Problems with your PC’s power should not be overlooked as
a potential source of virtually any hardware-related PC troubles.
While most of us tend to never give our Power Supply a second thought, it
is good to have at least a basic understanding of the computer’s Power Supply
and power requirements. There can
also be problems with your power external to the PC itself which should also
bear some consideration.
Between the Wall and Your PC
The raw power sent to your home or office by your local electric company while susceptible to spikes, surges, line noise, brown or black-outs is for the most part is just fine provided you use a good quality surge protector or UPS (uninterruptible power supply) but you should be aware that problems can occur between the wall socket and the PC power supply. The first place to look for a power problem is in the black power cord supplied with your PC case. Most of these are equal to the task but if you bought an inexpensive case you may have a substandard power cord. If the cord is warm to the touch you may want to look into purchasing a more heavy-duty one. Also, where your computer resides can have some effect of the quality of power it receives. Proximity to radio transmitters or electric motors – even of the household variety can affect the line noise and EMI (electromagnetic interference), so keep your distance from items such as CB or HAM radios, fans, air conditioners or refrigerators. Some devices in your own home or office produce line noise then pass it on to other devices throughout the power system. Better quality surge protectors, power filters or UPS systems will isolate devices that plug into them to prevent this type of power contamination. It is also wise to avoid overloading your surge protector or extension cords. If you even wonder that you have too many devices plugged in to a single source, you probably do and this is one area where it truly doesn’t pay to be cheap.
The Power Supply
Your PC’s internal power supply is responsible for converting your standard household current into a form of electricity that your computer can use. Since the power supply is responsible for providing power to every device in your computer; if it has a problem or is of substandard design or quality you may experience problems that you may not realize are actually the fault of the electrical system.
Switching power supplies, though capable higher efficiency
and reduced size, were until very recently notorious for generating excessive
electromagnetic interference (EMI) that affected the normal operation of nearby
electronic equipment such as the circuitry on your mainboard. Methods utilized
for reducing EMI use circuit design approaches such as adding snubbers and input
filters, adopting special pulse-width-modulation strategies, etc. While these
methods reduced EMI, they complicated the design process as well as increased
the production cost. In the past, these anti-noise components were added on a
trial-and-error basis during the final stage of the design process when EMI was
found to exceed the compliance limits (e.g., FCC and VDE). While adding to the
cost of earlier power supplies, many of these components were standardized into
today’s modern ATX power supply.
A high quality power supply with sufficient output capacity to meet the demands of your system should provide years of service and is essential for the proper operation of your PC. It is interesting to note the cost of good replacement power supplies is near to, and can sometimes even exceed the cost of a new case. What does this tell us??? Poor quality power supplies can cause numerous problems in both your hardware components and the way your software performs. Another consideration is your future expandability. High wattage, quality power supplies afford you all of the options available on today’s modern PC such as multiple hard drives, CD rewriters and DVD players and internal ZIP drives.
power supply also plays an integral role in cooling your system.
The fan integrated with the power supply’s housing is for many PCs the
major force in moving air into and out of the case.
Power supplies support either 110v, 220v or, more often,
both. Dual-voltage supplies normally have a selector switch mounted in the back
that sets which voltage you are using. If the power supply has a 110/220 switch,
make sure it is set correctly!!! An improperly set switch will prevent the power
supply from operating. Here in the
US, the possibility of damaging the device with an improperly set switch is slim
but a power supply set for 110v that receives 220v can easily burn up.
Not simply a power converter (such as your printer or
scanner might use), the PC power supply is responsible for the conversion of
standard household current (110v AC at 60 cycles per second here in the US) into
a variety of low-voltage DC currents of varying degrees of strength.
+5v: The standard voltage used by the mainboard and
most of the circuitry on expansion cards in the computer.
+12v: Used to power hard disk and CR-Rom drive
motors and similar devices. It can also be passed to the ISA system bus
slots for any legacy cards that require a higher voltage.
+3.3v: Pretty much exclusively used to provide power
to the CPU and system memory. While
most early CPUs ran at +5v the advent of the Pentium processor required a
significantly lower voltage. Many
of today’s new CPU use voltage (core) that are lower still.
In addition to 3.3v power for the processor. ATX style
power supplies also permit a type of software control of the power supply.
For system boards and BIOS that support this feature, the "Power
On" signal can be controlled by the mainboard’s BIOS to tell the
power supply when to turn itself off. This standby signal is a separate 5v
source to the mainboard from the standard 5v. Retaining its charge even when
the rest of the system is powered down, this allows for features which can
automatically turn the system on or off such as Wake-on-LAN, Wake-on-modem,
Keyboard Power On, and Shutdown by Clock.
-5V and -12V: Once used on older systems they are included for compatibility’s sake. Almost completely redundant on today’s PC.
A PC switching power supply will only function properly if there are components attached which will draw power from it. This is why a system without a hard drive installed will normally fail to power up properly.
Depending on the form factor of your system your PC needs
some form of switch to turn itself on. While
older 386 and 486 systems used a switch that was housed within the power supply
itself, today’s AT form factor system use physical pole/throw switches mounted
on the front of the case to send current to the power supply.
ATX form factor systems use a somewhat different design in that the
switch on the outside of the case is connected to the mainboard rather than the
power supply. This gives the BIOS
located on the mainboard control of the power supply as mentioned above. Since
the ATX form factor power supply is controlled by signaling from the mainboard
and BIOS, you should be aware that power is being supplied to the mainboard even
when the system is off. You should never work on a PC without first
disconnecting the power cord from the back of the case.