Diode applications include rectifiers, clippers, clampers, voltage multipliers, and Zener voltage regulators. Rectifiers convert AC to pulsating DC and are classified as half-wave or full-wave. Clippers control waveform shape by removing portions. Clampers combine a diode and capacitor to clamp an AC signal to a DC level. Voltage multipliers produce an output DC voltage that is an integer multiple of the peak AC input. Zener diodes act as voltage regulators, providing a constant output voltage at their breakdown voltage.

1. Diode Applications:
• Rectifiers
• Clippers
• Clampers
• Voltage Multipliers
• Zener Voltage Shunt Regulator

2. RECTIFIERS
Rectifiers are circuits which converts ac into
pulsating dc or bipolar signal into unipolar signals.
Rectifiers are grouped into two categories
depending on the period of conductions.
1. Half-wave rectifier
2.Full- wave rectifier.
1. Half-wave rectifier
•The transformer is employed in order to step-
down the supply voltage and also to prevent from
shocks.

3. • The diode is used to rectify the a.c. signal while ,
the pulsating d.c. is taken across the load resistor
RL.
• During the +ve half cycle, the end X of the
secondary is +ve and end Y is -ve . Thus, forward
biasing the diode. As the diode is forward biased,
the current flows through the load RL and a
voltage is developed across it.
• During the –ve half-cycle the end Y is +ve and end
X is –ve thus, reverse biasing the diode. As the
diode is reverse biased there is no flow of current
through RL thereby the output voltage is zero.

8. FULL-WAVE RECTIFIER
Full-wave rectifiers are of two types
• Centre tapped full-wave rectifier
• Bridge rectifier
Centre tapped full –wave rectifier
• The circuit diagram of a center tapped full wave rectifier is shown in
figure above. It employs two diodes and a center tap transformer.
The a.c. signal to be rectified is applied to the primary of the
transformer and the d.c. output is taken across the load RL.

9. WORKING OF CENTRE TAP FULL WAVE
RECTIFIER
• Current flows through the load resistance in the same
direction during the full cycle of the input signal.
• Centre tap transformer is used where secondary winding is
divided in two equal halfs at the middle point of the winding.
• +ve Half Cycle: Diode D1 is short circuited and D2 is open
circuited. Current flows through the upper half of the
secondary winding.

10. • -ve Half Cycle: Diode D2 is short circuited and D1 is open
circuited. Current flows through the lower half of the
secondary winding.
• Complete input and output waveform can be shown as:

11. Disadvantages of Centre tapped full –wave rectifier
• Since, each diode uses only one-half of the transformer
secondary voltage the d.c. output is comparatively small.
• It is difficult to locate the center-tap on secondary winding of
the transformer.
• The diodes used must have high Peak-inverse voltage.
2. Bridge Rectifier:
The bridge rectifier uses four diodes connected in bridge pattern.

12. OPERATION OF THE BRIDGE RECTIFIER
• +ve Half Cycle: Diode D1 and D3 are short circuited and D2
and D4 are open circuited. Current flows through D1 and D3
to give the output voltage across the resistor.
• -ve Half Cycle: · Diode D1 and D3 are open circuited and D2
and D4 are short circuited. Current flows through D2 and D4
to give the output voltage across the resistor.

13. • Complete input and output waveform can be shown as
Advantages of Bridge Rectifier:
• The need for center-taped transformer is eliminated.
• The output is twice when compared to center-tapped full
wave rectifier for the same secondary voltage.
• The peak inverse voltage is one-half(1/2) compared to center-
tapped full wave rectifier.
• Can be used where large amount of power is required.
Disadvantages of Bridge Rectifier:
• It requires four diodes.

18. • This is the double the efficiency due to half wave rectifier.
Therefore a Full-wave rectifier is twice as effective as a half-
wave rectifier.
• Comparison of Rectifiers

19. Clippers
 It controls the shape of the output waveform by removing or
clipping a portion of the applied wave . Also called wave
shaping circuits e.g. Half wave rectifier
 Applications-
In radio receivers for communication circuits.
In radars, digital computers and other electronic
systems.
Generation for different waveforms such as
trapezoidal, or square waves.
In television receivers for separating the synchronizing
signals from composite picture signals
Diode Equivalent circuit during operation
19

20. TYPES OF CLIPPER CIRCUITS
 Series- Diode is in series with the source
 Parallel- Diode is in parallel with the source
Clipper circuit which uses a DC battery is called a biased
clipper
SERIES CLIPPER operation
+ve half cycle- (0 <t< T/2)
Diode on ,FB and Short circuit
Current flow throw R and by KVL
-ve half cycle- (T/2<t< T)
Diode off, RB and open circuit
No current throw R drop is zero
:
VO=VR=Vi
Vo=0
-ve portion of i/p wave clipped also called –ve clipper 20

21. BIASED SERIES CLIPPER
(adding a DC battery in series to diode)
Assume Diode is ideal
the diode is on because of the 5v battery The
transition of the diode from one state to another
can be found out to be at Vi=-5v above which
the diode is ON and below which the diode is
OFF.
+ve Half Cycle:
Since the diode is on the output voltage
will be (Applying KVL)
Vi+5=VR
VO= Vi+5
-ve Half Cycle:
Since the diode is off VO=0.
Figure Shows the input and output
waveform
21

22. Examples of series clipper
22

23. PARALLEL CLIPPER
Assume ideal diode
+ve Half Cycle:
Diode is on as forward bias condition. Since no
voltage drop across the diode the output voltage
becomes
VO = VD=0
-ve Half Cycle
Diode off as reverse bias .
Since no current flows through the circuit the
output voltage VO=Vi.
Since the positive half cycle is clipped off in the
output it is called as a positive clipper circuit.
23

24. BIASED PARALLEL CLIPPER
Assume IDEAL Diode
Operation
The transition of the diode from one state to
another is at Vi=4v above which the diode is
OFF and below which the diode is ON.
+ve Half Cycle:
Since the diode is OFF (above 4v) the output
voltage will be (Applying KVL)
Vi= VO
-ve Half Cycle:
Since the diode is ON (below 4v) VO=4v.
Figure Shows the input and output waveforms
24

25. Examples Parallel clippers
25

26. CLAMPERS
 A diode and capacitor can be combined to “clamp”
an AC signal to a specific DC level. Also called DC
inserter
 Circuit contains Diode, capacitor and resistive load
 For additional shift an independent DC supply can be
introduced in the circuit.
The time constant τ=RC must be much larger than
Time period ‘T’
26

27. Procedure to analyze a clamper circuit
Consider the part of the input signal that will forward bias
the diode.
During the On state assume that the capacitor will charge up
instantaneously to a voltage level determined by the network.
Assume that during the diode is in OFF sate the capacitor will
hold on to its established voltage level.
The polarity of Vo must be same throughout the analysis.
Total swing of the total output must match the swing of the
input signal
27

28. -ve clamper analysis
-Diode is ON(Short Circuit)
in the positive half cycle.
Established voltage level
on the capacitor Vc=V
-During negative half cycle
the diode is OFF and the
output voltage is
Vo=VR= -Vi-Vc = -2V
-Total swing of output is -
2V which is same as the
total swing of the input.
Assume initially cap has zero
voltage and diode is ideal
28

29. Biased Clamper Circuit
29

30. Operation of Circuit
-ve half cycle
Diode is ON (S.C). So
applying KVL around
the input loop we
have
-20+Vc=5=0
Vc=25v and Vo=5v
+ve half cycle
diode is OFF. Applying
KVL around the
outside loop we have
10+25-Vo=0
Vo=35v
30

31. Input and output Wave forms
31

32. Summary of the Clamper Circuit
32

33. Voltage multipliers
A circuit whose input is an AC wave form but gives a DC
voltage as output and this DC voltage is an integer multiple of
peak AC input
Half wave voltage doubler: combination of +ve clamper
and half wave rectifier with capacitor filter
33

34. Circuit operation
Consider initially caps are discharged
-Ve half cycle of input
signal:
D1 is on while D2 is off and
C1 charges to peak value of
input
+ve half cycle of input:
D1 is cut off D2 is on by KVL
from input through C1 to C2
34

35. Full wave voltage doubler
+ve half cycle of input:
D1 is on D2 is off C1
charges through on
resistance of D1 till peak
value of input
35

36. -ve half cycle:
D1 is OFF and D2 is on
and C2 Charges up to
peak value of input
And total voltage at
output is sum of
voltages across both
capacitors which is
36

37. Voltage Tripler and Quadrupler Circuit
Voltage Tripler and quadruples are Just extension of
Half wave voltage doublers by adding more
combinations of diodes and capacitors as per req.
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38. Zener Shunt Regulator
38
IL
R
Vz
Iz
V RL
I=IL+Iz
Vz
RL
Iz
V Vz
• Above circuit is used as voltage regulator to provide
constant output voltage Vz
•Here Vz is breakdown voltage of zener diode

39. Zener Shunt Regulator
39
•If voltage across terminals of zener is less than Vz it
works like a normal diode in revers bias condition, so
replaced by open circuit.
•If voltage across terminals of zener is more than Vz it
works in breakdown region, so provide constant
voltage Vz , so replaced by voltage source of value Vz

47. LIGHT EMITTING DIODE
• A light-emitting diode (LED) is a diode that gives off visible
light when forward biased.
• Light-emitting diodes are not made from silicon or germanium
but are made by using elements like gallium, phosphorus and
arsenic.
• By varying the quantities of these elements, it is possible to
produce light of different wavelengths with colors that include
red, green, yellow and blue.
• For example, when a LED is manufactured using gallium
arsenide, it will produce a red light. If the LED is made with
gallium phosphide, it will produce a green light.

48. WORKING OF LED
• When light-emitting diode (LED) is forward biased, the
electrons from the n-type material cross the pn junction and
recombine with holes in the p-type material.
• When recombination takes place, the recombining electrons
release energy in the form of heat and light.
• In germanium and silicon diodes, almost the entire energy is
given up in the form of heat and emitted light is insignificant.
• In materials like gallium arsenide, the number of photons of
light energy is sufficient to produce quite intense visible light.

49. TUNNEL DIODE
• A conventional diode exhibits positive resistance when it is
forward biased or reverse biased.
• However, if a semiconductor junction diode is heavily doped
with impurities, it exhibits negative resistance (i.e. current
decreases as the voltage is increased) in certain regions in the
forward direction.
• Such a diode is called tunnel diode.
Working:
• The tunnel diode is basically a pn junction with heavy doping
of p-type and n-type semiconductor materials.
• In fact, a tunnel diode is doped approximately 1000 times as
heavily as a conventional diode.

50. • The heavy doping provides a large number of majority
carriers. Because of the large number of carriers, there is
much drift activity in p and n sections.
• This causes many valence electrons to have their energy levels
raised closer to the conduction region.
• Therefore, it takes only a very small applied forward voltage
to cause conduction.
• The movement of valence electrons from the valence energy
band to the conduction band with little or no applied forward
voltage is called tunneling.
• As the forward voltage is first increased, the diode current
rises rapidly due to tunneling effect.
• Soon the tunneling effect is reduced and current flow starts to
decrease as the forward voltage across the diode is increased.

51. • The tunnel diode is said to have entered the negative
resistance region.
• As the voltage is further increased, the tunneling effect plays
less and less part until a valley-point is reached.
• From now onwards, the tunnel diode behaves as ordinary
diode i.e., diode current increases with the increase in
forward voltage.
V/I Characteristics:
• As the forward voltage across the tunnel diode is increased
from zero, electrons from the n- region “tunnel” through the
potential barrier to the p-region.
• As the forward voltage increases, the diode current also
increases until the peak-point P is reached.
• The diode current has now reached peak current IP (= 2.2 mA)
at about peak-point voltage VP (= 0.07 V). Until now the diode
has exhibited positive resistance.

52. • As the voltage is increased beyond VP, the tunneling action
starts decreasing and the diode current decreases as the
forward voltage is increased until valley-point V is reached. At
valley-point voltage Vv = 0.7V
• In the region between peak-point and valley-point (i.e.,
between points P and V), the diode exhibits negative
resistance i.e., as the forward bias is increased, the current
decreases.
• This suggests that tunnel diode, when operated in the
negative resistance region, can be used as an oscillator or a
switch.

53. • When forward bias is increased beyond valley-point voltage
VV, the tunnel diode behaves as a normal diode. In other
words, from point V onwards, the diode current increases
with the increase in forward voltage i.e., the diode exhibits
positive resistance once again.
VARACTOR DIODE
• A junction diode which acts as a variable capacitor under
changing reverse bias is known as a varactor diode.

54. • When a pn junction is formed, depletion layer is created in
the junction area.
• Since there are no charge carriers within the depletion zone,
the zone acts as an insulator.
• The p-type material with holes (considered positive) as
majority carriers and n-type material with electrons (−ve
charge) as majority carriers act as charged plates.
• Thus the diode may be considered as a capacitor with n-
region and p-region forming oppositely charged plates and
with depletion zone between them acting as a dielectric.
• A varactor diode is specially constructed to have high
capacitance under reverse bias.
• For normal operation, a varactor diode is always reverse
biased. The capacitance of varactor diode is found as :

55. • where CT = Total capacitance of the junction
ε = Permittivity of the semiconductor material
A = Cross-sectional area of the junction
Wd = Width of the depletion layer
• When reverse voltage across a varactor diode is increased, the
width Wd of the depletion layer increases.
• Therefore, the total junction capacitance CT of the junction
decreases.
• On the other hand, if the reverse voltage across the diode is
lowered, the width Wd of the depletion layer decreases.
• Consequently, the total junction capacitance CT increases.