sluk wrote:
I have a question how could a 65W power adapter power up a motherboard with CPU alone already 65W+?
65W is the TDP of the E7200 CPU -- but this does not mean every E7200 actually draws 65W when "100% loaded" on every program. TDP has always been something of an average power estimate that system integrators have used to design the CPU cooling systems around. In the days of the P4 and Prescott, Intel's TDP figures were usually lower than the actual maximum power its CPUs could draw, but with the Core2 architecture, we've never been able to get anywhere close to the TDP of any processors. This also holds true for AMD chips. Keep in mind that Prime95 and CPUBurn, the most power demanding of any CPU stress utilities we've found, draw more power continuously than any real application you're ever likely to use, too.
The Power Notes on p.7 of the article tells of real measurements on that system:
Quote:
During thermal/load testing, the AC power consumption at full load started at 60W and increased slowly to a maximum of 66W. With the coolest configuration tested, the maximum power dropped slightly to 63W. This shows that the motherboard VRM and/or the DC/DC converter efficiency drops as they get hotter. It may also be the case that both were red-lined by the system's power demand when the system was not cooled adequately. The second fan caused no clearly measurable increase in power; the increase was probably within the margin of error of the power meter (under 1W).
Because AC power demand was 66W, we can surmise that the DC power output of the adapter was around 56W -- Antec specifies 85% min efficiency for the adapter. That tells you the real power demand of the CPU was probably not higher than 45W.
I've been power testing a brand new AMD Phenom2 965 rated for 125W TDP recently. At stock settings, our sample pulls only 108W at the 2x12V Aux12V socket, which is where the motherboard gets all the power for the CPU. 108W isn't actually all going to the CPU -- the 12V feed goes to the VRMs (DC/DC converters) which downvolts it to 1.25V for the CPU. There are conversion losses, energy lost as heat, which is why VRMs get hot. The best efficiency we can assume for any motherboard is probably ~90%. More typically it is less than that -- depends on the board class; a server board usually has higher efficiency. Anyway, all this means that our 125W TDP CPU only pulls maybe 95W with the most stressful utility we can throw at it.
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