3. Topic Covered
2. Diode Applications:
• Load line Analysis
• Series and Parallel Diode Configurations
• Rectifier
• Half-Wave Rectifier
• Full-Wave Rectifier
• Clippers
• Clampers
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4. Learning Outcomes
• The students should be able to:
1. Describe the basic operation and characteristics of a diode in
forward-bias and reverse-bias region.
2. Explain the I-V curve of the diode in forward-bias and reverse-
bias region.
3. Explain the operation and characteristics of a Zener diode,
Schottky diode and Photodiode.
4. Solve the load-line analysis.
5. Solve the equivalent circuit of series, parallel and series-
parallel diode circuits.
6. Explain the process of rectification by using half-wave and full-
wave rectifier.
7. Analyze the output voltage of clipper and clamper.
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6. Introduction
• From previous chapter, there are 2 types of
semiconductor materials:
• N-type majority carrier of electrons
• P-type majority carrier of holes
• By combining these 2 materials, the first solid-
state electronic device can be constructed:
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7. Semiconductor Diode
• Diode:
• an electronic component which has two terminals or
electrodes and act like a switch.
• Symbol:
• Basic function:
• It is used to ALLOW current flow through a circuit in
ONE DIRECTION and BLOCKING the current from
OPPOSITE direction.
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8. How diode is formed?
1. Doping process
• Formed by principle of
doping semiconductor
materials (silicon,
germanium, etc) to create
P-type and N-type of
semiconductors material.
2. P-N Junction
• Both P-type and N-
type material are
joint in close contact
thus creates a P-N
junction between
both materials.
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9. How diode is formed?
3. Diffusion process
• Some of free electrons in
n-region diffuse across
the junction and combine
with holes to form
negative ions and leave
behind positive ions in n-
region.
• A space charges builds up
and creating a depletion
region which preventing
further diffusion of
carriers across the
junction.
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10. How diode is formed?
4. A diode is formed!
• The diode is formed once the P-type and N-type are
placed in close contact and this will formed a
depletion region which has a potential value.
• This potential is known as potential barrier and it is
depending the material of semiconductor.
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11. Diode biasing method
• Term “bias”
• Refer to the application of an external voltage
across the two terminals of the device to
extract a response.
• 2 types of bias
• Forward bias
• Reverse bias
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12. Forward-Bias Condition (VD > 0 V)
• Forward-bias
• Established by applying a positive potential to the p-
type and negative potential to n-type.
• Force electrons in n-type and holes in p-type material
to recombine with the ions near the boundary and
reduce the depletion region width.
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13. Forward-Bias Condition (VD > 0 V)
• Depletion region reduced heavy majority flow across the
junction.
• Higher biasing voltage, depletion region continues to
decrease until a flood of electrons can pass through the
junction.
• Once the applied voltage exceed the knee voltage, the
current exponentially increased.
• Knee voltage:
• Refer to potential barrier of P-N junction depending on the
material of semiconductor.
• The voltage point where the current starts to rapidly increase.
• Si = 0.7 V
• Ge = 0.3 V
• GaAs = 1.2 V
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15. Reverse-Bias Condition (VD < 0 V)
• Reverse Bias
• By applying the positive terminal to the n-type and
negative terminal to p-type material.
• The uncovered positive ions in depletion region of n-
type material are increased due to large number of
electrons drawn to applied positive potential.
• Similar situation for p-type where
uncovered negative ions
increase in p-type material.
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16. Reverse-Bias Condition (VD < 0 V)
• In this condition, the depletion region become wider.
• Due to widening depletion region, it creates greater
barrier for majority carrier to cross the junction.
• However, there is still small current flow through the
junction due to minority carrier in depletion region.
• This current is called reverse saturation current (Is)
which typically in nA or seldom in µA except for high-
power devices.
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18. Breakdown Region
• Breakdown region
• A point where the applied
external voltage is too
negative (very high) in
reverse bias.
• Beyond this point, the
current increases at very
rapid rate.
• This reverse-bias potential
that cause rapid change is
called “breakdown
potential” (VBV)
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19. Breakdown Region
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• Voltage in reverse-bias increases increases
the velocity of minority carrier.
• This gain sufficient velocity and associated
kinetic energy to release additional carriers
through collisions between stable atomic
structures.
• As a result of ionization process, the valence
electrons absorb sufficient energy to leave the
parent atom.
20. Breakdown Region
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• These additional carriers contributes into
ionization process to the point where high
avalanche current is established.
• The maximum reverse-bias potential that can be
applied before entering the breakdown region is
called as peak inverse voltage (PIV rating) or
peak reverse voltage (PRV rating).
22. Ideal versus Practical Diode
• Ideal diode
• As mechanical switch.
• Forward bias (a)
• Act like a closed switch which allows the currents
flow through it.
• Reverse bias (b)
• Act like an open switch which blocks any currents
flow through it. (since the Is is too small and
approximated as 0 A).
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23. Ideal versus Practical Diode
• Ideal diode:
• In forward-bias = closed switch
• Resistance of diode = 0 Ω
• Example: At plot, voltage across diode is 0 V while
current is 5 mA.
• In reverse-bias = open switch
• Resistance of diode = ∞ Ω
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0
5
0
mA
V
I
V
R
D
D
F
mA
V
I
V
R
D
D
R
0
20
24. Ideal Equivalent Circuit
• For ideal equivalent circuit, the 0.7 V level can be
ignored in comparison to the applied voltage
level.
• Thus, the circuit is reduced to only ideal diode.
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25. Zener Diode
• Type of diode that is designed
to work in the reverse
breakdown region of its
operating curve.
• Two things happen when the
revere breakdown voltage is
reached
-The diode current increase
drastically
-The reverse voltage across the
diode remains relatively
constant.
• The voltage across a zener
diode operated in this region is
relatively constant over a range
of component current values
26. Analysisof Zener Diode
26
Zener diode equivalents for
(a) ‘on’ and (b) ‘off’ states
V > Vz = on
Vz constant
Vz > V = off
Open circuit
27. Zener Diode
• Specification sheet for 10 V, 500 mW, 20% Zener diode.
• The zener potential is expected to vary as 10V +/- 20% which
is from 8 V to 12 V.
• Test Current, IZT is defined by ¼-power level, therefore the
power rating of the zener diode:
• To calculate the power rating from the table:
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27
Z
ZT
Z V
I
P 4
max
mW
V
mA
PZ 500
)
10
)(
5
.
12
(
4
max
28. Zener Diode
• Zener potential of the zener diode is very
sensitive to the temperature of operation.
• Temperature coefficient can be used to find the
change in zener potential:
Where Tc = temperature coefficient
T1 = new temperature
T0 = room temperature
VZ = nominal Zener potential at 25ᵒC
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C
T
T
V
V
T Z
Z
C
/
%
100
/
0
1
29. Zener Diode
• Example 1
Analyze the 10-V Zener diode described by table below if
the temperature is increased to 100ᵒC (the boiling water
point)
• Answer:
• The new Zener potential, VZ’ = 10 + 0.54 = 10.54 V
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V
T
T
V
T
V Z
C
Z 54
.
0
)
25
100
(
100
)
10
)(
072
.
0
(
)
(
%
100
0
1
30. Zener Diode
• Note that from the table, the
temperature coefficient is
positive.
• Zener diode that has less
than 5 V of Zener potential
has negative temperature
coefficient Zener voltage
drops with an increasing of
temperature.
• For example: 3.6 V Zener has
negative temperature
coefficient.
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31. Application of Zener Diode:
Voltage regulator
• A circuit designed to maintain a constant voltage
despite anticipated variations in load current or input
voltage.
• Performs two functions:
-It reduces the ripple (variations) in the output voltage
-It ensures that the dc output voltage from the power
supply will remain relatively constant despite
variations in load current demand
• Analysis voltage regulator involves:
- VR with no load
- VR with load
32. Voltage regulator
Voltage regulator with no load
S
Z
(min)
i
(min)
Z
R
V
V
I
S
Z
(max)
i
(max)
Z
R
V
V
I
0
V
R
I
V Z
S
Z
i
Z
(max)
Z
diss
V
I
P
Assume: Vi varies from
Vi(min) and Vi(max).
Power maximum dissipated,
33. • Voltage regulator with load
-conditions 1. Vi and RL are fixed
2. Fixed Vi, Variable RL.
1. Vi and RL are fixed
• Step 1:check the state of the zener diode
- remove it from the network
- and calculate the voltage across the
resulting open circuit
• If V ≥VZ, the zener diode is ‘on’ but if V< VZ, the diode is
‘off’.
i
L
L
L V
R
R
R
V
V
34. • Step 2: Substitute the appropriate equivalent circuit and
solve for the desired unknowns.
Z
L V
V
L
R
Z I
I
I
L
L
L
R
V
I
R
V
V
R
V
I L
i
R
R
Z
Z
Z V
I
P
Substituting the zener for the ‘on’
situation
The power dissipated by
zener diode is determined by
using KCL
1. Vi and RL are fixed
35. (a) For the zener diode network given, determine
VZ, VR, IZ and PZ.
(b) Repeat part (a) with RL = 3kW.
Zener diode regulator
Examplecase 1
40. 2. Fixed Vi, Variable RL
• To determine the minimum load resistance that will turn the
zener diode on, calculate the value of RL that will result in a
load voltage .
• Any load resistance value greater than the RL will ensure that
the zener diode is in the ‘on’ state.
• Once the diode is in the ‘on’ state, the VR and IR remains fixed
at
R
V
V
V
R
Z
i
Z
(min)
L
(min)
L
Z
(min)
L
L
(max)
L
R
V
R
V
I
ZM
R
(min)
L
I
I
I
(min)
L
Z
(max)
L
I
V
R
41. Example:Case 2
a)For the network, determine the range of RL
and IL that will result in VL being maintained at
10V.
b)Determine the maximum wattage rating of
the diode.
44. Schottky Diode
• Schottky diode is also known as surface-barrier diode or
hot-carrier diode.
• Applications:
• Low-voltage/high-current power supplies
• Ac-to-dc converters.
• Radar systems
• Schottky TTL logic for computers
• Mixers
• Detectors in communication equipments
• Instrumentation
• Analog-to-digital converters.
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45. Schottky Diode
• Construction:
• A metal-semiconductor junction is created.
• Semiconductor is normally n-type silicon (p-type is
sometimes used)
• Host of different metal such as molybdenum,
platinum, chrome or tungsten are used.
• Different construction gives different characteristics:
• Increase frequency range
• Lower forward bias
• High level of ruggedness
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46. Schottky Diode
• In both material, electron is the majority
carrier.
• When both n-type and metal are joined,
electrons in n-type silicon immediately flow
into the adjoining metal, establishing heavy
flow of electrons.
• The electrons from n-type material are called
“hot carriers” due to having very high kinetic
energy compared to electron in metal.
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47. Schottky Diode
• Heavy flow of electrons into metal creates a
region near the junction surface similar to
depletion region on p-n junction diode.
• Additional carriers in metal establish a
“negative wall” in the metal at the boundary
between the two materials.
• Result “surface barrier” is created between
two materials and preventing any further
current.
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48. Schottky Diode
• The barrier at the junction for a Schottky diode is less
than the p-n junction diode in both forward and reverse-
bias regions.
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50. Photodiode
• A semiconductor p-n junction device which operation
region is limited to the reverse-bias region.
• Basic biasing arrangement:
• The light is applied to the junction.
• Usually, lens are used to
concentrate the light to the junction.
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51. Photodiode
• The light is applied to the junction result the energy
transfer from the traveling light waves (form of photons)
to the atomic structure increase number of minority
carriers increase level of reverse current.
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• Dark current current that
exist with no applied
illumination.
• The graph shows that the
current will only return to zero
when positive bias equal to VT
is applied.
52. Photodiode
• Application: Alarm System
• The reverse current continue
to flow as long as the light
beam is not broken.
• If someone/something are
crossing the door and the light
beam is interrupted, the
reverse current drops to the
dark level and sound the
alarm.
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53. Photodiode
• Application: Counter operation
• The reverse current continue to flow as long as the light
beam is not broken.
• As each item passed, the light beam is broken and
reverse current drops to the dark level.
• Each time the current drop to dark level, the counter is
increased by one.
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54. 2. Diode Applications
• Load line Analysis
• Series and Parallel Diode Configurations
• Rectifier
• Half-Wave Rectifier
• Full-Wave Rectifier
• Clippers
• Clampers
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55. Load line Analysis
• If the analysis is performed in a graphical manner,
a line can be drawn on the characteristics of the
device that represents the applied load.
• The intersection of the load line with the
characteristics will determine the point of
operation of the system; usually called “quiescent
point” or “Q-point”.
• This analysis is called load-line analysis 55
56. Load-Line Analysis
• This analysis is called load-line analysis.
• From Q-point, we can determine the diode
voltage, VDQ and level of IDQ
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57. Load-Line Analysis
• To determine the load-line
intersection:
• By using KVL:
• Intersections can easily be
determined by employing
anywhere on horizontal axis
ID = 0 and anywhere on
vertical axis VD = 0 V
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57
R
I
V
E
V
V
E
D
D
R
D
V
V
D
D
D
D
D
R
E
I
R
I
E
R
I
V
E
0
0
1. Set VD = 0 V:
58. Load-Line Analysis
2. Set ID = 0 A:
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58
A
I
D
D
D
D
D
E
V
R
V
E
R
I
V
E
0
)
0
(
The intersection of the
load line with the
characteristics will
determine the point of
operation of the system
59. Load-Line Analysis
• Example 2
For the series diode configuration in Figure 7 and the
characteristics in Figure 8, determine the VDQ, IDQ and VR.
• Answer:
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59
Figure 7
Figure 8
mA
k
R
E
I V
V
D D
20
5
.
0
10
0
V
E
V A
I
D D
10
0
mA
I
V
V
Q
Q
D
D
5
.
18
78
.
0
V
V
E
V DQ
R 22
.
9
78
.
0
10
60. Series Diode Configurations
• In this part, the approximate semiconductor
diode model is used for the analysis.
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60
Approximate
Model
Ideal Model
61. Series Diode Configurations
• Forward bias
• Substituting the equivalent model for the “on”
state diode.
• VD knee voltage
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61
K
D V
V
K
R V
E
V
R
V
I
I R
R
D
62. Series Diode Configurations
• Reverse bias
• Substituting the equivalent model for the “off”
state diode.
• VD E
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E
VD
V
R
R
I
R
I
V D
R
R 0
)
0
(
A
ID 0
63. Series Diode Configurations
• Example 3
For the series diode configuration in Figure 9,
determine VD, VR and ID.
• Answer:
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63
Figure 9
V
VD 7
.
0
V
VR 3
.
7
7
.
0
8
mA
k
R
V
I
I R
R
D 32
.
3
2
.
2
3
.
7
65. Series Diode Configurations
• Example 4
For the series diode configuration in Figure 10,
determine VD, VR and ID.
• Answer:
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65
Figure 10
V
E
VD 5
.
0
V
k
R
I
R
I
V D
R
R 0
2
.
1
)
0
(
A
ID 0
Due to insufficient applied
voltage.
66. Series Diode Configurations
• Example 5
Determine Vo and ID for the
series circuit in Figure 11.
• Answer:
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66
Figure 11
V
V
V
E
V K
K
o 5
.
9
8
.
1
7
.
0
12
2
1
mA
R
V
R
V
I
I o
R
R
D 97
.
13
680
5
.
9
67. Series Diode Configurations
• Example 6
Determine ID, VD2 and Vo for
the series circuit in Figure 12.
• Answer:
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67
Figure 12
V
k
R
I
R
I
V D
R
o 0
6
.
5
)
0
(
A
ID 0
V
V
V
E
V o
D
D 20
0
0
20
1
2
68. Series Diode Configurations
• Exercise 7.4
Determine I, V1, V2 and Vo for the series DC
configuration in Figure 13.
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Figure 13
69. Parallel Diode Configurations
• Example 7
Determine Vo, I1, ID1 and ID2
for the parallel diode
configuration in Figure 14.
• Answer:
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69
Figure 14
V
Vo 7
.
0
mA
k
R
V
E
R
V
I D
R
18
.
28
33
.
0
7
.
0
10
1
mA
mA
I
I
I D
D 09
.
14
2
18
.
28
2
1
2
1
70. Series-Parallel Diode Configurations
• Example 8
Determine the currents I1, I2 and
ID2 for the network in Figure 15.
• Answer:
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70
mA
k
R
V
I K
212
.
0
3
.
3
7
.
0
1
1
2
V
VK
VK
E
V 6
.
18
7
.
0
7
.
0
20
2
1
2
Figure 15
mA
k
R
V
I 32
.
3
6
.
5
6
.
18
2
2
2
mA
m
m
I
I
ID 11
.
3
212
.
0
32
.
3
1
2
2
71. Rectifier
• An electrical device that converts alternating
current (AC) to direct current (DC).
• The process is called rectification.
• Rectifiers are usually used as component of DC
power supplies and high-voltage direct current
power transmission.
• Rectifiers are important for applications such as
radio, television, computer or any other
electronic equipment which require a steady
constant DC current which similarly produced
by a battery.
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72. Rectifier
• The output of rectifier is smoothed by an
electronic filter to produce steady DC current.
• There are TWO types of rectifier:
• Half-wave rectifier
• Full-wave rectifier
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72
73. Half-Wave Rectifier
• Half-wave rectifier consists of one diode.
• Produces one sine pulse for each cycle of input
sine wave.
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74. Half-Wave Rectifier
• Conduction region (0 T/2)
• When the input sine wave goes positive, diode will be
in forward biased.
• The diode conducts and act like a closed switch.
• The diode letting the positive pulse of the sine wave to
appear across the load resistor
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75. Half-Wave Rectifier
• Non-conduction region (T/2 T)
• When the input sine wave goes negative, the diode
will be in reverse biased mode.
• At this condition, no current flow in the circuit.
• No negative voltage appear across the load resistor.
• The output voltage will be zero during the negative
cycle.
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77. Half-Wave Rectifier
• Half-wave rectification with the effect of using silicon
diode
• The applied signal must be at least 0.7 V before the diode can
turn ON.
• If the input signal is less than 0.7 V, the diode still in open circuit
state and output voltage is 0 V.
• During conduction, the different between input and output
voltage is VK = 0.7 V (for silicon).
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77
)
(
318
.
0 K
m
dc V
V
V
78. Half-Wave Rectifier
• Example 9
Refer to Figure 16, sketch the output voltage and
determine the dc level of the output of the
circuit.
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78
Figure 16
79. Half-Wave Rectifier
• Answer:
For Ideal diode:
For Silicon diode:
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79
V
V
V
V K
m
dc 14
.
6
)
7
.
0
20
(
318
.
0
)
(
318
.
0
V
V
V m
dc 36
.
6
)
20
(
318
.
0
318
.
0
80. Full-Wave Rectifier
• DC level obtained from sine wave input can be improved
100% using full-wave rectification.
• Full-wave rectifier has TWO types:
• Bridge Rectifier
• Center-Tapped Transformer
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80
81. Full-Wave Rectifier – Bridge Rectifier
• During positive half cycle
(0 T/2)
• Diode D2
and D3 are
forward biased and act as
closed switches appearing
series with load resistor to
allow current to flow
through resistor.
• Diode D1 and D4 are
reverse biased and act as
open switches and no
current flow.
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81
82. Full-Wave Rectifier – Bridge Rectifier
• During negative half cycle (T/2 T)
• Diode D1 and D4 are forward biased and act as closed
switches appearing series with load resistor to allow
current to flow through resistor.
• Diode D2 and D3 are reverse biased and act as open
switches and no current flow.
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82
83. Full-Wave Rectifier – Bridge Rectifier
• Full-wave rectified signal without silicon effect
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83
m
dc V
V 636
.
0
84. Full-Wave Rectifier – Bridge Rectifier
• Full-wave rectification with the effect of using
silicon diode
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84
)
2
(
636
.
0 K
m
dc V
V
V
85. Full-Wave Rectifier – Bridge Rectifier
• Example 10
Determine the output waveform for the bridge
circuit as shown in Figure 17 and calculate the
output dc level.
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85
Figure 17
86. Full-Wave Rectifier – Bridge Rectifier
• Answer:
• At positive cycle:
• Repeat for negative cycle:
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86
V
V
V
V K
m
dc 73
.
2
)
(
636
.
0
87. Full-Wave Rectifier – Center-Tapped
Transformer
• During positive half cycle
(0 T/2)
• Point A become
positive.
• D1 is in forward biased
and act as closed
switch.
• D2 is in reverse biased.
• The current flow
through D1 and
load resistor.
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87
88. Full-Wave Rectifier – Center-Tapped
Transformer
• During positive half cycle
(T/2 T)
• Point B become positive.
• D2 is in forward biased
and act as closed switch.
• D1 is in reverse biased.
• The current flow
through D2 and
load resistor.
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88
89. Clippers
• Clippers are the circuit that use diode to “CLIP” away a
portion of an input signal without DISTORTING the
remaining part of waveform.
• There are TWO categories of clippers:
• Series
• Diode in series with load
• Parallel
• Diode in parallel with load
• Simplest clipper half-wave rectifier depending the
direction of diode either it clip off the positive or
negative region.
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89
90. Clippers – Series Clippers
• Series clippers can be used to clip off either
positive or negative region.
• There are no boundaries on the type of signals;
other than sinusoidal.
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90
91. Clippers – Series Clippers
• Series clipper with a DC supply
• Assumption: Ideal Diode.
• Any positive voltage of supply will try to turn ON the
diode.
• But, the added DC supply oppose the applied voltage
and try to keep the diode in OFF state.
• Any supply voltage greater than DC supply will turn ON
the diode and establish the conduction through load R.
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92. Clippers – Series Clippers
• Transition condition:
• When the input supply = dc supply in the circuit.
• For ON region:
• For OFF region:
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V
vi
V
v
v i
o
V
vo 0
93. Clippers – Series Clippers
• Example 11
Determine the output waveform for the sinusoidal
input of Figure 18.
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Figure 18
94. Clippers – Series Clippers
• Answer:
• Find transition state:
• Using KVL:
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V
vi 0
5
V
vi 5
V
v
v i
o 5
95. Clippers – Series Clippers
• Example 12
Find the output voltage for the circuit in Figure 19.
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Figure 19
96. Clippers – Series Clippers
• Answer:
• For vi = 20 V (0 T/2), the diode is in conduction
mode, therefore the vo = 20 + 5 = 25 V.
• For vi = -10 V (T/2 T), the diode in OFF state,
therefore the vo = 0 V.
• The output waveform as below:
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98. Clippers – Parallel Clippers
• Example 13
Determine vo for the network in Figure 20.
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Figure 20
99. Clippers – Parallel Clippers
• Answer:
• Vo is determined by the combination
of 4V DC supply and diode.
• Transition voltage:
• At vi = 4V, vo = 4V when the diode ON.
• For vi >= 4V, the vo=4V and waveform
is repeated on the output.
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V
vi 4
100. Clippers – Parallel Clippers
• Example 14
Determine vo for the network in Figure 21 with
consideration of silicon diode with VK = 0.7 V.
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Figure 21
101. Clippers – Parallel Clippers
• Answer:
• Vo is determined by the combination
of 4V DC supply and VK diode.
• Transition voltage:
• At vi = 3.3V, vo = 3.3V when the diode
ON.
• For vi >= 3.3V, the vo=3.3V and
waveform is repeated on the output.
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V
vi 3
.
3
7
.
0
4
102. Clippers (Summary)
• Simple Series Clippers (Ideal Diodes)
• Biased Series Clippers (Ideal Diodes)
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104. Clampers
• Clamper is a circuit constructed of a diode, a resistor
and a capacitor that shifts a waveform to a different dc
level without changing the appearance of the applied
signal.
• The resistor and capacitor value will determine the time
constant, so that it sufficiently large to ensure
that the voltage across capacitor does not discharge
significantly during non-conducting diode region.
• Note that, the capacitor practically having a full charges
or discharges in 5 time constant,
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RC
5
105. Clampers
• Clamping circuit has a capacitor connected directly from input
to output with resistive element in parallel with output signal.
• During 0 T/2, the diode is in ON state and the vo=0V and
time constant is very short because of R has been shorted
(effective R is now is in the contact/wires of circuit)
• So, with short time constant, the charging
of capacitor to value of V is very quick.
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106. Clampers
• During T/2 T, the input is at negative
cycle.
• The diode is in OFF state, and R is back in
the
circuit.
• At this stage, the time constant is
sufficiently large to establish a discharge.
• Vo is parallel with resistor, so the output
voltage:
• Negative sign is because the polarity of 2V is
opposite the polarity defined by vo.
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V
vo 2
