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PE4505 Flash Cards > #2 Exam 🥲 > Flashcards

#2 Exam 🥲 Flashcards

Use if you want a headache

1
Q

Op amps are very close to ideal voltage amplifiers, what does that mean in terms of characteristics?

A

-infinite voltage gain
-infinite bandwidth
-infinite input impedance
-zero output impedance

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2
Q

How many stages are in the construction on an op amp

A

3
-input (differential amplifier)
-2nd (voltage amplifiers)
-last (output amplifiers) class b

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3
Q

What kind of gain is an operational amplifier?

A

Very High voltage gain

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4
Q

How is the input signal taken from each terminal?

A

The voltage difference between terminals

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5
Q

If there is said to be no voltage difference between the 2 inputs what will be the output?

A

There will be zero output

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6
Q

Due to op amps having input infinitely high what is the the input current said to be?

A

So small it’s regarded as zero

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7
Q

What is the output resistance of an op amp

A

Ideally zero but so small to ignore

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8
Q

What is offset with respect to op amp

A

Offset is a small amount of dc voltage that passes with inputs at zero

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9
Q

How is offset cancelled or compensated for?

A

The use of external circuitry

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10
Q

What voltage do most op amps req

A

Plus or minus 5-20 volts

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11
Q

If the signal is applied to the +ve input and the other is grounded what is the output said to be?

A

Inphase

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12
Q

If the signal is applied to the -ve input and the other grounded the output is said to be?

A

Antiphase

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13
Q

What input would an op amp have if one input is grounded/fixed to a reference voltage?

A

Single ended input

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14
Q

What is the positive terminal of an op amp referred to as

A

The non-inverting terminal (inphase)

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15
Q

What is the negative terminal of an op amp referred to as?

A

Inverting terminal (antiphase)

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16
Q

How much input and output impedance does an op amp have

A

High input impedance, low output impedance

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17
Q

What feedback would you add to make an op amp more stable and predictable?

A

Negative feedback

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18
Q

What is slew rate measured in

A

Micro per second

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19
Q

If the slew rate is stated at 1 can the output change 10volts during each microsecond

A

No, slew rate 1 means it can’t change more than 1 volt per microsecond

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20
Q

What does V(oi) mean

A

Input offset voltage

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21
Q

What is offset voltage drift defined as

A

Change in output voltage resulting from temperature changes

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22
Q

What is feedback

A

When a portion of the output is reinserted at the input (can be intentional or unwanted coupling)

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23
Q

Describe positive feedback and its other name

A

Also called regenerative feedback, its inphase with the input so gets added to it. Meaning more input will be amplified from the previous this will cause oscillations.

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24
Q

Describe negative feedback and its other name

A

Also called degenerative feedback, this feedback is antiphase (180*) so will cancel some of the input out. This will reduce the overall gain of the op amp but improves stability and amplifiers performance.

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25
Q

What is the name used when using a number of amplifier stages to produce a desired gain greater than 1 could provide

A

Cascade

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26
Q

What are the 3 types of distortion

A

-phase (signal delay through amplifier)
-frequency (harmonics affecting wave)
-amplitude

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27
Q

What windings would be found on the primary side of a step down transformer

A

Many turns of relatively small wire

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28
Q

What’s the primary purpose of a transformer core

A

Provide a circuit of low reluctance for magnetic flux

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29
Q

Why can’t you operate a transformer lower than the normal operating level (Hz decreased)

A

Because inductive reactance will decrease so current flow will increase, if large enough it will damage the transformer

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30
Q

Above or below a transformers normal operating level can you operate it safely?

A

Frequency above (increased)
This is due to the inductive reactance being increased and causing a voltage drop over the load so it won’t damage the transformer

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31
Q

How are transformers rated

A

In volt amperes

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32
Q

What is in the equation to calculate the average

A

Average = peak x 0.637

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33
Q

What is the output ripple frequency of a full wave rectifier

A

Double the supply frequency

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34
Q

2 disadvantages of a full wave rectifier

A

-needs a centre tap transformer
-diode PIV is double that of a half wave

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35
Q

2 disadvantages of a bridge rectifier

A

-needs 4 diodes
-there’s 2 diodes in series resulting in greater FWD voltage drop

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36
Q

What does a filter do

A

Smooths out DC

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37
Q

A capacitor opposes change in……

A

Voltage

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38
Q

A inductor opposes change in…..

A

Current

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39
Q

In an inductor filter as the load current increases what happens to the filtering effect

A

It also increases

40
Q

If the inductance value is becoming greater the filtering effect ……

A

Will become greater aswell

41
Q

What’s are the 2 types of voltage regulators

A

Series and shunt

42
Q

In a voltage regulator what are some reasons output voltage may vary

A

-Load current variations
-input or line voltage variations
-temperature variations (especially semiconductors)

43
Q

Why is a resistor in series with the zener diode of a shunt voltage regulator

A

So enough current flows through it for the sender diode to operate within its zener breakdown region

44
Q

What is the number corresponding to the positive supply in IC voltage regulators

A

Positive supply = 78xx

45
Q

What is the number corresponding to the negative supply in IC voltage regulators

A

Negative supply = 79xx

46
Q

An op amplifier has what gain

A

High voltage gain

47
Q

What is the inverting input

A

The negative terminal

48
Q

What class is the output amplifier (last stage of op amp)

A

Class b (180* of input cycle)

49
Q

An ideal op amp is said to have a voltage gain of….

A

Infinity

50
Q

What is a typical op amp voltage gain

A

About 200,000

51
Q

What stage in the op amp provides the most amount of gain

A

The 2nd stage the high gain voltage amplifier

52
Q

What input and output resistance should an op amp ideally have

A

Infinitely high input resistance with extremely low output resistance

53
Q

What is TCV(os) or known as drift

A

Temperature coefficient of input offset voltage
(A voltage that gets added to the input to force the output to zero)

54
Q

What type of feedback can be used to create an oscillator

A

Positive or regenerative

55
Q

What does V(os) stand for

A

Input offset voltage

56
Q

What varies input offset voltage

A

Temperature

57
Q

What is 78xx

A

Positive voltage regulator

58
Q

79xx

A

Negative voltage regulator

59
Q

What happens to the PIV for a halfwave rectifier containing capacitor filter

A

It will be double PIV=2V(max)

60
Q

What happens to the PIV of a full wave or bridge rectifier with a capacitor filter

A

The PIV I’ll remain unchanged

61
Q

What input line will the input offset voltage be applied to

A

In series with The inverting input terminal

62
Q

What are the degrees of each class a,ab,b,c

A

A-current flows for all 360degrees
AB-current flows less than 360 but more than 180
B-current flows for 180
C-current flows less than 180

63
Q

What is a Darlington transitor

A

2 transitors connected to make a high gain NPN transistor

64
Q

Drift can happen due to 3 things

A

-temp
-power supply variations
-ageing components

65
Q

What is a RC filter used for

A

To eliminate a con power supply rail

66
Q

What should phase splitters output be in respect to each other

A

Balanced

67
Q

What is cross over distortion

A

Distortion at a point when both transitors are in the OFF state at the same time

68
Q

How much cross over is there between classes, A,B,Ab

A

A-no crossover
B-large crossover
Ab-some crossover

69
Q

What does a solid load phase splitter do

A

Has simultaneous outputs from the collector and the emitter

70
Q

On a NPN in complementary symmetry what polarity needs to be applied for it to conduct

A

Positive on base

71
Q

On a PNP in complementary symmetry what polarity needs to be applied for it to conduct

A

Negative to the base

72
Q

How many stable states are there on an A stable multivibrator

A

No stable states

73
Q

How many stable states are there on a mono stable multivibrator

A

1 stable state (with one set of timing components removed)

74
Q

How many stable states are in a bistable multivibrator

A

2 stable states with no timing capacitors

75
Q

In a positive pulse steering trigger is the anode of the cathode held at what polarity potential

A

The anode is held at a negative potential

76
Q

In a negative pulse steering trigger is the anode of the cathode held at what polarity potential

A

The cathode is held at a positive voltage

77
Q

An LC tank is what

A

The simplest oscillating circuit

78
Q

What must the barkhausen feedback be

A

Must be exactly 1

79
Q

If the barkhausen feedback is 1 but other components change what will happen

A

The oscillations will stop

80
Q

The stability of an oscillator is due to what

A

The degree of which the output frequency or amplitude remain constant over predetermined period

81
Q

Define a series fed LC oscillator

A

All the current flows through a portion of the tuned circuit

82
Q

Define a shunt fed LC oscillator

A

None of the current flows through the tuned circuit

83
Q

What does a higher Q mean for bandwidth

A

The higher the Q the narrower the bandwidth

84
Q

Define f(s) in crystal oscillators

A

Frequency crystal has minimum impedance corresponding to series resonance

85
Q

Define f(p) in crystal oscillators

A

Frequency crystal has maximum impedance corresponding to parallel resonance between the crystal and its holder

86
Q

At operating frequency of a tank circuit is impedance at min or max

A

Maximum impedance and large feedback voltage developed

87
Q

What frequencies is the bandwidth between

A

Lower cutoff and upper cutoff

88
Q

How do you calculate decibel gain

A

The sum of decibel gains of the individual components

89
Q

What does a higher Q point mean

A

The hump is more pronounced and bandwidth narrows

90
Q

What do resonant circuits do

A

Designed to pass a range of frequencies and block others

91
Q

Statement:
Double power = +3db
Half power = -3db

A
91
Q

What is the -3db point on a response curve

A

The point where where the circuits gain falls off at high and low frequencies

92
Q

Requirements of oscillator output wave form

A

-constant frequency
-constant amplitude
-waveform purity

93
Q

Othe name for LC circuit

A

Tank circuit (inductor, capacitor)

94
Q

Statement
To over come the effect of the feedback factor being less that one is to have it more than one and reduced does to 1

A
95
Q
A

PE4505 Flash Cards (6 decks)

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