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Chapter 3

Chapter 3. Electricity and Power Supplies. You Will Learn…. How electricity is measured How to protect your computer system from damaging changes in electrical power About types of form factors and computer cases How to detect and correct power supply problems

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Chapter 3

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  1. Chapter 3 Electricity and Power Supplies

  2. You Will Learn… • How electricity is measured • How to protect your computer system from damaging changes in electrical power • About types of form factors and computer cases • How to detect and correct power supply problems • About Energy Start specifications

  3. Electricity: A Basic Introduction

  4. The Properties of Electricity continued…

  5. The Properties of Electricity

  6. Measuring Voltage with a Voltmeter

  7. Measuring Amps with an Ammeter

  8. Relationship Between Voltage and Current • Direct relationship • As electrical potential difference (or voltage) increases, electrical current increases • As voltage decreases, current decreases

  9. Relationships Among Voltage, Current, and Resistance • Voltage and current have a direct relationship • When voltage increases, current increases • Resistance has an inverse relationship with voltage and current • As resistance increases, either current or voltage decreases • As resistance decreases, either current or voltage increases (Ohm’s Law) • One volt drives a current of one amp through a resistance of one ohm

  10. AC (Alternating Current) • Cycles or oscillates back and forth rather than traveling in one direction • 60 times in one second (60 hertz) • Most economical way to transmit electricity to homes and workplaces • Can be forced to travel great distances by decreasing current and increasing voltage

  11. DC (Direct Current) • Travels in only one direction • Required by most electronic devices, including a computer (power supply acts as both a rectifier and a transformer) • Rectifier converts AC to DC • Transformer • Changes the ratio of current to voltage • Overall power stays constant

  12. Computer Power Supply

  13. Hot, Neutral, and Ground

  14. Hot, Neutral, and Ground • Short circuit occurs when electricity is allowed to flow uncontrolled from hot line to neutral line or from hot line to the ground • Fuses prevent too much current from flowing through the circuit • Neutral line to a house is grounded many times along the way and at breaker box

  15. Hot, Neutral, and Ground

  16. Common Electrical Components • Transistors • Capacitors • Diodes • Ground • Resistors

  17. Materials Used to Make Electrical Components • Conductors • Insulators • Semiconductors

  18. Transistor • Electronic device that can serve as a gate or switch for an electrical signal • Can amplify flow of electricity • Made of three layers of semiconductor material • Basic building block of an integrated circuit (IC) that is used to build a microchip

  19. Capacitor • Can hold an electrical charge • Smoothes out uneven flow of electricity through a circuit • Maintains a charge long after current is no longer present

  20. Diodes and Resistors • Diode • Semiconductor device that allows electricity to flow in only one direction • Resistor • Electronic device that limits amount of current that can flow through it

  21. Protecting Your Computer System: General Precautions • Make notes so you can backtrack • Remove packing tape and cellophane from work area • Keep components away from hair and clothing • Keep screws and spacers in an orderly place • Don’t stack boards on top of each other continued…

  22. Protecting Your Computer System: General Precautions • Don’t touch chips on motherboard or expansion cards • Don’t touch a chip with a magnetized screwdriver • Don’t use a graphite pencil to change DIP switch settings • Turn off a computer before moving it • Keep disks away from magnetic fields, heat, and extreme cold

  23. Protecting Against Electricity • Turn off power and unplug computer • Use a ground bracelet • Never touch inside of a computer while it is turned on • Never remove cover or put your hands inside monitor or power supply

  24. Static Electricity • Electrostatic discharge (ESD) • Electrical charge at rest • Brief flow of electricity caused by contact between two objects that had a difference in voltage potential • Can cause catastrophic or upset failure • Static control devices or methods: • Ground bracelet or static strap (except when working inside a monitor or with high-voltage equipment) • Ground mats • Static shielding bags

  25. Ground Bracelet

  26. Ground Mat

  27. Static Shielding Bags

  28. EMI (Electromagnetic Interference) • Caused by the magnetic field produced as a side effect when electricity flows • Radio frequency interference (RFI) can cause problems with radio and TV reception • Use a line conditioner to filter electrical noise causing the EMI

  29. Surge Protectionand Battery Backup • Devices that control electricity to a computer • Surge suppressors (surge protectors) • Power conditioners • Uninterruptible power supplies (UPSs) • Should have UL (Underwriters Laboratory) logo

  30. Surge Suppressors • Protect equipment against sudden changes in level of power • Shunt type, series type, or combination • Can come as power strips, wall-mounted units that plug into AC outlets, or consoles; some provide RJ-11 telephone jack to protect modems and fax machines • Data line protector (for phone line)

  31. Power Conditioners and UPSs • Provide protection against spikes • Regulate (condition) the power, providing continuous voltage during brownouts • Sometimes called line conditioners

  32. Uninterruptible Power Supply • Benefits • Conditions line for brownouts and spikes • Provides backup power during a blackout • Protects against very high potentially damaging spikes • Types • Standby device • Inline device • Line-interactive device

  33. Uninterruptible Power Supply

  34. Uninterruptible Power Supply • Intelligent UPS • Can be controlled and managed from utility software at a remote computer • Must have a serial port connection to PC and a microprocessor on board • What to consider when buying a UPS • Cost • UPS rating should exceed total VA or wattage output by at least 25% • Be aware of degree of line conditioning • Consider warranty, service policies, and guarantee

  35. UPS Manufacturers

  36. The Computer Caseand Form Factors • Form factor • Description of size, shape, and general makeup of a hardware component • Use same form factor for motherboard, case, and power supply

  37. XT (older, outdated) AT ATX (most popular) LPX NLX Backplane systems Most common form factors used on PCs: AT Baby AT ATX Mini-ATX Case, Power Supply, and Motherboard Form Factors

  38. AT Form Factor • Used on older motherboards • Uses full-size AT cases used by original IBM AT personal computer • Cannot be used with smaller AT cases or with newer ATX cases • Difficult to install, service, and upgrade • No longer produced by most manufacturers

  39. AT Motherboard

  40. Baby AT • Industry standard from 1993-1997 because of greater flexibility • Power supplies blow air out of computer case • Smaller motherboards fit into many types of cases • Problematic position of CPU in relation to expansion slots not resolved • Cables might not be long enough

  41. ATX • Superseded earlier AT and Baby AT form factors • Open, nonproprietary industry specification developed by Intel in 1995 • Easier to add and remove components • Greater support for I/O devices and processor technology • Lower costs • Better positioning of components on motherboard continued…

  42. ATX • Possible to reduce cable lengths, which can help reduce potential for EMI and corrupted data • Power supply and motherboard use single power connector (P1 connector) • Power supply fan blows air into case; cools processor directly • Soft switch feature • Other types of ATX boards (Mini-ATX, MicroATX, FlexATX )

  43. ATX Motherboard

  44. LPX and Mini LPX • Developed by Western Digital • Often used in low-cost systems • Expansion cards mounted on riser card that plugs into motherboard • Not easy to upgrade • Cannot handle physical size of recently developed processors • Not designed to handle higher temperature at which faster processors operate • Use low profile cases and slim-line cases

  45. LPX

  46. NLX • For low-end PC motherboards • Use low-profile cases • Provide greater support for current and up-and-coming processor technologies • Flexible; use space efficiently

  47. NLX

  48. Backplane Systems • Do not use a true motherboard, but a board that normally sits against back of a proprietary case that has slots for other cards • Active backplanes • Passive backplanes • Not generally used in PCs

  49. Types of Cases • Computer case (chassis) • Houses power supply, motherboard, expansion cards, drives • Lights and switches on front panel for controlling and monitoring PC • Needs to fit its intended use • Major categories • Desktop cases • Tower cases • Notebook cases

  50. Desktop Cases • Classic case with four drive bays and six expansion slots; sits on desktop and does double duty as a monitor stand • Being replaced by smaller and more space-efficient cases • For low-end desktop systems, compact cases follow either the NLX, LPX, or Mini-LPX form factor

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