# Electronic Devices and Circuits Questions and Answers – Bias Compensation

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Bias Compensation”.

1. The compensation techniques are used to_________
a) increase stability
b) increase the voltage gain
c) improve negative feedback
d) decrease voltage gain

Explanation: Usually, the negative feedback is used to produce a stable operating point. But it reduces the voltage gain of the circuit. This sometimes is intolerable and should be avoided in some applications. So, the biasing techniques are used.

2. Compensation techniques refer to the use of_________
a) diodes
b) capacitors
c) resistors
d) transformers

Explanation: Compensation techniques refer to the use of temperature sensitive devices such as thermistors, diodes, transistors, sensistors etc to compensate variation in currents. Sometimes for excellent bias and thermal stabilization, both stabilization and compensation techniques are used.

3. In a silicon transistor, which of the following change significantly to the change in IC?
a) VCE
b) IB
c) VBE
d) IE

Explanation: For germanium transistor, changes in ICO with temperature contribute more serious problem than for silicon transistor. On the other hand, in a silicon transistor, the changes of VBE with temperature possesses significantly to the changes in IC.

4. What is the compensation element used for variation in VBE and ICO?
a) diodes
b) capacitors
c) resistors
d) transformers

Explanation: A diode is used as the compensation element used variation in VBE and ICO. The diode used is of the same material and type as that of transistor. Hence, the voltage across the diode has same temperature coefficient as VBE of the transistor.

5. The expression for IC in the compensation for instability due to ICO variation_________
a) βI+βIO+βICO
b) βI+βIO
c) βIO+βICO
d) βI+βICO

Explanation: In this method, diode is used for the compensation in variation of ICO. The diode used is of the same material and type as that of transistor. Hence, the reverse saturation current IO of the diode will increase with temperature at the same rate as the transistor collector saturation current ICO.
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6. Which of the following has a negative temperature coefficient of resistance?
a) sensistor
b) diode
c) thermistor
d) capacitor

Explanation: The thermistor has a negative temperature coefficient of resistance. It means, its resistance decreases exponentially with increasing T. The thermistor RT is used to minimize the increase in collector current.

7. Which of the following has a negative temperature coefficient of resistance?
a) capacitor
b) diode
c) thermistor
d) sensistor

Explanation: The sensistor has a positive temperature coefficient of resistance. It is a temperature sensitive resistor. It is a heavily doped semiconductor. When voltage is decreased, the net forward emitter voltage decreases. As a result the collector current decreases.

8. Increase in collector emitter voltage from 5V to 8V causes increase in collector current from 5mA to 5.3mA. Determine the dynamic output resistance.
a) 20kΩ
b) 10kΩ
c) 50kΩ
d) 60kΩ

Explanation: ro=∆VCE/∆IC
=3/0.3m=10kΩ.

9. The output resistance of CB transistor is given by _________
a) ∆VCB/∆IC
b) ∆VBE/∆IB
c) ∆VBE/∆IC
d) ∆VEB/∆IE

Explanation: The ratio of change in collector base voltage (∆VCB) to resulting change in collector current (∆IC) at constant emitter current (IE) is defined as output resistance. This is denoted by ro.

a) that IE flows into transistor while IC flows out it
b) that IC flows into transistor while IE flows out it
c) that IB flows into transistor while IC flows out it
d) that IC flows into transistor while IB flows out it

Explanation: When no signal is applied, the ratio of collector current to emitter current is called dc alpha, αdc of a transistor. αdc=-IC/IE. It is the measure of the quality of a transistor. Higher is the value of α, better is the transistor in the sense that collector current approaches the emitter current.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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