This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Emitter Feedback Bias”.
1. 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 gain
Explanation: 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.
2. For an emitter feedback bias circuit, the value of VCC = 10V, RB = 10Kohm, RE=1Kohm and RC=2Kohm, if current flowing through collector is 0.5mA, what is the voltage difference between collector and emitter?
Explanation: VCC = Vce + IC RC + IE RE
Vce = VCC – IC RC – IE RE
Vce = 10-0.5-1
Vce = 8.5V.
3. For an emitter feedback bias circuit, RC is 10Kohm, Re= 5Kohm, RB = 1Kohm, If IC = 1mA, current gain is
Explanation: For emitter feedback bias circuit, current gain=RC/RE
There will be a change in phase of 180 degrees, current gain=10Kohm/5Kohm=2
Hence while designing an amplifier circuit depending on the gain value, the resistors RC and Re can be selected.
4. The feedback helps to maintain a constant gain value.
Explanation: From the equation IE = IC + IB, once the IE increases, the base current will reduce because of emitter feedback, resulting in a constant gain. In emitter feedback circuits, the resistance RE is used to provide negative feedback which is given to the base to maintain a constant gain.
5. 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 gain
Explanation: 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.
6. 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.
Explanation: VCC=Vce+IC RC + IE RE
7. 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 impedance
Explanation: 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.
8. Among the following statements which one is true according to feedback bias?
a) Fixed bias is more stable than emitter feedback bias
b) Fixed bias produces more feedback than emitter feedback bias
c) Emitter feedback bias is more stable than the fixed bias
d) Fixed and emitter bias have same stability and feedback
Explanation: Since S is having a linear relationship with beta in fixed bias, it is less stable, but in emitter feedback bias, S is not exactly linear with a beta. In fixed bias, even a small change in ICo changes the IC value very much, but due to negative feedback in emitter bias, ICo does not change the IC value maintaining its stability.
9. In order to make an amplifier which of the following biasing technique is used more?
a) Fixed bias
b) Self bias
c) Collector to base bias
d) Emitter feedback bias
Explanation: Since emitter feedback bias circuit, the output swing is very much stable and the design shows more stability to changes in temperature. Voltage divider circuit is the most used among all of the biasing technique because of its gain stability and impedance parameters.
10. 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 doubles
Explanation: 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.
Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.
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