Motherboard Forums


Reply
Thread Tools Display Modes

question on +3.3V current requirements

 
 





















David Johnstone
Guest
Posts: n/a

 
      01-03-2005, 11:10 AM


My question is general but in my case based on the
MSI Neo2 Platinum (Socket 939) board with Athlon 3000+
Winchester CPU.

The board takes +3.3V power from the PSU and supplies
the CPU with Vcore which is in the range 1.4 - 1.6 V,
in my config.

Question: does the DC-DC conversion on the motherboard
involve any "current gain", as would be the case with an
ac transformer? Or to put it another way, if my CPU were
to use up to (for example) 60A at 1.5V, does that mean
the PSU should be rated for (at least) 60A on the +3.3V
rail?

If so, that would mean that at least half the power goes
in ohmic losses on the conversion, right? So the MB would
be dissipating at least as much as the CPU?

If not so, can one estimate the efficiency of the conversion
somehow, and hence the PSU requirements?

TIA
David
 
Reply With Quote
 
Ed Light
Guest
Posts: n/a

 
      01-03-2005, 01:43 PM
According to this

http://takaman.jp/D/?english

the A-64's seem to be just using the 12v line.

--
Ed Light

Smiley :-/
MS Smiley :-\

Send spam to the FTC at

Thanks, robots.


 
Reply With Quote
 
David Johnstone
Guest
Posts: n/a

 
      01-03-2005, 11:08 PM
Hi Ed, very interesting, thanks.
That would explain the extra +12V connectors most newer
boards have next to the CPU socket and power supplies.
But if the CPU takes it's Vcore from +12V, what the hell
needs 30A and more at 3.3V then?!

"Ed Light" <> wrote in message news:r_bCd.6592$232.2378@fed1read05...
> According to this
>
> http://takaman.jp/D/?english
>
> the A-64's seem to be just using the 12v line.
>



 
Reply With Quote
 
Ed Light
Guest
Posts: n/a

 
      01-04-2005, 04:14 AM

"David Johnstone" <> wrote
> But if the CPU takes it's Vcore from +12V, what the hell
> needs 30A and more at 3.3V then?!


Some agp video cards, pci cards. They differ alot.
These articles test cards for what amps they're pulling at each voltage.
http://www.xbitlabs.com/articles/vid...powercons.html
http://www.xbitlabs.com/articles/vid...-nv-power.html
--
Ed Light

Smiley :-/
MS Smiley :-\

Send spam to the FTC at

Thanks, robots.


 
Reply With Quote
 
Chip
Guest
Posts: n/a

 
      01-04-2005, 11:02 AM

"David Johnstone" <> wrote in message
news:crcj6j$nq$00$...
> Hi Ed, very interesting, thanks.
> That would explain the extra +12V connectors most newer
> boards have next to the CPU socket and power supplies.
> But if the CPU takes it's Vcore from +12V, what the hell
> needs 30A and more at 3.3V then?!


Older motherboards drew more current from the 5v and 3.3v lines. PSU's are
simply trying to cover as many possible requirements as they can - to offer
the greatest compability.

And remember the "30A at 3.3V" spec (where did you get that from???) that a
PSU may quote, will be its *maximum* available current at that voltage,
assuming no load on the 5V (and also possibly the 12V) lines. In practice a
PSU rated at 30A at 3.3V will not deliver 30A. And apart from anything
else, 30x3.3 is only 99w. Its not a massive amount.

Chip


 
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
P4P800 deluxe 3.3V problem... TRON Asus 2 03-28-2008 10:56 AM
Complete upgrade (CPU, RAM, MBoard etc.) question Matt Asus 7 01-07-2008 02:29 PM
New theory/story: Stray electricity/cross talk low current erased parts of the BIOS. Skybuck Asus 8 06-07-2007 07:58 AM
K7S5A: Yellow question marks in XP SP2 rhino Elitegroup 1 02-21-2007 06:40 PM
WIRELESS ROUTER QUESTION Scotty Dell 12 12-10-2006 03:20 PM


All times are GMT. The time now is 03:09 PM.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43