Post on 01-Jun-2018
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An Electronic SystemAn Electronic System
Power Supply ExamplePower Supply Example
Louis E. FrenzelLouis E. Frenzel
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PrerequisitesPrerequisites
• To understand this presentation, you should have
the following prior knowledge: – Draw the struture of an ato!, inluding eletrons,
protons, and neutrons.
– Define resistane and ondutane.
– La"el an eletroni she!ati, indiating urrent flow.
– Define #h!$s and %irhhoff$s laws.
– Desri"e the harateristis of D& and '& (sine wave)
voltages.
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Student Learning OutcomesStudent Learning Outcomes
• *pon o!pletion of viewing this presentation, you
should "e a"le to:
– Define power supply.
– +a!e the !ain o!ponents in a o!!on linear
'& to D& power supply and eplain the purposeand funtion of eah.
– Define retifier and na!e two o!!on types.
–+a!e the o!ponent that transfor!s pulsatingD& into onstant D&.
– Define ripple and identify its origins.
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Power SupplyPower Supply
• 'll eletroni iruits need a power soure to
work.• For eletroni iruits !ade up of transistors
and-or &s, this power soure !ust "e a D&voltage of a speifi value.
• ' "attery is a o!!on D& voltage soure forso!e types of eletroni e/uip!ent espeiallyporta"les like ell phones and i0ods.
• 1ost non2porta"le e/uip!ent uses power
supplies that operate fro! the '& power line"ut produe one or !ore D& outputs.
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Power Supply CharacteristicsPower Supply Characteristics
• The input is the 345 volt 65 7z
'& power line. 'lternately, theinput !ay "e 485 volt '&.
• The power supply onverts the '& into D& and provides one or!ore D& output voltages.
• 9o!e !odern eletroni iruits
need two or !ore differentvoltages.
• &o!!on voltages are 8, 48,3;, 34,
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Components of a Power SupplyComponents of a Power Supply
• 1ain iruits in !ost power supplies.
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Power SupplyPower Supply
• The '& line is first passed
through a low pass filter ofthe for! shown in figure.
• This eli!inates noise on
the '& line fro! "othering
the power supply iruitsand prevents unwanted
signals fro! the power
supply fro! "eing
transferred "ak into the
'& line where they !ight
interfere with other
e/uip!ent.
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Transformer Transformer
• ' transfor!er is o!!only used to step the input '&voltage level down or up. 1ost eletroni iruitsoperate fro! voltages lower than the '& line voltage sothe transfor!er nor!ally steps the voltage down "y itsturns ratio to a desired lower level.
• For ea!ple, a transfor!er with a turns ratio of 35 to 3would onvert the 345 volt 65 7z input sine wave into a34 volt sine wave.
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ilter ilter
• The retifier produes a D& output "ut it is
pulsating rather than a onstant steady
value over ti!e like that fro! a "attery.
• ' filter is used to re!ove the pulsations and
reate a onstant output.
• The !ost o!!on filter is a large apaitor.
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Regulator Regulator
• The regulator is a iruit that helps !aintain a
fied or onstant output voltage.• &hanges in the load or the '& line voltage will
ause the output voltage to vary.
• 1ost eletroni iruits annot withstand thevariations sine they are designed to workproperly with a fied voltage.
• The regulator fies the output voltage to the
desired level then !aintains that value despiteany output or input variations.
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!C"!C Con#erter !C"!C Con#erter
• 1ost !odern power supplies also ontainone or !ore D&2D& onverters
• 1odern eletronis often de!and differentvoltages to funtion.
• ' D&2D& onverter hanges one D&voltage to another, higher or lower D&voltage.
• ' D&2D& onverter is used with a powersupply to prevent the need for a seond '&2D& supply.
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$ow Rectifiers %or&$ow Rectifiers %or&
• The si!plest for! of retifier isthe half wave retifier shown.
• #nly the transfor!er, retifierdiode, and load (>L) are shownwithout the filter and othero!ponents.
• The half wave retifier produes
one sine pulse for eah yle ofthe input sine wave.
• ?hen the sine wave goespositive, the anode of the diodegoes positive ausing the diode
to "e forward "iased. The diodeonduts and ats like a losedswith letting the positive pulseof the sine wave to appearaross the load resistor.
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$ow Rectifiers %or& 'continued($ow Rectifiers %or& 'continued(
• ?hen the sine wave goesnegative, the diode anode will"e negative so the diode will "ereverse "iased and no urrentwill flow.
• +o negative voltage will appearaross the load. The load
voltage will "e zero during theti!e of the negative half yle.
• 9ee the wavefor!s that showthe positive pulses aross theload. These pulses need to "eonverted to a onstant D&.
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)ridge Rectifier )ridge Rectifier
• 'nother widely used retifier isthe "ridge retifier. t uses fourdiodes.
• This is alled a full wave retifieras it produes an output pulsefor eah half yle of the inputsine wave.
• #n the positive half yle of theinput sine wave, diodes D3 andD4 are forward "iased so at aslosed swithes appearing inseries with the load.
• #n the negative half yle, diode
D3 and D4 are reverse "iasedand diodes D= and D8 areforward "iased so urrent flowsthrough the load in the sa!ediretion.
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$ow the ilter %or&s$ow the ilter %or&s
• ' large apaitor is onnetedaross the load resistor. Thisapaitor filters the pulses into a!ore onstant D&.
• ?hen the diode onduts, theapaitor harges up to thepeak of the sine wave.
• Then when the sine voltagedrops, the harge on theapaitor re!ains. 9ine theapaitor is large it for!s a longti!e onstant with the loadresistor. The apaitor slowlydisharges into the load
!aintaining a !ore onstantoutput.• The net positive pulse o!es
along reharging the apaitorand the proess ontinues.
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RippleRipple
• The apaitor does a good @o" of s!oothing the
pulses fro! the retifier into a !ore onstant D&.• ' s!all variation ours in the D& "eause the
apaitor disharges a s!all a!ount "etween thepositive and negative pulses. Then it reharges.This variation is alled ripple.
• The ripple an "e redued further "y !aking theapaitor larger.
• The ripple appears to "e a sawtooth shaped '&variation riding on the D& output.
• ' s!all a!ount of ripple an "e tolerated in so!eiruits "ut the lower the "etter overall.
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The Regulator The Regulator
• 1ost regulators are &s .
• These are feed"ak ontrol iruits thatatually !onitor the output voltage to detetvariations.
• f the output varies, for whatever reason, theregulator iruit auto!atially ad@usts theoutput "ak to the set value.
• >egulators hold the output to the desired value.• 9ine ripple represents hanges in the output,
the regulator also o!pensates for thesevariations produing a near onstant D&output.
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*n Summary*n Summary
• 'll eletroni iruits and e/uip!ent need a power supply,
usually one that supplies are very speifi D& voltage.• ' "attery is a near perfet D& supply "ut it is used !ainly
in porta"le appliations.
• 1ost e/uip!ent uses an '& to D& power supply.
• n !ost '& to D& supplies, the 345 volt '& line is firstfiltered then stepped up or down to the desired voltagelevel then retified into pulsating D&, then filtered to aonstant D&. ' regulator holds the output to a desiredlevel. ' D&2D& onverter !ay also "e used to generate
another D& voltage.• The two !ost o!!on retifiers are the single diode half
wave retifier and the four diode full wave "ridge retifier.