Author Topic: What is the motivation of intel to want PSUs that are 12V only?  (Read 7085 times)

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Offline epigramxTopic starter

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https://www.intel.com/content/dam/www/public/us/en/documents/guides/single-rail-power-supply-platform-atx12vo-design-guide.pdf

The introduction claims that it is high time for PSUs to become more efficient.
But why would they want to make other circuits less efficient?
 

Offline Rerouter

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #1 on: March 05, 2020, 10:13:43 am »
Almost all high power computer switching supplies are built around using the 12V rail, with RAM and onboard peripherals barely pulling anything from the 5V rail, and due to the whole molex/sata thing, even 3.3V rails are getting less popular, as its not hard to locally down convert from 5V.

the RAM and other mid current loads on a motherboard are not hard to shift back to the 12V rail, in fact a number of overclocking boards already do this to save costs on unique parts when you need high current power stages.

When you pulling say 40A @ 12V, loosing 2-3W in switching losses for the lower power low voltage rails may be much better if you gain back 30W on the initial conversion of that high current load.
 

Offline Zero999

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #2 on: March 05, 2020, 10:29:57 am »
Because losses in cables, at very low voltages are high. Assuming everything else is equal, halving the voltage, results in four times the losses in cables. This is because P = I2R, reducing the voltage requires double the current, for the same power and 22 = 4.

Modern switched mode power supplies can be very efficient, so it make more sense to distribute a higher voltage and perform the voltage regulation, as close to the load, as possible. This is done with mains electricity, which is transmitted over long distances, at high voltages >100kV and stepped down to lower and lower voltages near the the load: 10kV is common around towns and cities, with 120V to 400V only traveling a few hundred metres.
« Last Edit: March 05, 2020, 11:21:38 am by Zero999 »
 
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Offline epigramxTopic starter

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #3 on: March 05, 2020, 10:31:24 am »
Almost all high power computer switching supplies are built around using the 12V rail, with RAM and onboard peripherals barely pulling anything from the 5V rail, and due to the whole molex/sata thing, even 3.3V rails are getting less popular, as its not hard to locally down convert from 5V.

the RAM and other mid current loads on a motherboard are not hard to shift back to the 12V rail, in fact a number of overclocking boards already do this to save costs on unique parts when you need high current power stages.

When you pulling say 40A @ 12V, loosing 2-3W in switching losses for the lower power low voltage rails may be much better if you gain back 30W on the initial conversion of that high current load.
So you're implying they're going to favor very high power PCs with this and consider low power desktops a minority.
 

Offline bd139

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #4 on: March 05, 2020, 11:13:55 am »
I was getting all excited when I saw this mostly from the vain hope that they'd get rid of Molex connectors. But nope :(

As for the multiple voltages, this is a legacy hang back going back as far as the 1980s. Even latest normal ATX spec has -12V still. That needs to die.

If they introduce single voltage that means smaller, simpler, more reliable power supplies, easier to manage power supply efficiency etc. And every device can ship with its own slave switching converters to get whatever voltages it needs out. The biggest consumer in my PC is currently yanking 116.3A @ 1.475V which is quite frankly a shit load of current so I'd rather have that being converter right next to where it is being used which is exactly what's happening now.

Also if everything is 12V, consider laptops etc. If all peripherals standardise on that we're getting smaller desktop PCs too which would be mostly cooling rather than fat bundles of snakes in a gigantic box.
 
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Offline G7PSK

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #5 on: March 05, 2020, 11:25:02 am »
I can't see the problem, laptops have only one voltage input and do every thing onboard as do many of the ultra small computers, may also be easier for power factor correction on the mains.
 
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Offline epigramxTopic starter

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #6 on: March 05, 2020, 12:08:36 pm »
losses in cables
That's a good point, because the alternative is more efficient because there are usually lower losses in PCB connections.
That raises the question though why not go 15V or 20V or 24V since they are relatively human safe.
 

Offline Circlotron

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #7 on: March 05, 2020, 12:19:23 pm »
That raises the question though why not go 15V or 20V or 24V since they are relatively human safe.
My guess is because you would use a synchronous buck regulator for local conversion to the lower voltage, and when you start going to say 24V input to the reg you need a pair of mosfets with say 30V rating and consequently a higher RDSon figure than a lower voltage mosfet, hence higher conduction losses. Don't forget you have to switch the same current that goes out of the reg but at the voltage that goes in. Maybe 12V is the sweet spot?
 

Online tunk

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #8 on: March 05, 2020, 12:29:03 pm »
The cynic in me says it's because the total cost is lower.
A positive side effect may be higher efficiency.
 

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #9 on: March 05, 2020, 12:34:13 pm »
That raises the question though why not go 15V or 20V or 24V since they are relatively human safe.
My guess is because you would use a synchronous buck regulator for local conversion to the lower voltage, and when you start going to say 24V input to the reg you need a pair of mosfets with say 30V rating and consequently a higher RDSon figure than a lower voltage mosfet, hence higher conduction losses. Don't forget you have to switch the same current that goes out of the reg but at the voltage that goes in. Maybe 12V is the sweet spot?

12v is a nice compromise for gate drive
 

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #10 on: March 05, 2020, 01:10:41 pm »
The adoption of USB-C that supports adjustable voltage is phasing out a lot of 5V rail load.
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Offline madires

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #11 on: March 05, 2020, 01:17:48 pm »
Many high efficiency ATX PSUs have just a 12V secondary anyway, i.e. the other voltages are created by DC/DC converters fed by the 12V rail. This design improves the overall efficiency. No need to mess around with regulating multiple secondaries. Moving the DC/DC converters to the mainboard will help a little bit more with the efficiency.
 
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Offline tszaboo

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #12 on: March 05, 2020, 03:15:28 pm »
In the server world, this switch was made a long time ago . It resulted a much smaller power supply. An DC-DC stepdown is now probably cheaper than the wire and the connector. But I really hope they dont stop here, and finally design a successor for the ATX (not BTX) because this one is getting outdated. Without the 5.25" stuff if possible please. And power and data through 1 cable for drives please.
 
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Offline tooki

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #13 on: March 05, 2020, 04:12:30 pm »
Almost all high power computer switching supplies are built around using the 12V rail, with RAM and onboard peripherals barely pulling anything from the 5V rail, and due to the whole molex/sata thing, even 3.3V rails are getting less popular, as its not hard to locally down convert from 5V.

the RAM and other mid current loads on a motherboard are not hard to shift back to the 12V rail, in fact a number of overclocking boards already do this to save costs on unique parts when you need high current power stages.

When you pulling say 40A @ 12V, loosing 2-3W in switching losses for the lower power low voltage rails may be much better if you gain back 30W on the initial conversion of that high current load.
So you're implying they're going to favor very high power PCs with this and consider low power desktops a minority.
No, it's not "favoring" them. High-power PCs simply represent the larger challenge; low-power ones will still benefit.
 

Offline tooki

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #14 on: March 05, 2020, 04:14:03 pm »
In the server world, this switch was made a long time ago . It resulted a much smaller power supply. An DC-DC stepdown is now probably cheaper than the wire and the connector. But I really hope they dont stop here, and finally design a successor for the ATX (not BTX) because this one is getting outdated. Without the 5.25" stuff if possible please. And power and data through 1 cable for drives please.
And also, doesn't 12V only also make it super easy and efficient to provide battery backup using 12V SLA batteries, instead of complex and inefficient UPSs? I recall reading years ago about Google rolling its own motherboards using 12V only, with a connector for a 12V battery right on the mobo.
 

Offline OwO

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #15 on: March 05, 2020, 04:19:06 pm »
12V is still way too low. A 500W system would draw 42A, which is difficult to transport and requires huge connectors with many pins. 48V is more reasonable; the motherboard can then step it down to 12V and then to the individual voltages. DC-DC conversion stages are never a problem; I use single rail supply even for small modules (e.g. FPGA board + daughterboards), and always generate all rails locally.

EDIT: pretty sure google uses 48V at the server level and something like 400V DC at the rack level.

Personally I would go with 70V. It's the highest I can still comfortably touch and at this level the higher the better. The DC-DC converter on the motherboard doesn't have to be transformerless.
« Last Edit: March 05, 2020, 04:22:47 pm by OwO »
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Offline SiliconWizard

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #16 on: March 05, 2020, 04:35:50 pm »
12V is still way too low. A 500W system would draw 42A, which is difficult to transport and requires huge connectors with many pins. 48V is more reasonable; the motherboard can then step it down to 12V and then to the individual voltages. DC-DC conversion stages are never a problem; I use single rail supply even for small modules (e.g. FPGA board + daughterboards), and always generate all rails locally.
(...)

12V is part of the legacy I think, but there's another reason IMO. The idea of down-converting voltages more locally is generally a good one. But 12V is likely close to the sweet spot for the following reason: step-down converter ICs that operate with higher input voltages than this are just going to be much more expensive, as this gets into the "high-voltage" territory for current CMOS processes. 48V or over would make local step-down converting much more expensive. You could say that you can always chain them to overcome this, but then you have a chain of efficiencies which would make efficiency for the low voltages (which currently draw the most current on computer motherboards) pretty poor. Just a thought.
 

Online Gregg

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #17 on: March 05, 2020, 07:15:55 pm »
Single 12VDC would certainly make sense for a UPS type system; no inverter needed.   :-+
 

Offline Red Squirrel

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #18 on: March 05, 2020, 07:40:38 pm »
Would be cool if they made it 13.5v actually, would make power backup simpler, just needed a battery set to float voltage.   Currently, PCs have lot of power rails so doing a straight DC type backup would be too complex.   3.3v, 5v, 12v, -12v... I feel I'm missing one. Is there a -5v?

Really a 48v/54v standard would be cool.   That's how telecom gear works.
 

Offline ve7xen

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #19 on: March 05, 2020, 07:57:25 pm »
12V is still way too low. A 500W system would draw 42A, which is difficult to transport and requires huge connectors with many pins. 48V is more reasonable; the motherboard can then step it down to 12V and then to the individual voltages. DC-DC conversion stages are never a problem; I use single rail supply even for small modules (e.g. FPGA board + daughterboards), and always generate all rails locally.

EDIT: pretty sure google uses 48V at the server level and something like 400V DC at the rack level.

48V is the standard at the bladecentre level, many enterprise level servers will have an option for a redundant 48V-12V DC-DC converter instead of a line voltage AC-DC 12V PSU

The 12V only desktops I see have a really short, multiconductor PSU tail but I don't see much brand variety so that may not be typical

-48VDC is even more legacy than the 12V rail in ATX. It goes back to telco central office standards and their lead-acid battery plants, probably predates home computers entirely. Still common in telecom to have -48VDC as the main power distribution, so most gear you might find in a telco facility (networking, servers, etc.) will have a PSU option for that. It does make a lot of sense from a high reliability point of view, it's a simple design and easy to scale, but it also probably wouldn't be the choice if you were in a completely green field today.
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Offline mariush

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #20 on: March 05, 2020, 08:42:07 pm »
My guess is that this is requested a lot by OEM manufacturers like HP and Dell who want to reduce the number of wires and save a few pennies this way and get less complaints about proprietary / custom connectors on their power supplies.
HP is known for using custom connectors in their workstation systems for example, Dell also has some power supplies with custom connectors.

It's an OK move but it's sad that Intel didn't have the guts to go further and work with power supply and motherboard manufacturers to innovate further.
Seems like they just stuck to 12v standby and 12v to power everything.

I would like to see a new revision of the standard to introduce 20v (-10% .. 5%) (to allow possibility of powering a system from DC In barrel jack using 18.5v adapters common in laptops), while keeping 12v for backwards compatibility.
20v is standardized in USB, so having 20v and 12v would make it possible to use USB connectors to power a monitor for example, or fancier external storage.

It shouldn't be very hard for the psu to include some kind of microcontroller or something with a usb 1.0 or 2.0 connection to the system, allowing the system to communicate with the psu and enumerate capabilities ... 
For example i'm 12v only, i'm 12v and 20v, i'm 20v only (motherboard could have this tiny chip by the DC In connector and detect 12v or 18.5v..20v and pretend it's a psu with 12v only or 20v only ... useful for small systems with an APU that consume 40-60w max... power them from a 90w laptop adapter or a 200w atx psu)...
psu could also say current on each voltage, total wattage, indicate if the 12v is derived from 20v using dc-dc converters..
 motherboard can query and get number of fans, fan rpm, may even be able to tell psu to adjust fan rpm (but psu would have the final say as in motherboard can't override psu's safeties ... if psu controller needs to spin fan at 50% to keep cool, user would not be able to force fan to shut down)
maybe support rgb if the power supply has leds inside...

With just two output voltages it could be possible to have a current shunt on each 12v or each 20v pair of wires ... or worst case per 2x4 connector (eps, pci-e 6/8 pin etc)...

Some would argue 5v should also stay as an option , as that could allow future very low power laptops and tablets to be powered completely from a 10-15w 5v laptop adapter but nah, lots of usb chargers have option to go up to 12v or higher and dc-dc converters are tinier and tinier and more efficient.
« Last Edit: March 05, 2020, 08:44:36 pm by mariush »
 

Offline Circlotron

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #21 on: March 05, 2020, 08:59:31 pm »
That raises the question though why not go 15V or 20V or 24V since they are relatively human safe.
My guess is because you would use a synchronous buck regulator for local conversion to the lower voltage, and when you start going to say 24V input to the reg you need a pair of mosfets with say 30V rating and consequently a higher RDSon figure than a lower voltage mosfet, hence higher conduction losses. Don't forget you have to switch the same current that goes out of the reg but at the voltage that goes in. Maybe 12V is the sweet spot?
Further to this, to maintain the same peak to peak ripple current in the buck reg inductor, you need proportionally greater inductance as the input voltage goes up. More copper means greater losses.
 

Offline tszaboo

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #22 on: March 05, 2020, 10:41:24 pm »
Personally I would go with 70V. It's the highest I can still comfortably touch and at this level the higher the better. The DC-DC converter on the motherboard doesn't have to be transformerless.
Nah. There are only 28 buck converters from TI above 70V, with max current of 3A. There are over 240 with max voltage between 14 and 24V, with max current of 40A. And you dont end up with large ripple voltage and current, and big capacitors and inductors. 12V is a good compromise.
 

Offline ajb

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #23 on: March 05, 2020, 10:51:35 pm »
The cynic in me says it's because the total cost is lower.
A positive side effect may be higher efficiency.

The total cost is lower *because* it's more efficient, though, no cynicism required.  At least within the context of a desktop PC, what's the disadvantage of moving to a single power rail and PoL converters wherever needed?
 
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Offline David Hess

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Re: What is the motivation of intel to want PSUs that are 12V only?
« Reply #24 on: March 06, 2020, 12:44:41 am »
12V is part of the legacy I think, but there's another reason IMO. The idea of down-converting voltages more locally is generally a good one. But 12V is likely close to the sweet spot for the following reason: step-down converter ICs that operate with higher input voltages than this are just going to be much more expensive, as this gets into the "high-voltage" territory for current CMOS processes. 48V or over would make local step-down converting much more expensive. You could say that you can always chain them to overcome this, but then you have a chain of efficiencies which would make efficiency for the low voltages (which currently draw the most current on computer motherboards) pretty poor. Just a thought.

The ratio of input to output voltage for a transformer-less converter is a factor.  48 volts to 1 volt yields about a 2% duty cycle which makes things difficult, although not impossible, so it is usually better, and more efficient, to invert 48 volts to a lower voltage and then use a buck converter for the lowest voltage supplies.  Vicor actually sells inverters and regulated converters to do this.
 


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