This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Collector-Emitter Feedback Bias”.
1. 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 region
View Answer
Explanation: We use a collector emitter feedback to collect negative feedback and to maintain the transistor in an active region. To maintain stability in active region, the DC base biased voltage is resultant from the collector voltage VC.
2. What is the function of RE in the collector emitter feedback circuit?
a) To improve stability and decrease positive feedback
b) To improve stability and increase positive feedback
c) To improve stability and decrease negative feedback
d) To improve stability and increase negative feedback
View Answer
Explanation: In a collector feedback circuit, the emitter resistor provides additional stability along with increasing the negative feedback sent to the collector. The addition of the emitter resistance enables the transistor’s emitter to no longer be grounded to zero – volt potential.
3. In the circuit given below, assume VCC = 5V, VBE = 0.7V, RE = 10kΩ, RB = 20kΩ and β = 50. How much is the current IE?
a) 0.561mA
b) 0.335mA
c) 0.413mA
d) 0.513mA
View Answer
Explanation: Given values are VCC = 5V, VBE = 0.7V, RE = 10kΩ, RB = 20kΩ and β = 50.
To find the value of IE, we substitute the values in the below equation.
IE = (VCC – VBE) / (RE + (RB / β) )
IE = (5 – 0.7) / (10 + (20 / 50) )
IE = 4.3 / (10 + 0.4) = 0.413mA.
4. What happens if collector current increases in a collector emitter feedback circuit?
a) Emitter voltage increases therefore base voltage increases
b) Emitter voltage decreases therefore base voltage decreases
c) Emitter voltage increases therefore base voltage decreases
d) Emitter voltage decreases therefore base voltage increases
View Answer
Explanation: If the collector current VC is increased, the corresponding emitter current also increases. Which in turn causes the voltage across RE to increase. This in turn causes a proportional rise in the base voltage since VB = VE + VBE.
5. Why is collector emitter feedback better for linear circuits?
a) Independent of β
b) Dependent on β
c) Highly predictable
d) Not stable
View Answer
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.
6. 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 stability
View Answer
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.
7. In the circuit given below, assume VCC = 12V, VBE = 0.7V, RB = 330kΩ, RC = 3.3kΩ, RE = 2.7kΩ and β = 50. What is the base current IB?
a) 16.432µA
b) 17.856µA
c) 20.542µA
d) 17.936µA
View Answer
Explanation: Given values are VCC = 12V, VBE = 0.7V, RB = 330kΩ, RC = 3.3kΩ, RE = 2.7kΩ and β = 50.
To find the value of IB, we substitute the values in the below equation.
IB = (VCC – VBE) / (RB + β × (RC + RE))
IB = (12 – 0.7 / (330 + 50 × (2.7 + 3.3)) = 11.3 / (330 + 50 × 6) = 11.3 / 630 = 17.936µA.
8. 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)
View Answer
Explanation: 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.
9. How does the negative feedback help a collector emitter feedback circuit?
a) Helps make it more predictable
b) Provides opposing change in base voltage
c) Helps make it more predictable, provides opposing change in base voltage
d) It doesn’t affect
View Answer
Explanation: The negative feedback in a collector emitter feedback circuit provides a negative feedback which in turn helps make the circuit more predictable as it provides opposing change in the base voltage which cancels out any change in the collector current.
10. What are the disadvantages of collector emitter feedback bias circuits?
a) Requires few resistors
b) Provides a lot of stability
c) Provides negative feedback
d) Provides positive feedback
View Answer
Explanation: A collector emitter bias circuit provides negative feedback as well as requires multiples resistors for a small change. The negative feedback limits the frequency range it will work in. Higher frequencies will provide poor performance. It also requires a greater number of resistors just to provide a stability against a small parameter.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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