Inline PSU Tester
– User’s Guide
Page 5
Background
A power supply unit (or PSU) converts mains AC to low-voltage regulated DC power
for the internal components of a computer. The PSU normally su3.3 V, +5 V,
and +12 V and -12V to a PC. Older systems (before Pentium 4 and Athlon XP
platforms) were designed to draw most power from 5 V and 3.3 V rails, while the
newer machines draw most of their power from the 12 V rail. The −12 V supply is
primarily used to provide the negative supply voltage for RS-232 ports and is also
used by one pin on conventional PCI slots to provide a reference voltage for some
models of sound cards.
ATX and ATX12V standards
ATX (Advanced Technology eXtended) is a motherboard and power supply
configuration specification developed by Intel in 1995. The specification defines the
key mechanical dimensions, mounting point, I/O panel, power and connector
interfaces between a computer case, a motherboard and a power supply. There is also
another specification called ATX12V which only describes the PSU.
Major changes in ATX/ATX12V revisions
ATX Version
Introduction date
Main changes from previous version
ATX
1995
-
Created 20 pin main power cable
-
Included 4 pin peripheral power cable
-
Included floppy power cable
ATX12V 1.0
2000
-
Added 4 pin 12V power cable. Older
computers put most of their load on 3.3
and 5 volts. As time passed, computers
drew more and more of their load from
12V.
-
Added 6 pin auxiliary power cable. It was
added to provide extra wattage to
motherboards for 3.3 and 5 volts.
-
Increased 12V output power
ATX12V 1.3
2003
-
Added SATA power cable
-
Made -5V rail optional
-
Increased 12V output power
ATX12V 2.0
2003
-
Changed to 24 pin main power cable. The
24-pin main power connector was added
in ATX12V 2.0 to provide extra power
needed by PCI Express slots. The older 20
pin main power cable only has one 12V
line.
-
Removed 6 pin auxiliary power cable
-
Added 20A current limit to rails
-
Increased 12V output power
-
Reduced 3.3V and 5V output power
Table 1
As of now, the latest version is ATX12V v2.4, published in April 2013.