Power Supply

Power Supply Function & Operation• Converts 120-volt AC power source into

3.3v, 5v, 12v, -5v, -12v DC power source.– To run the system

• Negative voltages typically not used in modern systems– used in older floppy drives and serial ports and LAN

circuits.

• Sends Power Good signal during POST– the power supply also ensures that the system does not

run unless the power supplied is sufficient to operate the system properly.

Devices Powered by different Voltages

Voltage Devices Powered

+3.3V Chipsets, DIMMs, PCI/AGP cards, miscellaneous chips

+5V Disk drive logic, SIMMs, PCI/AGP cards, ISA cards, voltage regulators,

miscellaneous chips+12V Motors, voltage regulators (high

output)-5V Older Floppy Disk drives-12V Serial Ports and LAN circuits

The Power_Good Signal• In the absence of Power_Good, the timer chip holds

the reset line on the processor, which prevents the system from running under bad or unstable power conditions.

• When the timer chip receives the Power_Good signal, it releases the reset, and the processor begins executing whatever code is at address FFFF:0000 (usually the ROM BIOS).

PS_ON Power Supply• PS_ON, can be used to turn the power supply (and thus the

system) on or off via software. • It is sometimes known as the soft-power feature. • PS_ON is most evident when you use it with an operating

system, such as Windows 9x, that supports the Advanced Power Management (APM) or Advanced Configuration and Power Interface (ACPI) specification. – When you select the Shut Down the Computer option from the

Start menu, Windows automatically turns off the computer after it completes the OS shutdown sequence.

– A system without this feature only displays a message that it’s safe to shut down the computer.

Technically the Power Supply is:Technically, the power supply in your PC is described

as a constant voltage half-bridge forward converting switching power supply:

• Constant voltage means that the power supply puts out the same voltage to the computer’s internal components, no matter what the voltage of AC current running it or the capacity (wattage) of the power supply.

• Half-bridge forward converting switching refers to the design and power regulation technique used by most suppliers. This design is commonly referred to as a switching supply. Compared to other types of power supplies, this design provides an efficient and inexpensive power source and generates a minimum amount of heat. It also maintains a small size and a low price.

Power Supply Form FactorsThe shape and general physical layout (size) of a

component is called the form factor.– PC/XT

– AT/Desk

– AT/Tower

– Baby-AT

– LPX

• Allows us to upgrade and repair our systems by easily replacing physically (and electrically) interchangeable components.

• Having interchangeable parts means that we have a better range of choices for replacement items, and the competition makes for better pricing, too.

• SFX• ATX• SFX

Power Supply Form Factors

1995

Motherboard Form Factors

Power Supply Form Factors

• XT

8 3/4 " x 5 1/2" x 4 3/4"

• AT Mini-AT

6" x 8 1/2" x 5 7/8” 6" x 6" x 5 1/2"

• LPX

6.5”x5.9”x5.9”

• ATX NLX

5 1/2” x 5 7/8” x 3 3/8” 5 1/2" x 5 7/8" x 3 3/8"

AT Power Supply Connectors

LPX/AT Power Supply• Lacks 3.3 Volt Output

• Uses two 6-pin connectors P8 and P9

• Incorrect installation can damage system

• Some power switch wires are live

LPX /AT Power Supply Switch – Brown and blue wires are the live and neutral

feed. Always hot when power supply is plugged in.

– Black and white wires carry AC from the switch to the power supply. Hot only when power supply is ON.

– Green wire or green with yellow stripe is ground lead. Should be connected to case.

ATX Power Supply• Provides 3.3 Volt Output.

• Single 20-pin connector.

• Case switch goes to motherboard- uses 5v instead of 120v circuit.

• A few models have a true on-off switch on the rear of the unit.

ATX Power Supply for NLX style• NLX systems were designed to use ATX

power supplies,

• even though the case and motherboard dimensions are different.

• NLX - defines a low-profile case and motherboard design.

SFX Power Supply• SFX (Small form factor) power supply

designed to go with smaller Micro-ATX motherboard form factor in December of 1997.

• Used in many compact systems.

• 90w continuous/135wpeak - is enough for a system with 4 expansion slots and 3 devices.

• Lacks -5v.

• Lacks both Auxiliary (3.3V and 5V) and ATX12V power connectors.

Power Supply Connectors• Power connector to motherboard

• Power connector to CD and hard drives

• Power connector to floppy drive

• Y-adapter

AT/LPX Power Connectors P8/P9 or P1/P2

ATX 20-pin Connector Bottom view

Terminal side view: facing the terminal side.

ATX 20-pin Connector Top view

ATX 20-pin Connector Top view (wire side)

ATX 6-pin Auxiliary Connector

ATX12V Power Connector

ATX 6-pin (2x3) Optional Connector

Dell ATX 20-pin Connector Top view (wire side)

ATX 20-pin Connector Top view (wire side)

Dell ATX 6-pin Connector

ATX 6-pin Auxiliary Connector

Peripheral Power Connectors

BTX Power Connectors

BTX Power ConnectorsBTX Top View ATX Bottom View

BTX Power ConnectorsAnandtech:http://www.anandtech.com/casecooling/showdoc.aspx?i=1876&p=2http://www.anandtech.com/casecooling/showdoc.aspx?i=2276

Intel:http://www.intel.com/pressroom/kits/p4/btx/http://www.intel.com/cd/channel/reseller/asmo-na/eng/95349.htm

formfactors.org:http://www.formfactors.org/

Others:http://www.extremetech.com/article2/0,1558,1727916,00.asphttp://www.aselabs.com/articles.php?id=166

BTX Motherboards

BTX Motherboards

BTX Motherboards

BTX Motherboards

8” x 10.5” 10.4” x 10.5” 12.8” x 10.5”

BTX Cases

Power Supply Ratings

P = V × I

watts = volts × amps

ATX Power Supply Output Ratings

Compute ATX Power Output Ratings• If you compute the total output using the formula described

earlier, these power supplies seem to pro-duce an output that is much higher than their ratings.

• The 300W model, for example, comes out at 354.7 watts. • However, notice that the supply also has a maximum

combined output for the +3.3V and +5V of 150 watts. • This means you cannot draw the maximum rating on both

the 5V and 3.3V lines simultaneously, but must keep the total combined draw between them at 150W.

• This brings the total output to a more logical 308.5 watts (150W + 12Vx12A + 12w + 2w).

Power Supply Certifications• In Canada, electric and electronic products are listed

by the Canadian Standards Agency (CSA).

• In the United States is Underwriters Laboratories, Inc. (UL). UL standard #1950—the Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment, Third Edition—covers power supplies and other PC components.

Power-Use Calculations

Maximum Power Consumption in Amps per Bus Slot

Power Management• Turning the system off and on

• Cost of operation

• Damage to parts due to expansion (heating) and contraction (cooling)

• Changing the state of operation of a component

• Surge current

Power Protection Systems• Surge Protectors

– Absorb high voltage produced by lightning strikes.

• SPS (Standby Power Supplies)– Switches to a battery when power is cut off

• UPS (Uninterruptible Power Supplies)– System always runs from battery power

Power Supply Troubleshooting

• The following problems might be caused by a faulty power supply or house current to the PC.– Computer hangs for no reason. Might reboot

itself.– Memory errors occur occasionally.– Data is written incorrectly to hard drive.– Keyboard stops working at odd times.– Systemboard fails or is damaged.– Power supply overheats and becomes hot to

touch.

Energy Star Computers (The Green Star)

• Energy Star computers and peripherals have the Green Star, which indicates that they satisfy the requirements of the U.S. Environmental Protection Agency (EPA).

• The green standards are a set of specifications designed by the EPA to reduce overall power consumption in the U.S.

• The green PCs or devices has a standby program that causes the device to go into sleep mode when it is not being used.

• Sleep mode could be more properly labeled reduced power consumption mode.

• This is a state that an EPA compliant PC will go into when it is not in use.

• The EPA requirement for sleep mode is the device can use no more that 30 watts of power while asleep.

Energy Star PCs:• There are four types of power management

methods available for PCs: Advanced Power Management (APM). APM is used in

almost every new system today and is championed by Microsoft and Intel.

AT Attachment (ATA) for IDE drives.

Display Power Management Signalling (DPMS) standards for monitors and video cards.

Advanced Configuration and Power Interface (ACPI) - only with newer system BIOS and Windows 98

• The energy star features can normally be adjusted in the CMOS setup.

Green timer on the systemboard:

• Four system states, dependant on system’s current activity

• Doze time The doze time is the amount of time specified before the system will reduce its power consumption by 80%.

• Standby time The standby time is the amount of time specified before the system will reduce its power consumption by 92%.

• Suspend time The suspend time is the amount of time specified before the system will reduce its power consumption by 99%. Note that when a system has gone into suspend mode it will require a short warm-up period when activated again.

• Hard drive standby time The hard drive standby time is the amount of time specified before the system will temporarily shut down the hard drive.

Power Protection Systems• Protect system from surges, spikes, power

failures.

• High-quality power supplies are capable off shutting down systems during power disturbances.

Power-Protection Systems• Four common protection systems:

– Surge Suppressors– Line Conditioners– Standby power supplies (SPS)– Uninterruptible power supplies (UPS)

Case Form Factors• Full Tower

• Mini-Tower

• Desktop

• Low Profile (also called Slimline)

• ATX motherboards require ATX cases

Form Factors

• Systemboards have different physical dimensions.– known as form factor

• Have to match systemboard to case.

• Obsolete Form Factors– Baby-AT– Full-size AT– LPX (semi-proprietary, Western Digital)

Form Factors

• Modern Form Factors– ATX (used in most full-sized desktop/tower

systems.– Micro-ATX (smaller ATX)– Flex-ATX (smaller than Micro-ATX, used in low-

cost home PCs)– NLX (corporate desktop models)– WTX (workstations and servers)

• Proprietary Designs– Compaq, Packard Bell, Hewlett-Packard...

Components - Case

Styles:• Tower case

– The tower is like a desktop flipped on its side and can sit on the floor or on the desk.

• Desktop case.– Rectangular case that is wider than it is tall and

sits on the desk.

Tower Cases

Desktop Cases

Desktop Cases

Power Supplies

• Important component of PC

• Supplies clean, reliable DC power to computer.

• Converts 120V, 60 Hz, AC signal to +3.3V, +5V, +12V, -5V and -12V DC.

• Rated in WATTS

• Before power is provided to computer power supply runs through self-check.– Sends “Power Good” signal to computer when

it has passed the check.

Power Supplies

• Newer power supplies have PS_ON signal.– This allows the computer to be powered off

with software.