96 + Interview Questions in Transistor Biasing And Thermal Stabilization in Electronic Devices & Circuits Page 1 InterviewSolution

1.	The total thermal resistance of a power transistor and heat sink is 20°C/W. The ambient temperature is 25°C and (TJ)MAX=200°C. If VCE=4V, find the maximum collector current that the transistor can carry without destruction.(a) 3.67A(b) 7.56A(c) 2.19A(d) 4.16AI have been asked this question by my college professor while I was bunking the class.Asked question is from Thermal Stability in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The CORRECT OPTION is (C) 2.19A The EXPLANATION: PD =(TJ-TA)/ H =200-25/20=8.75W. Now, VCEIC= 8.75/4=2.19A.

Discussion

2.	Thermal runaway is_________(a) an uncontrolled positive feedback(b) a controlled positive feedback(c) an uncontrolled negative feedback(d) a controlled negative feedbackI had been asked this question in an interview for job.My doubt stems from Thermal Runaway topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct option is (a) an uncontrolled POSITIVE feedback To elaborate: Thermal runaway is a SELF destruction process in which an increase in temperature creates such a CONDITION which in turn increases the temperature again. This uncontrolled RISE in temperature causes the component to get damaged.

Discussion

3.	What is the Thevenin’s resistance (RTH) in a self bias shown below?(a) R1R2/R1+R2(b) R2/R1+R2(c) R1R2/R1-R2(d) R1/R1-R2This question was posed to me in an online interview.Query is from Self-Bias in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct option is (a) R1R2/R1+R2 For explanation I would say: The base current cannot be obtained directly from the KVL or KCL applications. A potential DIVIDER NETWORK is FORMED by R1 and R2.The VCC and VBE cannot come under a single equation. So, the circuit is changed with a THEVENIN’s resistance.

Discussion

4.	The base current for a BJT remains constant at 5mA, the collector current changes from 0.2mA to 0.3 mA and beta was changed from 100 to 110, then calculate the value of S.(a) 0.01m(b) 1m(c) 100m(d) 25mI got this question in unit test.My query is from Bias Stability topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct OPTION is (a) 0.01m To explain: Since the current in the above CASE, remains constant, THEREFORE STABILITY factor is 0.01 as it is DEFINED as the ratio of change in collector current to change in beta. S=change in collector current/change in beta=0.1mA/10=0.01m.

Discussion

5.	For a fixed bias circuit having RC=2Kohm and VCC=60V, IB=0.25mA and S=101, find Vce.(a) 12V(b) 10V(c) 5V(d) 2.5VThe question was posed to me in a job interview.The origin of the question is Bias Stability topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct CHOICE is (B) 10V To EXPLAIN: S = 1 + beta, => 100 = IC/IB => Ic = 25mA Vce = VCC – Ic RC Vce = 10V.

Discussion

6.	For a Voltage divider circuit having RC=R1=R2=RE=1KΩ, if VCC=20V, find IC when Vce = VCC?(a) 1mA(b) 2mA(c) 20mA(d) 0I had been asked this question in my homework.This is a very interesting question from The Operating Point topic in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» RIGHT ANSWER is (d) 0 The BEST I can EXPLAIN: when Vce = VCC, VCC = Vce-IC (RC+RE) => VCC-Vce = 0 = IC.

Discussion

7.	For a Fixed bias circuit having RC=2.2KΩ, RB=240Ω, VCC=12v and current amplification factor is 100 and the current flowing through the base is 20µA, the value if Collector current in saturation is_____________(a) 5.4mA(b) 3mA(c) 1mA(d) 0AThe question was posed to me in semester exam.This interesting question is from The Operating Point in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The CORRECT choice is (a) 5.4mA The EXPLANATION: VCE = VCC – IC RC For SATURATION, Vce = 0ICsat = VCC/RC = 5.4mA.

Discussion

8.	The thermal runway is avoided in a collector to base bias because_________(a) of its independence on β(b) of the positive feedback produced by the base resistor(c) of the negative feedback produced by the base resistor(d) of its dependence on βI got this question in exam.I would like to ask this question from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right choice is (c) of the negative feedback produced by the base resistor Easy explanation: The self destruction of a transistor due to increase temperature is called thermal run AWAY. It is AVOIDED by the negative feedback produced by the base resistor in a collector to base BIAS. The IC which is responsible for the DAMAGE is reduced by decreased output SIGNAL.

Discussion

9.	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 temperatureI got this question in final exam.My query is from Thermistor and Sensistor Compensation topic in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (a) Exponentially with an increase in TEMPERATURE Best 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.

Discussion

10.	The compensation technique uses __________(a) transformers(b) inductors(c) diodes(d) capacitorsThis question was addressed to me in a national level competition.The above asked question is from Thermistor and Sensistor Compensation in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The CORRECT option is (c) DIODES Best 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.

Discussion

11.	What is the function of a bias circuit?(a) To simplify the circuit(b) To provide a non – linear output(c) To optimize the power(d) To provide steady current or voltageI had been asked this question by my college director while I was bunking the class.My question is from Stabilization against Variations in VBE and Beta for Self Bias Circuit topic in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (d) To provide steady current or voltage The best I can EXPLAIN: The Q – point of a device is the direct current or voltage of a device when no INPUT is applied. The BIAS circuit is a part of the device with provides the steady current or voltage. It is DESIGNED by determining the necessary voltage and current LEVELS across each resistor.

Discussion

12.	The stability factor for a self biased transistor is_________(a) 1 – RTH/RE(b) 1 + RTH/RE(c) 1 + RE/RTH(d) 1 – RE/RTHThis question was addressed to me in homework.I need to ask this question from Self-Bias in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» CORRECT option is (b) 1 + RTH/RE To elaborate: The stability of the CIRCUIT is inversely PROPORTIONAL to the stability FACTOR. The emitter resistor is very large when compared to the Thevenin’s resistance. When β is not that large, then S=(1+ β)( RTH+ RE)/ (1+ β)RE+ RTH.

Discussion

13.	The collector current (IC) that is obtained in a collector to base biased transistor is_________(a) (VCC-VBE)/RB(b) (VCC+VBE)/RB(c) (VCE-VBE)/RB(d) (VCE+VBE)/RBThis question was posed to me in homework.The query is from Collector-to-Base Bias topic in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct CHOICE is (a) (VCC-VBE)/RB To explain: The collector current is analysed by the DC ANALYSIS of a TRANSISTOR. It involves the DC equivalent circuit of a transistor. The BASE current is first found and the collector current is OBTAINED from the relation, IC=IBβ.

Discussion

14.	What is the value of Stability factor for an ideal transistor?(a) 100(b) 1000(c) infinite(d) 0I had been asked this question in my homework.My question is from Bias Stability in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right choice is (d) 0 Best EXPLANATION: For a transistor, the IDEAL value of S is 0 which interprets that for a change in beta, there should not be changing. In Ideal transistor, the COLLECTOR current will vary only if either BASE or emitter current VARIES or hence for an ideal transistor the value of S is zero.

Discussion

15.	A silicon power transistor is operated with a heat sink HS-A=1.5°C/W. The transistor rated at 150W (25°C) has HJ-C=0.5°C/W and the mounting insulation has HC-S=0.6°C/W. What maximum power can be dissipated if the ambient temperature is 40°C and (TJ)MAX=200°C?(a) 70.6W(b) 61.5W(c) 37.8W(d) 56.9WThis question was posed to me during an online exam.My doubt is from Thermal Stability topic in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The CORRECT OPTION is (B) 61.5W For EXPLANATION: PD=(TJ-TA)/ HJ-C +HC-S +HS-A =200-40/0.5+0.6+1.5=61.5W.

Discussion

16.	When the power dissipation increases in a transistor, the thermal resistance_________(a) increases(b) cannot be predicted(c) decreases(d) remains sameI got this question in a national level competition.My enquiry is from Thermal Runaway topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct option is (c) decreases The BEST explanation: The power dissipation is directly PROPORTIONAL to thermal RESISTANCE. We have, TJ – TA = θPd in which we can observe θ ∝ 1/Pd. So, a device with LOW power dissipation has high thermal resistance.

Discussion

17.	The collector to emitter voltage (VCE) is obtained by_________(a) VCC – RCIC+RBIB(b) VCC – RCIC-REIE(c) VCC + RCIC(d) VCC + RCIBI have been asked this question in my homework.This question is from Self-Bias in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» RIGHT choice is (b) VCC – RCIC-REIE Best explanation: The collector to emitter voltage is obtained in order to find the operating POINT of a transistor. It is taken when there is no signal applied to the transistor. The point THUS obtained lies in the cut off region when the transistor is used as a switch.

Discussion

18.	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+βICOThis question was addressed to me during an interview.My query is from Bias Compensation in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (a) βI+βIO+βICO To EXPLAIN I would say: 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.

Discussion

19.	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 resistanceI had been asked this question during an internship interview.My question is taken from Thermistor and Sensistor Compensation topic in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct choice is (c) Base-to-Emitter voltage & Current Gain 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.

Discussion

20.	Why is collector emitter feedback better for linear circuits?(a) Independent of β(b) Dependent on β(c) Highly predictable(d) Not stableI got this question during an interview.The doubt is from Collector-Emitter Feedback Bias in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right option is (b) Dependent on β For explanation: Collector emitter FEEDBACK is better for LINEAR circuits as COMPARED to SELF – bias circuits as it is dependent on β. VOLTAGE divider bias circuits are highly predictable whereas self – bias circuits are independent of β. Therefore, for a collector emitter feedback bias linear circuits are preferred.

Discussion

21.	Which of the following statement is the main disadvantage of emitter feedback bias?(a) Reduces the gain(b) Positive feedback(c) Design is difficult(d) High output impedanceThe question was asked in semester exam.My question is based upon Emitter Feedback Bias topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct option is (a) Reduces the gain To explain: Due to the negative feedback, the voltage gain will reduce drastically compared to other biasing TECHNIQUES. Hence there will be a huge amount of power LOSS in the FORM of heat dissipated ACROSS emitter and COLLECTOR. Setting Q- Point is also difficult for emitter feedback circuit.

Discussion

22.	Comparing fixed and collector to base bias which of the following statement is true?(a) Fixed bias is more stable(b) Collector to base bias is more stable(c) Both are the same in terms of stability(d) Depends on the designI have been asked this question during an interview for a job.Question is from Bias Stability in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right CHOICE is (b) Collector to base bias is more STABLE The BEST I can explain: For fixed bias circuit, S = 1+BETA, more the beta, lesser the stability For collector to base bias S = (1+beta)/(1+beta(RC/RC+RB)) Hence collector to base bias is more stable.

Discussion

23.	What will be the temperature changes effects on the emitter feedback circuit?(a) Increases voltage gain(b) Increases current gain(c) Does not affect the gain(d) Decreases both current and voltage gainI had been asked this question in my homework.I want to ask this question from Emitter Feedback Bias in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct option is (c) Does not affect the gain For explanation I would SAY: Since the temperature changes IE value, these results in the increase of FEEDBACK through R_E, which in TURN reduces IB, resulting in constant gain, even though temperature EFFECTS beta and other transistor parameters, due to the feedback these effects are neutralized.

Discussion

24.	The condition to be satisfied to prevent thermal runaway?(a) ∂PC/∂TJ > 1/Q(b) ∂PC/∂TJ < 1/Q(c) ∂PC/∂TJ > 1/Q(d) ∂PC/∂TJ < 1/QThe question was posed to me in unit test.My question is taken from Thermal Stability topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» RIGHT answer is (b) ∂PC/∂TJ < 1/Q Easy explanation: PC is the power DISSIPATED at the collector junction. TJ is junction TEMPERATURE which varies. The difference between these temperatures is directly PROPORTIONAL to the power dissipation. Here, Q is called as thermal resistance which is proportionality CONSTANT.

Discussion

25.	Which of the following are true?(a) TJ – TA = θPd(b) TJ – TA = θ/Pd(c) TJ – TA = θ+Pd(d) TJ – TA = θ-PdI got this question during an interview.This intriguing question comes from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct ANSWER is (a) TJ – TA = θPd Easy explanation: The TJ is called as junction temperature which varies and TA is called as the AMBIENT temperature which is fixed. The DIFFERENCE between these temperatures is directly proportional to the power DISSIPATION. Here, θ is called as thermal resistance which is proportionality constant.

Discussion

26.	How does emitter resistor RE provides stability?(a) Consumes less power(b) Has an easier circuit design(c) Automatically biases the circuit(d) It does not provide stabilityThis question was posed to me in unit test.This is a very interesting question from Collector-Emitter Feedback Bias topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (c) Automatically BIASES the circuit Best explanation: In a COLLECTOR emitter feedback, the emitter resistor PROVIDES stability by automatically biasing the circuit using negative feedback. The negative feedback negates any change due to the collector CURRENT with an opposing change PROVIDED by the base bias voltage and thus helps maintain circuit stability.

Discussion

27.	Changes in the temperature will not affect the bias point.(a) True(b) FalseThis question was posed to me in an interview.My question is based upon The Operating Point in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct answer is (B) False Easiest explanation: The temperature changes the β value of the Transistor which wills in turn shifts the Q-point of the Transistor. Once the temperature changes, it will increase the mobility of ELECTRONS resulting in a CHANGE of system current, HENCE temperature does affect the transistor parameter.

Discussion

28.	The bias point of a transistor occurs when the supply voltage exceeds the breakdown voltage of a transistor.(a) True(b) FalseThis question was posed to me in class test.The above asked question is from The Operating Point in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct choice is (b) False For explanation I would say: Bias point can be set on the basis of DC load line that is Q point can be found out only WITHOUT APPLYING any INPUT. The DC load line is defined as the line drawn in response of collector current and base EMITTER VOLTAGE when no input is applied.

Discussion

29.	Which of the following biasing techniques are affected by thermal runaway?(a) self bias(b) collector to base bias(c) fixed bias(d) the biasing technique is identified by temperature effectThis question was posed to me in class test.The doubt is from Thermal Stability topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct option is (c) fixed bias Easy explanation: The collector current of a fixed bias TRANSISTOR is IC= β(VCC-VBE)/RB. When the TEMPERATURE is increased, the REVERSE saturation increases. The collector current ALSO increases. This in turn increases the current again which LEADS to damage of transistor.

Discussion

30.	Discrete transistors T1 and T2 having maximum collector current rating of 0.75A are connected in parallel as shown in the figure. This combination is treated as a single transistor to carry a single current of 1A, when biased with a self bias circuit. When the circuit is switched ON, T1 had draws 0.55A and T2 draws 0.45A. If the supply is kept ON continuously, it is very likely that_________(a) both T1 and T2 get damaged(b) both T1 and T2 will be safe(c) only T1 gets damaged(d) only T2 gets damagedThis question was addressed to me in an international level competition.My query is from Thermal Runaway topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (C) only T1 gets damaged The explanation: The T1 transistor is having more power dissipation as it is drawing 0.55A. When power dissipation increases, the TEMPERATURE increases and this leads to the ULTIMATE further increase in the CURRENT drawn by T1. The current drawn by T2 will be reduced as the sum of currents drawn by T1 and T2 should be constant.

Discussion

31.	When the temperature is increased, what happens to the collector current after a feedback is given?(a) it remains same(b) it increases(c) it cannot be predicted(d) it decreasesThis question was posed to me in an online interview.This key question is from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The CORRECT ANSWER is (d) it decreases Explanation: Before the feedback is applied, when the temperature is increased, the REVERSE saturation increases. The collector current also increases. When the feedback is applied, the BASE current increases with decreasing collector current and the THERMAL runway too.

Discussion

32.	Where does degeneration take place in a self – bias circuit?(a) Across RB(b) Across RE(c) No degeneration occurs(d) Across RCThe question was asked during an interview.The origin of the question is Stabilization against Variations in VBE and Beta for Self Bias Circuit in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct option is (b) Across RE The best I can explain: Degeneration or negative feedback occurs across RE which in turn stabilizes the FLUCTUATIONS of CURRENT IE due to temperature changes and variations in VBE and β.

Discussion

33.	What will happen if a capacitor is connected in parallel with RE in the amplifier design which uses emitter feedback bias circuit?(a) No changes(b) Gain value increases(c) Feedback increases(d) Gain value remains the same but feedback doublesThis question was posed to me at a job interview.I'm obligated to ask this question of Emitter Feedback Bias in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right answer is (b) Gain value increases To EXPLAIN I would say: Since the capacitor acts as a SHORT circuit during high frequency, there will be no feedback and HENCE gain increases. All of the current will flow to GROUND through a capacitor which acts as a short circuit.

Discussion

34.	Which of the following is true?(a) HC-A = HJ-C – HJ-A(b) HC-A = HJ-C + HJ-A(c) HJ-A = HJ-C – HC-A(d) HJ-A = HJ-C + HC-AI got this question by my college professor while I was bunking the class.This question is from Thermal Stability topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (d) HJ-A = HJ-C + HC-A For EXPLANATION I would say: HJ-C is THERMAL resistance between JUNCTION and CASE and HC-A is thermal resistance between case and ambient. The circuit DESIGNER has no control over HJ-C. So, a proper approach to dissipate heat from case to ambient is through heat sink.

Discussion

35.	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 biasI have been asked this question in quiz.The origin of the question is Thermistor and Sensistor Compensation topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct choice is (c) To provide maximum bias & thermal stabilization Easiest 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.

Discussion

36.	What is the compensation element used for variation in VBE and ICO?(a) diodes(b) capacitors(c) resistors(d) transformersThis question was addressed to me in an interview.This interesting question is from Bias Compensation in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (a) diodes For explanation I would SAY: 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.

Discussion

37.	What is the stability factor if RE = 8kΩ and RTH = 11kΩ?(a) 1.335(b) 2.375(c) 1.727(d) 0.272I got this question in an international level competition.This intriguing question originated from Stabilization against Variations in VBE and Beta for Self Bias Circuit in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right option is (b) 2.375 Explanation: STABILITY FACTOR is calculated by the following equation. On plugging in the GIVEN VALUES RE = 8kΩ and RTH = 11kΩ, we GET: S = 1 + RTH / RE S = 1 + 11 / 8 = 2.375.

Discussion

38.	Why do we need collector emitter feedback bias?(a) To provide a non – linear output(b) To maintain transistor in active region(c) To maintain transistor in saturation region(d) To maintain transistor in cut – off regionI had been asked this question in an online quiz.This intriguing question originated from Collector-Emitter Feedback Bias topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer»

Discussion

39.	For a Voltage divider bias circuit, having R1=R2=10KΩ, RC=4.7 KΩ, RE=1 KΩ, What is the value of collector current at saturation if VCC=10V?(a) 1A(b) 10mA(c) 0.87mA(d) 1maI have been asked this question by my school principal while I was bunking the class.This interesting question is from The Operating Point in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct option is (b) 10mA The best I can EXPLAIN: By USING THEVENIN’s lawVth=VccR2/(R1+R2)=10V ICsat=VCC/(RC+RE)=0.87mA.

Discussion

40.	When the temperature is increased, what happens to the collector current after a feedback is given?(a) it remains same(b) it increases(c) it cannot be predicted(d) it decreasesI have been asked this question by my college director while I was bunking the class.I would like to ask this question from Thermal Runaway topic in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right answer is (d) it decreases To EXPLAIN I WOULD say: Before the feedback is applied, when the temperature is increased, the reverse saturation increases. The collector current also increases. When the feedback is applied, the DROP across the EMITTER RESISTOR increases with decreasing collector current and the thermal runway too.

Discussion

41.	In the circuit, transistor has β =60, VBE=0.7V. Find the collector to emitter voltage drop VCE.(a) 5V(b) 3V(c) 8V(d) 6VThis question was posed to me during an online interview.The origin of the question is Collector-to-Base Bias in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right choice is (d) 6V For explanation: We KNOW, IC=(VCC-VBE)/RB By PUTTING the VALUES, we have IC=5.9mA. IE=IC/α. So, IE=5.99mA. VCE= VCC-RC(IC+IB). We have VCE=6V.

Discussion

42.	What is Stability factor?(a) Ratio of change in collector current to change in a current amplification factor(b) Ratio of change in collector current to change in base current(c) Current amplification factor(d) Ratio of base current to collector currentI have been asked this question during an online exam.This interesting question is from Bias Stability topic in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct ANSWER is (a) Ratio of change in collector current to change in a current AMPLIFICATION factor To EXPLAIN I would say: Stability factor is defined as the rate at which collector current CHANGES when Base to emitter VOLTAGE changes, keeping base current constant. It can also be defined as the ratio of change in collector current to change in base current when temperature changes occur.

Discussion

43.	Which type of temperature dependent resistor exhibits a positive temperature coefficient of resistivity?(a) Thermistor(b) Sensistor(c) Varistor(d) PhotoresistorI have been asked this question in an international level competition.Asked question is from Thermistor and Sensistor Compensation in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct option is (b) Sensistor The best 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.

Discussion

44.	What is the Thevenin’s voltage (VTH) in a self bias shown below?(a) VCCR2/R1+R2(b) VCCR1/R1+R2(c) VCCR2/R1-R2(d) VCCR2/R1-R2This question was posed to me in an internship interview.This intriguing question comes from Self-Bias in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct OPTION is (a) VCCR2/R1+R2 For explanation: The BASE current cannot be obtained directly from the KVL or KCL applications. The VCC and VBE cannot come under a single equation. So, the circuit is CHANGED with a Thevenin’s voltage (VTH) and Thevenin’s resistance.

Discussion

45.	Which of the following has a negative temperature coefficient of resistance?(a) sensistor(b) diode(c) thermistor(d) capacitorThe question was asked by my college director while I was bunking the class.I would like to ask this question from Bias Compensation in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right choice is (C) thermistor For explanation I WOULD say: 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.

Discussion

46.	Which of the following are true?(a) TJ-TA=θpd(b) TJ-TA=θ/pd(c) TJ-TA=θ+pd(d) TJ-TA=θ-pdThe question was posed to me in unit test.I want to ask this question from Thermal Stability in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Correct choice is (a) TJ-TA=θpd To elaborate: The TJ¬ is CALLED as JUNCTION temperature which varies and TA is called as the ambient temperature which is fixed. The difference between these TEMPERATURES is directly proportional to the power dissipation. Here, θ is called as thermal resistance which is proportionality constant.

Discussion

47.	Which of the following biasing techniques are prone to thermal runaway?(a) self bias(b) collector to base bias(c) fixed bias(d) the biasing technique is identified by temperature effectI had been asked this question in final exam.My question is from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right choice is (c) fixed BIAS Explanation: The collector current of a fixed bias transistor is IC= β(VCC-VBE)/RB. When the temperature is increased, the reverse saturation increases. The collector current ALSO increases. This in turn increases the current again which leads to damage of transistor.

Discussion

48.	For emitter feedback bias, to make IC independent of DC current gain, which of the following condition is required?(a) RC >> RB/dc current gain(b) RE >> RB/dc current gain(c) RB >> RC/dc current gain(d) Re >> RC/dc current gainThis question was posed to me in a job interview.This interesting question is from Emitter Feedback Bias in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» The correct answer is (a) RC >> RB/dc current GAIN To explain I would say: In ORDER to make the IC stable, the dc current gain has to be maintained in a proper CONSTANT value, and the Re value must be very much greater than (RB/ current gain). SINCE the value of RC becomes very high, this RESULTS in IC independent of beta.

Discussion

49.	How do you calculate the value of VCE ?(a) VCE = VCC + VC (RC + RE)(b) VCE = VCC – VC (RC + RE)(c) VCE = VCC – VC (RB + RE)(d) VCE = VCC + VC (RB + RE)The question was posed to me during an interview.This intriguing question originated from Collector-Emitter Feedback Bias topic in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» Right ANSWER is (b) VCE = VCC – VC (RC + RE) To elaborate: The VALUE of VCE can be calculated using this equation: VCE = VCC – VC (RC + RE) . It is the voltage between the collector and emitter terminal of the TRANSISTOR and is MEASURED as the output of the transistor.

Discussion

50.	For an emitter feedback bias Circuit having, RE=1Kohm, RC= 4.7Kohm, IB=0.005mA, IE = 1mA, VCC = 12V and Vce = 5V. Find the value of beta.(a) 254(b) 100(c) 1000(d) 500I have been asked this question in an interview.I'd like to ask this question from Emitter Feedback Bias in portion Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits
Answer» RIGHT CHOICE is (a) 254 Easy EXPLANATION: VCC=Vce+IC RC + IE RE IC=1.27mA Beta=1.27/0.005=254.

Discussion

Explore topic-wise InterviewSolutions in .

What is the Thevenin’s resistance (RTH) in a self bias shown below?(a) R1R2/R1+R2(b) R2/R1+R2(c) R1R2/R1-R2(d) R1/R1-R2This question was posed to me in an online interview.Query is from Self-Bias in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

For a fixed bias circuit having RC=2Kohm and VCC=60V, IB=0.25mA and S=101, find Vce.(a) 12V(b) 10V(c) 5V(d) 2.5VThe question was posed to me in a job interview.The origin of the question is Bias Stability topic in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

The stability factor for a self biased transistor is_________(a) 1 – RTH/RE(b) 1 + RTH/RE(c) 1 + RE/RTH(d) 1 – RE/RTHThis question was addressed to me in homework.I need to ask this question from Self-Bias in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

What is the value of Stability factor for an ideal transistor?(a) 100(b) 1000(c) infinite(d) 0I had been asked this question in my homework.My question is from Bias Stability in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

The collector to emitter voltage (VCE) is obtained by_________(a) VCC – RCIC+RBIB(b) VCC – RCIC-REIE(c) VCC + RCIC(d) VCC + RCIBI have been asked this question in my homework.This question is from Self-Bias in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Which of the following are true?(a) TJ – TA = θPd(b) TJ – TA = θ/Pd(c) TJ – TA = θ+Pd(d) TJ – TA = θ-PdI got this question during an interview.This intriguing question comes from Thermal Runaway in chapter Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Changes in the temperature will not affect the bias point.(a) True(b) FalseThis question was posed to me in an interview.My question is based upon The Operating Point in section Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits

Which of the following are true?(a) TJ-TA=θpd(b) TJ-TA=θ/pd(c) TJ-TA=θ+pd(d) TJ-TA=θ-pdThe question was posed to me in unit test.I want to ask this question from Thermal Stability in division Transistor Biasing and Thermal Stabilization of Electronic Devices & Circuits