10 - Power Supply

8/13/2019 10 - Power Supply

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How PC Power Supplies Workby Gary Brown

If there is any one component that is absolutely vital to the operation of a computer, it is thepower supply. Without it, a computer is ust an inert bo! full of plastic an" metal. #he powersupply converts the alternatin$ current %&C' line from your home to the "irect current %(C'nee"e" by the personal computer. In this article, we)ll learn how PC power supplies work an"what thewatta$eratin$s mean.

Power SupplyIn a personal computer %PC', the power supply is the metal bo! usually foun" in a corner ofthe case. #he power supply is visible from the back of many systems because it contains thepower*cor" receptacle an" the coolin$ fan.

This is a power supply removed from its PC case. The small,red switch at right, above the power-cord connector, is for

changing line voltages in various countries.

The interior of a power supply.

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Power supplies, often referre" to as +switchin$ power supplies+, use switcher technolo$y toconvert the &C input to lower (C volta$es. #he typical volta$es supplie" are

-.- volts

volts

/0 volts

#he -.-* an" *volts are typically use" by "i$ital circuits, while the /0*volt is use" to runmotors in "isk "rivesan" fans. #he main specification of a power supply is in watts. & watt isthe pro"uct of the voltagein volts an" the currentin amperes or amps. If you have beenaroun" PCs for many years, you probably remember that the ori$inal PCs ha" lar$e re"to$$le switches that ha" a $oo" bit of heft to them. When you turne" the PC on or off, youknew you were "oin$ it. #hese switches actually controlle" the flow of /01 volt power to thepower supply.

#o"ay you turn on the power with a little push button, an" you turn off the machine with amenu option. #hese capabilities were a""e" to stan"ar" power supplies several years a$o.#he operatin$ system can sen" a si$nal to the power supply to tell it to turn off. #he pushbutton sen"s a *volt si$nal to the power supply to tell it when to turn on. #he power supplyalso has a circuit that supplies volts, calle" 2SB for +stan"by volta$e+ even when it is

officially +off+, so that the button will work.

Switcher TechnologyPrior to /341 or so, power supplies ten"e" to be heavy an" bulky. #hey use" lar$e, heavytransformers an" hu$e capacitors %some as lar$e as so"a cans' to convert line volta$e at/01 volts an" 51 hert6 into volts an" /0 volts (C.

#he switchin$ power supplies use" to"ay are much smaller an" li$hter. #hey convert the 51*Hert6 %H6, or cycles per secon"' current to a much hi$her fre7uency, meanin$ more cyclesper secon". #his conversion enables a small, li$htwei$ht transformer in the power supply to"o the actual volta$e step*"own from //1 volts %or 001 in certain countries' to the volta$enee"e" by the particular computer component. #he hi$her*fre7uency &C current provi"e" bya switcher supply is also easier to rectify an" filter compare" to the ori$inal 51*H6 &C line

volta$e, re"ucin$ the variances in volta$e for the sensitive electronic components in thecomputer.

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In this photo you can see three small transformers (yellow inthe center. To the left are two cylindrical capacitors. The largefinned pieces of aluminum are heat sin!s. The left heat sin!has transistors attached to it. These are the transistors in

charge of doing the switching -- they provide high-fre"uencypower to the transformers. #ttached to the right heat sin! are

diodes that rectify #C signals and turn them into $C signals.

& switcher power supply "raws only the power it nee"s from the &C line. #he typical volta$esan" current provi"e" by a power supply are shown on the label on a power supply.

Personal computer power supply label.%S& is the standby voltage provided to the

power switch.

Switcher technolo$y is also use" to make &C from (C, as foun" in many of the automobilepower inverters use" to run &C appliances in an automobile an" in uninterruptible powersupplies. Switcher technolo$y in automotive power inverters chan$es the "irect current fromthe auto battery into alternatin$ current. #he transformer uses alternatin$ current to make thetransformer in the inverter step the volta$e up to that of househol" appliances %/01 2&C'.

Power Supply Standardi'ation8ver time, there have been at least si! "ifferent stan"ar" power supplies for personalcomputers. 9ecently, the in"ustry has settle" on usin$ :*base" power supplies. : is anin"ustry specification that means the power supply has the physical characteristics to fit astan"ar" : case an" the electrical characteristics to work with an : motherboar".

PC power*supply cables use stan"ar"i6e", keye" connectors that make it "ifficult to connect

the wron$ ones. &lso, fan manufacturers often use the same connectors as the power cablesfor "isk "rives, allowin$ a fan to easily obtain the /0 volts it nee"s. Color*co"e" wires an"in"ustry stan"ar" connectors make it possible for the consumer to have many choices for areplacement power supply.

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# PC power supply removed from its PC case. Cables andconnectors at right supply $C voltages.

&"vance" Power ;ana$ement#dvanced Power anagement (#Poffers a set of five "ifferent states that your systemcan be in. It was "evelope" by ;icrosoft an" Intel for PC users who wish to conserve power.11*watt switchin$ power supply will not necessarily use more power than a 01*watt

supply. & lar$er supply may be nee"e" if you use every available slot on the motherboar" orevery available "rive bay in the personal computer case. It is not a $oo" i"ea to have a 01*watt supply if you have 01 watts total in "evices, since the supply shoul" not be loa"e" to/11 percent of its capacity.

&ccor"in$ to PC Power ? Coolin$, Inc., some power consumption values %in watts' forcommon items in a personal computer are

PC Item )atts

&ccelerate" Graphics Port %&GP' car" 01 to -1W

Peripheral Component Interconnect %PCI' car" W

small computer system interface %SCSI' PCI car" 01 to 0Wfloppy "isk "rive W

network interface car" >W

1: C(*98; "rive /1 to 0W

9&;/1W per/04;

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011 9P; Inte$rate" (rive W

Power supplies of the same form factor%+form factor+ refers to the actual shape of themotherboar"' are typically "ifferentiate" by the watta$e they supply an" the len$th of thewarranty.

Power Supply Problems#he PC power supply is probably the most failure*prone item in a personal computer. It heats

an" cools each time it is use" an" receives the first in*rush of &C current when the PC isswitche" on. #ypically, a stalle" coolin$ fan is a pre"ictor of a power supply failure "ue tosubse7uent overheate" components. &ll "evices in a PC receive their (C power via thepower supply.

& typical failure of a PC power supply is often notice" as a burnin$ smell ust before thecomputer shuts "own. &nother problem coul" be the failure of the vital coolin$ fan, whichallows components in the power supply to overheat. ailure symptoms inclu"e ran"omrebootin$ or failure in Win"ows for no apparent reason.

or any problems you suspect to be the fault of the power supply, use the "ocumentationthat came with your computer. If you have ever remove" the case from your personalcomputer to a"" an a"apter car" or memory, you can chan$e a power supply. ;ake sure

you remove the power cor"first

, since volta$es are present even thou$h your computer isoff.

Power Supply Improvements9ecent motherboar" an" chipset improvements permit the user to monitor the revolutionsper minute %9P;' of the power supply fan via BI8S an" a Win"ows application supplie" bythe motherboar" manufacturer. ew "esi$ns offer fan control so that the fan only runs thespee" nee"e", "epen"in$ on coolin$ nee"s.

9ecent "esi$ns in Web serversinclu"e power supplies that offer a spare supply that can bee!chan$e" while the other power supply is in use. Some new computers, particularly those"esi$ne" for use as servers, provi"e re"un"ant power supplies. #his means that there aretwo or more power supplies in the system, with one provi"in$ power an" the other actin$ asa backup. #he backup supply imme"iately takes over in the event of a failure by the primarysupply. #hen, the primary supply can be e!chan$e" while the other power supply is in use.

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10 - Power Supply