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why the extra voltage?

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mrsteve0924

Cubed Beef Stew Member
Joined
Jul 4, 2013
Location
new york
never really understood why the CPU and graphics card need additional power. Seems all the voltages the board needs is supplied by the 24 pin atx.

if vcore is around 1.3v and GPU about .9v then where is all the extra voltage used? how many 12 volt lines do you need going to these devices?

is it that the board can't physically supply voltages past a certain point and these devices need to be directly fed by the PSU? even still doesn't explain the fact they use very little voltages.
 
The 24pin is for the board, essentially, more than that, but each has its own dedicated power lead. The board uses very little power in and of itself, however the CPU and GPUs use a lot more.

Try pushing 500W of 12v through a 22awg wire and see how long it lasts. ;)

The PCIe slot, PCIe2/3 is good for only 75W and as you likely know, most GPUs use more than that. I am sure you could use only the 24pin, but a complete redesign of the board and components would be required.
 
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Larger gauge is smaller numbers. It's a stupid system, but it's what we use so what the hell.
In any event, in answer to your question, the 12v (and, in some cases, 5v and 3.3v) are further regulated with Buck Regulators to make the lower voltages the CPU and such uses.
The CPU draws enough power that it needs more than the two 12v pins in the 24P connector can supply, especially when those pins are also supplying up to 75w for each PCIe slot.
A single Molex MiniFit-Jr (CPU power, PCIe power, atx24P connector) pin is rated for seven amps, at 12v that is 84 watts. Figure 90% efficiency in the buck regulator and a 95w CPU needs ~105w in input 12V. Of course, if you run the pins right at their maximum rating then you're opening yourself up to issues. Hence, lots of 12V and GND pins for the CPU and for GPUs.

Wire size is involved, but the connectors are generally the weak point. Crap PSUs that use 20gauge wire being the exception. That said, they will probably explode before the wire melts anyway.

The CPU having a dedicated cable also helps keep its input power clean and smooth. Multiple buck regulators feeding off a single cable can get pretty messy.
 
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