Post on 01-Jun-2018
transcript
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
1/31
11
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
2/31
22
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
+
=$
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
3/31
33
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
4/31
44
Question 4"hat #ould you e$pect to see displayed on an
connected across % in the limiter sho#n belo#
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
5/31
55
!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
)( =
=
+
=
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
6/31
66
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
Diode LimitersDiode Limiters
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
7/31
77
A positive limiter
A negative limiter
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
8/31
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
Diode LimitersDiode Limiters
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
9/31
99
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
10/31
1010
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
11/31
1111
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
12/31
1212
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
13/31
1313
Negative clamper operation
$lso %non asdc restorers'
(or a good clamping actiRCtime constant ) 10 fin
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
14/31
1414
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
15/31
1515
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
16/31
1616
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
17/31
1717
!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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
18/31
1818
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
19/31
1919
'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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
20/31
2020
%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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
21/31
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
22/31
2222
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
23/31
2323
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
24/31
2424
Signal traing t!"ni#u!$(
Input to output
Output to input
Trou/lesooting Tecni5ues
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
25/31
2525
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
26/31
2626
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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
27/31
2727
E"ample 7+,ect of a (#ortedDiode in a !ull- aveRecti"er:
2use should blo# * causeby short circuit
&,%#ill probably burnopen.
(ault $nal0sis
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
28/31
2828
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 $nal0sis
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
29/31
2929
Te complete Trou/lesooting8rocess
'he complete troubleshooting process'he complete troubleshooting process
i.i. Identify the symptom?s@.Identify the symptom?s@.
ii.ii. Cerform a po#er chec+Cerform a po#er chec+
iii.iii. Cerform a sensory chec+Cerform a sensory chec+iv.iv. Apply a signal tracing technique.Apply a signal tracing technique.
v.v. Apply fault analysisApply fault analysis
vi.vi. 9se component replacement to !$ the9se component replacement to !$ the
problem.problem.
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
30/31
3030
'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
8/9/2019 CHAP 2 - Diode Applications-UPDATED (Part2)
31/31
3131
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