Active Region MCQ Quiz - Objective Question with Answer for Active Region - Download Free PDF

The correct answer is option 3.

Bipolar junction transistor

• The Bipolar Junction Transistor (BJT) is a three-terminal device i.e. Base, Emitter, and Collector.
• There are two main types of bipolar junction transistors the NPN and the PNP transistor.
• The emitter is a heavily doped region of the BJT transistor, providing the majority of carriers into the base region.
• The base region is a thin, lightly doped region sandwiched between the emitter and collector.
• The majority of carriers flows from the emitter pass through the base region and its flow can be externally controlled.

Operating Modes of Transistor

• To obtain high switching speed in BJT-based logic circuits, transistors are operated in the saturation region.
• In the active region, the transistor works as a linear element because the Q point is chosen such that the performance is linear, and we don't see any harmonics in the output. Hence R is true.

Important Points

Explanation:

A transistor can be acted as

1) Resistor in the current mirror

2) Capacitor in the level shifter

3) Closed or ON switch in the saturation region

4) Open or OFF switch in the cut-off region.

5) Inverter in cutoff and saturation region

6) Amplifier in the active region

Hence in the active region of a transistor Emitter-Base junction is Forward biased and the Collector-Base junction is in reverse biased. 

• To obtain high switching speed in BJT-based logic circuits, transistors are operated in the saturation region.
• In the active region, the transistor works as a linear element because the Q point is chosen such that the performance is linear, and we don't see any harmonics in the output. Hence R is true.

Important Points

The correct answer is option 3.

Bipolar junction transistor

• The Bipolar Junction Transistor (BJT) is a three-terminal device i.e. Base, Emitter, and Collector.
• There are two main types of bipolar junction transistors the NPN and the PNP transistor.
• The emitter is a heavily doped region of the BJT transistor, providing the majority of carriers into the base region.
• The base region is a thin, lightly doped region sandwiched between the emitter and collector.
• The majority of carriers flows from the emitter pass through the base region and its flow can be externally controlled.

Operating Modes of Transistor

Explanation:

A transistor can be acted as

1) Resistor in the current mirror

2) Capacitor in the level shifter

3) Closed or ON switch in the saturation region

4) Open or OFF switch in the cut-off region.

5) Inverter in cutoff and saturation region

6) Amplifier in the active region

Hence in the active region of a transistor Emitter-Base junction is Forward biased and the Collector-Base junction is in reverse biased. 

• To obtain high switching speed in BJT-based logic circuits, transistors are operated in the saturation region.
• In the active region, the transistor works as a linear element because the Q point is chosen such that the performance is linear, and we don't see any harmonics in the output. Hence R is true.

Important Points

The correct answer is option 3.

Bipolar junction transistor

• The Bipolar Junction Transistor (BJT) is a three-terminal device i.e. Base, Emitter, and Collector.
• There are two main types of bipolar junction transistors the NPN and the PNP transistor.
• The emitter is a heavily doped region of the BJT transistor, providing the majority of carriers into the base region.
• The base region is a thin, lightly doped region sandwiched between the emitter and collector.
• The majority of carriers flows from the emitter pass through the base region and its flow can be externally controlled.

Operating Modes of Transistor

Explanation:

A transistor can be acted as

1) Resistor in the current mirror

2) Capacitor in the level shifter

3) Closed or ON switch in the saturation region

4) Open or OFF switch in the cut-off region.

5) Inverter in cutoff and saturation region

6) Amplifier in the active region

Hence in the active region of a transistor Emitter-Base junction is Forward biased and the Collector-Base junction is in reverse biased. 

V_B = -1.5 V

The negative value of V_B indicates that the base current is going (in to) the base which is the right direction for an npn BJT.

\({I_B} = \frac{{0 - \left( { - 1.5} \right)}}{{10\; \times \;{{10}^3}}} = 0.15\;mA\) 

V_E = V_B – 0.7 = -1.5 – 0.7 = -2.2 V

\({I_E} = \frac{{{V_E} - \left( { - 9} \right)}}{{10\; \times \;{{10}^3}}} = \frac{{ - 2.2\; +\; 9}}{{10\; \times \;{{10}^3}}} = 0.68\;mA\) 

I_C = I_E - I_B = 0.68 – 0.15 = 0.53 mA

V_C = 9 – (0.53 × 10) = 3.7 V

V_BC = -1.5 – 3.7 = -5.2

The transistor is operating in the active mode.

\(\beta = \frac{{{I_C}}}{{{I_B}}} = \frac{{0.53}}{{0.15}} = 3.53\) 

Concept:

For an NPN transistor to be in the active region, the emitter junction must be forward biased and the collector junction must be reverse biased.

For emitter junction to be forward biased, V_BB > 0.7 V

For collector junction to be reverse biased,

V_CB ≥ 0 V

V_CE - V_BE ≥ 0

VCE - VBE ≥ 0

VCE - 0.7 ≥ 0

V_CE ≥ 0.7

Calculation:

Given, V_BB = 7 V

∵ VBB > 0.7 V

The emitter is forward biased.

-V_BB + I_B(R_B) + V_BE = 0

-5 + IB(10) + 0.7 = 0

I_B = 0.43 mA

-V_CC + I_C(R_C) + V_CE = 0

VCE = +VCC - IC(RC) 

0.7 = 10 - IC(RC) 

∵ I_C = βI_B

0.7 = 10 - βIB(RC) 

0.7 = 10 - 50(0.43)(R_C)

50(0.43)(RC) = 9.3

RC = 0.43255 kΩ

RC = 432.55 Ω