The Stilt
Golden Member
- Dec 5, 2015
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Hmm, what about FIVR... Does that make boards vrm any simpler ? I would guess so, looking at the haswell boards.
Yes.
Because FIVR input voltage is much higher (1.8V nominal) than on any even remotely modern CPU, the motherboard VRM can be built to much lower standards than usually since the currents are significantly lower.
While the FIVR itself decreases the overall efficiency by quite a lot, the motherboard VRM on these boards is slightly more efficient than usual. Higher output voltage means the duty cycle is higher and the lower currents will reduce the losses through the VRM and the conduction path.
But still despite that, the overall efficiency of FIVR is smaller than on conventional configurations. FIVR operates at extremely high frequencies (due the physical inductor size, in core), around 450x faster (~140MHz) than convertional the VRMs found on motherboards and graphics cards.
Intel has not published the efficiency of newer FIVR implementations, however Haswell's FIVR had around 78% efficiency according to Intel.
The total efficiency of Haswell VRMs (motherboard + FIVR) is around 69% (78% FIVR, 88% motherboard), whereas a high-end conventional VRM on a motherboard can hit around 85% total efficiency on average.