W008/202
DUBLIN INSTITUTE OF TECHNOLOGY
KEVIN STREET.
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B Eng Tech (Electronics and Communications)
Year 11
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Semester 1 Examinations 2007
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ELECTRONICS 1
MR. A SHANAHAN
DR G FARRELL
Attempt Three Questions
33.3 marks per question
(2)
1
W008/202
Show how an operational amplifier, a resistor and a capacitor may be connected
together to form an integrator.
Show also how the above components may be connected together to form a
differentiator.
[9 marks]
Derive expressions for the output voltages of both circuits.
[9 marks]
If the output of an integrator is +5 V at time t = 0 sketch the variation of output
voltage with time for inputs of
(a) 3 V d.c.
(b) 2.6 V peak-to-peak sinusoid at a frequency of 160 Hz.
Where R = 1 k and C = 1 f.
[15 marks]
2
Give the circuit diagram of a Wien bridge network consisting of two equal value
resistors and two equal value capacitors.
Give clearly labelled gain and phase shift response plots for this network.
[5 marks]
Show how this network can be used as the feedback element in an operational
amplifier based self starting Wien bridge type sinusoidal oscillator.
[8 marks]
Concisely explain the operation of the circuit. Give relevant waveform diagrams to
support your explanation.
[10 marks]
Show that if the two resistors in the Wien bridge feedback network are both equal in
value to R and the two capacitors are both equal in value to C then the frequency of
oscillation is given by
Fosc = 1/2πRC
[10 marks]
3
Prove that the use of negative feedback reduces the gain and increases the bandwidth
of an amplifier by the same factor. Your answer should include a block diagram of an
(3)
W008/202
amplifier with open loop gain AOL in a negative feedback configuration with a
feedback element with gain B.
[13 marks]
An amplifier has the following open loop properties:
An output voltage of 1 V when the input voltage is 1 mV.
An output voltage of 1.25 V rms when the input voltage is 1.25 mV rms at all
frequencies up to approximately 90 Hz.
An output voltage of 0.885 V at a frequency of 100 Hz.
If this amplifier is used in a negative feedback configuration determine the feedback
factor for the closed loop gain to be 20 dB. Determine also the bandwidth of the
closed loop amplifier circuit.
[10 marks]
For the following values of input voltage and frequency determine the output voltage
of the amplifier in both the open loop and closed loop cases
(a) 3 mV rms @100 Hz
(b) 5 mV rms @10 kHz
[10 marks]
4
Explain what is meant by the terms line regulation and load regulation as applied to
power supplies.
[4 marks]
Give an expression for the load regulation of a power supply in terms of the no load
output voltage VNL and the full load output voltage VFL.
[4 marks]
Give clearly labelled graphs showing the variation in output voltage versus load
current for power supplies with
(a) Maximum current overload protection and
(b) Fold back current overload protection.
[8 marks]
Give the Thevenin equivalent circuit of a power supply. Hence derive an expression
for the voltage regulation in terms of the output resistance Ro and the full load RFL .
[12 marks]
A power supply has an output resistance Ro = 1.5 and supplies a full-load current of
500 mA to a 50  load.
(c) What is the percent voltage regulation of the power supply?
(d) What is the no load output of the power supply?
[5 marks]