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Lecture 27
Bipolar Junction Transistors
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Bipolar Junction Transistors
1. Understand bipolar junction transistor operation
in amplifier circuits.
2. Analyze simple amplifiers using the load-line
technique and understand the causes of
nonlinear distortion.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Tubes
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Deforest’s Audion
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Triode Tube
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Bardeen, Brittain and Shockley
Discovery of the transistor in 1947
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
First Transistor
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Initial Demonstration of Solid State
Amplification
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
First Integrated Circuit (IC)
Jack Kilby at Texas Instruments (1958)
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Early Integrated Circuit (IC)
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Chip Evolution
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
NPN and PNP Bipolar Junction
Transistors (BJT)
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm
NPN Bipolar Junction Transistor
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Bias Conditions for PN Junctions
The base emitter p-n
junction of an npn
transistor is normally
forward biased
The base collector p-n
junction of an npn
transistor is normally
reverse biased
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Bias Conditions for NPN Junctions
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm
Bias Conditions for NPN Junctions
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm
Bias Conditions for NPN Junctions
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm
Bias Conditions for NPN Junctions
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
http://www.mtmi.vu.lt/pfk/funkc_dariniai/transistor/bipolar_transistor.htm
Equations of Operation
  v BE
iE  I ES exp 
  VT
 
  1
 
From Kirchoff’s current law:
iE  iC  iB
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Equations of Operation
Define  as the ratio of collector current to emitter
current:
iC

iE
Values for  range from 0.9 to 0.999 with 0.99 being
typical. Since:
iE  iC  iB  0.99iE  iB  iB  0.01iE
Most of the emitter current comes from the collector
and very little (1%) from the base.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Equations of Operation
  v BE
iE  I ES exp 
  VT
 
  1
 
iC

iE
  vBE
iC   I ES exp 
  VT
 
  1
 
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Equations of Operation
iE  iC  iB
 iC
iB  iE  iC  iE 1 
 iE

  iE (1   )

  vBE
iB  (1   ) I ES exp 
  VT
 
  1
 
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Equations of Operation
Define  as the ratio of collector current to base
current:
iC

 
iB 1  
Values for  range from about 10 to 1,000 with a
common value being   100.
iC  iB
The collector current is an amplified version of the
base current.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Equations of Operation
  v BE
iE  I ES exp 
  VT
 
  1
 
  vBE
iC   I ES exp 
  VT
 
  1
 
  vBE
iB  (1   ) I ES exp 
  VT
iC  iB
iC
   0.99
iE
 
  1
 
iC

 
 100
iB 1  
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
The base region is very thin
Only a small fraction of the emitter current flows into the base
provided that the collector-base junction is reverse biased and the
base-emitter junction is forward biased.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.1
A certain transistor has  = 50, IES = 10-14A, vCE = 5 V, and iE = 10
mA. Assume VT = 0.026 V. Find vBE, vBC, iB, iC and .
  v BE
i E  I ES exp 
  VT
v BE
v BC
 
  1 For operation with iE  I ES
 
 v BE
i E  I ES exp 
 VT
 10  2 
 iE 
  718 .4 mV
  26 mV ln 
 VT ln 


14
 10 
 I ES 


 v BE  vCE  0.718V  5V  4.282V

50


 0.980
  1 51
iC  i E  9.80 mA
iB 
iC


9.80 mA
 196 A
50
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.



Exercise 13.2
Compute the corresponding values of  if  = 0.9, 0.99 and 0.999


1
0.9

1  0.9
9
  0 .9
0.99

1  0.99
 99
  0.99
0.999

1  0.999
 999
  0.999
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.3
A certain transistor operated with forward bias of the base-emitter
junction and reverse bias of the base-collector junction has iC = 9.5
mA and iE = 10 mA. Find the value of iB,  and .
iB  iE  iC  0.5 mA
iC 9.5mA
 
 0.95
iE 10 mA
iC
   19
iB
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Common-Emitter Characteristics
vBC
vCE
v BC  v BE  vCE
if v CE  v BE  v BC  0  reverse bias
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Common-Emitter Input
Characteristics
  vBE  
  1
iB  (1   ) I ES exp 
VT  



ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Common-Emitter Output
Characteristics
iC   iB for   100
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Amplification by the BJT
A small change in vBE results in a large change in iB if the
base emitter is forward biased. Provided vCE is more than a
few tenth’s of a volt, this change in iB results in a larger
change in iC since iC=iB.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Common-Emitter Amplifier
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of a Common
Emitter Amplifier (Input Circuit)
VBB  vin t   RBiB t   vBE t 
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of a Common
Emitter Amplifier (Output Circuit)
VCC  RC iC  vCE
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Inverting Amplifier
As vin(t) goes positive, the load line moves upward and to the
right, and the value of iB increases. This causes the operating
point on the output to move upwards, decreasing vCE  An
increase in vin(t) results in a much larger decrease in vCE so that
ELECTRICAL
the common
ENGINEERING: PRINCIPLES
emitter
ANDamplifier
APPLICATIONS, Fourth
is an
Edition,
inverting
by Allan R. Hambley,
amplifier
©2008 Pearson Education, Inc.
Load-Line Analysis of BJT
iBQ = 25 A
Assume VCC = 10V
VBB = 1.6V
RB = 40 k
RC = 2 k
Vin = 0.4sin(t)
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0  v BE  1.6
v BE
1.6V
 0 and vin  0  i B 
 40 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of BJT
iBmax= 35 A
Assume VCC = 10V
VBB = 1.6V
RB = 40 k
RC = 2 k
Vin = 0.4sin(t)
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0.4  v BE  2
v BE
2V
 0 and vin  0.4  i B 
 50 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of BJT
iBmin= 15 A
Assume VCC = 10V
VBB = 1.6V
RB = 40 k
RC = 2 k
Vin = 0.4sin(t)
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0.4  v BE  1.2
v BE
1.2V
 0 and vin  0.4  i B 
 30 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of BJT
iBQ = 25 A
iBmin= 15 A
iBmax= 35 A
VCEQ = 5V
VCEQ = 5V
iCEQ = 2.5 mA
VCEmin = 3V
VCEmax = 7V
10  2k iC  vCE
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of BJT
Voltage waveforms for the common emitter amplifier.
The gain is -5 (inverting).
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Clipping
When iC becomes
zero, we say that the
transistor is
cutoff.
When vCE  0.2 V, we
say that the transistor
is in saturation.

Amplification occurs in the active region. Clipping
occurs in the saturation or cutoff regions.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Clipping
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.5
vin (t )  0.8 sin(t )
iBQ  25 A
Find VCE max , VCEQ
and VCE min
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0  v BE  1.6
v BE
1.6V
 0 and vin  0  i B 
 40 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.5
vin (t )  0.8 sin(t )
iBmax  45A
Find VCE max , VCEQ
and VCE min
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0.8  v BE  2.4
v BE
2.4V
 0 and vin  0.8  i B 
 60 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.5
vin (t )  0.8 sin(t )
iBmin  5A
Find VCE max , VCEQ
and VCE min
VBB  vin t   RB i B t   v BE t 
1.6  vin  40 ki B  v BE
i B  0 and vin  0.8  v BE  0.8
v BE
0.8V
 0 and vin  0.8  i B 
 20 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.5
iBQ  25 A
VCEQ  5V
iCQ  2.5mA
iBmin  5A
VCE max  9V
iCmin  0.5mA
iBmax  45 A
VCE min  1V
iCmax  4.5mA
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.6
iBQ  15 A
vin (t )  0.8 sin(t )
VBB  1.2V
VBB  vin t   RB i B t   v BE t 
1.2  vin  40 ki B  v BE
i B  0 and vin  0  v BE  1.2
v BE
1.2V
 0 and vin  0  i B 
 30 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.6
iBmax  35A
vin (t )  0.8 sin(t )
VBB  1.2V
VBB  vin t   RB i B t   v BE t 
1.2  vin  40 ki B  v BE
i B  0 and vin  0.8  v BE  2
v BE
2V
 0 and vin  0.8  i B 
 50 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.6
iBmin  1A
vin (t )  0.8 sin(t )
VBB  1.2V
VBB  vin t   RB i B t   v BE t 
1.2  vin  40 kiB  v BE
i B  0 and vin  0.8  v BE  0.4
v BE
0.4V
 0 and vin  0.8  i B 
 10 A
40 k
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.6
i BQ  15 A
VCEQ  7V
iCQ  1.5mA
iBmin  1A
VCE max  9.8V
iCmin  1.0mA
i Bmax  35 A
VCE min  3V
iCmax  3.5mA
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
PNP Bipolar Junction Transistor
Except for reversal of current directions and
voltage polarities, the pnp BJT is almost
identical to the npn BJT.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
PNP Bipolar Junction Transistor
iC   i E
i B  (1   )i E
iC   i B
i E  iC  i B
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Common-Emitter Characteristics for a
PNP BJT
   v BE  
  1
iE  I ES exp 

V
  T  
   v BE
iB  (1   ) I ES exp 
  VT
 
  1

 
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.7
Find :
For VCE  6V, i C  2.5mA  i B  50 A
iC 2.5mA
 
 50
iB
50 A
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
Common emitter amplifier
0.8  vin  8000 iB  vBE  0
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
0.8  vin  8000 i B  v BE  0
vin  0
vin  0
vin  0.2
vin  0.2
vin  0.2
vin  0.2
iB  0
v BE  0.8
 0.8
v BE  0 i B 
 100 A
8000
i B  0 v BE  0.6
 0.6
v BE  0 i B 
 75 A
8000
i B  0 v BE  1
v BE
1
 0 iB 
 125 A
8000
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
i BQ  24 A
i Bmax  48 A
i Bmin  5A
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
Common emitter amplifier
9  3000 iC  vCE  0
vCE  9  3000 iC
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
Load line:
vCE  9  3000 iC
iC  0
vCE
vCE  9
9
 0 iC 
 3mA
3000
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Exercise 13.8
iBmax  48 A
VCE max  1.8V
i Bin  5A
VCE min  8.3V
i B  24 A
VCE  5.3V
ELECTRICAL ENGINEERING: PRINCIPLES
AND APPLICATIONS, Fourth Edition, by Q
Allan R. Hambley, ©2008 Pearson Education, Inc.
Q