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The figure below shows a circuit with two transistors, Q1 and Q2. having current gains β1 and β2 respectively.

The collector voltage Vc will be closest to
  • a)
    0.9 V
  • b)
    2.2 V
  • c)
    2.9 V
  • d)
    4.2 V
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
The figure below shows a circuit with two transistors, Q1and Q2. havin...
Concept:
  • A Darlington pair is a specific configuration of two transistors where the collector current of the first transistor feeds directly into the base of the second transistor.
  • It's technically a compound structure with two NPN or two PNP transistors. When a small current enters the base of the first transistor, it modulates a larger current flowing from the collector to the emitter.
  • This larger current is then fed into the base of the second transistor, which controls an even larger current from collector to emitter in the second transistor. The main advantage of this configuration is that it has significantly higher current and power gain (the multiplication of the current gains or β values of the two transistors) compared to a single transistor, thus it's often used when a high gain is required.
 
Explanation:
  • Let's denote the collector current of transistor Q1 as IC1, base current as IB1, and emitter current as IE1. Similarly, denote the collector current of transistor Q2 as IC2, base current as IB2, and emitter current as IE2.
  • Applying Kirchoff's voltage law to the left hand side of the loop containing the base connections: 

From the above equation, the base current of the first transistor will come out to be : 
Now, the collector current of the first transistor :
The collector current of the second transistor : 

Now, applying the Kirchhoff's voltage law to the collector side loop:
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The figure below shows a circuit with two transistors, Q1and Q2. having current gains β1and β2respectively.The collector voltage Vcwill be closest toa)0.9 Vb)2.2 Vc)2.9 Vd)4.2 VCorrect answer is option 'B'. Can you explain this answer?
Question Description
The figure below shows a circuit with two transistors, Q1and Q2. having current gains β1and β2respectively.The collector voltage Vcwill be closest toa)0.9 Vb)2.2 Vc)2.9 Vd)4.2 VCorrect answer is option 'B'. Can you explain this answer? for UGC NET 2025 is part of UGC NET preparation. The Question and answers have been prepared according to the UGC NET exam syllabus. Information about The figure below shows a circuit with two transistors, Q1and Q2. having current gains β1and β2respectively.The collector voltage Vcwill be closest toa)0.9 Vb)2.2 Vc)2.9 Vd)4.2 VCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for UGC NET 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The figure below shows a circuit with two transistors, Q1and Q2. having current gains β1and β2respectively.The collector voltage Vcwill be closest toa)0.9 Vb)2.2 Vc)2.9 Vd)4.2 VCorrect answer is option 'B'. Can you explain this answer?.
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