ATX12VO OPERATION, POWER CONNECTORS AND PINOUTS
WHAT IS ATX12VO?
ATX12VO is a single rail power supply standard developed by Intel. This standard eliminates 5V and 3.3V rails from desktop power supply leaving only 12V power and 12V standby. All other voltages requires for the processor and other PC components will have to be produced on the motherboard. Such architecture reduces the size and cost of the PSU and increases its efficiency. The size and cost are obviously reduced by eliminating additional outputs and simplifying transformer design. The efficiency is increased because higher voltage output generally has lower losses than lower voltage ones. This single rail approach was actually proposed by Google in 2006 white paper, but it took more than a decade until Intel came up with such specification. Note that ATX12VO platform does not necessarily reduce the overall cost and power consumption of the computer because additional power conversion is just shifted from PSU to the motherboard.
POWER CONNECTORS AND
PINOUTS
The main power connector for motherboard is 10-pin Mini-Fit Jr style, part number CP-01110031-X2 (CP01376S). The pinout diagram shows the front (i.e. pin-side) view. The colors represent recommended colors of the wires. There is no guarantee of course, that the manufacturers won't use other colors. Note that the diagram in Intel's design guide shows back view (i.e. from wires side). The pins for this header are rated at 9A maximum. Assuming some derating (8A/pin), such header can provide 288 watt. This is sufficient for most ATX and its derivatives (like SFX and TFX). Optional remote sensing allows to compensate for voltage drop on +12V cable wires by taking feedback from motherboard rather than from PSU board. However, if remote sense is used, only two power pins are left for the main rail. In this case, the cable can provide 192W (again, assuming 8A/pin).
If motherboard requires more wattage than the main cable can provide, the spec allows for additional connectors.
Extra board 6-pin connector 12V1 and CPU connector 12V2 are the same as in ATX2 systems. Additional power can be provided from 8-pin power connector 12V2 (see pinout diagram). It is sometimes called EPS connector because it was used in EPS server power supplies.
The Intel spec notes that CPU 12V2 rail should have a separate current limit to meet the requirements of EN 60950 and UL 60950. This is not new- there was always such requirement. In practice, as far as I know, most PSU manufacturers implement a combined current limit for all 12V rails. Separate current limit would require a separate regulator on 12V2, which would mean higher cost and extra complexity.
PCI EXPRESS CONNECTORS
The ATX12VO standard allows 6-pin or 8-pin connectors for PCI Express graphic expansion cards (sometimes called PEG). Old video cards have connectors with 6-pin. The newer ones per PCI Express specification 2.0 have 8 pins. Therefore many power supplies provide so-called 6+2 PCI-E cable, which works with both types. The 6+2 part has a detachable 2-pin piece that you can leave unplugged for the 6-pin card- see the diagram to the right. Note that 8-pin PCI-E connector looks similar to 8-pin extra power connector, but their pin designations are different and they should not be mixed up. PCI headers are usually labelled as such.
See also connectors and pinouts for ATX12V and for some brand name desktop computers.
<---------------------------------------------------------------------------------------------------------------------------------->