The Power Supply Conundrum

[dklingen]

OK,

I have seen numerous comments and reviews regarding the "requirement" for high dollar power supplies. We had been discussing it in the thread power supply recommendations which I shouldn't have.

I see post after post about the +12V rail current being the key to overclocking. Enlighten me, since the 3.3V rail powers the CPU. The +12V rail powers the PCI bus and the drives. See this link if you don't believe me: http://www.gruntville.com/reviews/PSUs/Antec_TruePower_550/page2.php

Why isn't the focus on the 3.3V rail?

I do believe there are poor quality PS manufactures out there to be wary of. However, I don't see the need to buy an expensive power supply. I have overclocked on stock power supplies without issue.

So, prove me wrong...

 

[sangyup81]

Does the 3.3v power the Chipset and Memory too? My CPU, Chipset, and RAM are undervolted right now. What about the +5v rail?

BTW, I'm using an OCZ Powerstream 420w.

 

[imported_whatever]

That is old information. Current CPUs are powered off of the 12v rail, which is why a Prescott, which pulls roughly 120W, can function on a power supply listed there (if you look at the 3.3v ratings, none of them manage to output 120W)

 

[sangyup81]

There's no date on that article. Starting with P4's motherboards had a +12v connector.

 

[dklingen]

Why would you want to regulate the 12V rail down to 1.xV for a CPU. Think of the heat the regulator would generate. Whatever, Please provide me with a link that supports your statement that Athlon64/Pentium4 use the 12V rail.

Thanks!

 

[Duvie]

Sorry that is what it is....

I believe the AGP/Vdimm and NB chipset are all off the 3.3v rail, but the cpu uses the 12v rail...On top of that the last few years starting with the northwoods cpu are requiring extra 12v to the board for cpu alone.....The vid cards are also taken supplemental 12v through the molex plugs on the boards...drives use 12v on the motors of the drive...

Bottom line 12v is big and even bigger once you start bumping vcore, ocing the cpu and vid card, and adding multple HDDs and DVD/burner drives....

 

[zakee00]

Originally posted by: dklingen
Why would you want to regulate the 12V rail down to 1.xV for a CPU. Think of the heat the regulator would generate. Whatever, Please provide me with a link that supports your statement that Athlon64/Pentium4 use the 12V rail.

Thanks!

if the PROCESSOR was using 12v, think of the heat THAT would generate!
its pretty obvious it uses the 12v rail, since all recent mobos have the new 12v connector for the processor. that was unnecessary earlier because processors didn't need the extra juice.
thats just the way processors work i guess, not everything needs a shatload of voltage nor would you want it that way.

 

[VirtualLarry]

Originally posted by: dklingen
Why would you want to regulate the 12V rail down to 1.xV for a CPU. Think of the heat the regulator would generate. Whatever, Please provide me with a link that supports your statement that Athlon64/Pentium4 use the 12V rail.
Thanks!

My guess is that the major issue is the supply current necessary, and due to the losses from the transmission cable, it's better if you can transfer the power using a higher voltage (lower current), as compared to a lower voltage (with higher current). I'm not an EE though.
The proof should be obvious - Intel specified that both ATX PSUs, and newer mobos, should all have that additional "P4 Ready" connector on them, the 4-pin molex that carries additional +12V current. Even more recently, they've moved to make the ATX PSU connector a 24-bit job, instead of 20-pin, and integrate those extra wires right into them. Hence the new ATX 2.0 standard.

 

[dklingen]

OK,

I concede - you guys are right. If you do the calculation. The 3.3V line typically has 28 amps max = 92.4 watts max. The 12V line is typically 18+ amps max = 216 watts max. Since the P4 and Athlon64 have a TPD over 100 watts each this makes sense. What is shocking is think how much current a microprocessor is drawing 100watts / 1.7V Vcore = ~59amps of current. That is just stunning!

Thanks for proving me wrong.

I still don't buy into the NEED for an expensive power supply (just one that has high currents on the 12V rail should be fine).

 

[piasabird]

The 5v rails are more for carrying messages. Think of a message like whether there is a network connection or there is a power drain so the power supply can come one, or there is a need for a USB device. Power on messages like for the modem, or the keyboard or the mouse also use messages. AMD systems may still be using a lot of 3.3V power for the CPU, However, a lot of boards are starting to also use power from the Intel CPU 4 contact square 12V Power Plug as a way of supplying extra power.