Power SuppliesChapter 6

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

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

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

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

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

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

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

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

Power switches

AT power switches simply turn the system on or offATX power switches use a feature called soft power

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

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

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

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

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

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

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

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

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

Preventing ESD

Get an anti-static wrist strapFollow the guidelines on page 369Read the Caution on page 368

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)