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Chapter 3:Bipolar Junction Transistors
Transistor ConstructionTransistor Construction
There are two types of transistors: • pnp• npn
The terminals are labeled: • E - Emitter
pnppnp
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
• E - Emitter• B - Base• C - Collector
npnnpn
22
Transistor OperationTransistor OperationWith the external sources, VEE and VCC, connected as shown:
• The emitter-base junction is forward biased• The base-collector junction is reverse biased
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
33
Currents in a TransistorCurrents in a Transistor
The collector current is comprised of two
BICIEI ++++====
Emitter current is the sum of the collector and base currents:
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
The collector current is comprised of two currents:
minorityCOI
majorityCICI +=
44
CommonCommon--Base ConfigurationBase Configuration
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
The base is common to both input (emitter–base) and output (collector–base) of the transistor.
55
CommonCommon--Base AmplifierBase Amplifier
Input CharacteristicsInput Characteristics
This curve shows the relationship between of input current (IE) to input voltage (VBE) for three output voltage
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
voltage (VBE) for three output voltage (VCB) levels.
66
This graph demonstrates the output current (I C) to an output voltage (VCB) for
CommonCommon--Base AmplifierBase Amplifier
Output CharacteristicsOutput Characteristics
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
an output voltage (VCB) for various levels of input current (I E).
77
Operating RegionsOperating Regions
• Active – Operating range of the amplifier.
• Cutoff – The amplifier is basically off. There is voltage, but little current.
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
current.
•• Saturation – The amplifier is full on. There is current, but little voltage.
88
EI
CI ≅
ApproximationsApproximations
Emitter and collector currents:
Base-emitter voltage:
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Silicon)(for V 0.7BEV =
99
Ideally: αααα = 1
Alpha (Alpha (αααααααα))
Alpha (αααα) is the ratio of IC to IE :
EICI
α =dc
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Ideally: αααα = 1In reality: αααα is between 0.9 and 0.998
Alpha (αααα) in the AC modeAC mode:
EICI
α∆
∆
ac =
1010
Transistor AmplificationTransistor Amplification
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage Gain:
V 50kΩ 5ma 10
mA 10
10mA20Ω
200mV
===
=≅
≅
====
))((RL
IL
V
iI
LI
EI
CI
iRiV
iIEI
Currents and Voltages:
1111
250200mV
50V===
iVLV
vA
CommonCommon––Emitter ConfigurationEmitter Configuration
The emitter is common to both input (base-emitter) and output (collector-emitter).
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
The input is on the base and the output is on the collector.
1212
CommonCommon--Emitter CharacteristicsEmitter Characteristics
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Collector Characteristics Base Characteristics
1313
CommonCommon--Emitter Amplifier CurrentsEmitter Amplifier Currents
Ideal CurrentsIdeal Currents
IE = IC + IB IC = αααα IE
Actual CurrentsActual Currents
IC = αααα IE + ICBO where ICBO = minority collector current
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
IC = αααα IE + ICBO
When IB = 0 µµµµA the transistor is in cutoff, but there is some minority current flowing called ICEO.
µA 0=−
=BI
CBOCEO
α
II
1
where ICBO = minority collector current
1414
ICBO is usually so small that it can be ignored, except in high power transistors and in high temperature environments.
Beta (Beta (ββββββββ))
In DC mode:
ββββ represents the amplification factor of a transistor. (ββββ is sometimes referred to as hfe, a term used in transistor modeling calculations)
CIβ =dc
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
In AC mode:
BIβ =dc
constantac =∆
∆=
CEVB
C
II
β
1515
Determining ββββ from a Graph
Beta (Beta (ββββββββ))
100
µA 10mA 1
µA) 20 µA (30mA) 2.2mA (3.2
β
7.5V
AC
CE
====
====
−−−−
−−−−====
====
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
108
A 25mA 2.7
β 7.5VDC CE
====
µµµµ==== ====
100====
1616
Relationship between amplification factors ββββ and αααα
1β
βα
++++====
1α
αβ
−−−−====
Beta (Beta (ββββββββ))
Relationship Between Currents
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Relationship Between Currents
BC βII ==== BE 1)I(βI ++++====
1717
CommonCommon––Collector ConfigurationCollector Configuration
The input is on the base and the output is on the emitter.
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
1818
CommonCommon––Collector ConfigurationCollector Configuration
The characteristics are similar to those of the common-emitter
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
common-emitter configuration, except the vertical axis is IE.
1919
VCE is at maximum and IC is at minimum (I Cmax= ICEO) in the cutoff region.
IC is at maximum and VCE is at minimum (V CE max = VCEsat = VCEO) in
Operating Limits for Each ConfigurationOperating Limits for Each Configuration
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
minimum (V CE max = VCEsat = VCEO) in the saturation region.
The transistor operates in the active region between saturation and cutoff.
2020
Power DissipationPower Dissipation
CCBCmax IVP ====
CCECmax IVP ====
Common-base:
Common-emitter:
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Common-collector:
ECECmax IVP ====
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Transistor Specification SheetTransistor Specification Sheet
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
2222
Transistor Specification SheetTransistor Specification Sheet
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
2323
Transistor TestingTransistor Testing•• Curve TracerCurve Tracer
Provides a graph of the characteristic curves.
•• DMMDMMSome DMMs measure ββββDC or hFE.
•• OhmmeterOhmmeter
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
2424
Transistor Terminal IdentificationTransistor Terminal Identification
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
2525