With Intel’s new Haswell platform just around the corner, many power supply companies have been rushing to get compatibility confirmed.
You may not know, but Intel’s Haswell C6/C7 power states require a minimum load of 0.05A on the 12V2 rail and many current power supplies will fail to provide that low a current. Many older power supply designs comply with ATX 12V V2.3 design guidelines meaning they only call for load of 0.5A on the CPU power rail. This will mean C6 and C7 power states will be disabled in the bios.
Although we have yet to test, there may be cases that the supplies will become unstable when the processors try to enter into these states. Additionally the problems get worse when we factor in that many power supply units do not report minimum currents supported by the 12V2 rail.
From what we hear, the problem may kick in when the CPU enters sleep mode but with a load on the power supply non primary +3.3V and +5V rails. If the load on these rails hits a certain point (different from PSU to PSU) the +12V can go out of spec – voltages greater than 12.6V. If the +12V is out of spec when the system steps out of sleep state the power supply protection may kick in and stop the power supply from running normally. This situation may involve the end user turning the power supply switch off and back on again.
A power supply that uses a DC to DC design for the non primary +3.3V and +5V rails will not have a problem with the new low power sleep states. The reason is based around the DC to DC converter, used to convert +12V to +3.3V and +5V. This design ensures that there will always be load on the +12V regards of the load the CPU places on the power supply.
Seasonic say “Our full lines of 80 PLUS Platinum and Gold power supplies have been designed to be ready to meet Haswell’s new technical requirements! The ultra efficient Platinum series, which also includes the industry leading true fanless models, and our long running, award winning X Series, which is now supported by the 80 PLUS Gold G series – are all Haswell READY! In addition, our 80 PLUS Bronze line up, consisting of the M12II-750 & 850W models, is also compatible to be used with Intel’s new Haswell Processors.”
Kitguru says: Worth checking into before you get a Haswell processor. You may need to budget for a new power supply as well.