790 likes | 1.07k Views
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
E N D
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 • About Energy Start specifications
The Properties of Electricity continued…
Relationship Between Voltage and Current • Direct relationship • As electrical potential difference (or voltage) increases, electrical current increases • As voltage decreases, current decreases
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
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
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
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
Common Electrical Components • Transistors • Capacitors • Diodes • Ground • Resistors
Materials Used to Make Electrical Components • Conductors • Insulators • Semiconductors
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
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
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
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…
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
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
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
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
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
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)
Power Conditioners and UPSs • Provide protection against spikes • Regulate (condition) the power, providing continuous voltage during brownouts • Sometimes called line conditioners
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
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
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
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
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
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
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…
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 )
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
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
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
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
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