Hardware Reference
In-Depth Information
The sense signals are used so that the graphics card can detect what types of connector(s)
are attached, and therefore how much total power is available. For example, if a graphics
cardneedsafull300Wandhasbothan8-pinand6-pinconnectoronboard,ifyouwereto
attach two 6-pin power supply connectors, the card would “sense” that it had only 225W
available and, depending on the design, it could either shut down or operate in a reduced
functionality mode.
Due to special keying on the 8-pin connector, it cannot be plugged into a 6-pin socket.
Because of this, many power supply manufacturers include 8-pin connectors made in a
“6+2” arrangement, where the portion containing the two extra pins can be disconnected,
leaving a 6-pin connector that will, of course, work in a 6-pin socket.
Caution
The 8-pin PCI Express Auxiliary Power Connector and the 8-pin EPS12V CPU Power Con-
nector use similar Molex Mini-Fit Jr. connector housings. Although they are keyed differ-
ently, the keying can be overcome by sufficient force such that you can plug an EPS12V
power connector into a graphics card, or a PCI Express power connector into a motherboard.
Either of these scenarios results in +12V being directly shorted to ground, potentially des-
troying the motherboard, graphics card, or power supply.
The6-pinconnectorusestwo+12Vwirestocarryupto75W,whereasthe8-pinconnector
uses three +12V wires to carry up to 150W. Although these figures are what the specific-
ations allow, the wires and terminals of each connector are technically capable of hand-
ling much more power. Each pin in the PCI Express auxiliary power connectors is rated
to handle up to 8 amps of current using standard terminals—more if using HCS or Plus
HCS terminals. By counting the number of terminals, you can calculate the power-hand-
ling capability of the connector (see Table 18.24 ).
Table 18.24 PCI Express Graphics Power Connector Maximum Power-Handling Capabilities
Even though the specification allows for a delivery capability of 75W (6-pin connector)
or 150 watts (8-pin connector), the total power-handling capacity of these connectors is at
 
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