This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Thermistor and Sensistor Compensation”.
1. Which type of temperature dependent resistor exhibits a positive temperature coefficient of resistivity?
a) Thermistor
b) Sensistor
c) Varistor
d) Photoresistor
View Answer
Explanation: Sensistor is a temperature dependent device whose resistance is dependent upon temperature. It has a direct variation with respect to change in temperature & hence usually appropriate for bias compensation.
Its functionality is accurately opposite to that of thermistor which exhibits negative temperature coefficient of resistivity.
As the resistance of sensistor increases due to increase in temperature, it is also supposed to have the property of positive temperature coefficient of resistivity.
2. The compensation technique uses __________
a) transformers
b) inductors
c) diodes
d) capacitors
View Answer
Explanation: Compensation techniques require the use of temperature sensitive devices such as thermistors, diodes, transistors, sensistors etc to compensate variation in currents. However, for excellent bias and thermal stabilization, both stabilization and compensation techniques are used.
3. Which of the following has a negative temperature coefficient of resistance?
a) Thtermistor
b) capacitor
c) sensistor
d) diode
View Answer
Explanation: The Thermistor decreases exponentially with respect to T. The Thermistor RT is used to minimize the increase in collector current. Thus it has a negative temperature coefficient.
4. Which process plays a crucial role in devising the independency of operating point over the variations in temperature or transistor parameters?
a) Bias stabilization
b) Bias compensation
c) Bias stabilization & compensation
d) NO process
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Explanation: Bias stabilization is a process which makes the operating (Q) point independent of change in temperature or any change in transistor parameters.
As Q-point exhibits its independent nature over the numerous variations, it plays a significant role in providing the stability to greater level especially for self-bias, fixed-bias and collector to base bias circuits.
Since the stability factor of circuit gets affected due to several variations, bias stabilization has a provision of maintaining the Q-point condition irrespective of the changes in temperature or transistor parameters and thereby ensuring the confined level of bias stability to circuits.
5. On which factor/s do/does the values of thermal resistance depend?
a) Size of transistor
b) Type of cooling system
c) Transistor size & cooling system type
d) Number of holes
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Explanation: The value of thermal resistance usually depends on the size of transistor, type of heat transfer mechanism and the type of cooling systems (natural cooling, forced air cooling, etc). It also depends on the thermal connectivity of device to a heat sink or metal chassis. Thermal resistance of a power transistor is always less than that of logic level transistor. The value of thermal resistance should be essentially small so as to allow the smooth flow of heat from the junction of the power transistor to the surrounding.
6. Which among the below mentioned parameters of transistors is/are likely to get affected or exhibit/s variations due to an increase in temperature?
a) Base-to-Emitter voltage (VBE)
b) Current Gain (βdc)
c) Base-to-Emitter voltage & Current Gain
d) Forward resistance
View Answer
Explanation: In a transistor, the junction temperature mainly depends on the quantity of current passing through it. As the temperature increases, various parameters of transistors exhibit variations. These parameters include; base-to-emitter voltage (VBE), current gain (βdc) & reverse saturation current (IICBO).
Due to an increase in temperature, base-to-emitter voltage (VBE) decreases and eventually tends to change the Q-point. Since the current gain is a function of collector current (Ic), variation in current gain also ultimately varies collector current.
7. Generally, the resistance of the thermistor decreases _______
a) Exponentially with an increase in temperature
b) Linearly with an increase in temperature
c) Linearly with the decrease in temperature
d) Exponentially with the decrease in temperature
View Answer
Explanation: Thermistor is widely applicable for several compensation techniques. It exhibits variation in its resistance with respect to change in temperature. As the resistance of the thermistor decreases with an increase in temperature, this property of thermistor is also regarded as negative temperature coefficient of resistivity.
8. What is /are the purpose/s of adopting stabilization and compensation techniques?
a) To provide maximum bias
b) To provide thermal stabilization
c) To provide maximum bias & thermal stabilization
d) To provide minimum bias
View Answer
Explanation: In some of the negative feedback circuits, the amplification level of AC signals gets ablated rapidly. Since it becomes complicated for the circuits to abide the loss of signals, it is essential to condense the drift in an operating point by means of compensation and stabilization. Compensation techniques comprise diode compensation, bias compensation using thermistor, sensistor & so on. They play a major role in given that maximum bias in addition to the thermal stabilization to the circuits.
9. Thermistors provide precise temperature measurements.
a) True
b) False
View Answer
Explanation: Thermistors can be used for precise temperature measurements. It controls the temperature and the compensation due to a large variation in resistance with temperature.
10. A Thermistor has low resistance.
a) True
b) False
View Answer
Explanation: Thermistors generally have an extremely high value of resistance. Cables with a shield are required for usage to minimize the interference.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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