Analog & Digital Electronics (Biasing of BJT) - Powerpoint Presentation, EEE Computer Science Engineering (CSE) Notes | EduRev

Computer Science Engineering (CSE) : Analog & Digital Electronics (Biasing of BJT) - Powerpoint Presentation, EEE Computer Science Engineering (CSE) Notes | EduRev

 Page 1


Analog & Digital Electronics
Course No: PH-218
BJT 
Lec-7: Biasing schemes and stability of BJT
Course Instructors:
 Dr. A. P. VAJPEYI
Department of Physics, 
Indian Institute of Technology Guwahati, India
1
Page 2


Analog & Digital Electronics
Course No: PH-218
BJT 
Lec-7: Biasing schemes and stability of BJT
Course Instructors:
 Dr. A. P. VAJPEYI
Department of Physics, 
Indian Institute of Technology Guwahati, India
1
Biasing of BJT
 Biasing refers to the application of D.C. voltages to setup the operating 
point in such a way that output signal is undistorted throughout the whole 
operation.  
 Also once selected properly, the Q point should not shift because of 
change of I
C
due to
(i)  ß variation due to replacement of the transistor of same type
(ii) Temperature variation
2
Stabilization
The process of making operating point independent of temperature 
changes or variation in transistor parameters is known as stabilization.
 Stabilization of operating point is necessary due to
 Temperature dependence of I
C
 Individual variations
 Thermal runaway     
Page 3


Analog & Digital Electronics
Course No: PH-218
BJT 
Lec-7: Biasing schemes and stability of BJT
Course Instructors:
 Dr. A. P. VAJPEYI
Department of Physics, 
Indian Institute of Technology Guwahati, India
1
Biasing of BJT
 Biasing refers to the application of D.C. voltages to setup the operating 
point in such a way that output signal is undistorted throughout the whole 
operation.  
 Also once selected properly, the Q point should not shift because of 
change of I
C
due to
(i)  ß variation due to replacement of the transistor of same type
(ii) Temperature variation
2
Stabilization
The process of making operating point independent of temperature 
changes or variation in transistor parameters is known as stabilization.
 Stabilization of operating point is necessary due to
 Temperature dependence of I
C
 Individual variations
 Thermal runaway     
Stabilization
Temperature dependence of I
C 
& Thermal runaway
CBO B
I ) 1 ( I + + = ß ß
C
I
 I
CBO
is strong function of temperature. A rise of 10
o
C doubles the I
CBO
and I
C
will increase ( ß+1) times of I
CBO
 The flow of I
C
produce heat within the transistor and raises the transistor 
temperature further and therefore, further increase in I
CBO
 This effect is cumulative and in few seconds, the I
C
may become large 
3
 This effect is cumulative and in few seconds, the I
C
may become large 
enough to burn out the transistor.
 The self destruction of an unstablized transistor is known as thermal 
runaway. 
Stability Factor
 The rate of change collector current I
C
with respect  to the collector leakage 
current I
CBO
is called stability factor, denoted by S.                 
) (
CBO
C
dI
dI
S =
Lower the value of S, better is 
the stability of the transistor.
Page 4


Analog & Digital Electronics
Course No: PH-218
BJT 
Lec-7: Biasing schemes and stability of BJT
Course Instructors:
 Dr. A. P. VAJPEYI
Department of Physics, 
Indian Institute of Technology Guwahati, India
1
Biasing of BJT
 Biasing refers to the application of D.C. voltages to setup the operating 
point in such a way that output signal is undistorted throughout the whole 
operation.  
 Also once selected properly, the Q point should not shift because of 
change of I
C
due to
(i)  ß variation due to replacement of the transistor of same type
(ii) Temperature variation
2
Stabilization
The process of making operating point independent of temperature 
changes or variation in transistor parameters is known as stabilization.
 Stabilization of operating point is necessary due to
 Temperature dependence of I
C
 Individual variations
 Thermal runaway     
Stabilization
Temperature dependence of I
C 
& Thermal runaway
CBO B
I ) 1 ( I + + = ß ß
C
I
 I
CBO
is strong function of temperature. A rise of 10
o
C doubles the I
CBO
and I
C
will increase ( ß+1) times of I
CBO
 The flow of I
C
produce heat within the transistor and raises the transistor 
temperature further and therefore, further increase in I
CBO
 This effect is cumulative and in few seconds, the I
C
may become large 
3
 This effect is cumulative and in few seconds, the I
C
may become large 
enough to burn out the transistor.
 The self destruction of an unstablized transistor is known as thermal 
runaway. 
Stability Factor
 The rate of change collector current I
C
with respect  to the collector leakage 
current I
CBO
is called stability factor, denoted by S.                 
) (
CBO
C
dI
dI
S =
Lower the value of S, better is 
the stability of the transistor.
Stability Factor
 The rate of change collector current I
C
with respect  to the collector leakage 
current I
CBO
at constant ß and I
B
is called stability factor, denoted by S.                 
CBO B
I ) 1 ( I + + = ß ß
C
I (1)
Differentiating equation (1) w.r.t I
C
CBO B
dI
) 1 ( )
I
( 1 + + = ß ß
d d ) 1 (
)
I
( 1
B
+
+ =
ß
ß )
I
( 1
) 1 (
 
B
d
S
ß
ß
-
+
=
4
C
CBO
C
B
dI
) 1 ( )
I
( 1 + + = ß ß
d S d
)
I
( 1
C
B
+ = ß )
I
I
( 1
C
B
d
d
ß -
Different biasing schemes
(i) Fixed bias (base resistor biasing)
(ii) Collector base bias
(iii) Emitter bias
(iv) Voltage divider bias
Page 5


Analog & Digital Electronics
Course No: PH-218
BJT 
Lec-7: Biasing schemes and stability of BJT
Course Instructors:
 Dr. A. P. VAJPEYI
Department of Physics, 
Indian Institute of Technology Guwahati, India
1
Biasing of BJT
 Biasing refers to the application of D.C. voltages to setup the operating 
point in such a way that output signal is undistorted throughout the whole 
operation.  
 Also once selected properly, the Q point should not shift because of 
change of I
C
due to
(i)  ß variation due to replacement of the transistor of same type
(ii) Temperature variation
2
Stabilization
The process of making operating point independent of temperature 
changes or variation in transistor parameters is known as stabilization.
 Stabilization of operating point is necessary due to
 Temperature dependence of I
C
 Individual variations
 Thermal runaway     
Stabilization
Temperature dependence of I
C 
& Thermal runaway
CBO B
I ) 1 ( I + + = ß ß
C
I
 I
CBO
is strong function of temperature. A rise of 10
o
C doubles the I
CBO
and I
C
will increase ( ß+1) times of I
CBO
 The flow of I
C
produce heat within the transistor and raises the transistor 
temperature further and therefore, further increase in I
CBO
 This effect is cumulative and in few seconds, the I
C
may become large 
3
 This effect is cumulative and in few seconds, the I
C
may become large 
enough to burn out the transistor.
 The self destruction of an unstablized transistor is known as thermal 
runaway. 
Stability Factor
 The rate of change collector current I
C
with respect  to the collector leakage 
current I
CBO
is called stability factor, denoted by S.                 
) (
CBO
C
dI
dI
S =
Lower the value of S, better is 
the stability of the transistor.
Stability Factor
 The rate of change collector current I
C
with respect  to the collector leakage 
current I
CBO
at constant ß and I
B
is called stability factor, denoted by S.                 
CBO B
I ) 1 ( I + + = ß ß
C
I (1)
Differentiating equation (1) w.r.t I
C
CBO B
dI
) 1 ( )
I
( 1 + + = ß ß
d d ) 1 (
)
I
( 1
B
+
+ =
ß
ß )
I
( 1
) 1 (
 
B
d
S
ß
ß
-
+
=
4
C
CBO
C
B
dI
) 1 ( )
I
( 1 + + = ß ß
d S d
)
I
( 1
C
B
+ = ß )
I
I
( 1
C
B
d
d
ß -
Different biasing schemes
(i) Fixed bias (base resistor biasing)
(ii) Collector base bias
(iii) Emitter bias
(iv) Voltage divider bias
Fixed Bias
D.C. Equivalent
 This form of biasing is also called base bias. The single power source 
is used for both collector and base of transistor, although separate 
batteries can also be used.
5
Using KVL in the base-emitter loop
V
CC
– I
B
R
B
–V
BE
= 0 ; I
B
= (V
CC
-V
BE
)/R
B
I
C
= ßI
B
= ß(V
CC
-V
BE
)/R
B
Using KVL in the collector-emitter loop
V
CC
– I
C
R
C
–V
CE
= 0; V
CE
= V
CC 
- I
C
R
C
Q(V
CE
,I
C
) is set
Read More
Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!

Related Searches

Analog & Digital Electronics (Biasing of BJT) - Powerpoint Presentation

,

EEE Computer Science Engineering (CSE) Notes | EduRev

,

Viva Questions

,

Objective type Questions

,

pdf

,

past year papers

,

study material

,

Exam

,

mock tests for examination

,

Analog & Digital Electronics (Biasing of BJT) - Powerpoint Presentation

,

Semester Notes

,

Extra Questions

,

Free

,

ppt

,

practice quizzes

,

Important questions

,

video lectures

,

Sample Paper

,

Previous Year Questions with Solutions

,

shortcuts and tricks

,

MCQs

,

Summary

,

EEE Computer Science Engineering (CSE) Notes | EduRev

,

Analog & Digital Electronics (Biasing of BJT) - Powerpoint Presentation

,

EEE Computer Science Engineering (CSE) Notes | EduRev

;