Lecture 3,4 in electronic circuits

this lecture contain about
 Full-Wave Rectifiers.
 Power Supply Filters.
 Diode Limiters.
 Diode Clippers.
 Diode Clampers.
 Completed Power Supply.

1. Dr. Allam Ameen
Assistant Professor
Egyptian Chinese University, Faculty of Engineering and Technology
Electronics Research Institute, Microstrip Department
Lecture 3
Spring 2025
Electronic Circuits
(MCT 123)

2. Last Lecture Topics
Dr. Allam Ameen Electronic Circuits
2
PN Junction.
Applications of PN Junction.
Diode.
Biasing of the Diode.
Diode Models.
V-I Characteristic of a Diode.

3. Today’s Topics
Dr. Allam Ameen Electronic Circuits
3
Half-Wave Rectifiers.
Full-Wave Rectifiers.
Power Supply Filters.
Diode Limiters.
Diode Clippers.
Diode Clampers.
Completed Power Supply.

4. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
4
Afull-waverectifierallowscurrenttoflowduringboththepositive
andnegativehalfcyclesorthefull360ºwhereashalf-waverectifier
allowsonlyduringone-halfofthecycle.
Theno.of+vealternationsistwicethehalfwaveforthesametime
interval
Theoutputfrequencyistwicetheinputfrequency.
Theaveragevalue–thevaluemeasuredonadcvoltmeter
p
AVG
V
V
2


5. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
5
Twice output
p
AVG
V
V
2

63.7% of Vp

6. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
6
TheCenter-TappedFull-WaveRectifier
Thismethodofrectificationemploystwodiodesconnectedtoa
secondarycenter-tappedtransformer.
Thei/pvoltageiscoupledthroughthetransformertothecenter-tapped
secondary.
Coupled input
voltage
Center-tap

7. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
7
TheCenter-TappedFull-WaveRectifier
+vehalf-cycleinputvoltage(forward-biasD1&reverse-biasD2)-the
currentpassthroughtheD1andRL
-vehalf-cycleinputvoltage(reverse-biasD1&forward-biasD2)-the
currentpassthroughD2andRL
Theoutputcurrentonbothportionsoftheinputcycleispassingin
thesamedirectionthroughtheload.
Theo/pvoltageacrosstheloadresistors–full-waverectifiers

8. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
8
During positive half-cycles, D1
is forward-biased and D2 is
reverse-biased.
During negative half-cycles, D2
is forward-biased and D1 is
reverse-biased.

9. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
9
EffectoftheTurnsRatioontheOutputVoltage
If n=1, V
p(sec)=V
p(pri)
If n=2,7.0
)()(

pripoutp
VV pri
VV2
sec
 7.0
2
)(
)(

prip
outp
V
V

10. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
10
Peak Inverse Voltage (PIV)
Maximum anode voltage:2
(sec)
1
p
V
D 2
(sec)
2
p
V
D
D1:forward-bias–its
cathodeisatthesame
voltageofitsanode
minusdiodedrop;This
isalsothevoltageon
thecathodeofD2.

11. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
11
PIV across D2:VV
V
V
V
PIV
p
pp
7.0
2
7.0
2
(sec)
(sec)(sec)


















 VVV
V
V
V
outpp
p
outp
4.12
7.0
2
)((sec)
(sec)
)(




We know that
Thus;VVPIV
outp
7.02
)(


12. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
12
Itemploysfourdiodesarrangedsuchthatcurrentflowsinthe
directionthroughtheloadduringeachhalfofthecycle.
WhenVin+ve,D1andD2FBandconductcurrent.Avoltageacross
RLlookslike+vehalfoftheinputcycle.Duringthistime,D3andD4
areRB.
WhenVin–ve,D3andD4areFBandconductcurrent.D1andD2are
RB.
The Bridge Full-Wave Rectifier

13. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
13
Used 4 diode:
2 diode in forward
2 diode in reverse
Without diode drop (ideal diode):(sec))( poutp
VV
2 diode always in series with load
resistor during +veand –vehalf cycle .
With diode drop (practical diode):VVV
poutp
4.1
(sec))(


14. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
14
p
AVG
V
V
2


15. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
15
For ideal diode, PIV= Vp(out)VVPIV
outp
7.0
)(

For each diode,
To protect the diodes:

16. Full-Wave Rectifiers
Dr. Allam Ameen Electronic Circuits
16
Example1:
DrawtheoutputvoltagewaveformforeachcircuitinFigure
belowandincludethevoltagevalues.

17. Solved Problems
Dr. Allam Ameen Electronic Circuits
17
Solution:
??????
�(���)=??????
�(??????�)−0.7=5−0.7=4.3??????

18. Solved Problems
Dr. Allam Ameen Electronic Circuits
18
Solution:
??????
�(���)=??????
�(??????�)−0.7=−50−−0.7=−49.3??????

19. Solved Problems
Dr. Allam Ameen Electronic Circuits
19
Example2:Determinethepeakoutputvoltageforthebridge
rectifiershownbesides.Assumingthepracticalmodel,what
PIVratingisrequiredforthediodes?Thetransformeris
specifiedtohavea12Vrmssecondaryvoltagefor120Vrms
acrosstheprimary.

20. Solved Problems
Dr. Allam Ameen Electronic Circuits
20
Solution:

21. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
21
To reduce the fluctuations in the output voltage of half / full-
wave rectifier –produces constant-level dc voltage.
It is necessary –electronic circuits require a constant source
to provide power & biasing for proper operation.
Filters are implemented with capacitors.
In most power supply –50/60 Hz ac power line voltage is
converted to constant dc voltage.
50/60Hz pulsating dc output must be filtered to reduce the
large voltage variation.

22. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
22
The small amount of fluctuation in the filter output voltage
is called ripple.
The simplest
powersupply
filterisformed
byconnectinga
largecapacitor
between the
rectifieroutput
andtheground.
Itisreferredto
ascapacitor-
inputfilter.

23. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
23
Capacitive Filter
Capacitivefilterissimplyacapacitorconnectedinparallelwiththeload
resistanceorconnectedfromtherectifieroutputtoground.
Duringthepositivefirstquarter-cycleoftheinput,thediodeisforward-
biased,allowingthecapacitorchargesrapidly,asillustratedinFigure.

24. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
24
Capacitive Filter
Whentheinputbeginstodecreasefrommaximum,thediodeisreverse-
biased,andthecapacitorslowlydischargesthroughtheloadresistance.Asthe
outputfromtherectifierdropsbelowthechargedvoltageofthecapacitor,the
capacitoractsasthevoltagesourcefortheload.

25. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
25
Capacitive Filter
Duringfirstquarterofthenextcycle,thediodewillagainbecomeforward-
biasedwhentheinputvoltageexceedsthecapacitorvoltage.Thecapacitoris
fastlychargingthroughthediode.

26. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
26
Thecapacitordischargerateisrelatedtothetimeconstant
ofthedischargecircuit(τ),whichequalsR
LC.
Thelargerthetimeconstantthesmallertherippleandthe
moreeffectivefilteringweget.
Hence,acapacitorwithrelativelylargecapacitanceisalways
usedinpowersupplyfilters.

27. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
27
Ifconnectedtothesamecapacitor,full-waverectifier
producessmallerripplethanhalf-waverectifier.
Thisisbecausethefull-waverectifierallowsasmallerdischarge
interval.

28. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
28
Theperformanceofthefilterismeasuredusingtheripple
factor(r).Thelesstheripplefactor,thebetterthefilter:DC
ppr
V
V
factorrippler
)(
_ 
where : = peak -to -peak ripple voltage)(ppr
V

29. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
29
Lowerripplefactorbetterfilter[canbeloweredby
increasingthevalueoffiltercapacitororincreasingtheload
resistance]

30. Power Supply Filters
Dr. Allam Ameen Electronic Circuits
30
V
DC= V
AVG= average value of filter’s output voltage.5.0
1
2
1
1
1
)(
)(
)()(




















CfRV
V
r
V
CfR
VV
V
CfR
V
LDC
ppr
rectp
L
AVGDC
rectp
L
ppr

31. Solved Problems
Dr. Allam Ameen Electronic Circuits
31
Example3:DetermineV
p(rect),V
r(pp),V
DC,andtheripplefactor
forthefilteredbridgerectifierwithaloadasshownbelow.

32. Solved Problems
Dr. Allam Ameen Electronic Circuits
32
Solution:

33. Solved Problems
Dr. Allam Ameen Electronic Circuits
33
Solution:

34. Diode Limiters
Dr. Allam Ameen Electronic Circuits
34
Thediodelimiter(clipper)isacircuitthatclipstheportionfrom
theinputwaveformthatfallseitheraboveorbelowcertain
referencelevel.
Limitingcircuitslimitthepositiveornegativeamountofaninput
voltagetoaspecificvalue.Itisveryusefulforprotection.
2basicclipperconfiguration:
Positiveclipper.
Negativeclipper.

35. Diode Limiters
Dr. Allam Ameen Electronic Circuits
35
Positive clipper
•Forward-biased diode when i/p is +vecycle.
•Reverse-biased diode when i/p is in –vecycle.
•o/p signal is limit/clip to +0.7V during +vecycle of i/p signal.

36. Diode Limiters
Dr. Allam Ameen Electronic Circuits
36
Negative clipper
•Reverse-biased diode act as open circuit during +vecycle.
•Forward-biased diode act as short circuitduring –vecycle.
•o/p signal is limit/clip to -0.7V during –vecycle of i/p signal.

37. Diode Limiters
Dr. Allam Ameen Electronic Circuits
37
Example4:Whatwouldyouexpecttoseedisplayedonan
oscilloscopeconnectedacrossRLinthelimitershownbelow.

38. Diode Limiters
Dr. Allam Ameen Electronic Circuits
38
Solution:
•The diode is forward biased and conducts when input voltage goes below -0.7V.
So, for –velimiter, the peak output voltage across RL is:
•The waveform is shown below:VV
k
k
V
RR
R
V
inp
L
L
outp
09.910
1.1
0.1
)(
1
)(




















39. Diode Limiters
Dr. Allam Ameen Electronic Circuits
39
Biased Limiters:
Usedcbiasingsource,V
BIAStosetlimitonthecircuitoutputvoltage.
Thisallowthecircuittoclipinputwaveformatvaluesotherthandiode
forwardvoltage,0.7V.
Ineachcircuit,biasvoltageisinserieswithshuntdiode.Asaresult,
thediodeconductsandclipsthei/pwaveformwhensignalvoltage
equalssumofV
FandV
BIAS.
2 type of biased limiter:
•Positive-biased limiter
•Negative-biased limiter

40. Diode Limiters
Dr. Allam Ameen Electronic Circuits
40
Positive limiter
•The voltage at point A must equal VBIAS+0.7V before diode become FB
and conduct.
•Once diode begin to conduct, voltage at point A is limited to VBIAS+0.7V,
so all i/p voltage above this level is clipped off.

41. Diode Limiters
Dr. Allam Ameen Electronic Circuits
41
Negative limiter
•Voltage at point A must go below –V
BIAS-0.7V to forward-bias the
diode and initiate limiting action.
•o/p signal is limit/clip to -0.7V during –vecycle of i/p signal.

42. Diode Limiters
Dr. Allam Ameen Electronic Circuits
42
Opposite Biased Limiters:
Usedcbiasingsource,V
BIAStosetlimitonthecircuitoutputvoltage.
IfV
BIASisconnectedisserieswiththediode,suchthattheirpolarities
areoppositetoeachother,thelimitercircuitpassesasmallportion
fromtheinputwaveformandrejectstherest.
2 type of biased limiter:
•Positive-opposite biased limiter
•Negative-opposite biased limiter

43. Diode Limiters
Dr. Allam Ameen Electronic Circuits
43
Positive-opposite biased limiter

44. Diode Limiters
Dr. Allam Ameen Electronic Circuits
44
Negative-opposite biased limiter

45. Diode Limiters
Dr. Allam Ameen Electronic Circuits
45
Avoltagedividercanbeusedtoprovidetherequiredbiasvoltage
(V
BIAS)asportionofasupplyvoltage(V
SUPPLY),accordingtothewell-
knownvoltage-dividerformula:
Theresistorsofthedivider(R
2andR
3)shouldbeverysmall
comparedtoR
1inordertohaveastiffvoltagedivider,andto
minimizetheACvoltagedropon(R
2||R
3)whichmayaffectV
BIAS.SUPPLYBIAS
V
RR
R
V










32
3

46. Diode Limiters
Dr. Allam Ameen Electronic Circuits
46
Thethreecommonlyusedvoltage-dividersareshownbelow:

47. Diode Limiters
Dr. Allam Ameen Electronic Circuits
47
Example5:Thecircuitbesidescombinesabiasedpositivelimiter
withabiasednegativelimiter.Determinetheoutputvoltagewaveform.

48. Diode Limiters
Dr. Allam Ameen Electronic Circuits
48
Solution:

49. Diode Limiters
Dr. Allam Ameen Electronic Circuits
49
Example6:Describetheoutputvoltagewaveformforthediode
limitershownbesides.

50. Diode Limiters
Dr. Allam Ameen Electronic Circuits
50
Solution:

51. Diode Clampers
Dr. Allam Ameen Electronic Circuits
51
ThediodeclamperisasimplebiasingcircuitthataddsDClevel
(positiveornegative)toanACvoltagewaveform.Itscircuitanalysisis
verysimilartothefilteredHalf-WaveRectifier(HWR),asthediodeand
capacitorarejustswapped.
Therearetwotypesofclampers:thepositiveclamperandthe
negativeclamper.
1.Apositiveclampershiftsitsinputwaveformsothatthenegative
peakofthewaveformisequaltotheclamperdcreferencevoltage.
2.Anegativeclampershiftsitsinputwaveformsothatthepositive
peakofthewaveformisequaltotheclamperdcreferencevoltage.

52. Diode Clampers
Dr. Allam Ameen Electronic Circuits
52
Positive Clamper

53. Diode Clampers
Dr. Allam Ameen Electronic Circuits
53
Negative Clamper

54. Diode Clampers
Dr. Allam Ameen Electronic Circuits
54

55. Diode Clampers
Dr. Allam Ameen Electronic Circuits
55
Example7:Whatistheoutputvoltagethatyouwouldexpectto
observeacrossR
Lintheclampingcircuitshownbesides?AssumethatR
C
islargeenoughtopreventsignificantcapacitordischarge.

56. Diode Clampers
Dr. Allam Ameen Electronic Circuits
56
Solution:
First+veQuarter-Cycle:thecapacitor
israpidlychargedthroughtheforward
biaseddiodeupto:
RestofCycles:thediodeisreversed-
biased,andthecapacitorisvery
slowlydischargingthroughR
L,
Hence:VVVV
inpC
3.237.0247.0
)(
 VVVVV
inCinout
3.23

57. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
57
Thebasicfunctionofzenerdiodeistomaintainaspecificvoltage
acrossitsterminalswithingivenlimitsoflineorloadchange.
Typicallyitisusedforprovidingastablereferencevoltageforuse
inpowersuppliesandotherequipment.
This particular zenercircuit will work to maintain 10 V across the load.

58. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
58
Azenerdiodeismuchlikea
normaldiode,theexception
beingisthatitisplacedinthe
circuitinreversebiasand
operatesinreversebreakdown.
Thistypicalcharacteristiccurve
illustratestheoperatingrange
forazener.Notethatits
forwardcharacteristicsarejust
likeanormaldiode.

59. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
59
Thezenerdiode’sbreakdown
characteristicsaredetermined
bythedopingprocess.Low
voltagezeners(>5V),operatein
thezenerbreakdownrange.
Thosedesignedtooperate<5V
operatemostlyinavalanche
breakdownrange.Zenersare
availablewith voltage
breakdownsof1.8Vto200V.
ZenerzoneDiode zone
Avalanche
zone

60. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
60
Note very small reverse
current (before “knee”).
Breakdown occurs @ knee.
Breakdown Characteristics:
•VZremains near constant
•VZprovides:
-Reference voltage
-Voltage regulation
•IZescalates rapidly
•IZMAXis achieved quickly
•Exceeding IZMAXis fatal

61. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
61
Regulation occurs between:
VZK-knee voltage
to
VZM-Imax

62. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
62

63. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
63

64. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
64
•Ideal Zenerexhibits a constant voltage,
regardless of current draw.
•Ideal Zenerexhibits no resistance
characteristics.
•Zenerexhibits a nearconstant voltage,
varied by current draw through the
series resistance ZZ.
•As Izincreases, Vzalso increases.

65. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
65
Tocompletethecharacterizationofazener
diode,theslopeoftheoffsetbreakdownline
ofthecharacteristiccurveisrepresentedby
adynamicimpedanceZZ,suchthat:
Usingthepreviouslydefineddynamic
impedance,theintersectionbetweenthe
extensionofthebreakdownlineandthe
voltageaxis,V
Z0,canbeobtained:

66. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
66

67. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
67
Example8:AzenerdiodehasZ
Zof20Ω.Thedatasheetgives
V
Z=6.8VatI
Z=37mA,andI
ZK=1mA.Whatisthevoltageacross
thezenerterminalswhenthecurrentis50mA?Whenthecurrentis
25mA?Usebothidealandpracticalmodelsofthezenerdiode.
Solution:

68. ZenerDiodes
Dr. Allam Ameen Electronic Circuits
68
Solution:

69. Regulation
Dr. Allam Ameen Electronic Circuits
69
Inthissimpleillustrationofzenerregulationcircuit,thezenerdiodewill
“adjust”itsimpedancebasedonvaryinginputvoltages.Zenercurrent
willincreaseordecreasedirectlywithvoltageinputchanges.Thezener
current,Iz,willvarytomaintainaconstantVz.
Note:Thezenerhasafiniterangeofcurrentoperation.
VZener
remains
constant

70. Regulation
Dr. Allam Ameen Electronic Circuits
70

71. Regulation
Dr. Allam Ameen Electronic Circuits
71
Inthissimpleillustrationofzenerregulationcircuit,thezenerdiodewill
“adjust”itsimpedancebasedonvaryinginputvoltagesandloads(R
L)to
beabletomaintainitsdesignatedzenervoltage.Zenercurrentwill
increaseordecreasedirectlywithvoltageinputchanges.Thezenercurrent
willincreaseordecreaseinverselywithvaryingloads.Again,thezenerhas
afiniterangeofoperation.
VZener
remains
constant

72. Regulation
Dr. Allam Ameen Electronic Circuits
72

73. Regulation
Dr. Allam Ameen Electronic Circuits
73
Example9:Determinetheminimumandmaximuminputvoltages
thatcanberegulatedbythezenerdiodeofthecircuitbesides,
knowingthatV
Z=5.1VatI
Z=49mA,I
ZK=1mA,I
ZM=196mA,
andZ
Z=7Ω.Calculatethepercentagelineregulation.

74. Regulation
Dr. Allam Ameen Electronic Circuits
74
Solution:

75. Regulation
Dr. Allam Ameen Electronic Circuits
75
Solution:

76. Regulation
Dr. Allam Ameen Electronic Circuits
76
Example10:(a)Determinethevalue
ofRthatshouldbeusedtoallowthe
maximumloadresistancetobeinfinity
(o.c.),andconsequentlytheminimum
loadcurrenttobezero.
(b)Findthemaximumloadcurrentand
minimumloadresistanceforregulation.
(c)Calculatetheloadregulation.Thedata
sheetofthezenerdiodegivesthe
followinginformation:V
Z=15VatI
Z=17
mA,I
ZK=0.25mA,I
ZM=66.7mA,andZ
Z
=14Ω.

77. Regulation
Dr. Allam Ameen Electronic Circuits
77
Solution:

78. Regulation
Dr. Allam Ameen Electronic Circuits
78
Solution:

79. Power Supply Regulators
Dr. Allam Ameen Electronic Circuits
79
Connectedtotheoutputofafiltered&maintainsaconstantoutput
voltage(orcurrent)despitechangesintheinput,loadcurrentor
temperature.
Combinationofalargecapacitor&anICregulator–inexpensive&
produceexcellentsmallpowersupply.
PopularICregulatorshave3terminals:
(i)inputterminal
(ii)outputterminal
(iii)reference(oradjust)terminal

80. Power Supply Regulators
Dr. Allam Ameen Electronic Circuits
80
Type number: 78xx (xx –refer to output voltage)
i.e7805 (output voltage +5.0V); 7824 (output voltage +24V)
Pin 1
Pin 2
Pin 3
The main component of this regulator is a zenerdiode.

81. Complete Power Supply Circuit
Dr. Allam Ameen Electronic Circuits
81
Gnd
Connected to the output
of filtered rectifier
Bridge-full wave
rectifier Filter Regulators

82. Dr. Allam Ameen Electronic Circuits
82