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what is the purpose of -ve voltage in PC?

 
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gchandrujs via HWKB.com
Guest
PostPosted: Thu May 24, 2007 8:22 am    Post subject: what is the purpose of -ve voltage in PC? Reply with quote
Hi,
I want to know what is the purpose of -ve voltages in PC ? for example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and i
would like to know the purpose of -ve voltages.

Also can you get me some links for easy understanding for power consumption
of a PC and SERVERS which can be in easily understandable manner?. In general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know what
power consumes generally PIII, PIV PCs consumes per hour ?

Thanks in advance
chandra

--
chandra

Message posted via HWKB.com
http://www.hwkb.com/Uwe/Forums.aspx/mainboard-asus/200705/1
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Paul
Guest
PostPosted: Thu May 24, 2007 8:22 am    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
gchandrujs via HWKB.com wrote:
Quote:
Hi,
I want to know what is the purpose of -ve voltages in PC ? for example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and i
would like to know the purpose of -ve voltages.

Also can you get me some links for easy understanding for power consumption
of a PC and SERVERS which can be in easily understandable manner?. In general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know what
power consumes generally PIII, PIV PCs consumes per hour ?

Thanks in advance
chandra


In my computer, the -12V is used by the RS-232 interface chip for the
serial port. They stopped using -5V years ago, but there are occasionally
motherboards that still use it. -5V has been removed from pin 18, on
the last couple of ATX power supply specifications.

There are several sites which offer to compute the power consumption
of a computer, based on the components used. But I haven't seen one
of those web sites yet, that does a good job. I used to like the
Takaman.jp site (because of its spreadsheet output format), but the
site is closed. The other sites tend to overestimate the power.

The Takaman site was archived here, but I'm not sure this is working
correctly right now. Anyway, this seems to work in Firefox OK. You
can select the line items, and get some idea of their contribution.

http://web.archive.org/web/20040411032947/http://www.takaman.jp/psu_calc.html?english

Anandtech offers some total power numbers here. So
the "average" 3GHz P4 computer is 122W idle and 195W busy.

http://www.anandtech.com/showdoc.aspx?i=2275&p=13

Paul
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gchandrujs via HWKB.com
Guest
PostPosted: Fri May 25, 2007 10:56 am    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
Dear Barry,

Thanks for your reply. So, i understand the negative voltages are just the
flow in opposite direction. Hope i am on right think. How can we mean to say
only particular direction the electricity flow which we say +ve voltages ?

If so, Serial ports are using -ve voltages, which mean the electricity flows
back from serial port to main supply or motherboard ? Whats the use in that ?

Please explain.

THanks in advance
chandra


Barry Watzman wrote:
Quote:
Negative voltages are just voltages where positive and negative are
reversed so that the electricity flows in the "other" direction.

Negative voltages are not used much any more, but one on a time were
common (RS-232 serial ports still use them, but once they were used by
other devices as well; for example, some old CPU chips and memory chips
required them).

Hi,
I want to know what is the purpose of -ve voltages in PC ? for example -5v, -
[quoted text clipped - 37 lines]
Regards
Chandra

--
chandra

Message posted via HWKB.com
http://www.hwkb.com/Uwe/Forums.aspx/mainboard-asus/200705/1
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Roger Hamlett
Guest
PostPosted: Fri May 25, 2007 3:21 pm    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
"gchandrujs via HWKB.com" <u25485@uwe> wrote in message
news:72b0b9fb7385d@uwe...
Quote:
Dear Barry,

Thanks for your reply. So, i understand the negative voltages are just
the
flow in opposite direction. Hope i am on right think. How can we mean to
say
only particular direction the electricity flow which we say +ve voltages
?

If so, Serial ports are using -ve voltages, which mean the electricity
flows
back from serial port to main supply or motherboard ? Whats the use in
that ?

Please explain.

THanks in advance
chandra
The flow is always _circular_. It is pumped round by the voltage 'source'.

As I already posted, it is the +ve voltages that have the flow
'backwards'!. The electrons here, flow out along the 0v (GND) wire, and
back in on the +ve wire. With the -ve voltages, the electrons flow out
along the -ve wire, and back in on the 0v wire.

Best Wishes

Quote:
Barry Watzman wrote:
Negative voltages are just voltages where positive and negative are
reversed so that the electricity flows in the "other" direction.

Negative voltages are not used much any more, but one on a time were
common (RS-232 serial ports still use them, but once they were used by
other devices as well; for example, some old CPU chips and memory chips
required them).

Hi,
I want to know what is the purpose of -ve voltages in PC ? for
example -5v, -
[quoted text clipped - 37 lines]
Regards
Chandra

--
chandra

Message posted via HWKB.com
http://www.hwkb.com/Uwe/Forums.aspx/mainboard-asus/200705/1
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William
Guest
PostPosted: Fri May 25, 2007 11:30 pm    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
news:Dve5i.3420$BN6.2434@newsfe6-gui.ntli.net...


Quote:
In fact the actual electron 'flow' in a circuit, is the opposite way to
the 'sign', so it is the -ve connection, that 'sources' electrons, and the
+ve ones, have the electrons flowing towards them!.

Good description Roger.

I always showed my schematics having the flow from positive to negative.
Few could call me out on this. And when they did, I would say "You can't
move an electron without a hole existing first" Which would shut them all
up. No one could disk me on that bs.

Thanks for the memories.

William
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William
Guest
PostPosted: Fri May 25, 2007 11:30 pm    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
"gchandrujs via HWKB.com" <u25485@uwe> wrote in message
news:72a4666beb021@uwe...
Quote:
Hi,
I want to know what is the purpose of -ve voltages in PC ? for
example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and i
would like to know the purpose of -ve voltages.

Also can you get me some links for easy understanding for power
consumption
of a PC and SERVERS which can be in easily understandable manner?. In
general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know
what
power consumes generally PIII, PIV PCs consumes per hour ?

Thanks in advance
chandra

--
chandra

Message posted via HWKB.com
http://www.hwkb.com/Uwe/Forums.aspx/mainboard-asus/200705/1


This is going to date me.

Us electronic guys used to use large voltages to get things done. Lots of
voltage, so things didn't get lost in the works. Tube stuff often used +-
400 volts, and transistor circuits used +-5v, and signal paths used +-12v
all the time. You had to, to get the signal from one place to another.
Those serial terminals might be 200 or more feet away from the computer
room, and those lines might be run alongside of who knows what. Those other
cables messing things up with their own noise. So the larger the signal,
the better. Made it easier to detect the signal on the receiving end.

Time marched on, and noise cancellation got better, signal detection got
easier, and noise levels dropped. Their was a certain "cemetery" to +-
voltages. That is, voltage above "ground" and voltage below "ground"
Ground being the potential of the dirt you were standing on, or the pole
sticking out of the ground you hooked your trusty multi-meter to to measure
whatever you wanted too.

You could just as easily used 0 to +24v for serial cables and call +12v
ground, (without having reference to "earth" ground). As I said, time
marched on, and the need for BIG signals was lost in small distance signal
distribution. Electronics got smaller, used less current, (per component)
and needed lower and lower voltages to operate. Electronics went from tubes
to transistors to complementary metal oxide semiconductors, (CMOS). CMOS
could run on anything from ~+-19 volts to ~+-3 volts when first introduced.
(I made lots of stuff out of the CD4000 series, the good old days now.)

Well, time marches on, and voltage is bad. It causes heat, and other bad
things to happen. (By the way, thermal expansion and contraction is the
number one cause of component failure in electronics!) So manufacturers go
out of their way to reduce voltage requirements of their IC's, be they CPU,
RAM, Controllers, Routers, or whatever. Usually you will see higher
voltages used around I/0 (Input /Output) circuits, but that will change too.
Lower voltages let us use smaller components for manufacturing too.

So you don't see much call for negative voltages, though that is relative,
and you don't see much need for any "relatively" large voltages in computers
anymore either. Computer manufacturers could stop using +12 volts if they
wanted to, but they would have to double the current ratings if they did,
W=VxI (watts equals volts times current). So if you half the voltage, you
double the current required to do the same job.

I could go on.

William
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Roger Hamlett
Guest
PostPosted: Fri May 25, 2007 11:31 pm    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
"William" <nospam@pacifier.com> wrote in message
news:135ei8qch6gj27b@corp.supernews.com...
Quote:

"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
news:Dve5i.3420$BN6.2434@newsfe6-gui.ntli.net...


In fact the actual electron 'flow' in a circuit, is the opposite way
to the 'sign', so it is the -ve connection, that 'sources' electrons,
and the +ve ones, have the electrons flowing towards them!.

Good description Roger.

I always showed my schematics having the flow from positive to negative.
Few could call me out on this. And when they did, I would say "You
can't move an electron without a hole existing first" Which would shut
them all up. No one could disk me on that bs.

Thanks for the memories.

William
Oh God, not holes!....

It it is obvious that all electronics is actually divine, since at heart,
it is all holey... :)

Best Wishes
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GMAN
Guest
PostPosted: Wed May 30, 2007 12:12 am    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
In article <f33g9b$e5d$1@aioe.org>, Paul <nospam@needed.com> wrote:
Quote:
gchandrujs via HWKB.com wrote:
Hi,
I want to know what is the purpose of -ve voltages in PC ? for example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and i
would like to know the purpose of -ve voltages.

Also can you get me some links for easy understanding for power consumption
of a PC and SERVERS which can be in easily understandable manner?. In general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know what
power consumes generally PIII, PIV PCs consumes per hour ?

Thanks in advance
chandra


In my computer, the -12V is used by the RS-232 interface chip for the
serial port. They stopped using -5V years ago, but there are occasionally
motherboards that still use it. -5V has been removed from pin 18, on
the last couple of ATX power supply specifications.

There are several sites which offer to compute the power consumption
of a computer, based on the components used. But I haven't seen one
of those web sites yet, that does a good job. I used to like the
Takaman.jp site (because of its spreadsheet output format), but the
site is closed. The other sites tend to overestimate the power.

The Takaman site was archived here, but I'm not sure this is working
correctly right now. Anyway, this seems to work in Firefox OK. You
can select the line items, and get some idea of their contribution.

http://web.archive.org/web/20040411032947/http://www.takaman.jp/psu_calc.html?e
nglish

Anandtech offers some total power numbers here. So
the "average" 3GHz P4 computer is 122W idle and 195W busy.

http://www.anandtech.com/showdoc.aspx?i=2275&p=13

Paul
That last link is to info 2.5 years old.
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Paul
Guest
PostPosted: Wed May 30, 2007 11:17 pm    Post subject: Re: what is the purpose of -ve voltage in PC? Reply with quote
GMAN wrote:
Quote:
In article <f33g9b$e5d$1@aioe.org>, Paul <nospam@needed.com> wrote:
gchandrujs via HWKB.com wrote:
Hi,
I want to know what is the purpose of -ve voltages in PC ? for example -5v, -
3.3v, -12v. It knows to a common man that +ve voltages flows current and i
would like to know the purpose of -ve voltages.

Also can you get me some links for easy understanding for power consumption
of a PC and SERVERS which can be in easily understandable manner?. In general
we identifying power consumption by adding all the power consumption of
peripherals like keyboard, motherboard, PCI devices etc., But May i know what
power consumes generally PIII, PIV PCs consumes per hour ?

Thanks in advance
chandra

In my computer, the -12V is used by the RS-232 interface chip for the
serial port. They stopped using -5V years ago, but there are occasionally
motherboards that still use it. -5V has been removed from pin 18, on
the last couple of ATX power supply specifications.

There are several sites which offer to compute the power consumption
of a computer, based on the components used. But I haven't seen one
of those web sites yet, that does a good job. I used to like the
Takaman.jp site (because of its spreadsheet output format), but the
site is closed. The other sites tend to overestimate the power.

The Takaman site was archived here, but I'm not sure this is working
correctly right now. Anyway, this seems to work in Firefox OK. You
can select the line items, and get some idea of their contribution.

http://web.archive.org/web/20040411032947/http://www.takaman.jp/psu_calc.html?e
nglish

Anandtech offers some total power numbers here. So
the "average" 3GHz P4 computer is 122W idle and 195W busy.

http://www.anandtech.com/showdoc.aspx?i=2275&p=13

Paul
That last link is to info 2.5 years old.


The original question was about a P4, so I tried to find a number for
a P4 computer.

I've just measured my own computer, but because I don't have a Kill-o-Watt
type meter, I have to use other techniques to do the measurement, and
cross check the results.

This computer is a P4 Northwood, running at 3.2GHz. The OS is Win2K.
I'm using the Halt option for the OS idle loop, which is why the processor
power is so low at idle. (I.e. Running RMclock with Halt enabled, since
my idle loop is not using Halt for some reason.)

These are DC measurements on the main power cable, at idle.

3.3 @ 9.67A 31.9 W
5 @ 0.63A 3.15
12 @ 0.49A (fans?) 5.88
-12 @ 0.03A 0.36
+5VSB @ 0.40A 2.00

This is the processor measurement. The current jumps to about 4 amps
at idle, if no Halt instruction is used. The reason I mention this,
is I've been working on my idle power consumption recently, as the
computer seemed to be a bit too warm at idle.

12 @ 1.17A CPU 14.04W

This is for my hard drive and optical drive.

5 @ 0.42, 12 @ 0.24 HDD 4.98W
5 @ 0.08, 12 @ 0 ODD 0.40W

The video card has a separate power connector (9800Pro).
Part of the video card power flows through the main motherboard
power connector, so this is not the total video card power, just
the component drawn through the aux connector.

5 @ 3.32, 12 @ 0.17 video 18.64W

The total power is 81.35W, as measured at the output side of the
power supply. The power supply gets hot while it is running, and
that is a measure of its "inefficiency". The label on a typical cheap
supply, might say it is 70% efficient. To estimate the power at the
AC wall plug, divide by the estimated efficiency.

81.35W / 0.70 = 116W.

I did measure the A.C. current at the wall plug. The current
and voltage at idle were 1.669A @ 120.5 VAC.

The reason for the discrepancy, is the power factor. My power
supply is not PFC corrected. The power factor will be about 0.7 or
so. (The current waveform on the AC input, is out of phase with
the voltage waveform. The real component of the power, is about
70% of the measured current.)

So, if I take (120.5V * 1.669A) * 0.70 = 140.2W

If I had uses an active PFC power supply, then my ammeter
reading could be used directly without an unknown fudge factor.
At least, if the load on the PSU was high enough.

http://www.xbitlabs.com/articles/other/display/psu-methodology_8.html

So I can measure the power consumed, after a fashion, but I'm not
set up to do a power measurement without a fudge factor.

The processor power thing is a bit strange. I could swear I've done
this measurement before, did it in both Linux and Win2K, and in
both OSes, the idle processor draws 1.1 amps from the 2x2 ATX12V
power connector. Now, for some reason, the Win2K install is drawing
4 amps at idle, while Linux is still at 1.1 amps. By using RMclock,
that program installs its own idle loop, complete with Halt instruction.
Using RMclock the idle current on the processor cable is 1.1 amps again.
My suspicion is that the antivirus software I was testing, may have
buggered with it, but I don't know how to verify what is going on.
In any case, with Halt working, room temp right now is 23C,
case temp is 25C, and CPU is 28C.

With Orthos running, the AC measured current jumps from 1.669A to
about ~2.5A (some fluctuation). CPU temp is 41C.

Paul
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