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Elecs- Indiabix (Terms) > Electronic Devices 5- Voltage Reg to Thryristors > Flashcards

Electronic Devices 5- Voltage Reg to Thryristors Flashcards

1
Q

The 7812 regulator IC provides ________.
5 V
–5 V
12 V
–12 V

A

12 V

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2
Q

Voltage regulators keep a constant ________ output voltage when the input or load varies within limits.
dc
ac
ripple

A

dc

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3
Q

In which period is the capacitor filter discharged through the load in a full-wave rectifier?
The time during the positive cycle
The time during which the diodes are not conducting
The time during which the diode(s) is (are) conducting
The time during the negative cycle

A

The time during which the diodes are not conducting

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4
Q

The 7805 regulator IC provides ________.
5 V
–5 V
12 V
–12 V

A

5 V

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5
Q

What is the range of the voltage level of the LM317 adjusted voltage regulator?
0 V to 5 V
1.2 V to 37 V
–5 V to –24 V
5 V to 24 V

A

1.2 V to 37 V

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6
Q

Switching regulator efficiencies can be greater than ________ percent.
60
70
80
90

A

90

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7
Q

The 7912 regulator IC provides ________ .
5 V
–5 V
12 V
–12 V

A

-12V

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8
Q

What is the typical dropout voltage for the 7812 fixed positive voltage regulator?
4 mV
100 mV
1.5 V
2 V

A

2V

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9
Q

What is the ratio of the period of the output voltage to the period of the input voltage in a full-wave rectifier?
0
0.5
1
2

A

0.5

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10
Q

If the value of full-load voltage is the same as the no-load voltage, the voltage regulation calculated is ________ %, which is the best expected.
0
1
99
100

A

0

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11
Q

A switching regulator that is configured as a voltage-inverter produces what type of output?
an ac output with opposite phase to the input ac
a dc output that is the negative of the dc input voltage
an output that is a higher voltage than the input voltage
an ac output from a dc input voltage

A

a dc output that is the negative of the dc input voltage

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12
Q

What is the purpose of an additional RC filter section in a power supply circuit?
Increase the dc voltage component
Increase the ac voltage component
Decrease the ac voltage component
None of the above

A

Decrease the ac voltage component

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13
Q

In which period is the capacitor filter charged in a full-wave rectifier?
The time during the positive cycle
The time during which the diodes are not conducting
The time during which the diode(s) is (are) conducting
The time during the negative cycle

A

The time during which the diode(s) is (are) conducting

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14
Q

The ________ regulator is less efficient than the ________ type, but offers inherent short-circuit protection.
series, shunt
shunt, series

A

shunt, series

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15
Q

In which of the following applications is a pulsating dc voltage suitable?
Battery charger
Radio
Stereo system
Computer

A

Battery charger

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16
Q

In a series regulator, what is the purpose of fold-back limiting?
to provide more current in the case of a short circuit
to limit output voltage if input voltage goes too high
to bypass the pass-transistor, if the pass-transistor should fail
to provide current up to a maximum, but drop current to a lower value when the output becomes shorted, to prevent overheating of the device

A

to provide current up to a maximum, but drop current to a lower value when the output becomes shorted, to prevent overheating of the device

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17
Q

In a simple series regulator circuit, which of the following components is the controlling element?
Load resistor
Zener diode
Transistor Q1
None of the abov

A

Transistor Q1

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18
Q

In an improved shunt regulator, which of the following components sets the reference voltage?
Transistor Q1
Zener diode
Transistor Q2
RS

A

Zener diode

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19
Q

________ regulation can be defined as the percentage change in the output voltage for a given change in load current.
Line
Load

A

Load

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20
Q

How many diodes conduct in the full-wave bridge rectifier while the capacitor is being charged?
1
2
3
4

A

2

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21
Q

How many terminals does a 7800 series IC regulator have?
2
3
4
none of the above

A

3

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22
Q

What are the typical values of Vref and Iadj for the LM317 adjustable voltage regulator?
1.0 V, 100 mA
1.5 V, 100 mA
1.25 V, 100 μA
1.25 V, 10 mA

A

1.25 V, 100 μA

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23
Q

Which component(s) set(s) the voltage across the load in a basic transistor shunt regulator?
Zener diode
Transistor base-emitter voltage
Both the Zener diode and the transistor base-emitter voltage
None of the above

A

Both the Zener diode and the transistor base-emitter voltage

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24
Q

Voltage regulation requires
only line regulation.
only load regulation.
a constant load.
load and line regulation.

A

load and line regulation.

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25
Q

Across which of the following components of a power supply does the average (dc) voltage exist?
Diodes
Secondary of the transformer
Capacitor filter
None of the above

A

Capacitor filter

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26
Q

Switching regulators are more efficient than linear regulators and are particularly useful in ________-voltage, ________-current applications.
high, high
low, high
high, low

A

low, high

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27
Q

For what range of load current can voltage regulators be selected for operation?
Hundreds of picoamperes to tens of nanoamperes
Hundreds of picoamperes to tens of milliamperes
Hundreds of milliamperes to tens of amperes
None of the above

A

Hundreds of milliamperes to tens of amperes

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28
Q

The 7905 regulator IC provides ________.
5 V
–5 V
12 V
–12 V

A

-5V

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29
Q

What type of regulator offers inherent short-circuit protection?
shunt regulators
series regulators
three-terminal regulators
switching regulators

A

shunt regulators

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30
Q

In a shunt linear regulator, the control element is a(n) ________ in parallel with the load.
inductor
capacitor
transistor

A

Transistor

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31
Q

For what range of fixed regulated voltages do the series 78xx regulators provide regulation?
+5 V to +24 V
+5 V to +24 V
–5 V to –24 V
None of the above

A

+5 V to +24 V

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32
Q

In a series linear regulator, the control element is a(n) ________ in series with the load.
inductor
capacitor
transistor

A

transistor

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33
Q

________ regulation can be defined as the percentage change in the output voltage for a given change in the input voltage.
Line
Load

A

Line

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34
Q

A ________ -wave rectified signal has less ripple than a ________ -wave rectified signal and is thus better to apply to a filter.
full, half
half, full

A

full, half

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35
Q

Only the condition betaA = ________ must be satisfied for self-sustained oscillations to result.
0
–1
1
None of the above

A

1

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36
Q

At what phase shift is the magnitude of betaA at its maximum in the Nyquist plot?
90º
180º
270º
0º

A

180º

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37
Q

Which of the following improvements is (are) a result of the negative feedback in a circuit?
Lower output impedance
Reduced noise
More linear operation
All of the above

A

All of the above

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38
Q

The feedback signal in a(n) ________ oscillator is derived from an inductive voltage divider in the LC circuit.
Hartley
Armstrong
Colpitts

A

Hartley

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39
Q

The attenuation of the three-section RC feedback phase-shift oscillator is
1/9.
1/30.
1/3.
1/29.

40
Q

For a phase-shift oscillator, the gain of the amplifier stage must be greater than ________.
19
29
30
1

41
Q

Which of the following is (are) the determining factor(s) of the stability of a feedback amplifier?
A
Phase shift between input and output signals
Both A and the phase shift between input and output signals
None of the above

A

Both A and the phase shift between input and output signals

42
Q

What is the minimum frequency at which a crystal will oscillate?
seventh harmonic
third harmonic
fundamental
second harmonic

A

fundamental

43
Q

The feedback signal in a(n) ________ oscillator is derived from a capacitive voltage divider in the LC circuit.
Hartley
Armstrong
Colpitts

44
Q

Sinusoidal oscillators operate with ________ feedback.
positive
negative

45
Q

Which of the following is required for oscillation?
betaA > 1
The phase shift around the feedback network must be 180º.
Both betaA > 1 and the phase shift around the feedback network must be 180º.
None of the above

A

Both betaA > 1 and the phase shift around the feedback network must be 180º.

46
Q

A circuit that can change the frequency of oscillation with an application of a dc voltage is sometimes called
a voltage-controlled oscillator.
a crystal oscillator.
a Hartley oscillator.
an astable multivibrator.

A

a voltage-controlled oscillator.

47
Q

In order to start up, a feedback oscillator requires
negative feedback less than 1.
positive feedback greater than 1.
unity feedback equal to 1.
no feedback.

A

positive feedback greater than 1.

48
Q

What is the ratio of the input impedance with series feedback to that without feedback?
1 + betaA
betaA
beta
1

49
Q

Which of the following oscillators is (are) tuned oscillators?
Colpitts
Hartley
Crystal
All of the above

A

All of the above

50
Q

What is the ratio of the output impedance with series feedback to that without feedback?
1
1 + betaA
betaA
A

51
Q

One condition for positive feedback is that the phase shift around the feedback loop must be ________°.
0
90
180
45

52
Q

At what phase shift is the magnitude of A at its minimum in the Nyquist plot?
90º
180º
270º
0º

53
Q

What is the total phase shift requirement, around the feedback loop, for a phase-shift oscillator?
90°
180°
270°
360°

54
Q

The lead-lag circuit in the Wien-bridge oscillator has a resonant frequency at which the attenuation is
1/2.
1/4.
1/3.
1/5.

55
Q

The start-up gain of an oscillator must be ________ one.
equal to
less than
greater than

A

greater than

56
Q

In the IC phase-shift oscillator, what should the ratio of feedback resistor Rf to R1 be?
Zero
Greater than –29
Less than 29
Any value

A

greater than -29

57
Q

At series resonance, the impedance of a crystal is
minimum.
maximum.
equal.
zero.

58
Q

For frequencies up to 1 MHz, the ________ is the most widely used type of sinusoidal RC oscillator.
Wien-bridge
phase-shift
twin-T

A

Wien-bridge

59
Q

The twin-T oscillator produces a ________ response.
low-pass
high-pass
band-pass
band-stop

60
Q

What is the typical value of quality factor for crystal oscillators?
20,000
1000
100
10

61
Q

Which of the following improvements is (are) a result of the negative feedback in a circuit?
Higher input impedance
Better stabilized voltage gain
Improved frequency response
All of the above

A

All of the above

62
Q

In the Wien bridge oscillator, which of the following is (are) frequency-determining components?
R1 and R2
C1 and C2
R1, R2, C1, and C2
None of the above

A

R1, R2, C1, and C2

63
Q

A certain oscillator has a tap on the inductor in the tank circuit. This oscillator is probably
a Colpitts oscillator.
a Clapp oscillator.
a crystal oscillator.
a Hartley oscillator.

A

a Hartley oscillator.

64
Q

At parallel resonance, the impedance of a crystal is
minimum.
maximum.
equal.
zero.

65
Q

Which of the following is (are) feedback?
Voltage-series
Voltage-shunt
Current-series
All of the above

A

All of the above

66
Q

What is the relationship between the series and parallel resonant frequencies of a quartz crystal?
They are equal.
Parallel resonant frequency is approximately 1 kHz higher than series resonant frequency.
Series resonant frequency is approximately 1 kHz higher than parallel resonant frequency.
none of the above

A

Parallel resonant frequency is approximately 1 kHz higher than series resonant frequency.

67
Q

An op-amp integrator has a square-wave input. The output should be
a sine wave.
a triangle wave.
a square wave.
pure dc.

A

a triangle wave

68
Q

A ________ filter rejects all frequencies within a specified band and passes all those outside this band.
low-pass
high-pass
band-pass
band-stop

69
Q

Filters with the ________ characteristic are useful when a rapid roll-off is required because it provides a roll-off rate greater than –20/dB/decade/pole.
Butterworth
Chebyshev
Bessel

70
Q

A ________ filter significantly attenuates all frequencies below fc and passes all frequencies above fc.
low-pass
high-pass
band-pass
band-stop

71
Q

The bandwidth in a ________ filter equals the critical frequency.
low-pass
high-pass
band-pass
band-stop

72
Q

Filters with the ________ characteristic are used for filtering pulse waveforms.
Butterworth
Chebyshev
Bessel

73
Q

Which filter exhibits a linear phase characteristic?
Bessel
Butterworth
Chebyshev
all of the above

74
Q

The critical frequency is defined as the point at which the response drops ________ from the passband.
–20 dB
–3 dB
–6 dB
–40 dB

75
Q

Filters with the ________ characteristic provide a very flat amplitude in the passband and a roll-off rate of –20 dB/decade/pole.
Butterworth
Chebyshev
Bessel

A

Butterworth

76
Q

Which filter exhibits the most rapid roll-off rate?
Bessel
Butterworth
Chebyshev
all of the above

77
Q

Which filter has a maximally flat response?
Bessel
Butterworth
Chebyshev
all of the above

A

Butterworth

78
Q

One important application of a state-variable ________ filter with a summing amplifier is to minimize the 60 Hz “hum” in audio systems.
low-pass
high-pass
band-pass
band-stop

79
Q

A third-order filter will have a roll-off rate of
–20 dB/decade.
–40 dB/decade.
–60 dB/decade.
–30 dB/decade.

A

–60 dB/decade.

80
Q

A ________ filter passes all frequencies within a band between a lower and an upper critical frequency and rejects all others outside this band.
low-pass
high-pass
band-pass
band-stop

81
Q

The ________ can be externally programmed to turn on at a desired anode-to-gate voltage level.
UJT
PUT
SCR
SCS

82
Q

You need a very efficient thyristor to control the speed of an AC fan motor. A good device to use would be
a 4-layer diode.
a PUT.
a triac.
a BJT.

83
Q

An application of a(n) ________ is in a lighting system for power interruptions.
SCR
SCS
diac
triac

84
Q

The silicon-controlled switch (SCS) is similar in construction to the
triac.
diac.
SCR.
4-layer diode.

85
Q

The ________ can conduct current in either direction and is turned on when a breakover voltage is exceeded.
SCR
diac
SCS
triac

86
Q

You need to design a relaxation oscillator circuit. The most likely device to use might be
an SCR.
a UJT.
a triac.
a 4-layer diode.

87
Q

You have the schematic diagram of several types of circuits. Which of these circuits most likely uses a triac?
an oscillator
an ac motor control
a programmable oscillator
an amplifier

A

an ac motor control

88
Q

The ________ is like a diac with a gate terminal.
triac
SCR
SCS
none of the above

89
Q

You have a need to use a device to trigger an SCR. A good one to use might be
an SCS.
a UJT.
a 4-layer diode.
a PUT.

90
Q

The SCR can be triggered on by a pulse at the
gate.
anode.
cathode.
none of the above

91
Q

Which of the following devices might best be used to control an electric motor?
an SCS
a PUT
an SCR
a diac

92
Q

You have a light-dimmer circuit using an SCR. In testing the circuit, you find that IG = 0 mA and the light is still on. You conclude that the trouble might be one of the following:
the SCR is open.
the switch is faulty.
the gate circuit is shorted.
this is normal; nothing is wrong.

A

this is normal; nothing is wrong.

93
Q

How many semiconductor layers are thyristors constructed with?
2
3
4
5

94
Q

Your boss has asked you to recommend a thyristor that will enable you to turn it on with a pulse and also turn it off with a pulse. Which of the following should you recommend?
an SCR
an SCS
a PUT
a triac

95
Q

An SCR acts to control the speed of an electric motor by ________ the ________ of the pulse delivered to the motor.
varying, width
increasing, amplitude
decreasing, gate width
none of these

A

varying, width

Elecs- Indiabix (Terms) (6 decks)

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