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ECE 4991 Electrical and Electronic Circuits Chapter 10. Where We Are. Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors Chapter 3 – More harder networks to analyze and the notion of equivalent circuits - PowerPoint PPT Presentation
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ECE 4991 Electrical and Electronic ECE 4991 Electrical and Electronic CircuitsCircuits
Chapter 10Chapter 10
2
Where We AreWhere We Are• Chapter 2 - The basic concepts and practice at
analyzing simple electric circuits with sources and resistors
• Chapter 3 – More harder networks to analyze and the notion of equivalent circuits
• Chapter 4 – Capacitors and inductors added to the mix
• Chapter 5 – Analyzing transient situations in complex passive networks
• Chapter 8 – New subject – the wonders of operational amplifiers as system elements
• Chapter 9 – Introduction to semiconductors – the basics and diodes – more network analysis
• Chapter 10 – Bipolar junction transistors and how they work – now you can build your own op amp
3
What’s Important in What’s Important in Chapter 10Chapter 10
1. Definitions
2. How bipolar transistors work
3. Building a transistor
4. Transistor basics
5. Collector characteristics
6. Load lines and operating points
4
1. Definitions1. Definitions
• Bipolar transistor
• Emitter
• Base
• Collector
• NPN, PNP
• Gain ()
• Cutoff region
• Active linear region
• Saturation region
• Breakdown region
• Load lines
• Operating points
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2. How Bipolar Transistors 2. How Bipolar Transistors WorkWork
• Transistors are made by creating a PNP (or NPN) “sandwich”
• Carriers are “emitted” by the emitter and “collected” by the collector
• The base controls how much gets through
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Transistor OperationTransistor Operation• A small amount of base current can
control a large amount of collector current
• Gain = IC / IB =
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Transistor Operation in Transistor Operation in SiliconSilicon
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3. Building a Transistor3. Building a Transistor
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Transistor FabricationTransistor Fabrication
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4. Transistor Basics4. Transistor Basics
VBB
RB
+
VCC
RC
+
Typical NPN transistor schematic
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There are four operating There are four operating regions for a transistorregions for a transistor
VBB
RB
+
VCC
RC
+
1. Cutoff Region – Both junctions reverse-
biased – Very little base or collector current
2. Active Linear Region – BE junction forward
biased, CB junction reverse-biased –
amplifying mode
3. Saturation Region – Both junctions forward
biased – low VCE – switch mode
4. Breakdown Region – Determines the
operating limits of the device
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5. Collector Characteristics5. Collector Characteristics
VBB
RB
+
VCC
RC
+
“Collector characteristic” is a plot of
collector current versus collector-
emitter voltage for different base
currents
13
Collector CharacteristicsCollector Characteristics
“Collector characteristic” is a plot of
collector current versus collector-
emitter voltage for different base
currents
14
Real Transistor Collector Real Transistor Collector CharacteristicsCharacteristics
IB
= 10 µA, 20 µA, 30 µA, ... , 80 µA
15
6. Load Lines and Operating 6. Load Lines and Operating PointsPoints
IB
= 10 µA, 20 µA, 30 µA, ... , 80 µA
16
Consider this schematic…Consider this schematic…
VBB
RB
+
VCC
RC
+
• VCC = 15V, RC = 1000, VBB = 3V
• Design a circuit that operates around
the center of the active region collector
characteristics
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First, generate a load line, First, generate a load line, then set the operating pointthen set the operating point
VBB
RB
+
VCC
RC
+
• VCC = 15V, RC = 1000 ,
VBB = 3V
• What is IC @ VCE = 0?
• What is VCE @ IC = 0?
• Generate load line
• Pick desired IB
• Set RB to get it IB
= 10 µA, 20 µA, 30 µA, ... , 80 µA
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Practice with BipolarsPractice with Bipolars
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Practice with BipolarsPractice with Bipolars
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Practice with BipolarsPractice with Bipolars
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Practice with BipolarsPractice with Bipolars
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Practice with BipolarsPractice with Bipolars
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Practice with BipolarsPractice with Bipolars