Power Supplies

In this reading, you will learn how to select the correct power
supply for a personal computer (PC) to support the main
components of the PC.

As you learned in a previous video, computer systems require a

direct current (DC) of electricity to operate. However, power
companies deliver electricity in alternating currents (AC). AC
power can damage the internal components of a computer. To
solve this problem, computer power supplies are used to convert
the AC from the wall socket to DC. Power supplies also reduce
the voltage delivered to the computer’s internal components.

Computer architecture
Computer architecture refers to the engineering design of
computers and the interconnecting hardware components that
together create computing devices that meet functional,
performance and cost goals. Power supplies are part of the
hardware layer of a computer’s architecture. You learned earlier
about the other major hardware components of a computer’s
architecture, including the motherboard, chipsets, CPUs, RAM,
storage, peripherals, expansion slots and cards, etc. These
components in uence the size and type of power supply a
computer needs.

Selecting a power supply

Local input voltage
A main consideration when selecting a computer power supply is
the voltage delivered to common wall sockets in your country.
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 Power standards for input voltages can vary from country to
country. The most common voltage inputs are 110-120 VAC and
220-240 VAC. VAC stands for volts of alternating current.

• Voltages in the Americas

North, Central, and parts of South America use the 110-127 VAC
standard for common wall sockets. Computers and power
supplies sold in these regions are designed to use this level of
power.

• Voltages for most of the world

Most countries use the 220-240 VAC standard for common wall
sockets. Computers and power supplies sold in these areas are
designed to use this higher voltage.

Please visit

WorldStandards “Plug, socket & voltage by country”

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to nd your country’s voltage standards.

It is important to use the correct voltage power supply or power

converter for the computer’s voltage speci cations. Imagine that
you have a customer who imported a PC from a country that uses
a different standard for input voltage. You will need to adapt the
input power to protect the computer. Some options for doing this
might include:

• Replace the power supply with a unit that uses the

appropriate voltage for the target country.
• Install a power supply model that includes a dual-voltage
switch that can be toggled from 110-120VAC to
220-240VAC.
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 • Plug the computer into an external power converter that then
plugs into a normal wall socket. Power converters can be
purchased from any store that sells international travel
merchandise.
Without a power converter, the following problems may be
experienced:

If a But the wall

The result will be
compute socket
r needs delivers
220-240V 110-120VAC not enough power for the
AC computer to run properly
110-120V too much power, which will
220-240VAC
AC damage the computer’s
internal parts

Motherboard engineering speci cations

The motherboard and form factor speci cations document will
provide a list of compatible power supply types to help you select
the correct part. The ATX form factor is the most common
motherboard design for full-sized, personal desktop computers.
You may also nd a version of the ITX form factor in smaller
computers. The form factor size and components embedded in
the motherboards will create a starting point for the minimum
power supply wattages required.

Power consumption of components

The number of internal components and peripherals the computer
will need to support will also determine the minimum wattage a
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power supply must provide. For example, a basic computer that is
designed for word processing and sur ng the Internet should work
with a standard power supply. However, some computers may
need higher wattage power supplies to support items like a
powerful CPU, multiple CPUs, multiple hard drives, video
rendering applications, a top-tier graphics processing unit (GPU)
for gaming, and more.

Voltages and pin connectors

The internal hardware components of a computer require varied
input voltages to operate. Voltage regulators embedded in the
motherboard of the computer control the amount of power that is
delivered to the computer’s various internal components.

Voltage Examples of components that use each

voltage level
3.3V DIMMs, chipsets, and some PCI/AGP cards
5V SIMMS, disk drive logic, ISA, and some voltage
regulators
12V Motors and voltage regulators with high outputs

The computer’s power supply plugs into an adapter on the

computer’s motherboard. The wiring for this connection uses color
coded wires. Each wire color carries a different voltage of
electricity to the motherboard or serves as a grounding wire. A
standard ATX motherboard power adaptor has either 20-pins or
24-pins to connect these wires. The 20-pin design is an older
technology. The 24-pin connector was developed to provide more
power to support additional expansion cards, powerful CPUs, and
more. The 24-pin connector has become the standard for today’s
personal computer power supplies and motherboards.
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 The power supply will have multiple connectors that plug into the
motherboard, hard drives, and graphic cards. Each cable has a
speci c purpose and delivers the appropriate amount of electricity
to the following parts:

Connections from a PC power supply (ATX 2)

1. Floppy disk drive (obsolete)

2. "Molex" universal (e.g. IDE hard drives, optical drives)
3. SATA drives
4. Graphics cards 8-pin, separable for 6-pin
5. Graphics cards 6-pin
6. Motherboard 8-pin
7. Motherboard P4 connector, can be combined to 8-pin
mainboard connector 12V
8. ATX2 24-pin, divisible 20+4, and can therefore also be used
for old 20-pin connections
9.
You will learn how to install a power supply and connect these
power cables later in this module.

Key takeaways
When selecting a power supply for a computer, the following
items should be taken into consideration:

1. Wall socket input voltage standard for the country where the
computer will be used;
2. The number and power consumption needs of the
computer’s internal components;
3. The motherboard model and form factor engineering
speci cations and requirements.
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Resources for more information
For more information on these topics, please visit:

• Plug, socket & voltage by country

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- List of countries around the world and their voltage
standards for common wall sockets and plug types.
• How to Diagnose and Replace a Failed PC Power Supply
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- Step-by-step illustrated instructions on how to diagnose a
power supply failure and replace it on a desktop PC.