Question 1
AIM: To investigate the characteristics of a diode-logic circuit.
- Connect the circuit diagram as shown in Figure 1.
- Ask the Supervisor to check the circuit connection.
- You are provided with Table 2.
Table 2
VS (V) |
VD (V) |
ID (mA) |
0.0 |
|
|
0.5 |
|
|
0.8 |
|
|
1.0 |
|
|
2.0 |
|
|
5.0 |
|
|
8.0 |
|
|
10.0 |
|
|
- Switch on the power supply unit.
- Set the input d.c. of the power supply unit to 0 V.
- Read and record the ammeter and voltmeter readings in Table 2.
- Set the input d.c. of the power supply unit to 4 V.
- Read and record the ammeter and voltmeter readings.
- Repeat steps (g) and (h) for the other corresponding values of VS in Table 2.
- Switch off the power supply unit.
- Plot a graph of current I (mA) on the vertical axis against voltage VD (V) on the horizontal axis.
NOTE: For reverse biased, the graph is in the region between the negative horizontal axis and negative vertical axis.
- From the graph, determine the breakdown voltage of the diode.
Observation
The expected responses were:
Table 2
VS (V) |
VD (V) |
ID (mA) |
0.0 |
0.0 |
0.0 |
0.5 |
3.0 - 4.0 |
0.0 |
0.8 |
4.0 - 5.0 |
0.0 |
1.0 |
4.5 - 5.2 |
0.0 |
2.0 |
4.5 - 5.5 |
0.0 |
5.0 |
4.5 – 5.8 |
0.0 – 2.0 |
8.0 |
4.5 – 6.5 |
1.5 – 5.0 |
10.0 |
4.5 – 6.5 |
6.0 – 12.0 |
(k) A non-linear curve from origin (0, 0) in the negative space.
(l) Breakdown voltage of 5.5 – 6.5 V
Both experiments required candidates to connect the circuits as shown in Figures 1 and 2, vary the inputs VS (V) as instructed and record output VD (V) and ID (mA). The Chief Examiner reported that majority of the candidates were able to vary the inputs combinations as expected and record the necessary outputs as required. It was however noted that a good number of these candidates could neither plot the graphs as appropriate nor make reasonable deductions from their graphs.
.