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 voltagemeans 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 switchingrefers 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 Factors The 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 • 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"
ATX NLX 5 1/2” x 5 7/8” x 3 3/8” 5 1/2" x 5 7/8" x 3 3/8"
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
ATX 20-pin Connector Bottom view Terminal side view: facing the terminal side.
BTX Power Connectors BTX Top View ATX Bottom View
BTX Power Connectors Anandtech: http://www.anandtech.com/casecooling/showdoc.aspx?i=1876&p=2 http://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.asp http://www.aselabs.com/articles.php?id=166
BTX Motherboards 8” x 10.5” 10.4” x 10.5” 12.8” x 10.5”
Power Supply Ratings P = V × I watts = volts × amps
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 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.