does emit a lot of RFI, and its case shields that annoying field. Some still escapes via the power cord, very little via the internal leads to the mobo. And a PSU does have dangerously high voltages (200 VDC usually) on exposed components. Then you need a transformer to provide the desired voltages that are isolated from the line voltage. Filtering, regulation and over-voltage/current limits are easier to contain within a separate case. There were some old (VERY OLD!) HP models that had an integrated PSU on the mobo.. cumbersome and heavy!

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PostPosted: Sat Sep 25, 2010 3:45 am 
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I can't stop myself from thinking that people have flamed my suggestion without thinking it through. :mb_furious::

I never proposed that the initial AC LV to DC ELV was done on mobo - I said..

Quote:
Would it not be cleaner and more efficient to have the PSU just produce +5V and +12V


Today’s motherboards have their own DC-DC converter to produce ~1V @>100A. Why can't the converter convert from 12V? I would not be surprised if they were not converting from the 12V already to reduce the current transported around the board.

Does the motherboard need any other voltages? -12V at 0.5A - no expense or bulk to mirror the +12V on board.

I did some reasearch.

http://www.mini-box.com/picoPSU-160-XT

So there already is an ATX plug in PSU - albeit not harvesting enough currants to satisfy the appetite of a high powered CPU, but enough current for low power CPUs.
Hard to tell, but it looks like it uses a ZVC topology?

http://static.googleusercontent.com/ext ... _paper.pdf

Google use 12V only PSUs for their server farms to save energy and money!

Looks like it could also make sense to also drop the 5V from the PSU - maybe the 5V could be a plug in converter which breaks out to provide +5V and +12V for drives and accessories.

Back in the day memory and CPU used 3.3V so it made sense for the PSU to produce this at high current. This is no longer the case, so why go through all the difficulty of producing a low voltage at high current (which is hard) and cabling it to the motherboard if it is not even required?

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PostPosted: Sat Sep 25, 2010 6:36 am 
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is your picoPSU to the ATX standard? No.
why is Google also using +12V-only PSUs? So they don't need a DC-to-AC converter in case of a power failure = cheaper.

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PostPosted: Sat Sep 25, 2010 11:42 am 
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evasive wrote:
is your picoPSU to the ATX standard? No.


The Pico is no way near high powered enough to meet the standard, but it does demonstrate that a cheap plug in module could produce -12V and +5V from a +12V supply. The same package could significantly beef up on the +5V supply if it not also have to supply +3.3V, and a dedicated form factor standard could allow a larger footprint for the module.

evasive wrote:
why is Google also using +12V-only PSUs? So they don't need a DC-to-AC converter in case of a power failure = cheaper.


The white paper was Google announcing that they were working to promote a +12V only PSU as a general PC standard incl. home use). If a company like Google promotes an idea then surely it must have at least a little credence (even if it did not come to fruition).

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PostPosted: Sat Sep 25, 2010 2:25 pm 
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Nobody ever said it wasn't POSSIBLE, just not practical. Integrated PSU's will be along soon enough, I think, but not within any kind of reasonable timeframe. RIght now, electronics designs need that seperation.........I mean, can you imagine the noise that would come out of an onboard soundcard with the PSU built into the board? Add another $100 for a nice soundcard with noise canceling circuitry built in to that expanded price list. You'll also be limited on your video cards, since it wouldn't be feasable (or even possible) to change PSU's for a larger one to support that GTX975 eight core card you want.

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 Post subject: Re: PC PSU.. Why?
PostPosted: Sat Sep 25, 2010 3:48 pm 
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Twisty wrote:
Would it not be cleaner and more efficient to have the PSU just produce +5V and +12V, then have the other voltages converted either on the motherboard, or via a plug in module..?

The modern processor needs a +3.3 volt source. That is further reduced by power transistors to 1.4 volts or other levels needed in the CPU operation. Plus the +5 volts through regulators. Add up the amps consumed by the +3.3 and +5 volt needs.. you are up around 75 amps or so, likely higher with faster CPU types. Minimal, the supply or source would have to provide 100 amps combined for just those needs. Then there may be 35 amps or more drawn from the +12 volt source. If there were only a source for +12 volts, then the minimal current would be on the order of 150 amps or higher. That would equate to 15+ amps at 120 volts, per Ohm's Law. The PSU for computers and other electronics uses a very high-frequency core transformer to convert pulsed (switched) DC of around 200 volts. The secondary windings are indeed robust, capable of minimal 60 amps continuous in some models. But the number of turns in that core transformer are low for the secondary, compared to the primary. The input for a PSU is typically 115 volts AC, but through a process of conversion to DC it rises to nearly 200 VDC. The actual current draw on the AC mains is 200 watts, or about 2 amps maximum (average).

Yes, there are many special-design computers for use on only a +12 volt supply.. for mobile or military needs. But the alternator on such vehicles must put out over 100 amps, to keep the other systems and vehicle battery topped off. The use of an "Atom" CPU by Intel or similar is designed to switch state rapidly from idle to full bore, as needed.. conserving energy. If a standard CPU were used, the current draw would be nearly a continuous high level unless the system were in a 'sleep' mode. All laptops use a battery that is typically 12~14 volts. The voltages for the CPU needs are provided by on-board regulators. But the CPU is designed for extreme energy conservation. If a standard CPU were installed, likely battery life would be only a few minutes.. if that.

In a nutshell.. possible, yes.. practical, no, as there are other avenues of design that address such needs.

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PostPosted: Sat Sep 25, 2010 11:10 pm 
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What I would be looking for first, and has already been done by Zalman, is a proprietary design integraged into the case itself. Thin, wall mounted, fanless, but powerful enough to handle mid-range components. Or, if you prefer, an iMac or similar all-in-one with a specially designed power unit.

Karl's dead on in the power department, modern systems are simply too powerful to allow for a small, in-built PSU on the motherboard that would require nothing but a wall wart like a laptop. I kinda disagree on the desktop processor point, for how long were desktop P3's put in lappies (like mine) but still retained good battery life? They never did it with a P4 to my knowlege, those have always been mobile and far less powerful on the draw.

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