Characteristics of NPN Transistor

Working as an Amplifier

• Emitter Base: Forward biased
• Collector Base: Reverse biased
• Voltages:
  • VBE: Voltage between base and emitter
  • VCE: Voltage between collector and emitter

Input vs Output Characteristics

• Input Characteristics: Changing VBE affects input current
• Output Characteristics: Changing VCE affects output current (IC)

Experiment Setup

• Objective: Examine how VCE affects IC
• IB (Base Current): Must remain constant during the experiment to isolate the effect of VCE on IC

Graph of IC vs VCE

• Behavior:
  • In reverse bias, IC is mostly independent of VCE
  • Plot shows constant IC value for a specific IB (e.g., 10 μA)
  • IC can be an amplified value of IB (e.g., 100 times the IB)

Effect of VCE on IC

• If VCE drops below 0.7V, the PN junction becomes forward biased:
  • Forward Bias Effects:
    • Depletion width decreases, making electron flow harder
    • Electrons diffuse into base region
  • This causes IC to drop and be dependent on VCE

Amplification Conditions

• For Amplification:
  • Operate in the region where the collector base junction is reverse biased
  • Avoid the forward-biased region to ensure IC is an amplified version of IB

Experiment with Different IB Values

• Doubling IB:
  • Doubling IB (e.g., 20 μA) doubles IC in the reverse bias region
• Tripling IB:
  • Tripling IB further increases IC linearly

Conclusion

• Amplification Region: Ensure high enough VCE to maintain reverse bias
• Graph Regions:
  • Reverse bias region maintains IC as amplified
  • Forward bias causes IC to drop

Common Emitter Connection

• Definition: Emitter is common in both input and output circuits
• Symbol: CE mode/connection
• Superiority: Common emitter is considered superior for amplification

Other Connection Modes

• Other modes (e.g., common base, common collector) exist but are not covered in this context
• Common emitter mode is preferred in non-engineering contexts for simplicity and effectiveness