Hardware Reference
In-Depth Information
Tip
Although older PC/XT power supplies do not have a connection at connector P8 pin 2, you
still can use them on AT-type motherboards, or vice versa. The presence or absence of the +5V
on that pin has little or no effect on system operation because the remaining +5V wires can
usually carry the load.
Note that all the AT/LPX-type power supplies use the same connectors and pin configurations; to my
knowledge there were never nonstandard variations.
ATX and ATX12V Motherboard Power Connectors
Power supplies conforming to the original ATX and ATX12V 1.x form factor standards or variations
thereof use the following three motherboard power connectors:
• 20-pin main power connector
• 6-pin auxiliary power connector
• 4-pin +12V power connector
The main power connector is always required, but the other two are optional depending on the
application. Consequently, a given ATX or ATX12V power supply can have up to four combinations
of connectors, as listed here:
• Main power connector only
• Main and auxiliary
• Main and +12V
• Main, auxiliary, and +12V
The most common varieties are those including the main only and those with the main and +12V
connectors. Most motherboards that use the +12V connector do not use the auxiliary connector, and
vice versa.
20-Pin Main Power Connector
The 20-pin main power connector is standard for all power supplies conforming to the ATX and
ATX12V 1.x power supply form factors and consists of a Molex Mini-Fit Jr. connector housing with
female terminals. For reference, the connector is Molex part number 39-01-2200 (or equivalent), and
the standard terminals are part number 5556 (see
Figure 18.21
). This is a 20-pin keyed connector
with pins configured, as shown in
Table 18.5
.
The colors for the wires listed are those the ATX
