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EXPERIMENT 07 BJT TRANSISTOR COMMON EMITTER AMPLIFIER

🔬 Experiment 07 — BJT Characteristics & Common-Emitter Amplifier

The bipolar junction transistor, or BJT, is one of the fundamental building blocks of electronic circuits. It can operate as an amplifier or as a switching device.

🎯 Experiment Objective

To study the input and output characteristics of an NPN transistor in the common-emitter configuration and to understand how a small base current can control a larger collector current.

The experiment also demonstrates the basic principle of a common-emitter amplifier.

👨‍🎓 Think Before You Start
  • Why can a transistor provide current amplification?
  • What is the relationship between base current and collector current?
  • What happens when a transistor enters saturation?
  • Why is the common-emitter configuration widely used for amplification?

📚 1. Theory

BJT Structure

A bipolar junction transistor has three terminals: Emitter (E), Base (B), and Collector (C). For an NPN transistor, a small current injected into the base controls a substantially larger collector current.

Common-Emitter Configuration

In the common-emitter configuration, the emitter is the common reference terminal. The input is applied between base and emitter, while the output is measured between collector and emitter.

IC ≈ β IB

where β, or hFE, is the DC current gain of the transistor.

Operating Regions

Common-Emitter Amplification

A small AC signal applied to the base can produce a larger voltage variation at the collector. The common-emitter amplifier generally produces a phase inversion between its input and output voltage.

Av = Vout / Vin

🧩 2. Select Experiment

🟢 Ready. Press SCAN, then scroll down immediately. Watch Sections 4 and 6 come alive point-by-point.

🔌 3. Virtual BJT Circuit

📊 4. Live Measurements

VBE 0.60 V
IB 0.00 µA
VCE 5.00 V
IC 0.00 mA
β 100
Region CUT-OFF
Press here, then scroll down immediately. Keep this left panel visible while the transistor curve grows on the right.
⚡ LIVE CHARACTERISTIC SCAN
Ready — ACTIVATE THE EXPERIMENT, then SCROLL DOWN immediately to watch Sections 4 and 6 become MAGIC LIVE.
ACTIVATE EXPERIMENT → SCROLL DOWN immediately → WATCH the measurements and transistor curve come alive slowly, point-by-point. This is your hands-on MAGIC LIVE moment.

📡 5. Common-Emitter Amplifier

Input Amplitude 0.10 V
Output Amplitude 0.00 V
Voltage Gain 0.00
Phase 180°

Input and Output Waveforms

The common-emitter amplifier produces an amplified output with approximately 180° phase inversion in the simplified simulation.

📈 6. Transistor Characteristic Curves

● LIVE SCAN TRACE ● OPERATING POINT Multiple β / IB curves

For output characteristics, the graph shows collector current IC against collector-emitter voltage VCE for several base-current levels.

🔬 7. Engineering Analysis

Adjust the transistor parameters to observe the relationship between base current, collector current and collector voltage.

📝 8. Student Observation Table

Set a measurement point and click ADD OBSERVATION.

Trial VBE IB VCE IC Region

🎯 9. Identify the Transistor Operating Region

Move VBE and VCE controls to explore cut-off, active and saturation operation.

🎓 10. Experiment Conclusion

Complete the experiment to observe how the BJT operates as a current-controlled device and how it can be used for amplification.

❓ 11. Student Quiz

Q1. The three terminals of a BJT are:
Q2. In the active region, approximately:
Q3. In a common-emitter amplifier, the output is normally:
Q4. A transistor in cut-off is approximately:
Q5. The parameter β represents approximately:

🤖 CHITTI

GARRF Robotics & Engineering AI Mentor

Need help understanding transistor operation? Ask CHITTI for guidance.

💡 Try asking:

"What is a BJT?"

"What is transistor beta?"

"Explain cut-off, active and saturation."

"Why does a common-emitter amplifier invert the signal?"

"What is the difference between a transistor switch and transistor amplifier?"

👨‍🎓 12. How to Perform Experiment 07

  1. Select Output Characteristics.
  2. Choose a transistor β value.
  3. Set a base-emitter voltage.
  4. Vary VCE gradually.
  5. Observe collector current IC.
  6. Record several measurements.
  7. Repeat the experiment with a different base voltage.
  8. Identify cut-off, active and saturation regions.
  9. Switch to Common-Emitter Amplifier.
  10. Adjust the input signal amplitude.
  11. Observe the amplified output and phase inversion.
  12. Complete the observation table and quiz.
⭐ Engineering Thinking Challenge

If the base current is increased while the transistor remains in the active region, what should happen to the collector current?

⚠️ Real Laboratory Safety

Important:

In a physical circuit, transistor voltage and current ratings must always be respected. Excessive collector current or power dissipation can permanently damage the transistor.

👩🏽‍🏫
CHAMUNDIAI TEACHER • Experiment 07
CURRENT VIEWIntroduction
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I am ready to teach Experiment 07 — BJT Characteristics & Common-Emitter Amplifier. Press Start Lesson when you are ready.
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