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TRANSCRIPT
Lecture #3 ( 2 weeks)
Transistors
Instructor: Dr. Ahmad El-Banna
Benha University Faculty of Engineering at Shoubra
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ECE-291 Electronic Engineering
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Agenda
BJT Structure
Basic Operation
Transistor as an Amplifier
Transistor as a Switch
DC & AC Analysis 2
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BIPOLAR JUNCTION TRANSISTOR (BJT) STRUCTURE
BJT symbol
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Transistor Packages
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Basic Operation • Biasing & Operation
• Transistor Currents
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BJT Configurations
Configuration Input Output
Common Emitter Base Collector
Common Base Emitter Collector
Common Collector Base Emitter
• Base terminal can’t be output • Collector terminal can’t be input
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BJT Parameters
• The dc current gain of a transistor is the ratio of the dc collector current (IC) to the dc base current (IB) and is designated dc beta (βDC).
• Typical values of βDC range from less than 20 to 200 or higher. • βDC is usually designated as an equivalent hybrid (h)
parameter, hFE, on transistor datasheets.
• The ratio of the dc collector current (IC) to the dc emitter current (IE) is the dc alpha (ɑDC).
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Transistor DC Model
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Ic= βIB
Collector characteristic curves Operation Regions • Active • Cut-off • Saturation
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Active Region
BJT as an Amplifier
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Phase shift = 180
re = 26 mv/ IE
IE = IC + IB
Voltage gain magnitude:
BJT as a Switch
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The Phototransistor
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Phototransistor Application Relay circuits driven by a phototransistor
• A relay is an electrically operated switch. • relays use an electromagnet to
mechanically operate a switch
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Optocouplers
• Basic optocouplers
Examples of optocoupler packages
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Project
LED Transmitter
Phototransistor Circuit
Motion Detection Alarm
Alarm Circuit
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555 Timer Siren Circuit
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Siren Using Op-Amp
http://bestengineeringprojects.com/electronics-projects/electronic-siren/
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Transistor Bias Circuit • What’s Biasing?
• Bias establishes the dc operating point (Q-point) for proper linear operation of an amplifier.
• Why? • If an amplifier is not biased with correct dc voltages on the input and
output, it can go into saturation or cutoff when an input signal is applied.
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Q-point Adjustment
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DC Load Line
• Variations in collector current and collector-to-emitter voltage as a result of a variation in base current.
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Waveform Distortion
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VOLTAGE-DIVIDER BIAS
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Loading Effects of Voltage-Divider Bias
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Thevenin’s Theorem Applied to Voltage-Divider Bias
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Linear Amplifier
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C.E. AC Analysis
• DC Analysis: Capacitors Open Circuit (See before)
• AC Analysis: Capacitors short Circuit DC supply ground
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AC r-parameter Model
Input resistance Output resistance Voltage gain Current gain Power gain
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Multistage Amplifier
• A two-stage common-emitter amplifier.
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Project II Audio Preamplifier for PA System
Pre AMP, chapter 4 Class AB Power AMP, chapter 7
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• For more details, refer to:
• Chapters 4-6, T. Floyd, Electronic Devices and Circuit Theory, 11th edition, Prentice Hall.
• The lecture is available online at: • http://bu.edu.eg/staff/ahmad.elbanna-courses/12136
• For inquires, send to:
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