Radio,Television And Electronic Paper 2, WASSCE (SC), 2022

Question 4

 

Fig. 2 is the circuit diagram of a regulated d.c. power supply unit drawn by an RTV student during a practical session.

 

 

 

 

 

 

 

 

 

 

(a).      State three errors committed by the student in the circuit diagram.

(b).      Using the same components as shown in Fig. 2, sketch a correct circuit diagram with the

expected output waveform.

(c).      From the diagram sketched in 4 (b), state the function of:

    1. D1 and D2;
    2. C2;
    3. DZ;
    4. L.

 

 

Observation

 

The Chief Examiner reported that a large percentage of the few candidates attempted question 4 did not respond well to 4(b).

 

The expected responses were:`

 

(a) Errors committed by the student in the circuit diagram

  • D2 connected in the wrong | reverse direction | polarity
  • C2 connected in the wrong | reverse direction | polarity
  • Dz connected in the wrong | reverse direction | polarity

  (b) Corrected circuit diagram with the expected output waveform
Circuit diagram

 

 

                               Output Waveform

 

 

                                               
(c) Functions of listed components
(i) D1and D2: Rectification | converts a.c. from the transformer to pulsating d.c.
(ii) C2: filtering | removing pulses from the d.c. | smoothening.

  • Dz: regulation | maintaining constant output irrespective of load, RL value.
  • L: filtering | combines with C1 and C2 to filter the ac ripples; it blocks the flow of ac components of current