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1. Bipolar Junction Transistor: Structure and Applications Presented by: Umair Sajid ,Ibrar Younis Electrical Engineer At: TeReSol Pvt. Ltd. Sheikh Zayed Bin Sultan Road, Sector H, DHA Phase II, Islamabad Presented To: Dr. Shahzad Project Director at TeReSol Pvt. Ltd.

2. Table of Contents 1. Introduction 2. Structure of BJT 3. Working Principle 4. Modes of Operation 5. BJT Configurations 6. Applications 7. Advantages & Limitations

3. Live Demonstration: Gesture-Controlled Car Introduction What is Bipolar Junction Transistor? “The Bipolar Junction Transistor (BJT) is a semiconductor device that controls current flow.” Called bipolar because it involves two types of charge carriers: Electrons (majority carriers in NPN). Holes (majority carriers in PNP). Used mainly as: Amplifier → strengthens weak signals. Switch → controls large current using small current. First invented in 1947 at Bell Labs (revolutionized electronics).

4. Made of three semiconductor regions : Emitter (E): Heavily doped, injects majority carriers Base (B): Thin & lightly doped, allows carriers to pass through. Collector (C): Moderately doped, large area to collect carriers. There are two types: NPN Transistor: Electrons are majority carriers. PNP Transistor: Holes are majority carriers Symbols: NPN (arrow outwards), PNP (arrow inwards). Structure of BJT

5. Basic Idea: Small current at the base controls large current between collector & emitter . In NPN transistor : Base-Emitter junction is forward biased → electrons flow from emitter to base. Most electrons cross into collector due to reverse bias → current amplification. In PNP transistor : Holes flow from emitter to base → collected at collector. Current Gain ( β): β =   Working Principle

6. Modes of Operation Region Of Operation Emitter-base Junction Collector-Base Junction Application Cut-off Reverse biased Reverse biased BJT acts as OFF switch Active (Forward Active) Forward biased Reverse biased BJT used as amplifier Inverse Active Reverse biased Forward biased Rarely used in practice Saturation Forward biased Forward biased BJT acts as ON switch

7. Common Base (CB): Input between emitter & base, output between collector & base. Low input resistance, high voltage gain & Rarely used. 2. Common Emitter (CE): Input between base & emitter, output between collector & emitter. Moderate input resistance, high current & voltage gain. Widely used in amplifiers. 3. Common Collector (CC): Input between base & collector, output between emitter & collector. High input resistance, unity voltage gain. Works as a buffer or impedance matching. BJT Configurations

8. Amplification: Audio amplifiers , signal processing , communication devices . Switching (on/off control) : Logic gates, microcontrollers, power supplies. Oscillators & Waveform Generators: Used in RF circuits and signal generators. Motor Drivers & Power Control: In robotics, automation, and control circuits. Current Regulation: Used in biasing and reference circuits. Applications

9. Advantages: High current gain (up to 100–200). Faster switching speed than vacuum tubes. Low cost, compact size. Can handle both analog and digital signals. Limitations: More power consumption than FETs. Generates more heat → requires cooling in power applications. Sensitive to temperature variations. Lower input impedance compared to MOSFETs. Advantages & Limitations