Transcript Power Supply Wattage

Power Supply
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Objectives
• In this chapter, you will:
– Understand power supply
– The most common computer power supplies
are built to conform with the ATX form factor.
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Power Supply: Switcher Technology
• Instead of the linear design, PCs use
switching power supplies.
• The full name for this sort of design is
actually "constant-voltage, half-bridge
forward-converting switching power
supply", but don't worry, that won't be on
the final exam. :-)
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Power Supply
• Warning: Power supplies
generate high voltages internally
and can be dangerous.
• Unless you have been specifically
trained to work inside power
supplies, you should not open
one.
• Even with the unit unplugged
dangerous electricity can remain
stored within its components for
some time
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Power Supply
• Power supplies, often referred to as
"switching power supplies", use
switcher technology to convert the AC
input to lower DC voltages.
• However, the PC power supply's job
isn't as simple as that of a standard
power converter,
– such as the kind you might plug into your
car's lighter socket to let you run a TV off
your car battery.
• The power supply in your PC provides
all of the different voltages your
computer needs to operate properly.
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Watts
• The main specification of a power supply is in
watts.
• A watt is the product of the voltage in volts
and the current in amperes or amps.
– The electrons that flow through the wire is referred to as
Current, measured in AMPS.
1W=1V×1A
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Power Supply
• A Power Supply does not supply
power; electrical power comes from
your local utility company.
• The Power Supply converts the power
from alternating current to direct
current at levels that the system
requires.
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AC vs. DC
• Alternating current works fine for certain
appliances and has the added advantage of
being easy to distribute over long distances,
but many devices will not work on AC.
– Just a few examples of this are telephone answering
machines, many types of audio equipment, some
kinds of battery chargers, and in the PC world,
certain types of printers , external modems and
other peripherals.
• Two indicators that a device actually uses DC
inside are: the ability of the device to run on
batteries, and the presence of a device
outside the unit that powers it.
– These small "bricks" with one plug for the wall and
another for the device are often called AC adapters
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Power Supply: Switcher Technology
•
The switching power supplies used today are
much smaller and lighter. They convert the 60Hertz (Hz, or cycles per second) current to a
much higher frequency, meaning more cycles
per second.
–
•
This conversion enables a small, lightweight transformer
in the power supply to do the actual voltage step-down
from 110 volts (or 220 in certain countries) to the
voltage needed by the particular computer component.
The main disadvantage of a switching supply is
that it generates high-frequency signals within it
as part of its conversion process, which can
radiate out of the unit and cause interference to
other electronic devices (inside or outside the
PC).
–
For this reason, you will always see PC power supplies
encased in metal boxes for shielding.
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Voltages
• Voltage is the pressure that pushes the
electrons through the conductor (wire).
Voltage is measured in Volts.
• PC usually uses120 volt power to the
power supply.
• The typical voltages supplied are:
– 3.3 volts
– 5 volts
– 12 volts
• The 3.3- and 5-volts are typically used
by digital circuits,
• The 12-volt is used to run motors in disk
drives and fans.
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Power Supply Standardization
• Over time, there have been at least six
different standard power supplies for
personal computers.
• Recently, the industry has settled on
using ATX-based power supplies.
• ATX is an industry specification that
means the power supply has the
physical characteristics to fit a standard
ATX case and the electrical
characteristics to work with an ATX
motherboard.
• PC power-supply cables use
standardized, keyed connectors that
make it difficult to connect the wrong
ones.
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Power Supply Wattage
• Computer power supplies are
rated based on their maximum
output power.
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Small Form Factor - 15A (250W)
Mini-Tower - 25A (300-350W)
Mid-Tower - 35A (400-500W)
Full Tower - 40A (600-650W)
Dual Video Card (SLI) - 60A (850W+)
Power supplies used by gamers and
enthusiasts mostly range from
450 W to 1400 W.
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Power Supply Wattage
• Power Requirements for typical systems.
• Item Power
requirement
• OLDER CPUs
20-40 Watts
• Athlon XP – Pentium IV 60-90 Watts
• motherboard
20-60 Watts
• RAM
20 Watts /256 MB
• PCI Card
5–10 Watts
• AGP Video
20–50 Watts and more
• CPU Case Fan
2 – 4 Watts
• 5400 RPM Hard Drive 5 – 10 Watts
• 7200 RPM Hard Drive 5 – 15 Watts
• 10000 RPM Hard Drive 5 – 20 Watts
• Floppy Drive
5 Watts
• CD / DVD
10 – 20 Watts
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Voltage used
3.3 Volts
12 Volts
3.3, 5.0, 12 Volts
3.3 Volts
3.3 Volts
5, 12 Volts
12 Volts
5, 12 Volts
5, 12 Volts
5, 12 Volts
5, 12 Volts
5, 12 Volts
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Power Supply Wattage
• A 400-watt switching power supply
will not necessarily use more
power than a 250-watt supply.
• A larger supply may be needed if
you use every available slot on the
motherboard or every available
drive bay in the personal computer
case.
• It is not a good idea to have a 250watt supply if you have 250 watts
total in devices, since the supply
should not be loaded to 100
percent of its capacity.
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Mother Board with a Pentium 4 processor, 256 MB RAM,
a 7200 Rpm Hard Drive, a floppy drive, a CD and an AGP
Card.
o Mother Board ----------------------------- 50 Watts
o Pentium 4 ---------------------------------- 90 Watts
o 256 MB RAM ------------------------------ 20 Watts
o Hard Drive --------------------------------- 15 Watts
o Floppy Drive ------------------------------- 5 Watts
o CD -------------------------------------------- 20 Watts
o AGP Video Card -------------------------- 50 Watts
Total System Power: 250 Watts
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Power Supply Problems
• The PC power supply is probably the most
failure-prone item in a personal computer.
• Typically, a stalled cooling fan is a predictor
of a power supply failure due to subsequent
overheated components.
• A typical failure of a PC power supply is often
noticed as a burning smell just before the
computer shuts down.
• Failure symptoms include random rebooting
or failure in Windows for no apparent
reason.
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Power Supply Problems
• Despite its critical role, the power
supply is one of the most ignored
and under-studied components in
the PC.
• In fact, some people don't even
bother to check out what power
supply is included when they
purchase a case!
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Case and Cover
• Every PC power supply comes
surrounded by a metal case with a metal
cover.
• The case isolates the components inside
the power supply from the rest of the
PC.
• Power supplies are usually intended to
be considered as "black boxes" and not
serviced by individual PC owners.
• Ventilation slots or holes are placed into
the case in key locations to allow the
power supply fan to provide air flow
over critical components.
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PC Power Switch
• Older form factor desktop XT
cases had the power switch at
the back of the machine, usually
on the right side of the case.
Baby AT power supply
– This switch was actually inside the power
supply itself, with a hole cut out in the
case so that it could be reached from the
outside.
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Turn on PC
• Today you turn on the power with a
little push button, and you turn off the
machine with a menu option.
• These capabilities were added to
standard power supplies several years
ago.
• The operating system can send a signal
to the power supply to tell it to turn off.
The push button sends a 5-volt signal to
the power supply to tell it when to turn
on.
• The power supply also has a circuit that
supplies 5 volts, called VSB for "standby
voltage" even when it is officially "off",
so that the button will work.
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remote PC power supply switch
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PC Power Switch
• One consequence of the "soft power" method of operating
the power supply comes into play if there is a power failure.
– Imagine that you have a PC running unattended. There's a power outage,
and the system shuts down.
– Several hours later, the power comes back on.
– With an old-fashioned mechanical power switch, the system would
immediately restart, because as soon as the power was restored the power
supply would turn on.
– With an ATX/NLX, SFX or WTX form factor supply however, the power supply
would sit there waiting for a "turn on" signal from the motherboard!
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External Voltage Selector Switch
• PC power supplies support 110V input,
220V input or both.
– Dual-voltage supplies normally have a selector
in the back that controls which voltage you are
using; obviously, you want to make sure it is set
correctly.
• There are also some supplies that will
automatically support either 110V or
220V without a selector switch, but
these are often found only on more
expensive units.
– 100-127V in North America, parts of South
America, Japan, and Taiwan;
– 220-240V in most of the rest of the world
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Connectors
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Typically, power supplies have the following connectors:
PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it
with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire (it is usually green).
This connector is the largest of all the connectors.
ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the
motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor.
4-pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller
connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one
red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the
red wire is +5 V, and the yellow wire is +12 V.
4-pin Berg power connectors (usually called Mini-connector or "mini-Molex"): This is one of the smallest
connectors that supplies the floppy drive with power. In some cases.
Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional
power if it is needed.
Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs. This
connector supplies power at three different voltages: +3.3, +5, and +12 volts.
6-pin Most modern computer power supplies include 6-pin connectors which are generally used for PCI
Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power
supplies.
6+2 pin For the purpose of backwards compatibility, some connectors designed for use with PCI Express
graphics cards feature this kind of pin configuration.
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Connectors
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Typically, power supplies have the following connectors:
PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it
with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire (it is usually green).
This connector is the largest of all the connectors.
ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the
motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor.
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Connectors
•
•
4-pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller
connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one
red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the
red wire is +5 V, and the yellow wire is +12 V.
4-pin Berg power connectors (usually called Mini-connector or "mini-Molex"): This is one of the smallest
connectors that supplies the floppy drive with power. In some cases.
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Connectors
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Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional
power if it is needed.
Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs. This
connector supplies power at three different voltages: +3.3, +5, and +12 volts.
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Connectors
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6-pin Most modern computer power supplies include 6-pin connectors which are generally used for PCI
Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power
supplies.
6+2 pin For the purpose of backwards compatibility, some connectors designed for use with PCI Express
graphics cards feature this kind of pin configuration.
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Power outage
• Power outages are categorized into three
different phenomena, relating to the
duration and effect of the outage:
– A dropout is a momentary (milliseconds to seconds)
loss of power typically caused by a temporary fault
on a power line. Power is quickly (and sometimes
automatically) restored once the fault is cleared.
– A brownout is a drop in voltage in an electrical
power supply, so named because it typically causes
lights to dim. Such malfunctions are particularly
damaging to electric motors.
• The voltage from power companies is generally between 115
and 120 Volts AC, during a brownout the power could drop to
less than 110 volts.
– A blackout refers to the total loss of power to an
area and is the most severe form of power outage
that can occur.
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Protecting computer systems from power outages
• Computer systems and other electronic
storage devices are susceptible to data
loss or hardware damage that can be
caused by the sudden loss of power.
• To protect against this, the use of an
Uninterruptible power supply or UPS can
provide a constant flow of electricity in
the event that a primary power supply
becomes unavailable for a short period of
time.
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Power Surge
• An unexpected increase in the amount of
electrical voltage in an electrical line. A
power surge can provide too much power
to a computer or electrical device
generally causing damage to that device
making the device not operate at all or
improperly.
– In electrical engineering, spikes are fast, short
duration electrical transients in voltage
(voltage spikes), current (current spike), or
transferred energy (energy spikes) in an
electrical circuit.
• Users can help prevent power surges with
surge protectors.
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Review
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Alternation Current – The type of power delivered by the electric company where
current flows in one direction then stops and reverses direction
AMP - The measure of current in an electrical circuit
Blackout – Total loss of power
Brownout - When the voltage delivered by the power company drops to a less than
expected level
Direct Current – The type of power delivered by batteries, the voltage is constant
EMI – Electromagnetic Interference is electrical interference caused by nearby devices
that have electromagnets, like motors, or transformers
RFI – Radio Frequency Interference is electrical interference caused by other electronic
devices operating nearby
Spike – When the power increases for a very short period of time
Surge - When the voltage increases to higher than normal for a duration of time
Surge Suppressor – Device used to absorb voltage spikes
Volt - The Measure for Voltage
Watt - The measure of Power
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