AC and DC Conversion Basics

8/9/2019 AC and DC Conversion Basics

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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.

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AC and DC Conversion Basics