Question 6
Figure 2 is the block diagram of an open loop control system to be converted to a closed loop control system.
(a)Re-draw Figure 2 to show the corresponding closed loop control system
Figure 2
(b)State:
(i)two advantages of negative feedback;
(ii)two application of negative feedback.
OBSERVATION
Majority of the candidates that responded to this question did not terminate the feedback signal at the comparator, and lost some marks as consequence. Most of them responded correctly to the other part of the question.
The expected answers were:
(a)Diagram of the corresponding closed loop system
Diagram showing:
- arrow from the feedback network to the input
- arrow from the output to the feedback network
- the feedback Network
(b)(i)Advantages of negative feedback
- better stability
- less distortion
- improved frequency response
- increased input resistance
- decreased output resistance
- increased bandwidth
(ii) Applications of negative feedback
- Amplifiers e.g. OP-amp
- Regulated Power Supply
- Large bandwidth amplifiers
- Improved laboratory oscillators