Transistor and its type and applications

Presented by
Muhammad Samar Roll No. 09
Muhammad Usama Roll No. 10
Department BS Physics
Semester 8th
Presentation topic Transistors
Presented to Doctor Nosheen Kanwal
 Superior college Mian Channu

Transistor
 The word transistor means transferred
and Resistor
 The transistor is a semiconductor device
used as switch and amplifier
 It has three terminal for connection to
external circuit
 Transistor have two types
1. Bipolar Junction Transistor (BJT)
2. Field EffectTransistor (FET)

Bipolar Junction Transistors
 The transistor is a three-layer
semiconductor device consisting of either
two n- and one p-type layers of material
or two p- and one n-type layers of
material.
 The former is called an npn transistor,
while the latter is called a pnp transistor
 So, there are two types of BJT-
i) pnp transistor ii) npn transistor

Bipolar Junction Transistors
In each transistor following points to be
noted-
i) There are two junction, so transistor can
be considered as two diode connected
back to back.
ii) There are three terminals.
iii)The middle section is thin than other.

Naming of Transistor Terminals
 Transistor has three section of doped
semiconductor.
 The section one side is called “emitter” and
the opposite side is called “collector”.
 The middle section is called “base”.
Transistor
symbol

1) Emitter:
 The section of one side that supplies
carriers is called emitter.
 Emitter is always forward biased wr
to base so it can supply carrier.
 For “npn transistor” emitter supply
holes to its junction.
 For “pnp transistor” emitter supply
electrons to its junction.

2) Collector:
The section on the other side that
collects carrier is called collector.
 The collector is always reversed biased
wr to base.
For “npn transistor” collector receives
holes to its junction.
 For “pnp transistor” collector receives
electrons to its junction.

3) Base:
The middle section which forms two pn
junction between emitter and collector is
called Base.

Some important factors to be
remembered-
 The transistor has three region named
emitter, base and collector.
 The Base is much thinner than other
region.
 Emitter is heavily doped so it can inject
large amount of carriers into the base.
 Base is lightly doped so it can pass most of
the carrier to the collector.
 Collector is moderately doped.

Some important factors to be
remembered-
 The junction between emitter and base is
called emitter-base junction(emitter diode)
and junction between base and collector is
called collector-base junction(collector
diode).
 The emitter diode is always forward biased
and collector diode is reverse biased.
 The resistance of emitter diode is very
small(forward) and resistance of collector
diode is high(reverse).

Transistor Operation
1)Working of npn transistor:
 Forward bias Is
applied to emitter-
base junction and
reverse bias is applied
to collector-base
junction.
The forward bias in the emitter-base junction
causes electrons to move toward base.This
constitute emitter current, IE

1)Working of npn transistor:
 As this electrons flow toward p-type
base, they try to recombine with holes.As
base is lightly doped only few electrons
recombine with holes within the base.
These recombined electrons constitute
small base current.
The remainder electrons crosses base
and constitute collector current.

2)Working of pnp transistor:
 Forward bias is
applied to emitter-
base junction and
reverse bias is applied
to collector-base
junction.
The forward bias in the emitter-base junction
causes holes to move toward base.This
constitute emitter current, IE

2)Working of pnp transistor:
 As this holes flow toward n-type base,
they try to recombine with electrons.As
base is lightly doped only few holes
recombine with electrons within the base.
These recombined holes constitute small
base current.
The remainder holes crosses base and
constitute collector current.

Transistor Operating Modes
 Active Mode
 Base- Emitter junction is forward and
Base-Collector junction is reverse biased.
 Saturation Mode
 Base- Emitter junction is forward and
Base-Collector junction is forward biased.
 Cut-off Mode
 Both junctions are reverse biased.

Transistor Connection
 Transistor can be connected in a circuit in
following three ways-
1) Common Base
2) Common Emitter
3) Common Collector

Common Base Connection
 The common-base terminology is derived from
the fact that the base is common to both the
input and output sides of the configuration.
 First Figure shows common base npn configuration and second figure
shows common base pnp configuration.

Common Base Connection
 Current amplification factor ( ) :
The ratio of change in collector current to the
change in emitter current at constantVCB is
known as current amplification factor, .
 Practical value of is less than unity, but in
the range of 0.9 to 0.99
V
constant CB
E
C
at
I
I





Expression for Collector Current
Total emitter current does not reach the
collector terminal, because a small portion of it
constitute base current. So,
Also, collector diode is reverse biased, so very
few minority carrier passes the collector-base
junction which actually constitute leakage
current, .
 So, collector current constitute of portion of
emitter current and leakage current .
B
C
E I
I
I 

CBO
I
 E
I
CBO
I
0
CB
E
C I
I
I 


Expression for Collector Current

Characteristics of common base
configuration
 Input Characteristics:
VBE vs IE characteristics is
called input characteristics.
 IE increases rapidly with
VBE . It means input
resistance is very small.
 IE almost independent of
VCB.

Characteristics of common base
configuration
Output Characteristics:
VBc vs Ic
characteristics is called
output characteristics.
 IC varies linearly
withVBc ,only whenVBc
is very small.
 As,VBc increases, IC
becomes constant.

Input and Output Resistance of common
base conf.
 Input Resistance: The ratio of change in
emitter-base voltage to the change in
emitter current is called Input Resistance.
 Output Resistance: The ratio of change in
collector-base voltage to the change in
collector current is called Output
Resistance.
E
BE
i
I
V
r



C
BC
I
V
r



0

Common Emitter Connection
 The common-emitter terminology is derived from
the fact that the emitter is common to both the
 First Figure shows common emitter npn configuration and second
figure shows common emitter pnp configuration.

Common Emitter Connection
 Base Current amplification factor ( ) :
 In common emitter connection input current is bas
current and output current is collector current.
 The ratio of change in collector current to the
change in base current is known as base current
amplification factor, .
 Normally only 5% of emitter current flows to base,
so amplification factor is greater than 20. Usually th
range varies from 20 to 500.


B
C
I
I





Characteristics of common emitter
configuration
 Input Characteristics:
VBE vs IB characteristics is
called input characteristics.
 IB increases rapidly with
VBE . It means input
resistance is very small.
 IE almost independent of
VCE.
IB is of the range of
micro amps.

Characteristics of common emitter
configuration
 Output Characteristics:
VCE vs Ic
characteristics is called
output characteristics.
 IC varies linearly
withVCE ,only whenVCE
is very small.
 As,VCE increases, IC
becomes constant.

Input and Output Resistance of common
emitter conf.
• Input Resistance: The ratio of change in
emitter-base voltage to the change in base
current is called Input Resistance.
• Output Resistance: The ratio of change in
collector-emitter voltage to the change in
collector current is called Output Resistance.
B
BE
i
I
V
r



C
CE
I
V
r



0

Common Collector Configuration
 The common-collector terminology is derived from
the fact that the collector is common to both the
 First Figure shows common collector npn configuration and second figure
shows common collector pnp configuration.

Common Collector Configuration
 Current amplification factor ( ) :
 In common emitter connection input current is
base current and output current is emitter current.
 The ratio of change in emitter current to the
change in base current is known as current
amplification factor in common collector
configuration.
 This circuit provides same gain as CE configuration
as,

B
E
I
I




C
E I
I 



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