CHAP 2 - Diode Applications-UPDATED (Part2)

8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)

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OBJECTIVEOB

JECTIVE

Analyze the operation of diode limiting, clampingAnalyze the operation of diode limiting, clamping

circuit, voltage multipliers and interpret and usecircuit, voltage multipliers and interpret and use

diode data sheet.diode data sheet. Determine V of biased limiter & used voltage-Determine V of biased limiter & used voltage-

divider bias to set limiting level.divider bias to set limiting level.

Discuss voltage doublers, triplers & quadruples.Discuss voltage doublers, triplers & quadruples.

Identify V & current ratings.Identify V & current ratings.

Determine the electrical characteristics of a diode.Determine the electrical characteristics of a diode.

Analyze graphical dataAnalyze graphical data

elect an appropriate diode for a given set ofelect an appropriate diode for a given set ofspeci!cations.speci!cations.

2-4 Diode Limiting &Clamping Circuits


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Diode LimitersDiode Limiters

Diode limiters/clippers that limits/clips the portion of signal voltage above or

below certain level.

Limiting circuits limit the positive or negative amount of an input voltage to a

specific value.

When i/p is +ve the diode becomesFB limited to +0.7 V because cathode is atground.

When i/p 0.7 V!diode isRB o/p voltage li"es ve part of i/p voltage

#urn the diode around!negative part of i/p voltage is clipped off.

When diode isFB!negative part of i/p voltage!diode drop !0.7V

in

L

L

out VRR

RV

+

=$


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Question 4"hat #ould you e$pect to see displayed on an

connected across % in the limiter sho#n belo#


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!olution Question 4!olution Question 4

'he diode is for#ard biased and conducts'he diode is for#ard biased and conducts

#hen input voltage goes belo# -(.)V. o, for#hen input voltage goes belo# -(.)V. o, for*ve limiter, the pea+ output voltage across*ve limiter, the pea+ output voltage across% is% is

'he #aveform is sho#n belo#'he #aveform is sho#n belo#

VV

k

kV

RR

RV inp

L

L

outp 09.910

1.1

0.1)(

1

)( =

=

+

=


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Biased Limiters

#he level to which an ac voltage is limited can be ad%usted b& adding bias voltage

VBIAS in series with diode.

Voltage at point ' ( VA= VBIAS+ 0.7V)forward!biased * conduct. ,o- all Vin >

VAis clipped off. or ve level- then VA= -VBIAS- 0.7V to forward!biased.

#urning diode around- +ve limiter modified to limit Voutto the portion of Vin

waveform above VBIAS 0.7V.

!ve limiter below !VBIAS- 0.7V.

& tuning the diode around! the +ve limiter can modified to limit the o/p voltage

to the portion of the i/p voltage waveform above VBIAS-0.7V

1egative limiter limit the o/p voltage to the i/p voltage belowVBIAS+0.7V



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A positive limiter

A negative limiter


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Voltage-Divider Bias

'he bias voltage source * used to illustrate thebasic operation of diode limiters can be replace by aresistive voltage dividerthat derives the desiredbias voltage from dc Vsupply.

VBIAS* set by the resistor values according to thevoltage-divider formula

'he desired amount of limitation can be attained bya po#er supply or voltage divider. 'he amountclipped can be adusted #ith dierent levels ofVBIAS.

'he bias resistor // %0- the for#ard current 88

SUPPLYBIAS V

RR

RV

+

=23

2



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E"ample #0.+etch the output voltage #aveform as

sho#n in the circuit combining a positivelimiter #ith negative limiter in 2igure 3-0.

Figure 5-1

+15V

-15V

6V 6V


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4. A student construct the circuit assho#n in 2igure 3-4. Describe the output

voltage #aveform on oscilloscope 564.

Figure 5-2

+20V

-20V

CH2

+15V


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Diode Clampers

A diode clamper adds a D5 level to an A5voltage. 'he capacitor charges to the pea+ ofthe supply minus the diode drop. Once charged,the capacitor acts like a battery in series#iththe input voltage. 'he A5 voltage #ill 7ride8along #ith the D5 voltage. 'hepolarityarrangement of the diode determines whetherthe ! voltage is negative or positive.

2or negative clamper, the diode is turn around.

A negative dc voltage is added to the inputvoltage to produce the output.

Positive clamper operation


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Negative clamper operation

$lso %non asdc restorers'

(or a good clamping actiRCtime constant ) 10 fin


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A Clamper Application:

A clamping circuit is often used in 'V

receivers as a dc restorer.'he incoming composite video signal is

normally processed through capacitivelycoupled ampli!ers that eliminate the dc

component, thus losing blac+ and #hitereference levels and the blan+ing level.1efore applied to the picture tube, thesereference level must be restored.

Diode Clampers


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9se clamping action to increase pea+ recti!edvoltages #ithout necessary to increase inputtransformer:s voltage rating.

;ultiplication factors t#o, three or four. 'hree types of voltage multipliers

< Voltage doubler

- *al+ , ae oltage doubler

- (ull , ae oltage doubler

< Voltage tripler

< Voltage "uadrupler

Voltage multipliers are used in high-voltage, lo#current a lications, i.e 'V receivers.

2-# Voltage .ultiplier


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Voltage Dou/ler

Half-ave voltage Doubler:

5lamping action can be used to increase pea+recti!ed voltage. =nce 50and 54charges to the

pea+ voltage they act li+e t#o batteries in series,eectively doubling the voltage output. 'he currentcapacity for voltage multipliers is lo#.

6alf-#ave voltage doubler operation. Vpis the pea+ se

1y applying >irchho:s a# at ?b@

$3 CpC VVV += ~ approimatel! 2Vp"negle#ting $io$e $rop %2&

PIV = 2Vp


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!ull-ave voltage doubler:Arrangement of diodes and capacitors ta+esadvantage of both positive and negative pea+s tocharge the capacitors giving it more current

capacity.

forward-bias

charges

!econdar0 oltage positie!econdar0 oltage negatie

forward-bias

outputcharges

Voltage Dou/ler


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Voltage triplersVoltage triplersandand #uadruplers#uadruplersutilizeutilize threethreeandandfourfourdiode capacitor arrangements, respectively.diode capacitor arrangements, respectively.

Voltage triplerVoltage triplerandand #uadrupler#uadrupler gives outputgives output $V$Vppandand %V%Vpp, respectively., respectively.

'ripler output is ta+en across'ripler output is ta+en across !!&&and 5and 5, thus, thus VVoutout''$V$Vpp

Buadrupler output is ta+en acrossBuadrupler output is ta+en across !!((andand !!%%, thus, thus

VVoutout' %V' %Vpp

CIV for both casesCIV for both cases )IV ' (V)IV ' (Vpp

Voltage Triple Voltage Quadruple

Voltage Tripler & Voltage Quadrupler


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'he data sheet for diodes and other devicesgives detailed information about speci"cc#aracteristics suc# as t#e variousma$imum current and voltage ratings%temperature range% and voltage versuscurrent curves *V+I characteristic.

It is sometimes a very valuable piece of

information, even for a technician. 'here arecases #hen you might have to select areplacement diode #hen the type of diodeneeded may no longer be available.

'hese are the absolute ma$. values under

2-1 Te Diode Data !eet


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%ating%ating ymboymboll

0E((0E((00

0E((0E((44

0E(0E(((

9I'9I'

Cea+ repetitive reverseCea+ repetitive reversevoltagevoltage

"or+ing pea+ reverse"or+ing pea+ reversevoltagevoltage

D5 bloc+ing voltageD5 bloc+ing voltage

VV----

VV-/-/

VV--

3(3( 0((0(( 4((4(( VV

onrepetitive pea+onrepetitive pea+

reverse voltagereverse voltageVV-S-S F(F( 04(04( 4E(4E( VV

rms reverse voltagerms reverse voltage VV-*rms-*rms 33 )()( 0E(0E( VV

Average recti!edAverage recti!edfor#ard current ?single-for#ard current ?single-phase, resistive load,phase, resistive load,F(6z, 'F(6z, 'AAG )3G )3

oo55

IIoo00

AA

onrepetitive pea+onrepetitive pea+

surge current ?surgesurge current ?surge

applied at rated loadapplied at rated load

II0S0S( ?for( ?for

00

AA

.a"imum 3ating


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2121FIGURE 2-56FIGURE 2-56 A sele#tion o' re#ti'ier $io$es (ase$ on maimum ratings o'A sele#tion o' re#ti'ier $io$es (ase$ on maimum ratings o'))** ) )F,F, an$ ) an$ )....//

.a"imum 3ating


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OBJECTIVEOBJECTIVE 'roubleshoot diode circuits using accepted'roubleshoot diode circuits using accepted

techniques.techniques.

Discuss the relationship bet#een symptom &Discuss the relationship bet#een symptom &

cause, po#er chec+, sensory chec+,cause, po#er chec+, sensory chec+,component replacement method and discusscomponent replacement method and discuss

the signal tracing technique in the threethe signal tracing technique in the three

variations.variations.

2ault analysis.2ault analysis.

=ur study of these devices and ho# they #or+leads more eective troubleshooting. Jcient

troubleshooting requires us to ta+e logical steps insequence. >no#ing ho# a device, circuit, orsystem works #hen operating properly must be+no#n before any attempts are made to

troubleshoot. 'he symptoms sho#n by a defective

2- Trou/lesooting


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6ere are some helpful troubleshootingtechni#ues&oer C#ec' ometimes the obviouseludes the most pro!cient troubleshooters.5hec+ for fuses blo#n, po#er cordsplugged in, and correct battery placement.(ensor) C#ec' "hat you see or smellmay lead you directly to the failure or to asymptom of a failure.Component Replacement ducated

guess#or+ in replacing components issometimes eective. (ignal *racing oo+ at the point inthe circuit or system #here you !rst losethe signal or incorrect signal.

Trou/lesooting Tecni5ues


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Signal traing t!"ni#u!$(

Input to output

Output to input

Trou/lesooting Tecni5ues


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5an be applied #hen you measure an incorrect

voltage at a test point using signal tracing andisolate the fault to a speci!c circuit.E"ample 6

+,ect of an penDiode in a Half-

ave Recti"er:Kero oLp voltage=pen diode brea+sthe current path fromtransformer secondary

#inding to the!lter and load resistor* no load current.=ther faults open

transformer #inding,o en fuse or no in ut

(ault $nal0sis


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E"ample 2

+,ect of an pen Diode in a !ull-aveRecti"er:

'he eect of either of t#o diodes is open diode,the oLp voltage #ill have large than normal ripplevoltage at F( 6z rather than at 04( 6z.

Another fault * open in one of the halves of thetransformer secondary #inding.

=pen diode give same symptom to bridge full-#ave recti!er.

?ee 2igure 4-F@

(ault $nal0sis


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E"ample 7+,ect of a (#ortedDiode in a !ull- aveRecti"er:

2use should blo# * causeby short circuit

&,%#ill probably burnopen.

(ault $nal0sis


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E"ample 4

+,ect of a fault "lter capacitor:

Open* oLp is full-#ave recti!ed voltage

Shorted* the oLp is (V 3eaky* increase the ripple voltage on

the oLp

E"ample #

+,ect of a !ault) *ransformer:

=pen primaryLsecondary #inding of a

transformer * (V oLp

(ault $nal0sis


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Te complete Trou/lesooting8rocess

'he complete troubleshooting process'he complete troubleshooting process

i.i. Identify the [email protected] the symptom?s@.

ii.ii. Cerform a po#er chec+Cerform a po#er chec+

iii.iii. Cerform a sensory chec+Cerform a sensory chec+iv.iv. Apply a signal tracing technique.Apply a signal tracing technique.

v.v. Apply fault analysisApply fault analysis

vi.vi. 9se component replacement to !$ the9se component replacement to !$ the

problem.problem.


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'he basic function of a po#er supply to give us a

smooth ripple free D5 voltage from an A5 voltage.

6alf-#ave recti!ers only utilize half of the cycle toproduce a D5 voltage.

'ransformer 5oupling allo#s voltage manipulationthrough its #indings ratio

2ull-"ave recti!ers eJciently ma+e use of the#hole cycle. 'his ma+es it easier to !lter.

'he full-#ave bridge recti!er allo#s use of the fullsecondary #inding output #hereas the center-tapped full #ave uses only half.

2iltering and %egulatingthe output of a recti!erhel s +ee the D5 volta e smooth and accurate


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imiters are used to set the output pea+?s@ toa given value.

5lampers are used to add a D5 voltage to anA5 voltage.

Voltage ;ultipliers allo# a doubling, tripling,or quadrupling of recti!ed D5 voltage for lo#current applications.

'he Data heet gives us useful informationand characteristics of device for use inreplacement or designing circuits.

'roubleshooting requires use of common

sense along #ith proper troubleshooting

CHAP 2 - Diode Applications-UPDATED (Part2)

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Transcript of CHAP 2 - Diode Applications-UPDATED (Part2)