Unit 2 Part – C

Q1. Input & Output Characteristics of CE Configuration

1️⃣ Input Characteristic (IB vs VBE):

• Resembles forward-biased diode curve.
• Base current increases exponentially with VBE.

2️⃣ Output Characteristic (IC vs VCE):

• Shows three regions:
  1. Cut-off Region → No IC, both junctions reverse-biased.
  2. Active Region → IC ∝ IB (used for amplification).
  3. Saturation Region → IC maximum, transistor fully ON.

3️⃣ Uses:

• To determine Q-point and transistor operation region.

Q2. Fixed Bias, Collector-to-Base Bias & Voltage Divider Bias

1️⃣ Fixed Bias:

• Resistor Rb from base to Vcc.
• Simple, but poor thermal stability.

2️⃣ Collector-to-Base Bias:

• Rb connected from collector to base.
• Provides negative feedback → improved stability.

3️⃣ Voltage Divider Bias:

• Two resistors (R1, R2) form divider to set base voltage.
• Emitter resistor Re improves stability.
• Most widely used biasing method.

Comparison:

Type	Stability	Components	Use
Fixed	Poor	Simple	Basic
Collector–Base	Moderate	2 resistors	Improved
Voltage Divider	Best	4 components	Industrial circuits

Q3. Construction & Working of NPN Transistor

1️⃣ Construction:

• Two N-type separated by thin P-type base.
• Emitter: heavily doped, Base: thin & lightly doped, Collector: moderately doped.

2️⃣ Working:

• Emitter-base forward biased, collector-base reverse biased.
• Electrons from emitter → base → collector.
• Base current small, controls large collector current.

3️⃣ Application:

• Used as current amplifier, switch, and oscillator.

Q4. CE, CB, and CC Configurations

Use:

• CE: Amplifier
• CB: High frequency applications
• CC: Impedance matching

Unit 2 Part – C Tamil

Q1. Input & Output Characteristics of CE Configuration

Definition:
Common Emitter (CE) configuration-இல் transistor amplify பண்ணும் circuit arrangement.
Input = Base–Emitter, Output = Collector–Emitter terminals.

1️⃣ Input Characteristics (IB vs VBE):

• Forward bias apply பண்ணும்.
• Graph similar to diode forward characteristic.
• VBE ↑ → IB ↑ exponentially.
• Base current small, few microamperes range.

2️⃣ Output Characteristics (IC vs VCE):

• Reverse bias at collector junction.
• Curves for different IB values plot பண்ணப்படும்.
• Cut-off Region: IB = 0, transistor OFF.
• Active Region: IC ∝ IB → used for amplification.
• Saturation Region: IC maximum, transistor fully ON.

3️⃣ Use:
இந்த characteristic curves மூலம் transistor-இன் Q-point (operating point) fix பண்ணலாம்.

Q2. Fixed Bias, Collector-to-Base Bias, Voltage Divider Bias

1️⃣ Fixed Bias:

• Base resistor RB direct-ஆ VCC-க்கு connect பண்ணப்படும்.
• Simple circuit but poor stability.
• Temperature change-ஆனாலும் IC vary ஆகும்.

2️⃣ Collector-to-Base Bias:

• RB collector-இல் இருந்து base-க்கு connect பண்ணப்படும்.
• Negative feedback கிடைக்கும் → better stability.
• Thermal runaway reduce ஆகும்.

3️⃣ Voltage Divider Bias:

• Two resistors R1 & R2 voltage divider network.
• Emitter resistor RE stability improve பண்ணும்.
• Most stable bias method in amplifiers.

Comparison Table:

Bias Type	Stability	Components	Use
Fixed	Poor	Simple	Basic circuits
Collector–Base	Moderate	2 resistors	Feedback improve
Voltage Divider	Best	4 components	Amplifiers

Q3. Construction and Working of NPN Transistor

Construction:

• Two N-type materials separated by thin P-type base.
• Emitter: heavily doped → more electrons emit.
• Base: thin & lightly doped → few recombination.
• Collector: moderately doped → collects electrons.

Working Principle:

1. Emitter–Base junction forward biased, Collector–Base reverse biased.
2. Electrons from emitter enter base → few recombine → remaining reach collector.
3. Small base current (IB) controls large collector current (IC).
4. Hence transistor acts as current amplifier.

Applications:

• Used as amplifier, switch, oscillator circuits.

Q4. CE, CB, and CC Configurations

1️⃣ Common Emitter (CE):

• Input: Base–Emitter, Output: Collector–Emitter.
• High voltage & current gain, phase shift = 180°.
• Widely used amplifier configuration.

2️⃣ Common Base (CB):

• Input: Emitter–Base, Output: Collector–Base.
• Low input impedance, High output impedance.
• Current gain ≈ α (<1).
• Used for high frequency applications.

3️⃣ Common Collector (CC):

• Input: Base–Collector, Output: Emitter–Collector.
• Voltage gain ≈ 1, current gain high.
• Used for impedance matching (Buffer stage).

Summary Table: