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Chapter 4. Electricity and Power Supplies. You Will Learn…. How electricity is measured How to protect your computer system against damaging changes in electrical power About different form factors and computer cases How to detect and correct power supply problems

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chapter 4

Chapter 4

Electricity and Power Supplies

you will learn
You Will Learn…
  • How electricity is measured
  • How to protect your computer system against damaging changes in electrical power
  • About different form factors and computer cases
  • How to detect and correct power supply problems
  • About Energy Star specifications
measures of electricity
Measures of Electricity


Page 121

  • Measures potential differences
  • Electrical force created by the potential difference in electron charge flowing between 2 points
  • Measured in units called volts
  • Negative to positive flow
  • Measures when power is on


Page 122

  • Ampere = unit of measurement for electrical current
  • Amps remain constant throughout electrical system
  • Current: volumn of electrons flowing through an electrical system


relationship between voltage and current
Relationship Between Voltage and Current
  • Direct relationship
    • As the electrical potential difference (voltage) increases, the electrical current increases
    • As the voltage decreases, the current decreases
  • Standard unit of measurement for electrical resistance
  • Resistors are devices used in electrical circuits to resist the flow of electricity
  • As resistance decreases, electricity increases

Paragraph Page 124

relationship among voltage current and resistance
Relationship 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) V=I/R or Volts = Amps/Ohms
  • One volt drives a current of one amp through a resistance of one ohm
  • Total amount of power needed to operate an electrical device
  • Measured in watts
  • Calculated by multiplying volts by amps in a system (W = V x A)
ac and dc
AC and DC
  • AC (alternating current)
    • Means of sending power over extended distances
    • Cycles back and forth rather than traveling in only one direction
    • Most economical way to transmit electricity
  • DC (direct current)
    • Travels in only one direction
    • Type of current required by most electronic devices, including computers
    • Computer power supplies function as both a transformer and a rectifier

Device that changes ratio of current to voltage (reduces voltage to a usable level)

Device that converts AC to DC

power supply function
Power Supply Function


Chapter questions 2-6

hot neutral and ground1
Hot, Neutral, and Ground
  • Hot: inbound current
  • Neutral: outbound current
  • Ground: protection for neutral line against short circuits
  • Short circuit
    • Occurs when electricity is allowed to flow uncontrolled from hot line to neutral line or from hot line to the ground
  • Fuse
    • Designed to prevent too much current from flowing through the circuit
    • Rated in amps

Paragraph 127

hot neutral and ground3
Hot, Neutral, and Ground

Receptacle tester

materials used to make electronic components
Materials Used to Make Electronic Components
  • Conductors: easily conducts electricity (gold or copper)
  • Insulators: resists flow of electricity (glass or ceramic)
  • Semiconductors: falls between conductors & insulators—ability to conduct electricity when charge is applied (silicon)


some common electronic components
Some Common Electronic Components

Device that can hold electrical charge for period of time & smooth the uneven flow through a circuit

Device serves as a gate or switch for electrical signal & can amplify the flow


protecting your computer system
Protecting Your Computer System
  • General safety precautions
  • Protecting against electricity
  • Protecting against electrostatic discharge (ESD or static electricity) and electromagnetic interference (EMI)
  • Surge protection and battery backup
protecting against electricity
Protecting Against Electricity
  • When working inside a computer
    • Turn off the power
    • Unplug the computer
    • Use a ground bracelet


static electricity
Static Electricity
  • Ground yourself and computer parts, using static control devices or methods
    • Ground bracelet or static strap
    • Ground mats
    • Static shielding bags
  • Caution: Don’t wear a ground bracelet when working inside a monitor or with high-voltage equipment such as a laser printer
electromagnetic interference
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 protection and battery backup
Surge Protection andBattery Backup
  • Devices that filter AC input
    • Surge suppressors (or surge protectors): protect against sudden changes in power level
    • Power conditioners
    • Uninterruptible power supply (UPS)
      • Also provides backup power

Alters power to provide continuous voltage

Tips on 136

uninterruptible power supply
Uninterruptible Power Supply
  • Benefits
    • Condition line for brownouts and spikes
    • Provide backup power during a blackout
    • Protect against very high spikes that could damage equipment

Spikes: temporary voltage surges

Brownouts: temporary voltage reductions

what to consider when buying a ups
What to Consider WhenBuying a UPS
  • Cost
  • Rating should exceed your total VA or wattage output by at least 25%
  • Degree of line conditioning
  • Warranty, service policies, and guarantee
computer case and form factors
Computer Case and Form Factors
  • Form factor
    • Describes the size, shape, and general makeup of a hardware component
    • Must match for motherboard, power supply, and case
case power supply and motherboard form factors

ATX (most popular)



Backplane systems

Most common form factors used on PCs:


Baby AT



Case, Power Supply, and Motherboard Form Factors
types of cases
Types of Cases
  • Desktop cases
  • Tower cases
    • Minitower
    • Midsize (most popular)
    • Full-size
  • Laptop cases
detecting and correcting power supply problems
Detecting and Correcting Power Supply Problems
  • Measuring the voltage of a power supply
  • Upgrading and installing power supplies
  • Troubleshooting the power system and power supply
measuring the voltage of a power supply
Measuring the Voltage of a Power Supply
  • Use a multimeter
    • Before using, tell it three things
      • Whether to measure voltage, current, or resistance
      • Whether the current is AC or DC
      • What range of values it should expect
    • How to measure voltage
    • How to measure current
    • How to measure continuity
how to measure the voltage of a power supply
How to Measure the Voltage of a Power Supply
  • How to measure the power output for AT and ATX motherboards
  • Procedure for a secondary storage device
upgrading your power supply
Upgrading Your Power Supply
  • Sometimes necessary when you add new devices
  • Easiest way to fix a power supply you suspect is faulty is to replace it
introduction to troubleshooting
Introduction to Troubleshooting
  • Categories of problems
    • Problems that prevent the PC from booting
    • Problems that occur after a successful boot
  • Learn as much as you can by asking questions of the user
troubleshooting the power system guidelines and questions
Troubleshooting the Power System: Guidelines and Questions
  • Any burnt parts or odors?
  • Everything connected and turned on? Loose cable connections? Computer plugged in?
  • All switches turned on? Computer? Monitor? Surge protector? UPS? Separate circuit breaker? Wall outlet good?
  • If fan is not running, turn off computer: Connections to power supply secure? Cards securely seated?
troubleshooting the power system1
Troubleshooting the Power System
  • Troubleshooting the power supply itself
  • Troubleshooting the power supply fan
  • Power problems with the motherboard
  • Overheating
energy star systems the green star
Energy Star Systems(The Green Star)
  • Satisfy energy-conserving standards of the U.S. EPA
  • Generally have a standby program that switches the device to sleep mode when it is not in use
  • Apply to computers, monitors, printers, copiers, and fax machines
power management methods
Power Management Methods
  • Advanced Power Management (APM)
  • AT Attachment (ATA) for IDE drives
  • Display Power Management Signaling (DPMS) standards for monitors and video cards
  • Advanced Configuration and Power Interface (ACPI)
power management features
Power Management Features
  • Green timer on motherboard
  • Doze time
  • Standby time
  • Suspend time
  • Hard drive standby time
energy star monitors
Energy Star Monitors
  • Most adhere to DPMS specifications which allow for the video card and monitor to go into sleep mode simultaneously
  • View and change energy settings in Desktop Properties window (Windows 2000)
chapter summary
Chapter Summary
  • How to measure electricity
  • The power supply and backup power sources
  • How to measure power supply output
  • How to change a defective power supply
  • Introduction to form factors
  • How Energy Star devices save energy