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Why does CPU have 12V input?

Mobby Dick
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Go to solution Solved by samcool55,

12V comes in and gets turned down to the voltage required by the CPU by the CPU VRM.

The reason it uses 12V and not 5V is because 12V is also easy to work with and you can use lower amps to get the same wattage.

 

Also Vdroop is easier to handle at a higher voltage because you have more room to work with.

 

edit: the VRM is around the CPU and most mid/high-end boards have some form of cooling on it.

That's why you usually see heatsinks around the socket, it's cooling the VRM.

Posted

I was wondering today why a CPU has a 12V input, while using ca. 1.3V-1.4V. Wouldn't it be enough to have a 5V input or even less? Also it would be easier to cool the voltage converters (is this the right english word lol?), wouldn't it?

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unless im mistaken, the PCIE cards are on the 12V rail

the molex/sata are on 5V

the CPU power on the 3.3V rail

im not sure what the 24 pin is on

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http://www.playtool.com/pages/psurailhistory/rails.html

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7 minutes ago, DXMember said:

http://www.playtool.com/pages/psurailhistory/rails.html

 

8 minutes ago, 007agentHP said:

unless im mistaken, the PCIE cards are on the 12V rail

the molex/sata are on 5V

the CPU power on the 3.3V rail

im not sure what the 24 pin is on

 

Quote

 A modern CPU has its own converter on the motherboard which converts 12 volts to whatever voltage the CPU requires. 

According to this the CPU is on the 12V rail, right? Or am I completely retarded?

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  • Solution

12V comes in and gets turned down to the voltage required by the CPU by the CPU VRM.

The reason it uses 12V and not 5V is because 12V is also easy to work with and you can use lower amps to get the same wattage.

 

Also Vdroop is easier to handle at a higher voltage because you have more room to work with.

 

edit: the VRM is around the CPU and most mid/high-end boards have some form of cooling on it.

That's why you usually see heatsinks around the socket, it's cooling the VRM.

If you want my attention, quote meh! D: or just stick an @samcool55 in your post :3

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2 minutes ago, Mobby Dick said:

 

 

According to this the CPU is on the 12V rail, right? Or am I completely retarded?

Everything is on 12V except for USB, those are on 5V directly

we use higher voltage because then we can work with smaller currents and transfer the power more efficiently

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In short, transferring power is easier/more efficient at higher voltages than lower ones. The reasons behind this are in the laws of physics. Power is equal to voltage multiplied by current. Wires aren't perfect conductors, and their losses are proportional to current. Higher current, higher losses. For the same power, if you use a higher voltage and lower current, you have less loss.

 

CPUs do run at very low voltages, so at some point it still has to be converted. This is done on the mobo, close to the CPU, so they can minimise the distance that power has to travel. A high end overclocked CPU could take over 100A, which would fry normal household wiring if you were to try shifting that!

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19 minutes ago, 007agentHP said:

unless im mistaken, the PCIE cards are on the 12V rail

the molex/sata are on 5V

the CPU power on the 3.3V rail

im not sure what the 24 pin is on

PCIe: 12v (from the motherboard)

CPU: 12v

Molex/SATA: 12v and 5v

24pin connector: everything

USB: 5v (from the motherboard)

6/8-pin GPU connector: 12v

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24 minutes ago, 007agentHP said:

the CPU power on the 3.3V rail

I thought CPU power was on the 12V rail...both my modular/semi-modular PSUs support CPU power on PCIe ports/slots which should enforce that it's 12V even more? 

 

25 minutes ago, 007agentHP said:

im not sure what the 24 pin is on

The 24pin has them all ;) 

Looking at my signature are we now? Well too bad there's nothing here...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What? As I said, there seriously is nothing here :) 

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