Power Supply (SMPS)

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Power Supply


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AC AND DCElectricity can be either AC, alternating current, or DC, direct current.Alternating current (AC) goes back and forth, or oscillates, rather

than traveling in only one direction. AC is the most economical way totransmit electricity. y decreasing current and increasing voltage, wecan force alternating current to travel long distances. !hen alternatingcurrent reaches its destination, it is made more suitable for driving ourelectrical devices by decreasing voltage.

Direct current (DC" travels in only one direction and is the type ofcurrent that mostelectronic devices re#uire, including computers. Arectifer is a device that converts AC to DC, and an inverter is a devicethat converts DC to AC.

A transormer is a device that changes the ratio of voltage to current.

$he transformer does not change the amount of power.


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%ull wave recti&er demo.mp'


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(nstead of throwing away e)tra input energy like linear powersupply , a switching power supply creates a feedback loop.%eedback senses the output voltage, then switches the primaryDC voltage duty cycle as needed to maintain steady levels at the

output.

AC line voltage entering the supply is immediately converted topulsating DC, then &ltered to provide a primary DC voltage. *oticethat unlike a linear supply, AC is not transformed before

recti&cation. +n startup, the switching transistor is turned on ando- at a high fre#uency usually /0k12 to '0k12", and a long dutycycle the amount of time that a signal is 3on,4 compared to itsoverall cycle" creates a pulsating DC used as the primary signalfor a stepdown transformer. $he duty cycle of pulsating DC will

a-ect the AC voltage level generated on the transformer5ssecondary. Secondary voltage is rerecti&ed and re&ltered to forma secondary dc voltage that is actually applied to the load. $heduty cycle is continuously ad6usted by the sensing7switchingcircuit.

Switching power supplies can reach e8ciencies higher than 9:;.


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lock diagram o a switching power supp


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Simplifed diagram o a switching powersupply


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%orm %actor!hen we assemble a new system, or replace components in an e)istingsystem, the motherboard, power supply, and case must all be

compatible. $he standards that describe the si2e, shape, and ma6orfeatures of these components so that they work together are calledorm actors

According to the form factor of the motherboard, you must select thesame form factor for the case and power supply.

=sing a matching form factor for the motherboard, power supply, andcase assuresyou that>

$he motherboard &ts in the case.

$he power supply cords to the motherboard provide the correctvoltage, and theconnectors match the connections on the board.$he holes in the motherboard align with the holes in the case to &) theboard to the case.1oles in the case align with ports coming o- the motherboard.%or some form factors, wires for switches and lights on the front of the


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!"#$S %& &%' &AC!%'S


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A! &%' &AC!%'A! (Advanced !echnology $*tended) is the most commonly usedform factor today. (t is an open, nonproprietary industry speci&cationoriginally developed by (ntel in ?@@:, and has undergone severalrevisions since then.$he &rst A$ power supplies and motherboards used a single powerconnector called the #+ connector that had /0 pins. $hese pinsprovided B. volts, B: volts, B?/ volts, ?/ volts, and an optional andrarely used : volts.


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!hen processors began to re#uire more power, the A$ ersion /.?speci&cations added a 'pin au)iliary connector near the processor socketto provide an additional ?/ of power. A power supply that provides this'pin ?/volt power cord is called an A!+,- power supply


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ater, when PC( E)press slots were added to motherboards, more powerwas re#uired and a new A$ speci&cation A$ ersion /./" allowed for a/'pin P? connector, which is backward compatible with the /0pin P?connector. $he e)tra ' pins on the connector provide B?/ volts, B:volts, and B. volts pins.

A /0pin power cord plugged into a /'pin P? connector on an A$motherboard


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Pinout of the /'pin power connector

?/ /'


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Another feature of an A$ motherboard is a sot switch. sometimescalled the sot power feature that can turn o- the power to a systemafter the shutdown procedure is done. (n addition, (+S setup can becon&gured to cause a keystroke or network activity to power up the

system wake on A*". !hen a user presses the power switch on thefront of the case while the computer is on, the +S goes through a normalshutdown procedure before powering o-.

/%0 !% S$1$C! A #%0$' S2##1"!hen selecting a power supply, match the form factor to that used by

the case and motherboard, make sure it provides the connectors youneed, and match the wattage capacity to the re#uirements of thesystem. =se a power supply that is rated about 0 percent higher thanyou e)pect the system will use. Power supplies that run at less thanpeak performance last longer and don5t overheat. $o know what si2epower supply you need, add up the wattage re#uirements of all

components, and add 0 percent.


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!"#$S %& C%#2!$' CAS$S

Several types and si2es of cases are on the market for each form factor.

$he computer case, sometimes called the chassis, houses the powersupply, motherboard, e)pansion cards, and drives. $he case has lightsand switches on the front panel that can be used to control and monitorthe PC.

S2'3$ #'%!$C!4%N AND BA!!$'"


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S2'3$ #'%!$C!4%N AND BA!!$'"BAC52#$he power supplies in most computers can operate over a wide range ofelectrical voltage inputsF however, operating the computer under these

conditions for e)tended periods of time can shorten the power supply5slife and also the computer5s. Also, electrical storms can end a computer5slife #uite suddenly. $o prevent such things, consider installing followingdevices to &lter AC input.

Power strips that provide additional outlets without providing any

protection fromchanges in AC powerSurge protectors which protect e#uipment against power spikes orsurgesoltage Stabili2ers that condition or smooth out the highs and lows inoltage

=ninterruptible Power Supplies =PS" that provide backup power

S2'3$ #'%!$C!%'SA surge protector. also called a Spike Buster. protects e#uipmentagainst suddenchanges in power level, such as spikes from lightning

strikes. $he device typically provides one or more power outlets, an on7o-switch, and a rotection li ht.

Th S t UPS


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The Smart UPSA Smart 2#S (also called an 4ntelligent 2#S) can be controlled bysoftware from a computer. $o accommodate this feature, a =PS has a=S connection to the PC and a microprocessor on board. Someactivities this utility software and a smart =PS can do as following>

Diagnose the =PS G attery and schedule tests.


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SUMMARYA form factor is a set of speci&cations for the si2e and con&guration ofhardware components, such as cases, power supplies, andmotherboards.$he most common form factor today is A$ and

Power Supply (SMPS)

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