Power Supply Unit (PSU)
August 24, 2004
Choosing a PSU for a P4 processor
based system
Intel P4 PC needs an 12
V power connector that output
a minimum current rating
of 8-10 A, so ask your local
shop for a ATX12V power supply.
ATX provides 5 output voltage
rails (+3.3V, +5V, +12V, -5V,
and –12V.)
Power supplies such as SFX-12V
are available for micro-ATX
systems that may have lower
power requirements.
Micro-ATX provides 4 output
voltage rails (+3.3V, +5V, +12V,
and -12V).
A power supply of 250 watts
or greater is recommended
when building a typical DIY
system.
Caution:
Failure to use an ATX12V or
SFX12V power supply a P4 processor
based system may result in damage
to the mobo and/or power supply.
Note: "ATX12V"is
a superset of the original ATX
power supply specification.
The extra +12V power connector
enables the delivery of more
current to the Pentium 4 processor-based
boards.
How to identify the PSU
is suitable for P4?
Look for the +12V 4-pin
connector. This indicates
that the power supply is an
ATX12V or SFX-12V.
The absence of the +12V 4-pin
connector indicates that the
power supply is an ATX version
and should not be used with
a Pentium 4 processor.
Connectors found on a typical
ATX12V power supply
The 20-pin main ATX motherboard
power supply connector (Molex
39-01-2200)
ATX 12V connector (required
for some Pentium 4 motherboards)
(Molex 39-01-2040)
ATX auxiliary power connector
(Molex 8993)
A peripheral power connector
(Molex 15-24-4048)
A peripheral connector Y-splitter
A floppy power connector (Molex
22-01-1044)
Protective feature of the
ATX12V PSU
A good PSU should provide good,
clean, DC current that’s
free of spikes, dips, and noise
to the mobo.
Most PSU perform a series of
internal checks and tests before
powering up the system.
If the checks are okay, the
PSU sends a signal to the motherboard
called Power_Good, and that
signal must be maintained continuously
while the computer is on.
The power supply would cease
to send the Power_Good signal
if the power circuit encounters
problem and produces voltage
that falls out of safety range
for the mobo. This would cause
the mobo to shutdown itself
to prevent damage.
Conditions that can cause the
Power_Good signal to fail include
brownouts, blackouts, and surges.
Thus, the Power_Good signal
is one way for the PSU to protect
the PC from outside harm.
Wake On LAN
Wake on LAN is a function that
allows remote server on a network
to wake the computers. Typical
usage: backup servers, maintenance
programs, remote control automation.
The PC must be in a "sleeping"
state in order to be waken up.
The PSU provides PS_ON (power
on) and SVSB(SV Standby) lines
to power the PC even when the
system is already shutdown.
So while doing any fixing of
the PC, ALWAYS remember to unplug
the power cable to the PC, or
at least turn off the power
mains. Failing to do so, may
damage the system components
when you meddle with the components
in it.
What are the driving factors
in determining the life of the
power supply?
PSU won't last for ever. Like
everything on earth, it will
die on day...
Try to put your PC in a cool
place. Continuous intense heat
may shorten the life of the
PSU. This also applies to any
other components in the PC.
The PSU cooling fan may be
another life factor because
it is a moving part. To maximize
the life of PSU, choose a PSU
that is equipped with ball
bearing cooling fans.
What is the meaning of PFC?
PFC is an abbreviation for
Power Factor Correction.
It is a technique for harmonic
reduction in power supply source
current. There are two
types of PFC, namely active
and passive
Conclusion
PSU is one of the components
in the PC that has high failure
rate, beside hard disk. This
could be due to its moving part
nature - the cooling fan. Mechanical
part subjects to daily wear
and tear.
Also, power circuits tend to
produce a lot of heat. Intense
heat is very harmful to the
circuit components if the system
is to operate for long hours.
So it is best to locate your
PC in a cool environment.
It is worth to replace the
PSU with a better one, one with
higher watts as by doing so
can greatly enhance the stability
of the entire system. Also look
for features like ball-bearing,
PFC, etc.
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