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Derive
an expression for the closed-loop voltage gain of a non-inverting amplifier
which uses an op amp with input resistor Rin and feedback resistor
Rf, stating the assumptions in your derivation. |
6
marks |
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Assumptions: |
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The input resistance of the op amp is very large. So, current does not
flow into it.
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The op amp is not saturated. So, the differential input p.d. is almost
zero.
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Consider Rin |
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Consider Rf |
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Combining (1), (3) and (4), we have |
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| b. |
Discuss,
with a suitable graph, how the output voltage varies with the input voltage
for a non-inverting amplifier. |
2
marks |
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1 |
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Suppose the saturated output voltage of the
circuit is ±6V and the gain is 5. When the input voltage is small,
the output voltage varies linearly with the input. But when the input is
too large, the op amp saturates. |
1 |
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| c. |
Sketch
a diagram for a voltage follower. Explain the key feature of a voltage
follower used in measuring the voltage of a charged capacitor. |
3
marks |
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Voltage follower used in measuring the voltage of a charged
capacitor |
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Key features |
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very high input resistance, so the charge on the capacitor is not affected.
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output voltage is exactly equal to the input voltage. No conversion is
necessary.
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| d. |
Design
a circuit using an op amp in open-loop configuration that automatically
switches on or off a highway lamp according to light intensity. |
5
marks |
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5 |
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