CHAPTER 5
Power Supply
Chapter Overview
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Power Supplies
Power Supply Problems
Computer Power Supply Unit
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(Computer PSU) typically is designed to convert 110
V or 230 V AC power from the mains to usable lowvoltage DC power for the internal components of the
computer. The most common computer power
supplies are built to conform with the ATX form
factor The official specifications were released by
Intel in 1995, and have been revised numerous
times since, the most recent being version
2.3,[1] released in 2007. This enables different
power supplies to be interchangeable with different
components inside the computer..
Overview of Power Supplies
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The standard power supply
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Converts AC to DC
“Conditions” power by evening out changes.
Requires a fan
Standard power in U.S. is 110 volts
alternating current (VAC) oscillating at 60
hertz (Hz).
You must consider physical size, wattage, and
connector types when replacing a power
supply.
Power Supply Sizes
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Power supply sizes are based on the type of case and
motherboard connections.
The AT-style is found on older computers and earlier
Pentium systems.
The ATX-style (current technology) is found on
Pentium II and later systems.
You should compare the existing power supply with
the new one before replacing it.
On –off power control circuit. Not the button on ATX
boards is built into the MB, on AT style it comes from
the PS.
AT style
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The AT form factor is the first modern form factor to be widely
used. AT (Advanced Technology) was released in 1984 by IBM
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ATX style
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The ATX (for Advanced Technology Extended) form factor
was created by Intel in 1995. It was the first big change in
computer case and motherboard design in many years.
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24-pin ATX12V 2.x power supply connector(20-pin omits the last four: 11, 12, 23 and 24)
Color
Signal
Pin
Pin
Signal
+3.3 V
Color
Orange
Orange
+3.3 V
1
13
Orange
+3.3 V
2
14 −12 V
Blue
Black
Ground
3
15 Ground
Black
Red
+5 V
4
16 Power on
Black
Ground
5
17 Ground
Black
Red
+5 V
6
18 Ground
Black
Black
Ground
7
19 Ground
Black
Grey
Power good
8
20 No connection
Purple
+5 V standby
9
21 +5 V
Red
Yellow
+12 V
10
22 +5 V
Red
Yellow
+12 V
11
23 +5 V
Red
Orange
+3.3 V
12
24 Ground
Blac
+3.3 V sense
Brown
Green
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Power Supply Wattage
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A watt is a unit of electrical power equivalent
to one volt-ampere.
Total wattage needs are determined by
adding the power required for each device,
plus more power for startup.
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General-use computers require 130–205 watts.
Servers and high-performance workstations
require 350–500 watts.
AC and DC Voltages
Alternating Current (AC)
Alternating Current (AC) flows one way, then the other way,
continually reversing direction. An AC voltage is continually
changing between positive (+) and negative (-).
Direct Current (DC)
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Direct Current (DC) always flows in the same direction, but
it may increase and decrease. A DC voltage is always
positive (or always negative), but it may increase and
decrease
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Power Supply Connectors
Connections to Peripheral Hardware
Extenders and
Splitters
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Extenders are wire sets
that have a molex
connector on each end,
used to extend power
connection.
Splitter
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A splitter increases the number of
connections.
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Power Failures
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Power failures can have internal or external causes.
External failures, which are more common, include
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Surges ( increase in the voltage source, very high voltage for a
very short time)
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Spike ( very short over voltage measured in nanoseconds)
Sags (decrease of voltage at the power source)
Brownouts ( sage lasts longer than 1 second)
Blackouts ( complete power failure)
Power Protection Devices
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A surge suppressor
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Filters the effects of voltage spikes and surges
Smoothes out power variations
An uninterruptible power supply (UPS) is an
inline battery backup.
Power Supply Problems
Alternative
Direct
Chapter Summary
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The AT-style power supply is used for older
motherboards and the ATX-style power
supply is used for newer motherboards.
Peripheral devices use Molex connectors and
mini connectors.
Different types of power failures can cause
computer problems and can damage
computer equipment.
Surge suppressors and UPS devices can
protect computer equipment.