Jon Gerow · 06-26-2006 · Category:
Defining the connectors of an ATX power supply
As stated earlier, there
are several connectors on an ATX power supply. Several connectors with several
different wires providing several different voltages. In this section, we'll
take a look at each of the connectors on a typical ATX power supply.
connector is a 20-pin ATX power supply connector. As you can see from the
color-code to the left of the photo, it supplies many
different voltages (+3.3V, +5V, +12V, -12V, -5V) as well as a number of ground
wires and a couple signal wires ("Pwr On" which is how the motherboard
tells the power supply to turn on and "Pwr Good" which reports back
that the voltage of 3.3V and 5V are within spec) There's also a +5V stand by
(+5VSB) that constantly
supplies power to the board even when the PC is off. This voltage is used for
several different CMOS functions like Wake On LAN, Wake On Ring, etc.
The connector above is still an ATX main power connector, but
is of the 24-pin variety. One each additional +3.3V, +5V, +12V and Ground have
been added to the connector.
Some people will tell you that 24-pin connectors are for PCI-e
boards. Funny. PCI-e slots don't use +5V and I can think of a few AGP based
boards that have a 24-pin main power connector.
Fact is, the extra 4-pins simply provide more power to the
motherboard over more wires. This reduces resistance, heat and can provide
unusual to see motherboards with 24-pin connectors on them. Likewise, it's
not unusual to still see power supplies with only 20-pin power connectors.
If you end up with such a mismatch, don't sweat. Use the 20-pin power connector
in the 24-pin socket, as shown in the above photo, and chances are your PC
will work just fine. The above is actually a production model eMachine, built
by FIC, that came from the factory with a 20-pin power supply, despite the
24-pin connector on the board.
main power connectors allow the user to "break
away" the extra four pins so the connector can easily be used in a 20-pin motherboard.
The four pins that are "broken off" need to be tucked away somewhere
inside the PC. These wires can not be connected anywhere else in the PC.
The above left connector
is called a "+12V" and is the
defining characteristic that differentiates an ATX power supply from an ATX12V
power supply. It's also
known as the "P4" connector because they were initially introduced only on
Pentium 4 boards. The connector comprises of two +12V wires and two grounds
and provides voltage to the CPU.
The connector on the right
is called the "EPS connector." It's
typically used on SSI or SMP boards, mostly of the server variety. Essentially,
two of the +12V connectors side by side and comprises of four +12V leads and
four grounds. A quad rail SSI power supply tends to have each pair of +12V
leads on this connector on it's own rail, essentially providing each CPU in
a dual CPU arrangement it's own dedicated rail. Recently, high performance
boards (like the Asus P5N32-SLI Deluxe) have added an EPS connector to provide
better amperage, through more leads.
Like the 20 and 24-pin
ATX main power connectors, EPS and +12V connectors are interchangeable. A
4-pin +12V connector will fit in an EPS receptacle and an EPS connector can
fit into a +12V receptacle if you leave four pins hanging off the edge.
In fact, some power supplies
actually provide an 8-pin EPS that can be split into two 4-pin connectors
(see below left,) one of which can be used for the +12V connector.
The connector in the upper right photo is the PCI Express power connector.
Similar to the +12V and EPS connectors, it consists of only +12V leads and
ground leads. Three of each, to be precise. This connector is used to provide
additional power for PCI-e video cards. Only so much power can be pushed through
the tiny little slot soldered to your motherboard's PCB. By using this connector,
better voltage can be delivered to your video card's GPU because there is less
The above left connector is the most common, and most certainly the most
unchanged connector, of any PC power supply. It's technically called a "peripheral
power connector," although most of us call it a "Molex." Molex is quite a misnomer,
actually. Like Kleenex and Tabasco, Molex is a brand and the company actually
has part numbers for every connector you'd ever find on a power supply or motherboard
and not just the peripheral power connector. And although there are a number
of companies other than Molex making these connectors, we still call them "Molex."
This connector is used for optical drives, hard drives, fans... pretty much
any device in a PC that doesn't have a connector specifically designed for
it. This connector supplies both +12V (yellow wire) and +5V (red wire) and
has two grounds. Typically, the +12V is used to power motors while the +5V
is used to power logic boards.
On the right, we have a floppy power connector. It's wired the same way as
a peripheral power connector with one +12V, one +5V and two grounds, but is
considerably smaller in size for use with devices like floppies, LS120's and
Finally, we have the SATA power connector. This connector provides
power to Serial ATA devices. It provides +12V and +5V just like a peripheral
power connector, but also provides +3.3V. +3.3V has yet to be utilized by SATA
drives, which is why SATA drives currently function properly with standard
peripheral power connectors, but may be implemented in the near future.
- The PC power supply:
- The PC power supply label:
- Defining the connectors of an ATX power supply
- ATX power supplies DO NOT turn on at the flip of a switch
- Testing your power supply's voltage: Software vs. Multimeter
- Power Supply Efficiency
- The Derating Curve
- Power Factor Correction
- The resistance of modular connectors, adapters and splitters