BJT Biasing and Stability Questions and Answers

Q: In a CE configuration, an emitter resistor is used for ...............

The emitter resistor is used for stabilization of the operating point.If the collector current rises, for example because \(\beta\) or the temperature increases, the voltage across \(R_{E}\) rises with it. That reduces the base-emitter voltage, which reduces the base current and pulls the collector current back. This DC negative feedback keeps the Q-point steady against transistor variation and thermal runaway.An emitter resistor does not bypass AC signals; the capacitor placed across it does that, so that the resistor stabilises DC without cutting the AC gain. It does not provide collector bias. Unbypassed, it actually reduces the gain, so 'higher gain' is the opposite of its effect.

Q: In a common-emitter amplifier, the purpose of the emitter resistor is to

The emitter resistor is there to provide thermal stability.If temperature rises, the collector current tends to rise with it, because leakage current and beta increase. The extra current raises the voltage across the emitter resistor, which lowers the base-emitter voltage and pulls the current back. This negative feedback holds the Q-point steady and prevents thermal runaway.An unbypassed emitter resistor actually reduces gain and raises the input impedance, so 'increase gain' and 'reduce input impedance' are the reverse of what happens. It does not significantly reduce the output impedance.

111.

In a CE configuration, an emitter resistor is used for ...............

A.Stabilization
B.AC signal bypass
C.Collector bias
D.Higher gain

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

The emitter resistor is used for stabilization of the operating point.

If the collector current rises, for example because \(\beta\) or the temperature increases, the voltage across \(R_{E}\) rises with it. That reduces the base-emitter voltage, which reduces the base current and pulls the collector current back. This DC negative feedback keeps the Q-point steady against transistor variation and thermal runaway.

An emitter resistor does not bypass AC signals; the capacitor placed across it does that, so that the resistor stabilises DC without cutting the AC gain. It does not provide collector bias. Unbypassed, it actually reduces the gain, so 'higher gain' is the opposite of its effect.

Discuss in Forum

112.

In a common-emitter amplifier, the purpose of the emitter resistor is to

A.Increase gain
B.Reduce input impedance
C.Provide thermal stability
D.Reduce output impedance

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: C

The emitter resistor is there to provide thermal stability.

If temperature rises, the collector current tends to rise with it, because leakage current and beta increase. The extra current raises the voltage across the emitter resistor, which lowers the base-emitter voltage and pulls the current back. This negative feedback holds the Q-point steady and prevents thermal runaway.

An unbypassed emitter resistor actually reduces gain and raises the input impedance, so 'increase gain' and 'reduce input impedance' are the reverse of what happens. It does not significantly reduce the output impedance.

Discuss in Forum

113.

Biasing is done in class A mode to

A.save power
B.improve stability
C.reduce number of sources
D.both (B) and (C)

Exam Year(s)

UGC NET - 2012,

Answer: D

Biasing in class A mode fixes the operating point near the middle of the load line so that the device conducts for the full cycle. The key accepts both the improvement of stability and the reduction in the number of sources: a properly designed bias network, such as the voltage divider with an emitter resistor, keeps the operating point steady against changes in temperature and in transistor parameters, and it lets a single supply provide both the base bias and the collector supply, which removes the need for separate sources. Saving power is not the aim, because a class A stage draws current throughout the cycle and is the least efficient class. So both (B) and (C) hold, which is the last option. The answer is both (B) and (C).

Discuss in Forum

114.

In a bipolar transistor, stability factor for a fixed bias circuit is given by

A.\(S = \dfrac{1}{1 + \beta}\)
B.\(S = \dfrac{1}{\beta - 1}\)
C.\(S = (\beta - 1)^{2}\)
D.\(S = \beta + 1\)

Exam Year(s)

UGC NET - 2013,

Answer: D

For a fixed bias circuit the stability factor is \(S = \dfrac{\partial I_C}{\partial I_{CO}} = \beta + 1\), the fourth option. In fixed bias the base current is set by the supply and the base resistor, so any leakage current \(I_{CO}\) is amplified by the full factor \(1 + \beta\) at the collector, which makes this circuit the least stable.

The values \(1/(1+\beta)\) and \(1/(\beta - 1)\) are less than one, which would mean good stability, and this is true of potential-divider bias and not of fixed bias. \((\beta - 1)^2\) has no such origin.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: BJT Biasing and Stability Questions and Answers || BJT Biasing and Stability MCQ Questions and Answers || BJT Biasing and Stability GK Questions and Answers || BJT Biasing and Stability GK MCQ Questions || BJT Biasing and Stability Multiple Choice Questions and Answers || BJT Biasing and Stability GK || GK on BJT Biasing and Stability || Analog Electronics Questions and Answers || Analog Electronics MCQ Questions and Answers || Analog Electronics GK Questions and Answers || GK on Analog Electronics

BJT Biasing and Stability Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications