what needs 12V power?

[Wayne]

Probably a dumb question, won't be my first. But other than disk drive
motors and fans, what computer component needs all the 12V amperage in
new high power supplies?

I have an older Antec TruePower 380 watt supply, which furnishes
28A 3.3V, 30A 5V, and 18A 12V. Runs fine with four disks and a DVD. I
do have to disable Cool&Quiet to prevent hangs with the X2 chip, dont
know if that is power supply related or not. Runs fine without C&Q, but
it started my thinking about power, and if I need more.

My AMD X2 4800+ CPU runs on 1.35V. I always assumed this comes from the
3.3V, but I dont know how they increase amps to 67A. Could only be
with a transformer, but I am not aware of one. A toriod I suppose?
But 3.3V must be wrong, it must come from 12V, to have approx 12/1.35
= 8.9x current multipler... so 67A is closer to 67/8.9 = 7.5 amps at
12V. Is that conceptually right?

SDRAM memory runs at 2.6V or thereabouts.

My Nvidia video board chip (7600GS) is spec'd at 1.1V. Video boards
have extra power cables now, but I thought it was about 12V?

Big new power supplies, like the 720 watt Enermax, typically provide
25A 3.3V, 30A 5V, and 80A or 90A in three or four 12V sources.

Which is less 3.3V amps and same 5V amps as in my puny 380 watt job, of
roughly half power.

I can understand the isolation of multiple windings, but who uses all
that 12V amperage? Is it the source for the lower voltages? Probably
that higher multiplier is how they get greater current with a
transformer? But then what are the lower voltages used for?

What am I missing?

Generally, how are the 3.3V, 5V, and 12V allocated out to resources?

Thanks

 

[Yousuf Khan]

Probably a dumb question, won't be my first. But other than disk drive
motors and fans, what computer component needs all the 12V amperage in
new high power supplies?

Interesting question, one I haven't thought of in a long time.

I have an older Antec TruePower 380 watt supply, which furnishes
28A 3.3V, 30A 5V, and 18A 12V. Runs fine with four disks and a DVD. I
do have to disable Cool&Quiet to prevent hangs with the X2 chip, dont
know if that is power supply related or not. Runs fine without C&Q, but
it started my thinking about power, and if I need more.

That's interesting. I just finally got C'n'Q working on a friend's
computer for the first time, after downloading a BIOS update, and AMD
processor driver updates in XP. It's amazing how much quieter that
system is after that, it almost feels like its not on. Of course he's
only running a single-core A64 3000+, not a dual-core yet. I think he's
looking for a dual-core update soon.

Have you tried the BIOS update and processor driver update?

My AMD X2 4800+ CPU runs on 1.35V. I always assumed this comes from the
3.3V, but I dont know how they increase amps to 67A. Could only be
with a transformer, but I am not aware of one. A toriod I suppose?
But 3.3V must be wrong, it must come from 12V, to have approx 12/1.35
= 8.9x current multipler... so 67A is closer to 67/8.9 = 7.5 amps at
12V. Is that conceptually right?

I had read sometime back that what you're saying is right. The processor
is driven off of the 12V lines rather than the 3.3V lines, and that the
volts and amps are transformed within the motherboard. The reason they
said was because the 12V lines provided more reliable clean current
source than the 3.3V line does.

I can understand the isolation of multiple windings, but who uses all
that 12V amperage? Is it the source for the lower voltages? Probably
that higher multiplier is how they get greater current with a
transformer? But then what are the lower voltages used for?

Some of them might be legacy and may not be really used anymore. Or they
all plug into the motherboard simultaneously and the motherboard routes
the appropriate voltage lines to the appropriate devices on it.

Yousuf Khan

 

[Wayne]

That's interesting. I just finally got C'n'Q working on a friend's
computer for the first time, after downloading a BIOS update, and AMD
processor driver updates in XP. It's amazing how much quieter that
system is after that, it almost feels like its not on. Of course he's
only running a single-core A64 3000+, not a dual-core yet. I think he's
looking for a dual-core update soon.

Have you tried the BIOS update and processor driver update?

Yes, both, however I never actually installed C&Q drivers. IMO, there
apparently are none for X2 - apparently the new AMD cpu driver provides it
for X2. And it works, it does the C&Q things, but it hung every day or two
on my X2 chip Others also report X2 hangs at the AMD forums. Disabling C&Q
solved my X2 4800+ hangs, fine now, but I have not heard others report the
same result. I was wondering if it was powersupply, perhaps it cannot shift
gears so quickly (am making this up).

I had read sometime back that what you're saying is right. The processor
is driven off of the 12V lines rather than the 3.3V lines, and that the
volts and amps are transformed within the motherboard. The reason they
said was because the 12V lines provided more reliable clean current
source than the 3.3V line does.

A 12V transformers higher multipler would allow the extremely high 1.3V
current with less current from the PS, so it seems logical. I'm just
wondering how universal this is for all the other low voltages used now? My
understanding is that PC Express video uses 12V in the extra connectors too.

But I dont get any feel for knowing how much 12V we need to provide.

 

[The little lost angel]

Probably a dumb question, won't be my first. But other than disk drive
motors and fans, what computer component needs all the 12V amperage in
new high power supplies?

But 3.3V must be wrong, it must come from 12V, to have approx 12/1.35
= 8.9x current multipler... so 67A is closer to 67/8.9 = 7.5 amps at
12V. Is that conceptually right?

Generally, how are the 3.3V, 5V, and 12V allocated out to resources?

Generally as you have guessed, modern processors and graphics chip
draw primarily on the +12V output for power. This is partly due to
much higher efficiency and stability converting AC and using 12V for
high power usage rather than lower voltages.

For 5V, these are still used by USB, drives. 3.3V for RAM, SATA drives
and other onboard logic. Both are also used by PCI/PCI-E cards. At
least as far as I know