VGA power.... very difficult question for you!

Graphics card power supply.... very difficult question for you!

Hi guys,
I would like to understand how the VGA power is handled by the motherboard....
I try to explain:
If I have a PCI-E 3.0 graphics card that requires 100watts (TDP=100w) how much power is supplied by the
PCI-E slot and how much is supplied by the 6pin auxiliary connector

A friend says that the graphics card receives all the necessary current from the 6pins aux connector (if present), but I read
in a magazine that the PCI-E slot always provides more power up to 75w, while just above the 75w is given by the 6pins
connector.... who do you think is right?
If it's true that the mainboard PCI-E slot must always provide at least 75w, I think that over time, the mainboard's
circuits perhaps will degrade

Thanks to anyone who can explain to me.

 

Im not an expert but from what i know the PCI-E can provide up to 75W.

The rest of the power is fed directly from the PSU from the 6 Pins and 8 Pins.
If a GPU comes with 6 or 8 pins plugs it is because it needs more energy than what the PCI-E slot can provide, so ALWAYS connect it/them.

 

It is not "VGA power", or "HDMI power", or "DVI power". The motherboard does not know what will be installed in its PCIe slots. It could be a graphics card, but it could be sound card, network card, tuner, or some other type card.

That depends on the card - not the motherboard. And ONLY graphics cards are allowed to pull more than 25W via the slot. A properly designed graphics card will pull a maximum of 75W via the bus slot, but it is important to note that 75W is derived from both 3.3V and 12VDC. And only 3.3V is delivered via the bus.

A good card will pull most of its 12V needs via the separate 12V ATX PCIe power cables from the PSU.

Typically, if you don't connect them, the graphics card will not fire up when the computer is booted. In other words, we have no choice. If a graphics card requires separate power connections, it requires they be connected.

 

I'm sorry, you're right!...
in fact for me VGA is the graphics card..... VGA connection instead is another thing.

Sorry but I don't understand what you mean.... 75W provided by the PCI-E slot is only 3.3V? ....then the current
will be very high!! (75/3.3=22.7ampere)
However if there is the 6pins plugs, the graphics card power supply how it's divided between the PCI-E slot and the 6pins
connector.... The bus slot always supplies 75W even if the graphics card is equipped with 6pins connector?....this I don't
understand...

 

Well, that's still wrong. VGA is just a graphic "protocol". VGA is not a card, not a connector, not a cable, not a monitor. That said, you can have a VGA card, VGA connector, etc., just as you can have a HDMI card, HDMI cable, etc.

No. Sorry. My fault. I was not very clear.

I said, "only 3.3V is delivered via the bus". I should have said, "3.3V is delivered via the bus through the slot only". Meaning the slot supports up to 75W from 3.3V and 12V. Power hungry cards require more power so they get that in the form of 12VDC only (no 3.3 and no 5V) via the extra PCIe power cables. Those cables carry 12V only.

 

It's right, perfect explanation!..... You're really prepared!

Ok, I understand now...... but you did not answered to the most important question for me:
For example, if I have a graphics card that need 100watts, how the power-supply (100w) should be divided between
the PCI-E slot and the 6pins connector??
When there is the 6pins plug on the card, can he to provide all the current that the card need, or not?

Thanks for your kindness... and patience!

 

I'd guess that the Graphics card will pull all of the 75W available from the PCI-E bus and the remaining 25W will be taken from the PSU through the 6 Pin plug.
Also remember that if your GPU is specced for 100W it doesnt means it will use 100W all the time, it will only use that when under full load.

 

Mighty good advice! Maybe there is a bit more that needs to be understood before the complete information is gained. VGA is only the type of card format and as stated not relative to power. Each type of card has its own power requirements. If you look at the power supply power leads inside the power supply, you will see that all the red (5v) wires are tied to its own rail. All yellow (12v) wires are tied to its own rail. Each 4 pin (flat) plug has two black (common wires, the two center pins), one yellow 12 v, one red 5 v. Now the 3.3 v is derived through the motherboard glands. It is not meant for the high current source! You would have to have a circuit diagram of the graphic card to make sure which pin is used. Some divide the current through different wires. (All same color for voltage needed). The mother board doesn't know what you are using in its slots! Therefore it has to be designed to handle a given requirement. Possibly by dividing its source from separate pins. Some graphic cards may have the extra plugs for more current. ALWAYS CONNECT THEM! As stated the glands have current limits.
If you need 100 watts form the 5 volt rail, it would mean that it would have to be able to support 20 Amps! This is a bit too much and can be divided with extra pins going to the same rail inside the power supply. This is only an example. Maybe it does need part of the 100 watt from the 12 volt rail. Then the yellow wires would be needed and the amount of current from the five volt rail would be lowered. Only the design engineer would need to know this. Usually, if a graphic board fits, it is designed to work! Special cards have special needs and has to be followed.
When I design anything, the power is sourced from the main supply rail through multi pins to lower the overall pin resistance. Therefore less heat is developed causing breakdowns. To make a long story short, MAKE SURE YOU FOLLOW THE MANUFACTURING INSTRUCTIONS TO THE LETTER! If there are extra requirements for power, always connect them. If you can't or don't have the proper plugs, the card probably isn't designed for that motherboard anyway!
This is only general information. Read your graphic card's instructions closely!
Good luck.

 

That depends on the capability of the power supply. A 300W supply may not provide enough current on the 12V rail for the card where a 500W PSU could.

I don't think so. My "guess" (and I am pretty sure it is correct) is a card needing power from an extra power connection will "NOT" pull maximum 12V power through the slot, but instead through the extra cable(s). This will (1) minimize motherboard heat issues and (2) preserve much of the 12V running through the motherboard for other connected devices that are powered just through motherboard connections. The card will certainly pull any 3.3 or 5V through the slot it needs though.

@ Royzx - it is critical to understand there is no standard color coding requirement for PSUs! I sure wish there was but there isn't. There is a "recommended" color code, but not a required code, and sadly, not all PSU makers conform to the recommended color coding. Therefore, it is essential to note that when discussing "red" wires here and "yellow" wires there, they do NOT always mean the same thing.

Because anything that plugs into the wall can kill, I advise against anyone who is not a qualified electronics technician to stay out of power supplies! Do not open them. Do not stick anything inside them (except maybe a wooden Popsicle stick to hold the fan(s) stationary while blasting out the dust). There are NO "user-serviceable" parts inside a PSU!

Ummm, no. Sorry but that is not correct. An ATX PSU provides +12VDC, +5VDC, and +3.3VDC (as well as +5Vsb standby voltage) to the motherboard. The motherboard's voltage divider circuits do not create or "derive" 3.3V. Motherboard power/voltage divider circuits do, however, provide 1.x volts and 2.x volts for RAM and the CPU, and other motherboard components.

 

So apparently it's difficult to determine how much current is supplied by the PCI-E bus, and how much instead by
the 6pins aux connector....

I've given this topic because I'm very undecided about the graphics card to buy:
I'm not a gamer, so I need a card which consumes not much power and that requires a little current also from the
PCI-E bus, so as not "to ruin" the mainboard early!
However if possible, I would like a graphics card having decent hardware-acceleration performances with
videoediting softwares like Adobe Premiere CS6 and After effects CS6...

So my choice will be between nVidia GTX650 with TDP=64w and having the auxiliary 6pins connector (for example
the Gigabyte GV-650OC-2GI or the EVGA 02G-P4-2651-KR) or the new nVidia GTX750 with TDP=55w, but WITHOUT aux
6pins connector (for example the EVGA 02G-P4-2752-KR or the Zotac ZT-70701-10M)

The GTX750 is more powerful and consumes less, but unfortunately pulls all the current through the PCI-E bus ...sigh!!
....and this is not "beneficial" for the mainboard!
Which is the best for a long life of mainboard?

 

This information is not important. Why do you feel it is? We know it is 75W max through the slot. And we know that all cards are different.

What is important is (1) the card does not draw too much current through the slot and that would not happen unless there was a major component failure and (2) that the PSU has the necessary connectors and at least the minimum current needed to power the card, and the remaining computer components. That's all that matters.

Not a factor. Don't worry about it. All you need to worry about is (2) above.

 

Ehi guys, excuse me if I return to this topic, but I found a very interesting articles about the power consumption of graphic card through
the PCI-e slot and through the 6pins plug, take a look here:

http://electronics.stackexchange.co...ull-power-from-both-the-slot-and-the-external

and here: http://www.jonnyguru.com/forums/showthread.php?t=5104

For example it's said that into graphics cards there are multiple power districts across the board and drive them from the PCI-e slot and
the cables separately (probably via a power switching controller) and they're all running on a common ground from the same PSU, so it works
quite nicely. Usually you'll see the VRAM and peripheral logic running from the PCI-e slot supply, and the GPU itself running from the PSU.

This would be very good because it means that the current is divided almost equally between the PCI-E slot and the 6pin aux connector!....then
the mainboard circuits related to the PCI-E slot, will never be overloaded.
What do you think about??

 

Not all that is said in your first link is true. Polynomial says,

That is not true. While there "may" be a supply that allows that, for example, some PSUs with single rails, that is only because the cables go back to the same tap. But some PSUs have more than one "independent" 12V rail that are isolated and/or balanced internally through "added" intelligence (control circuitry) - depending on the sophistication of the design (read: $$$).

The ATX12V Form Factor PSU Design Guide, Ver 2.2, March 2005 governs how all PC power supplies will function. If it does not specify the rails can be connected by the user (and it doesn't) then for sure, you cannot - UNLESS that is an added design feature of that specific PSU.

 

Ok, probably what you say is right....., but I wanted to point out that the graphics cards equipped with the 6pins plug the necessary
current is almost equally divided between the Pci-e slot and the 6pins plug...... also with modest power cards.
Then probably the mainboard Pci-e slot will never come to deliver the maximum 75watt.....and this would be very good for life
of mainboard.....are you agree?

 

Not really. And I say that because power demands with most computer components are not anywhere near constant for any length of time. A "static" (no animation) display takes very little horsepower. Once a pixel is set, it takes little to no additional input from the card until its setting needs to change.

Even with advanced 3D animated gaming, the animation is happening with just a few of the "objects" being displayed. Most of the background, for example, remains the same so the card does not need to continually reprocess all that data. And when the entire image changes, it does so in about 1/60th of a second (based on refresh settings). In other words, even when pressed, the card rarely maxes out power and does not max out power for very long even if it is maxed out.

Also, the motherboard is designed to support that power. In fact, many boards have 2 or even 3 slots that may pull lots of power through the board. So, no big deal AS LONG AS the case is providing an adequate supply of cool air through the case, and you, the user, fulfill your user-responsibilities of keeping the case interior, vents, fans and boards/cards clean of heat trapping dust.

 

Ok, Thank you very very much Bill-Bright for your valuable explanations!! .....and for your patience!

One last thing to conclude:
On my mainboard type Asus P8H77-V, which is equipped with two PCI-E slots, can I safely install a graphics card such as GTX-750Ti (for example
the model Zotac ZT-70601-10M) even if the 6pins aux connector is missing?
About the power supply (PSU) should not have any problem because it's a 500watt unit, and precisely the Corsair CX500 model.

Thanks again

 

What do you mean? Missing from where?

If a graphics card has an auxillary power connection, it MUST be connected to a compatible power supply. If a card does not have any extra power connections, none need be connected as all the power will come via the slot.