Power Supplies Chapter 6

Understanding Electricity Electricity is simply a flow of negatively charged particles, called electrons, through matter Materials 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 wires all standard power in the US is AC The 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 DC 2 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 use Pictures 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” connector Testing 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 PC DC flows in 1 direction, making big loops AT power connectors (pg ) –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 off ATX 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 watts for a power supply –average PC with 2 hard drives and CD-ROM uses average of 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 problem Power 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 parts Read 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 strap Follow the guidelines on page 369 Read 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)