power supplies chapter 6. understanding electricity electricity is simply a flow of negatively...
TRANSCRIPT
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Power SuppliesChapter 6
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Understanding Electricity
Electricity is simply a flow of negatively charged particles, called electrons, through matterMaterials in which electrons flow freely are called conductors
Two types of electricity– AC - alternating current– DC - direct current
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Understanding Electricity
Current - amount of electrons moving past a certain point on a wire– measured in amperes (amps)
Voltage - pressure of the electrons through the wire– measured in volts
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AC Power
The flow of electrons “alternates” direction in the wiresall standard power in the US is ACThe 3-prong connections– hot - smaller rectangular hole– neutral - larger rectangular hole– ground - small round hole
The combination of hot and neutral wires supplies the path for AC
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The Power Supply
Acts as a transformer turning 115 volt AC into 3.3, 5, and 12 volt DC2 types comprise over 99 percent of all power supplies in PC’s– AT - older style– ATX - dominates today’s systems
AT’s are fading from usePictures on page 336
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Power Supply
AT & ATX have a number of common features:– Power connection - plugs into a power outlet– Motherboard power - connection to give
motherboard power– Power switch - to turn the system on and off– Peripheral connections - to give internal devices
power– Fan - cools the inside of the power supply and
provides air flow for the case
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Power Connections
Power supply connects to the power cord via a standard “IEC-320” connectorTesting AC power, check 3 things:– hot outputs 115 V– neutral connects to ground (0 V output)– ground connects to ground (0 V output)
Test these with a multimeter
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Motherboard Power
DC power comes out of your power supply ready to work, and provides electricity for all the components in the PCDC flows in 1 direction, making big loopsAT power connectors (pg. 344-346)– a pair of connectors P8 & P9 link to AC to PS– when installing P8 & P9 make sure that the black ground
wires are next to each other so you don’t put the wrong one in the socket
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Motherboard power
ATX connection– uses a single P1 connector– plugs into recognizable white P1 socket– you can’t install it incorrectly because of special
notches on the connector
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Power switches
AT power switches simply turn the system on or offATX power switches use a feature called soft power
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AT power switches
Come in only 2 common types: rocker or plunger
When replacing make sure that you match – black to white– brown to blue– if not installed correctly you will blow a circuit
AT doesn’t allow you to hibernate, because it automatically turns system off
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ATX power switches
Use a feature called soft power – as long as the ATX system has AC power from the
wall socket, it’s always “on”
Many ATX PS have a real on/off switch which can be used if it needs to be off
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Connections to peripherals
3 different types of connectors from your power supply to your peripherals:
– Molex connectors - primarily used for devices that need both 12V and 5V of power
• most common type of connection• notches are called chamfers• difficult, though not impossible, to put upside down• if in backwards, will damage device
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Connections to peripherals
– Mini connectors - primarily used on 3.5 floppys• easy to install upside down - BE CAREFUL• can damage device if inserted incorrectly
– Submini connectors - main purpose is to provide 5V to an LED light
• small two hole connector
if you need more connectors to power devices you can purchase splitters p.359
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Wattage and sizes
Most PCs use about 200-230 watts for a power supply– average PC with 2 hard drives and CD-ROM uses
average of 115-130 watts– average PC uses 200 watts during boot up
When replacing, play it safe and take old power supply with you so that it fits
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When power supplies die
Fail in 2 ways: – hard and easy
Easy - the computer will not start and the fan in the power supply will not turn– check to see if its plugged in– check with a voltmeter (p. 361)– throw away if its dead, it’s a pain to fix– could also be a broken switch
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When power supplies die
Hard - one of the internal electronics of the power supply has begun to fail– failures are always intermittent
For example: if you are booting your computer and it locks from time to time, it could very well be a power problemPower supplies break more often than any other part in PC, except for floppy drives
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ESD
Electrostatic discharge - occurs when static electricity stops resting and moves– Conductors - already discussed– Insulators - materials that do not easily transfer charges
Humans can accumulate electrical potentials well over 25,000 volts: as little as 30 volts can destroy some PC partsRead chart on page 367
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ESD
Types of ESD Damage:– Upset failures - occur when a small ESD cause minor gate
leakage• unexplained loss of data
– Latent catastrophic - occur when the ESD damage causes the transistor junction to weaken
• called ZINGS
– Direct catastrophic - occur with ESD shocks of more than 300 volts
• called ZAPS
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Preventing ESD
Get an anti-static wrist strapFollow the guidelines on page 369Read the Caution on page 368
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Surge suppressors & UPS
Surge suppressor – protects from spikes or power surges– read info. on page 371
Uninterruptible power supply (UPS)– protects your computer in the even of a power dip (brownout)
or power outage (blackout)
2 types of UPS– Online (uses a battery) *better– Stand-by (kicks in when volts drop to 80-90)