Why do so many peeps think...

[spldart]

...AMD processors get power off the 12 volt line?
I know for a fact that AMD cpu's derive their current off the 5 volt line through the switch mode supply on most every mobo.

[Player0]

You're actually wrong.

Go check out AMD's design specs. It specifically sais in multiple places that the CPU get's its power from the 12v supply.

The power mosfets on almost every board I can think of connect to the 12v line.

So, all those people think it...cause they are right hehe :)

[lechumbl]

Hi all,

Mine is powered off of my 9 volt line. :D
Maybe that is why it doesn't run too well??

Take care..........

[spldart]

I've checked multiple Asus and Abit mobo's...The power fets on the board are tied to the 5 volt line. And when I overclock the 5 volt line is the one that starts sagging.
Whattup with that?

[Drake]

Aye, I've noticed it's always my 5v line that dips and never my 12v.

[spldart]

Just confirmed that some TYAN mobo's use 5 volt line for CPU power.

[spldart]

Somebody who has addressed what I'm talking about http://www.hexus.net/review.php?review=442&page=4

[PCGenious]

yea my 5v line is always screwed when I oc never the 12v line. doesnt intel use the 12v line.

[spldart]

Originally posted by PCGenious
yea my 5v line is always screwed when I oc never the 12v line. doesnt intel use the 12v line.

About as much as I know about the Intel boards is they have started using that extra little plug to bring over 12 volts to reinforce the 5 volt line being used to for powering the processor on the newer boards. A technique the AMD board manufacturers would seem to be duplicating for those power hungry processors that put undo load on the 5 volt line.

[PCGenious]

why dont some amd manufacturers just take advantage of that connector?

[Player0]

Spldart, the Abit and Asus motherboards use the 12v to supply the CPU voltage. The 5v reading is the line level which CONTROLs the mosfets, not the actual power that feeds the CPU.

The 5v line sags for other reasons. But the 12v line DOES supply the CPU its power to probably every AMD motherboard .

Again, according to AMDs motherboard design spec, the CPU is supposed to be powered from the 12v line.

But, you dont have to beleive me :)

[Drake]

If you buy a good all-around PSU, why should it matter anywho :p

P.S. Rhyme not intended :p

[4.6POWER]

athlons and P4 both draw their usable current from the 12V line... prior cpu setups used the lower voltage lines. I had this same dilemma argument a while back... I forgot how I sorted it out, but I just thought I'd post up to confirm player0's post.

[spldart]

I just went in with my fluke 83 dmm and my leader O-scope. This is basically how it schematics out.

http://24.243.159.133:91/5vcpu.jpg

Switch rate on the ASUS mobo was 105khz and 12 volt line was not involved in providing power to the cpu. In face the 12 volt line show very little load in general.

I am definitely right on this.

[Player0]

Spldart, attached is the powersupply schematic from the old Asus A7V133. Its similar to all modern Athlon boards (although getting a schematics for anything is hard.

If you dont beleive the schematic, then please read:

http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26003.pdf

This is the AMD Builders and System info guide. This has all the information on power issues regarding athlons. As you can CLEARLY read for yourself, the CPU draws its current off the 12v line.

If you still dont beleive me after this, well...I dont know what I can tell ya man. You yourself asked why everyone beleived this. Because everyone is right. If everyone is right, maybe you should re-evaluate your position.

[spldart]

I decided to prove once in for all....

http://24.243.159.133:91/atxplug.jpg

I then spliced the 12 volt line going into this mobo for an ammeter check.

http://24.243.159.133:91/12voltlinesplice.jpg

Then the fluke 83 was set on Ampere/autoranging...

http://24.243.159.133:91/362ma.jpg

This 362 Milliamp reading was taken cruning seti...

http://24.243.159.133:91/crunchseti.jpg


Proof that the only load on the 12 volt line was the fan on the heat sink for the cpu. I have no other 12 volt perhipreals on this compy. HD is outta laptop so 5 volt only and the cd rom is not hooked up at this time. That 362 ma reading is the entirety of the 12 volt load on the psu.

[spldart]

My socket a mother boards are different...

http://24.243.159.133:91/minesdifferent.jpg

And as far as I can tell there are many more set up like this too.

[Player0]

http://www.intersil.com/data/an/AN9906.pdf

This is the datasheet of the HIP6301 power controller used on most of the Abit motherboards. The reference design here also shows the converter using 12v.

So. I dont know. Your motherboard test is interesting. Was the CPU at 100% load? Not that it would matter much. What is the amperage draw from the 5v line? Its interesting tho, it goes agaist everything Ive heard/been told so far.

[Gabriel]

Funny, mine is powered of my wall socket which should be at least 120... go figure

(lame humor from the non OC graphics guy)
giggle

[spldart]

Originally posted by Player0
So. I dont know. Your motherboard test is interesting. Was the CPU at 100% load? Not that it would matter much. What is the amperage draw from the 5v line? Its interesting tho, it goes agaist everything Ive heard/been told so far.

That was the purpose of my last image...Seti runs in all tests.

I broke the 4 main 5 volt line going to the atx connector. I went to make a current test but Uh Oh...My fluke got pissed. It only measures up to 10 amps. I got an instant OL reading :eek: :D
Mobo got pissed that the meter wouldn't handle passing that much current either. I can only assume it was dropping to much power in the resistance of the added circuit path length cuz the mobo started beeping.

[Player0]

I dont know spld, I got in to an arguement about this very same thing before because I thought it was 5v too. But after I saw all the evidence those guys showed me, I ended up 'understanding' it differently.

I can't possibly think of anyway the board could use so little current from the 12v line unless its not being used. You got the right wire correct? You could always hook a large wirewound resistor in series with the multimeter, and use that to get adjusted readings under high amperage to see what the 5v line is drawing.

That does have interesting connotations though. If the motherboard really only is usind a few milliamps, it means running peltiers off the 12v really isnt a bad thing at all. In fact, you can probably get away with leaving only 1-2amps for the rest of the system.

[spldart]

You'll have to pardon me but I'm done taking risks with my personal Mobo's. I've found evidence online for what I think is the case and my tests have confirmed it to my satisfaction. I almost went out and yanked the 60 amp meter I have added in my car for the auxillary battery system :eek:
I know that the 5 volt line is being loaded well past 50 watts and the 12 volt line is only being tapped for a tad over 4 watts.

BTW it's not hard to just check some voltages to find which lines are carrying which voltages but I did use http://wired.hard.ru/data/pin_atxpower.shtml to double check my work.
I'll let you know if I get courageous and do another ammeter check with the big meter.