<< Power supply specifications >>
It has been 10 years since the specification of ATX power supply
was provided. Many specification changes have been carried out during
the period. For example, connectors, optional output, etc.
As to electrical specification which was widely changed, -5V output
became optional. With this change, existing motherboard may not
be acceptable to new power supplies. Also, as recent trend of ATX
power supply, several channels of +12V output are being equipped
to supply stable power because power consumption is increasing due
to higher speed of CPU and Graphic board.
The change history of ATX power supply is shown below.
Widely changed point is addition of Aux power connector
and suggestion of +12V power connector of ATX12V specification
as an potion. (Photo 2.6) Aux power connector is 6-pin connector
for +3.3V and +5V output. It is recommended to use when 18A
or more of +3.3V output is required.
+12V power connector is 4-pin connector for 2 channels of
+12V. Due to larger current required for higher performance
of CPU and AGP, +12V power connector is added because 20-pin
connector cannot afford required voltage due to voltage drop.
The intention for this is to decrease the voltage drop in
copper pattern by connecting the connector close to CPU and
AGP. Power supply labeled ATX2.03 corresponding is on sale,
but existing power supply with 20-pin connector is likely
acceptable unless motherboard requires power supply corresponding
Table 2.3 shows Pinout assignment of Aux power connector
and +12V power connector
Photo 2.6 6Pin Aux power connector 6-pin Aux power connector
(Left) 4-pin +12V power connector (Right)
Table 2.3 Pinout assignment of Aux power connector
and +12V power connector
Pinout assignment of Aux power connector
Pinout assignment of +12V power connector
* COM is zero volt level of secondary output.
<< What does the output cable color mean? >>
The color of output cables are various, such as red, white, yellow,
etc. Power supply for PC has several outputs including 5V.
In ATX 2.01 specification, the color or each output is defined as
shown in Table 2.4 However, the coloring belongs to ATX 2.01 specification
in this case.
You need to be careful with coloring. Some manufacturers dare not
use "green" but green/white as ground line to avoid confusion.
Also, individual specification (labels, etc.) must be confirmed
as individual product/manufacturer may
adopt different coloring system (Photo 2.7). However, as to Red
for +5V, Yellow for +12V, and Black for COM, they
are in common in many power supplies.
Table 2.4 Color coding of output cable
Input / Output / Signal
Photo 2.7 Relation between output and color must be confirmed
with product label. Some power supplies have a label that
shows acceptable output current for each output.
<< Source of PC power supply specification >>
PC power supply is compatible with other manufacturer' products
and replaceable. The motherboard or other peripheral devices can
be connected to the power supply without problems as well. This
is because the specifi-cation of PC power supply is standardized
and each power supply manufacturer follows the standard to develop.
You can refer the standard on the Internet below.
In addition, you can refer not only ATX but microATX specification.
Please visit the URL as various PC-related information is disclosed.