Electronic Devices and Circuit Theory
Boylestad
Bipolar Junction Transistors
Chapter 3
Ch.3 Summary
Transistor Construction
There are two types of pnp
transistors:
pnp and npn
The terminals are labeled:
E - Emitter npn
B - Base
C - Collector
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Ch.3 Summary
Transistor Operation
With the external sources, VEE and VCC, connected as
shown:
The emitter-base
junction is forward
biased
The base-collector
junction is reverse
biased
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Ch.3 Summary
Currents in a Transistor
Emitter current is the sum of the
collector and base currents:
I I I
E C B
The collector current is comprised of
two currents:
I I I
C C (majority) CO (minority)
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Ch.3 Summary
Common-Base Configuration
The base is common to both input (emitterbase) junction
and output (collectorbase) junction of the transistor.
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Ch.3 Summary
Common-Base Amplifier
Input Characteristics
This curve shows the
relationship between
of input current (IE) to
input voltage (VBE) for
three output voltage
(VCB) levels.
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Ch.3 Summary
Common-Base Amplifier
Output Characteristics
This graph
demonstrates
the output
current (IC) to
an output
voltage (VCB)
for various
levels of input
current (IE).
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Operating Regions
Active
Operating range of the amplifier.
Cutoff
The amplifier is basically off. There is
voltage, but little current.
Saturation
The amplifier is fully on. There is current,
but little voltage.
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Approximations
Emitter and collector currents:
IC IE
Base-emitter voltage:
VBE 0.7 V (for Silicon)
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Ch.3 Summary
Alpha ()
Alpha () is the ratio of IC to IE :
IC
dc
IE
Ideally: =1
In reality: falls somewhere between
0.9 and 0.998
Alpha () in the AC mode:
IC
ac
IE
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Transistor Amplifier
V 200 mV
IE I i i 10 mA
Ri 20
Currents and I I Voltage Gain:
C E
Voltages: I I 10 mA
L i VL 50 V
Av 250
V I R (10 mA )( 5 k ) 50 V Vi 200 mV
L L
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Common-Emitter
Configuration
The emitter is common to
both input (base-emitter)
and output (collector-
emitter) circuits.
The input is applied to the
base and the output is
taken from the collector.
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Common-Emitter Characteristics
Collector Characteristics Base Characteristics
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Ch.3 Summary
Common-Emitter Amplifier Currents
Ideal Currents IE = IC + IB IC = IE
Actual Currents IC = IE + ICBO where ICBO = minority
collector current
ICBO is usually so small that it can be ignored, except in high
power transistors and in high temperature environments.
When IB = 0 A the transistor is in ICBO
cutoff, but there is some minority ICEO IB 0 A
current flowing called ICEO. 1
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Beta ()
represents the amplification factor of a transistor.
IC
In DC mode: dc
IB
IC
In AC mode: ac VCE constant
IB
ac is sometimes referred to as hfe, a term used in transistor
modeling calculations
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Beta ()
Determining from a Graph
( 3.2 mA 2.2 mA)
AC
( 30 A 20 A)
1 mA
V 7.5 V
10 A CE
100
2.7 mA
DC VCE 7.5 V
25 A
108
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Beta ()
Relationship between amplification factors and :
1 1
Relationship Between Currents:
IC IB IE ( 1)IB
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Common-Collector Configuration
The input is on the
base and the
output is on the
emitter.
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Common-Collector Configuration
The characteristics
are similar to those
of the common-
emitter amplifier,
except the vertical
axis is IE.
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
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Ch.3 Summary
Operating Limits
VCE is maximum and IC is
minimum in the cutoff
region.
IC (max) ICEO
IC is maximum and VCE is
minimum in the saturation
region.
VCE (max) VCE ( sat ) VCEO
The transistor operates in the active region between saturation and cutoff.
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Power Dissipation
Common-base:
PCmax VCBIC
Common-emitter:
PCmax VCE IC
Common-collector:
PCmax VCE IE
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Transistor Specification Sheet
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Transistor Specification Sheet
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Transistor Specification Sheet
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Transistor Testing
Curve Tracer Provides a graph of the characteristic curves.
DMM Some DMMs measure DC or hFE.
Ohmmeter:
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
Ch.3 Summary
Transistor Terminal Identification
Electronic Devices and Circuit Theory 2013 by Pearson Higher Education, Inc
Boylestad Upper Saddle River, New Jersey 07458 All Rights Reserved
