Question 2
AIM: To investigate how to set the output voltage of LM 317 I.C. voltage regulator.
Figure 2
-
(a)Connect the circuit diagram as shown in Figure 2.
(b)Ask the supervisor to check the circuit connection.
(c)You are provided with Table 2.
Table 2
R2(kΩ) |
Vout (V) |
|
33 Ω |
|
|
47 Ω |
|
|
100 Ω |
|
|
470Ω |
|
|
1kΩ |
|
|
-
(d)Close switch (S).
(e)Set Vin to12 V by adjust the power supply unit.
(f)Read and record in Table 2, the corresponding value of output voltage (Vout ).
(g)Open switch (S).
(h)Replace R2 with 2.2 kΩ resistor.
(i)Repeat steps (e) to (g) for the other values of R2 in Table 2.
(j)Complete Table 2by computing the values of Vx.
(k)From your results in (j), compare the values of Vout and Vx.
(l)State how the output voltage of the LM 317 I.C. voltage regulator circuit is set.
Observation
The expected responses were:
TABLE 2
R2(kΩ) |
Vout (V) |
VX = 1.25[ |
1 |
2.50 |
2.500 |
2.2 |
4.12 |
4.000 |
3.3 |
5.42 |
5.375 |
4.7 |
7.20 |
7.125 |
5.6 |
8.46 |
8.250 |
+ 1]
(k)Comparison:
- The values of VOUT are approximately the same as that of Vx.
- VOUT and Vx increases as R2 increases
(l)Output voltage setting is by varying the value of R2
The chief examiner reported that a few candidates responded well to question 2.