Applied Electronics - BU
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Applied Electronics Instructor:
Dr. Ahmad El-Banna
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Day#2
Summer 2016
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Agenda
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Transistors Structure
Basic Operation
Bias Circuits (DC Analysis)
Models (AC Analysis)
Troubleshooting
Practical Applications
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
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Collector characteristic curves Operation Regions • Active • Cut-off • Saturation
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Active Region A
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BJT as an Amplifier
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Phase shift = 180
re = 26 mv/ IE
IE = IC + IB
Voltage gain magnitude:
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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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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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Other Bias Circuits
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Base Bias Emitter Bias
Other Bias Circuits..
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Emitter Feedback Bias Collector Feedback Bias
Note: Different bias circuits has different stability levels against beta and/or temperature changes
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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FET vs. BJT
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One of the most important characteristics of the FET is its high input impedance.
Typical ac voltage gains for BJT amplifiers are a great deal more than for FETs.
FETs are more temperature stable than BJTs, and FETs are usually smaller than BJTs, making them particularly useful in integrated-circuit (IC) chips.
FET vs. BJT..
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FET Constructions
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FET Characteristics
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JFET & MOSFET Symbol
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Other MOSFETS
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• VMOS AND UMOS POWER MOSFETs • CMOS
• MESFET
TROUBLESHOOTING 34
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Testing with DMM
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Testing with DMM..
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Testing with DMM...
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Voltage Divider circuit
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2-stage Amplifier
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FET circuits
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PRACTICAL APPLICATIONS 41
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Relay Driver
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Light Control
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Maintaining fixed load current
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Alarm System
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Logic gates
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Voltage level indicator
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Audio Mixer
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Preamplifier
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Voltage controlled resistor
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Security Alarm System
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Security Alarm System..
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Temperature to Voltage Converter
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Audio Preamplifier
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Active Antenna
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References
• Floyd, chapters:4-6,8-9
• Boylestad, chapters: 3-8
• For enquires:
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