Applied Electronics - BU

Applied Electronics Instructor:

Dr. Ahmad El-Banna

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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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References

• Floyd, chapters:4-6,8-9

• Boylestad, chapters: 3-8

• For enquires:

• [email protected]

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Applied Electronics - BU

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