Zener Diode and Varactor Diode: Presented By

ZENER DIODE AND
VARACTOR DIODE
PRESENTED BY: DEBANGSHU BHATTACHARYYA (Roll No.-19)
DEEPAK SHARMA (Roll No.-24)
INDRAJIT SINGH (Roll No.-27 )
INDRAJIT GHOSH (Roll No.-28)
NANDUDULAL JENA (Roll No.-43 )
CONTENTS
A. ZENER DIODE
Introduction
General characteristics of diode
Zener diode
Breakdown Characteristics
Ideal and practical model
Applications
B. VARACTOR DIODE
Basic concepts
Types and symbol
Important criteria
Characteristics
Operation
Applications
2
INTRODUCTION
zener diode is a silicon pn junction device. It is

designed for operation in the reverse -breakdown
region. Its breakdown voltage is carefully set by
controlling the doping level during manufacture. The
basic function of zener diode is to maintain a specific
voltage across its terminals within given limits of line
or load change. Typically it is used for providing a
stable reference voltage for use in power supplies and
other equipments.
General Diode Characteristics

Forward Biased Region
v>0
Reversed Biased
Region v < 0
Breakdown Region v <
-VZK
The diode iv relationship

4
Zener Diodes Breakdown

Once reverse voltage exceeds a threshold value of
Characteristics
diode VZK, this voltage is called breakdown voltage.

VZK
Z Zener, K Knee
At K Knee
VZ remains near
constant
IZ escalates rapidly
IZMAX is achieved
quickly
VZ provides:
-Reference
voltage
-Voltage
Zener Diodes Operating

Range
A zener diode is
much like a normal
diode, the
exception being is
that it is placed in
the circuit in
reverse bias and
operates in
reverse
breakdown.
Operating range
Zener Diodes Ideal

Model
Zener Diodes Ideal Eqv.

Circuit
Ideal Zener exhibits a

constant voltage,
regardless of current draw.
Ideal Zener exhibits no
resistance characteristics.
Iz
0
Vz=Vzo +
Iz*0
=Vzo
8
Zener Diodes Practical

Model
Zener Diodes Practical

Eqv. Circuit
Zener exhibits a near
constant voltage, varied
by current draw through
the series resistance RZ.
Iz
Vzo
As Iz increases, Vz also
increases.
VZ VZ 0 I Z RZ
10
Zener DiodeTemperature Effect

Temperature coefficient of Zener is Known as Temco
& expressed in mv/co
Temco depends upon:
Zener Voltage
Operating Current
Zener Diode whose
Vz < 5V temco is negative
Vz = 5V temco is zero
Vz > 5V temco is positive
11
Zener DiodeTemperature Effect

Temco compensation by use using positive temperature
coefficient diode of app 2mv/c0 in series in forward biased
configuration
temco component
Zener diode have been replaced with voltage regulator

I.C => more efficient & flexible
12
Zener Diode Applications

1. Zener
Regulator
Supply voltage includes
a large ripple component
+
Vo
-
Voltage regulator performance can

be measured
Zener regulator
Line Regulation & Load Regulation
Vo is an output of the zener regulator
Line Regulation = Vo/Vs that is as constant as possible in spite
Load Regulation = Vo/IL
of
the ripples in the supply voltage VS
and the variations in the load current
13
Expression of performance : Zener

regulator
(Vs -Vo )
(Vo -V zo)
IL
R
rz
V
o
Vo Vzo(
R
r
) VS ( z ) - I L(rz ||R)
R rz
R rz
IL
Only the first term on right hand side is desirable one

Second and third terms depend upon Supply Voltage Vs
Vo
rz
/
and Load current IL V

(r R)
s
Line Regulation = Vo
- (rz ||R)
I L
Load Regulation =
14
Expression of performance : Zener

regulator
I
+
V
o
IL
An important consideration for the design is

To ensure that current through the zener
diode never becomes too low i.e less
than IZK or Izmin
Minimum zener current Izmin occurs when
Supply Voltage Vs is at its minimum
VSmin
Load current IL is at its maximum
(Vs min VZO - rz I z min )
ILmax
(I z min I L max )
where I L max
VZ 15
Zener Regulation with a Varying Input

Voltage
(a) As the input voltage increases, the output voltage

remains constant(Izk<Iz<Izm)
(b) As the input voltage decreases, the output voltage

remains constant(Izk<Iz<Izm)
16
Zener Diode
Applications
Zener diodes can used in ac applications to limit voltage
swings to desired levels. Part (a) shows a zener used to
limit the positive peak of a signal voltage to the selected
voltage. When the zener is turned around, as in part (b), the
negative peak is limited by zener action and the positive
voltage is limited to + 0.7 V.
17
Limiter
s
Applying a sine wave to a limiter can result in clipping

off its two peaks.
18
Varactor Diode
Variable Capacitor
Depletion layer acts as junction capacitance
Depletion layer varies Capacitance
Used for voltage controlled Tuning Circuit
Depletion Region
Metallic Plate
Dielectric
19
Varactor Diode
When a reverse voltage is applied to a p-n junction ,
the depletion region, is essentially devoid of carriers
and behaves as the dielectric of a capacitor.
The depletion region increases as reverse voltage
across it increases; and since capacitance varies
inversely as dielectric thickness, the junction
capacitance will decrease as the voltage across the
p-n junction increases.
By varying the reverse voltage across a p-n junction
the junction capacitance can be varied .
20
If the depletion widens, does

the capacitance increase or
decrease?
A
C= d
Hint:
Notice that as the effective
plate separation widens,
the capacitance will
decrease.
p
Pl
n
ate
ate
Pllectric
Die
VBIAS +
21
TYPES OF VARACTOR DIODES

Abrupt and hyper abrupt type : When the
changeover p-n junction is abrupt then it is called
abrupt type. When change is very abrupt, they are
called hyper abrupt type. They are used in
oscillators to sweep for different frequencies.
Gallium-arsenide varactor diodes : The

semiconductor material used is gallium arsenide.
They are used for frequencies from 18 GHz up to
22
Characteristics of
varactor diode
Low-noise : produce much less noise than

most conventional amplifiers.
Low cost
High reliability
Light weight
Small size
23
Operation of varactor diode
It has a p-n junction of

semiconducting
material and is always reverse
biased.
The depletion zone width
depends on the applied
voltage and this makes the
capacitance vary with the
applied voltage.
24
Applications of
varactor
diode
1. Frequency
multiplier It is used
where
its difficult to generate microwave signals.

produce relatively high power outputs at
frequencies up to 100GHz
does not have gain ; in fact, it produces a signal
power loss
output can be as high as 80% of the input
25
Applications of
varactor diode
2. Parametric Amplifiers - named for the

time-varying parameter, or value of capacitance,
associated with the operation.
Since the underlying principle of operation is
based on reactance, the parametric amplifier is
sometimes called a Reactane Amplifier.
26
Applications of
varactor diode
3. Tuning - Since the frequency can be made to

vary they are used as electronic tuning devices in
tuners for television, mobiles, radios etc..
4. Other ApplicationsThey are used in PLL, voltage controlled

oscillators, harmonic generation, electronic tuning
devices in tuners for television, mobiles,
parametric amplification, AM radios, voltage-
27
References:1.WikiPedia
2.Google
3.Microelectronic Circuit by Sedra
Smith
28
THANK
YOU
29

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ZENER DIODE AND

zener diode is a silicon pn junction device. It is

General Diode Characteristics

The diode iv relationship

Zener Diodes Breakdown

diode VZK, this voltage is called breakdown voltage.

Zener Diodes Operating

Zener Diodes Ideal

Zener Diodes Ideal Eqv.

Ideal Zener exhibits a

Zener Diodes Practical

Zener Diodes Practical

Zener DiodeTemperature Effect

Zener DiodeTemperature Effect

Zener diode have been replaced with voltage regulator

Zener Diode Applications

Voltage regulator performance can

Expression of performance : Zener

Only the first term on right hand side is desirable one

and Load current IL V

Expression of performance : Zener

An important consideration for the design is

Zener Regulation with a Varying Input

(a) As the input voltage increases, the output voltage

(b) As the input voltage decreases, the output voltage

Applying a sine wave to a limiter can result in clipping

If the depletion widens, does

TYPES OF VARACTOR DIODES

Gallium-arsenide varactor diodes : The

Low-noise : produce much less noise than

Operation of varactor diode

It has a p-n junction of

its difficult to generate microwave signals.

2. Parametric Amplifiers - named for the

3. Tuning - Since the frequency can be made to

4. Other ApplicationsThey are used in PLL, voltage controlled

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