Intel has worked hard on raising the efficiency of the new Haswell processors and not the least the circuits will consume very little power when idle. It has now been revealed that Haswell may be too efficient for some of our current power supplies that are not specified to maintain the low voltage that is required.
The new Haswell architecture sports super efficient sleep modes that will minimize power consumption of, e.g. notebooks when sleeping. Sources to VR-Zone have stated that the new sleep modes C6 and C7 may be incompatible with ATX power supplies on the market today. The reason is the extremely low voltage the processor draws from the units.
With Ivy Bridge and third generation Core processors Intel had specified a lowest possible current of 0.5 Ampere. With Haswell and fourth generation Core processors this is lowered by 90% to 0.05 Ampere. This results in extremely low power consumption at only 0.6 watt on the 12 V rail, but may also become a potential problem.
Especially older power supplies and those in the budget range may have a hard time supplying currents at these low levels. This is since both the ATX12V v2.3 specification and Intel’s last generation processor circuits only required a minimum load of 0.5 Ampere.
If the power supply can’t supply currents of the right strength it will trigger the UVP or OVP protections and shut down the system all together. At the same time, the biggest problem could be that few manufacturers specify the lowest possible load of their power supplies, which could make it a real journey to try and find out if current and future power supplies can deliver the currents required.
To avoid problems, motherboard makers recommend adding BIOS settings for activating and deactivating the new C6/C7 sleep modes to avoid compatibility problems. Notebooks will have the most to gain from these new sleep modes, but since these are designed and assembled by the same company it should not be an issue.
