PSU Myths...Busted

Tagged: Power Supply, psu, Technology
Source: Antec - Read the full article
Posted: 6 years 27 weeks ago

Myth 1: Only Single Rail Power Supplies Can Power Up High-end Graphics Cards!

Some forums users and even some major companies are spreading the idea that single +12V rail power supplies power up the latest graphics cards in a better way, in order to market their products or to scare other users. This is of course total nonsense. To understand this matter better, let’s examine some different scenarios and how the actual power is being distributed to the graphics cards.

There are different kinds of graphics cards in the market today, and depending on the performance of the chip they come with, they have different levels of power consumption as well. The total amount of power that a graphics card consumes is called its thermal design power, or TDP. Graphics cards are usually connected to power supplies by PCI-Express connectors. The number and type of connectors that a card has, howe- ver, can vary wildly. Some cards have one 6-pin PCI-E connector, some have two; some others come with one 6-pin and one 8-pin PCI-E conne- ctor (sometimes referred to as a 6+2-pin PCI-E connector) and again others have none at all. In general you can say that the higher the perform- ance of the graphics card, the more power the graphics card will consume and the higher its TDP will be. All of today’s high-end cards come with a 6-pin and an 8-pin PCI-E jack (sometimes referred to as a 6+2-pin PCI-E jack).

NOTE: Not many people know that some power is also delivered through the PCI-E slot itself – that is, the slot on the motherboard right where you plug the card in. The PCI-E slot is powered by the 24-pin ATX connector attached to the motherboard.

The maximum power distribution for all of the connectors and slots that are able to connect to a graphics card is as follows:

PCI-E slot on the motherboard
(powered by the 24-pin ATX Connector) 

6-pin PCI-E (PEG) Connector
Up to 200 Watts (~17A)
Up to 75 Watts (6.25A) x2 with SLI
and x3 with Triple-SLI 

6+2-pin PCI-E (PEG) Connector 
Up to 200 Watts (~17A)

NOTE: The additional pins of the 6+2-pin PCI-E connector are both ground, and not additional +12V cables as is commonly thought.

All together, a graphics card could theoretically have a power consumption of up to 300 Watts. And, as you can see, regardless of which graphics card you use, there is more than one way for power to be distributed to it: 75W at 6.25A, just from the PCI-E slot, and up to another 200W (at around 17A) from each PCI-E Graphics (PEG) connector. As we’ll see, because of the way this power is being distributed, there is no way that you could possibly overload one of the different +12V rails on an Antec power supply (provided it has the right maximum output wattage).



Elmex8's picture
Joined: 04/23/2009
Posts: 140

I just want to say


Anyway...its not a huge myth it is just a miss understanding that a card switches to the pci-e connectors fully. Most people think about pci-e connector as just that - a connector that connects the GPU to the rest of the components.

Cooler Master HAF 922 | Intel Core i5 750 stock clock | ASUS P7P55D Deluxe | Corsair XMS3 DDR3 4GB |
Asus HD5770 Cu Core | Corsair H50 Cooler  |Windows 7 Ultimate 64 bit | Microsoft Habu |
Logitech Classic Keyboard | Cooler Master 700W Silent Power | ASUS VH236H 23inch |

Joined: 05/24/2008
Posts: 99

Kinda off topic, but did any 1 notice that the cards in the "SLI" Diagram had a displayport, HDMI and 2xdvi? That means those are ATI cards, not nvidia silly antec :P