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UKCAA MODULE 4 ELECTRONIC FUNDAMENTALS > Transistors > Flashcards

Transistors Flashcards

1
Q

What are the three terminals of a Bipolar Junction Transistor (BJT)?

A

The three terminals of a BJT are the base (B), the collector (C), and the emitter (E).

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2
Q

Which terminals are present in a unijunction transistor?

A

A unijunction transistor has an emitter terminal (E), a “base 1” terminal (B1), and a “base 2” terminal (B2).

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2
Q

What is a phototransistor and how does it operate?

A

A phototransistor is a semiconductor device that senses light levels and alters the current flowing between the emitter and collector based on the light received. It is essentially a BJT with a clear case to allow light to fall on the base-collector junction.

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3
Q

What distinguishes a phototransistor from a regular BJT in terms of its structure?

A

A phototransistor is distinguished from a regular BJT by having a clear case that allows light to fall on the base-collector junction, which affects the current flow based on light intensity.

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3
Q

What are the terminals of a Junction Field Effect Transistor (JFET)?

A

The terminals of a JFET are the gate (G), drain (D), and source (S).

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4
Q

How are the symbols for NPN and PNP phototransistors different from those for regular BJTs?

A

The symbols for NPN and PNP phototransistors include arrows indicating the direction of light influence, distinguishing them from regular BJTs which do not have these arrows.

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5
Q

What are the names of the terminals in a Metal Oxide Semiconductor Field Effect Transistor (MOSFET)?

A

The terminals in a MOSFET are called the gate (G), drain (D), and source (S).

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6
Q

In what type of transistor is the collector terminal replaced by a second base terminal?

A

In a unijunction transistor, the collector terminal is replaced by a second base terminal.

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6
Q

Describe the terminals of an N-channel JFET.

A

The terminals of an N-channel JFET are the gate (G), drain (D), and source (S).

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7
Q

What is the function of the base terminal in a Bipolar Junction Transistor (BJT)?

A

The base terminal in a BJT controls the current flow between the collector and emitter terminals.

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8
Q

Name some common applications of transistors.

A

Transistors are used in amplifiers, switches, voltage stabilizers, signal modulation, and oscillators.

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8
Q

Who invented the transistor and what are the origins of its name?

A

The transistor was invented by Bell Telephone Laboratories. The name is an abbreviation of the words “transconductance” or “transfer” and “varistor”.

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9
Q

What is a transistor and what are its primary functions?

A

A transistor is a semiconductor device used to amplify or switch electrical signals and power.

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9
Q

How are transistors classified based on their structure?

A

Transistors are classified into Junction Transistors and Field Effect Transistors (FETs).

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10
Q

What materials are commonly used to manufacture transistors?

A

Transistors are commonly made from silicon, germanium, and gallium-arsenide.

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10
Q

How do transistors differ from mechanical switches in terms of operation?

A

Unlike mechanical switches, transistors use small digital and analog signals to control their switching on and off. They can switch very quickly, reaching speeds of tens or even hundreds of MHz.

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11
Q

What are the two main types of Field Effect Transistors (FETs)?

A

The two main types of FETs are Junction FET (JFET) and Metal Oxide Semiconductor FET (MOSFET).

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12
Q

What are the two main types of Junction Transistors?

A

The two main types of Junction Transistors are Unijunction Transistors (UJTs) and Bipolar Junction Transistors (BJTs).

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13
Q

What is the mnemonic for remembering the differences between NPN and PNP transistors?

A

The mnemonic for NPN is “Not Pointing iN” (arrow not pointing in), and for PNP, it is “Pointing iN Proudly” (arrow pointing in).

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14
Q

Describe the structure of a Bipolar Junction Transistor (BJT).

A

A BJT consists of three parts of P- or N-type semiconductor material, creating two depletion areas. It can be arranged in either a PNP or NPN configuration, with terminals named Emitter (E), Base (B), and Collector (C).

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15
Q

How do Field Effect Transistors (FETs) control current?

A

FETs control current by using an electric field created by a weak electrical signal coming in through one electrode, which affects the entire transistor.

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16
Q

What is the fundamental difference between JFET and BJT devices in terms of current control?

A

In a JFET, the gate current is practically zero when the junction is biased, whereas the base current in a BJT is always greater than zero.

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17
Q

How does the current flow in a Junction Field Effect Transistor (JFET)?

A

In a JFET, the current flows through a channel between the source and drain, which is controlled by the voltage applied to the gate.

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18
Q

How is an N-channel FET turned on and off?

A

An N-channel FET is turned on by setting the gate voltage to 0V, allowing maximum current flow from drain to source. To turn it off, a negative voltage is applied to the gate, reducing the current flow until it ceases completely.

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19
Q

Why are FETs extremely sensitive to static charges?

A

FETs are extremely sensitive to static charges because the gate current is very small (usually in microamperes), making them highly responsive to voltage changes.

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20
Q

mnemonic for remembering the differences between PNP and NPN transistors is?

A

For NPN:

Not Pointing iN: The arrow in the symbol points outwards (Not Pointing In).

For PNP:

Pointing iN Proudly: The arrow in the symbol points inwards (Pointing In Proudly).

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21
Q

What is a transistor?

A

A transistor is a type of semiconductor device that can both conduct and insulate electric current or voltage, acting as a switch and/or an amplifier.

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22
Q

How does a transistor act as a switch?

A

When a transistor is fully on or saturated, it acts like a switch, with a small input voltage controlling a large current flow from the collector to the emitter.

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23
Q

How does a transistor act as an amplifier?

A

When a transistor operates in the region between cut-off and saturation, it acts like an amplifier, where a small voltage at the base controls a larger current flow between the collector and the emitter.

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24
Q

What is required for a bipolar junction transistor (BJT) to function correctly?

A

A BJT must be properly biased, meaning its two PN junctions must be properly biased to function correctly.

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25
Q

What happens when a transistor is reverse-biased?

A

When a transistor is reverse-biased (external voltage applied between the base and collector), the collector-base junction acts like a reverse-biased PN diode and will not conduct.

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26
Q

What happens when a transistor is forward-biased?

A

When a transistor is forward-biased (external voltage applied between the base and emitter), the emitter-base junction acts like a forward-biased PN diode and will conduct.

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27
Q

What occurs at the emitter junction when it is forward biased?

A

When the emitter junction is forward biased, electrons from the N-type emitter combine with holes in the P-type base, causing current to flow from the emitter through the base to the collector.

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28
Q

What is the effect of the base being lightly doped compared to the emitter?

A

The light doping of the base compared to the emitter causes insufficient holes in the base for the electrons from the emitter, facilitating the flow of current from the emitter through the base to the collector.

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29
Q

How is an NPN transistor formed?

A

An NPN transistor is formed by subjecting an N-type semiconductor crystal to a trivalent impurity to form a P-type region, followed by a pentavalent impurity to form a small N-type region within the P-type region. Terminals are added to these regions, labelled collector, base, and emitter.

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30
Q

What is the function of the emitter in a transistor?

A

The emitter emits charge carriers.

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31
Q

What is the role of the base in a transistor?

A

The base regulates the emission of charge carriers from the emitter.

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32
Q

What does the collector do in a transistor?

A

The collector collects the charge carriers emitted by the emitter.

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33
Q

How are the junctions within a transistor similar to diodes?

A

Each junction within a transistor (collector-base and base-emitter) constitutes a P-N junction, forming barrier layers similar to diodes.

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34
Q

What happens at the emitter junction of a PNP transistor when a voltage is applied?

A

When voltage is applied to the emitter-base junction of a PNP transistor, free electrons and holes are forced towards the emitter junction, narrowing the depletion area and allowing current (IB) to flow through the emitter-base circuit.

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34
Q

Describe the current flow in an NPN transistor operational circuit.

A

In an NPN transistor circuit, the collector has a positive voltage relative to the emitter. When the base-emitter voltage exceeds 0.7 V, the base-emitter diode becomes conductive, allowing current to flow from the emitter to the base. The majority of charge carriers are swept by the collector’s electric field, contributing to the collector current (IC).

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35
Q

How is the emitter current (IE) in a transistor calculated?

A

The emitter current (IE) is the sum of the collector current (IC) and the base current (IB), given by IE = IC + IB.

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36
Q

What is the current gain (β) of a common emitter transistor configuration?

A

The current gain (β) of a common emitter transistor configuration is the ratio of the collector current (IC) to the base current (IB), denoted as β = IC/IB.

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37
Q

How are transistors controlled in any type of circuit?

A

Transistors are always controlled between the base and the emitter, regardless of the circuit type chosen.

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37
Q

What are the three basic configurations of transistor circuits?

A

The three basic configurations are Common-Emitter (CE) Circuits, Common-Collector (CC) Circuits, and Common-Base (CB) Circuits.

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37
Q

What defines a Common-Emitter (CE) Circuit?

A

In a CE circuit, the emitter is the common reference electrode for the input and output circuits. It allows amplification of both current and voltage, offering medium input impedance, medium output impedance, medium current gain, and medium voltage gain.

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38
Q

What defines a Common-Collector (CC) Circuit?

A

In a CC circuit, the collector is the common reference electrode for the input and output circuits.

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38
Q

What is the significance of the collector resistance in a CE circuit?

A

Maximum current amplification in a CE circuit is achieved when the collector resistance is 𝑅𝐶.

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39
Q

What is another name for a Common-Collector (CC) Circuit and why is it called that?

A

A Common-Collector circuit is also known as an emitter follower or impedance converter because it has high input impedance, low output impedance, voltage gain less than one, and large current gain.

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40
Q

What defines a Common-Base (CB) Circuit?

A

In a CB circuit, the base electrode is the common reference electrode for the input and output circuits. It has low input resistance and high output resistance.

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41
Q

What are the typical characteristics of a Common-Base (CB) Circuit?

A

The typical characteristics are low input resistance, high output resistance, and suitability for high-frequency applications.

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41
Q

Why is a CB circuit especially useful for high-frequency applications?

A

A CB circuit is useful for high-frequency applications because harmful capacitances between the collector and the base, as well as between the emitter and the base, are connected to the ground.

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42
Q

How is a transistor’s input and output circuit defined in any configuration?

A

The input circuit is formed by the base and the emitter, and the output circuit is formed by the collector and the emitter.

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43
Q

what is this?

A

common base

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44
Q

what is this?

A

common collector

45
Q

what is this?

A

common emitter

46
Q

What is a multimeter used for when testing a bipolar junction transistor (BJT)?

A

A multimeter is used to test the base-to-emitter P-N junction and the base-to-collector P-N junction of a BJT, and to identify the polarity (NPN or PNP) and the leads (emitter, base, collector) of the transistor.

46
Q

What is the first step in testing a transistor with a multimeter?

A

The first step is to remove the transistor from the circuit to ensure accurate test results and then select the Diode position on the multimeter.

47
Q

How do you test the base-to-emitter junction of an NPN transistor using a multimeter?

A

Connect the positive lead from the multimeter to the BASE (B) and the negative lead to the EMITTER (E). A good NPN transistor will show a voltage drop between 0.45 V and 0.9 V.

48
Q

What result should you expect when testing the base-to-emitter junction of a PNP transistor?

A

When testing a PNP transistor, ‘OL’ (Over Limit) should show on the multimeter.

49
Q

How do you test the base-to-collector junction of an NPN transistor?

A

Keep the positive lead on the BASE (B) and connect the negative lead to the COLLECTOR (C). A good NPN transistor will show a voltage drop between 0.45 V and 0.9 V.

50
Q

What result indicates a good PNP transistor when testing the base-to-collector junction?

A

For a good PNP transistor, ‘OL’ (Over Limit) should show on the multimeter.

50
Q

How do you test the emitter-to-base junction of an NPN transistor?

A

Connect the positive lead from the multimeter to the EMITTER (E) and the negative lead to the BASE (B). A good NPN transistor will show ‘OL’ (Over Limit).

51
Q

What should the multimeter read when testing the emitter-to-base junction of a PNP transistor?

A

The multimeter should show a voltage drop between 0.45 V and 0.9 V for a good PNP transistor.

52
Q

How do you test the collector-to-base junction of an NPN transistor?

A

Connect the positive lead to the COLLECTOR (C) and the negative lead to the BASE (B). A good NPN transistor will show ‘OL’ (Over Limit).

53
Q

What result indicates a good PNP transistor when testing the collector-to-base junction?

A

The multimeter should show a voltage drop between 0.45 V and 0.9 V for a good PNP transistor.

54
Q

How do you test the collector-to-emitter junction of a transistor?

A

Connect the positive lead to the COLLECTOR (C) and the negative lead to the EMITTER (E). For a good NPN or PNP transistor, the meter should read ‘OL’ (Over Limit). Swapping the leads should also result in ‘OL’.

55
Q

How can you determine which lead is the emitter on an unmarked transistor?

A

Use the voltage drop; the emitter-base junction typically has a slightly higher voltage drop than the collector-base junction.

55
Q

What should you conclude if a transistor measures contrary to the expected results in the testing steps?

A

If a transistor measures contrary to the expected results, consider the transistor to be bad.

56
Q

What limitation does this testing method have regarding the transistor’s performance?

A

This test only verifies that the transistor is not shorted or open; it does not guarantee that the transistor is operating within its designed parameters. It should only be used to determine whether to ‘replace’ the transistor or “move on to the next component”.

57
Q

What are the two main uses of transistors?

A

The two main uses of transistors are for electronic switching and amplification.

57
Q

What do amplifier classes represent?

A

Amplifier classes represent the amount of the output signal which varies within the amplifier circuit over one cycle of operation when excited by a sinusoidal input signal.

57
Q

How are amplifier classes mainly grouped?

A

Amplifier classes are mainly grouped into classically controlled conduction angle amplifiers (A, B, AB, C) and switching amplifiers (D, E, F, G, S, T).

58
Q

What is the Quiescent Point (Q-point) in an amplifier?

A

The Quiescent Point (Q-point) is the point on the load line of the amplifier’s characteristics curve where the amplifier operates at its optimum.

59
Q

What is a key characteristic of Class A amplifiers?

A

Class A amplifiers have the highest linearity and operate in the linear portion of the characteristics curve, with the transistor always having current flowing through it.

59
Q

What is the main disadvantage of Class A amplifiers?

A

The main disadvantage of Class A amplifiers is their low efficiency, around 30%, and the generation of significant amounts of heat.

60
Q

How does a Class B amplifier improve efficiency compared to a Class A amplifier?

A

Class B amplifiers improve efficiency by using two complementary transistors in a push-pull arrangement, each amplifying only half of the waveform, reducing power loss.

61
Q

What is crossover distortion in Class B amplifiers?

A

Crossover distortion occurs in Class B amplifiers at the zero-crossing point of the waveform due to the dead band of the input base voltages from -0.7 V to +0.7 V.

62
Q

How do Class AB amplifiers reduce crossover distortion?

A

Class AB amplifiers reduce crossover distortion by allowing both transistors to conduct simultaneously around the crossover point with a small bias voltage.

63
Q

What is the efficiency of Class AB amplifiers?

A

Class AB amplifiers have an efficiency of about 50% to 60%.

64
Q

Why are Class C amplifiers not suitable for audio applications?

A

Class C amplifiers are not suitable for audio applications due to their high distortion and non-linearity, despite their high efficiency of around 80%.

65
Q

What does the hFE value on a small signal transistor indicate?

A

The hFE value indicates the DC current gain or amplification factor of the transistor.

66
Q

What are some specific applications of small signal transistors?

A

Small signal transistors are used in ON/OFF switches, LED drivers, relay drivers, audio mute functions, timer circuits, infrared diode amplifiers, and bias supply circuits.

67
Q

What is the primary use of small switching transistors?

A

Small switching transistors are primarily used for switching, though they can also be used for amplification.

68
Q

What is a unique feature of power transistors?

A

Power transistors are connected to a heat sink to dissipate excess power as heat and prevent overheating.

69
Q

What are Darlington transistors?

A

Darlington transistors are two BJTs connected together to provide a high current gain equal to the product of the current gains of the two transistors.

70
Q

What are high-frequency transistors used for?

A

High-frequency transistors are used for small signals alternating at high frequencies and for high-speed switching applications.

71
Q

What is the function of phototransistors?

A

Phototransistors operate depending on the intensity of light incident on them; they are used to detect light and control current flow based on light exposure.

72
Q

How do photo-FETs differ from photo-BJTs?

A

Photo-FETs generate gate current using light to control the current flow between drain and source terminals, and they are more sensitive to light than photo-BJTs.

72
Q
A
73
Q
A
74
Q

What determines the classification of an amplifier?

A

The classification of an amplifier is determined by the quiescent DC operating point (Q-point) on the load line of the amplifier’s characteristics curve.

74
Q

In what applications are Class C amplifiers commonly used?

A

Class C amplifiers are commonly used in high-frequency sine wave oscillators and radio frequency amplifiers.

75
Q

What is the conduction angle for a Class A amplifier?

A

The conduction angle for a Class A amplifier is 360 degrees.

76
Q

What is the conduction angle for a Class B amplifier?

A

The conduction angle for a Class B amplifier is 180 degrees.

77
Q

What is the conduction angle for a Class AB amplifier?

A

The conduction angle for a Class AB amplifier is between 180 and 360 degrees.

78
Q

What is the conduction angle for a Class C amplifier?

A

The conduction angle for a Class C amplifier is less than 180 degrees.

79
Q

What are the primary concerns for low-frequency power amplifiers?

A

The primary concerns for low-frequency power amplifiers are power output, efficiency, and distortion.

80
Q

What is the efficiency of a Class A single-ended amplifier output stage?

A

The efficiency of a Class A single-ended amplifier output stage is less than 33%.

81
Q

Why are Class A amplifiers used only for small power outputs in power amplifiers?

A

Class A amplifiers are used only for small power outputs due to their low efficiency and significant heat generation.

82
Q

What is the main purpose of biasing in a transistor?

A

The main purpose of biasing is to set the conditions for switching the transistor from non-conducting to conducting (off and on).

83
Q

Name the three basic types of transistor biasing methods.

A

Base-current Bias (Fixed Bias), Self-Bias, and Combinational Bias.

83
Q

What happens if the applied voltage in a transistor is too low to maintain bias?

A

If the applied voltage is too low, there will be too little current to maintain transistor bias, causing the transistor to cut off.

84
Q

What are the drawbacks of self-bias?

A

Self-bias is only partially effective in stabilizing against temperature changes and reduces amplification due to negative feedback.

84
Q

What is a drawback of fixed bias (base-current bias)?

A

Fixed bias is thermally unstable, leading to the risk of thermal runaway and potential distortion due to changes in temperature.

85
Q

How does self-bias provide thermal stability?

A

Self-bias uses feedback from the collector to the base, which helps stabilize the collector current by opposing changes caused by temperature variations.

86
Q

How does combinational bias improve over fixed bias and self-bias?

A

Combinational bias combines fixed and self-biasing methods, providing better stability and overcoming some disadvantages of the other two methods.

87
Q

What role does the bypass capacitor (CE) play in a combinational bias circuit?

A

The bypass capacitor (CE) ensures minimal AC signal degeneration while maintaining DC thermal stability.

88
Q

What is the function of coupling capacitors in transistor circuits?

A

Coupling capacitors pass AC signals and block DC voltages, preventing shifts in the operating point and ensuring correct biasing of the transistor.

89
Q

Describe the effect of a decoupling/bypass capacitor in a transistor amplifier circuit.

A

A decoupling capacitor removes AC noise by providing a path for high-frequency signals to ground, yielding a clean DC signal.

90
Q

What is a Darlington transistor, and why is it used?

A

A Darlington transistor is a pair of transistors that act as a single transistor with high current gain, used to switch larger load currents with a smaller base current.

91
Q

Define positive feedback in the context of transistor amplifiers.

A

Positive feedback occurs when the output signal is fed back in phase with the input signal, increasing the amplitude of the output signal.

92
Q

What is negative feedback, and what are its benefits in amplifiers?

A

Negative feedback is when the output signal is fed back out of phase with the input signal, which decreases gain but increases stability, bandwidth, and reduces distortion.

93
Q

Explain series-shunt feedback and its typical use.

A

Series-shunt feedback, or series voltage feedback, is a system where the feedback voltage is in series with the input, commonly used in voltage amplifiers to control voltage gain.

94
Q

What is the primary effect of shunt-series feedback in amplifiers?

A

Shunt-series feedback, or shunt current feedback, primarily controls current gain by feeding back a signal proportional to the output current in parallel with the input.

95
Q

Describe the series-series feedback configuration and its application.

A

Series-series feedback, or series current feedback, converts the output current signal into a feedback voltage, increasing input and output impedances, used in transconductance amplifiers.

96
Q

What is the effect of shunt-shunt feedback on amplifier impedance?

A

Shunt-shunt feedback reduces both input and output impedance, suitable for transresistance amplifiers.

97
Q

What causes ringing in amplifier circuits?

A

Ringing is caused by transient effects due to capacitance in the amplifier circuit, including the load and feedline capacitances.

98
Q

What is the consequence of clipping in an amplifier?

A

Clipping occurs when the amplifier is driven too high, causing the output to saturate and distort the signal by flattening the peaks.

99
Q

How does parasitic feedback affect amplifier performance?

A

Parasitic feedback, due to unwanted capacitance, can create additional positive or negative feedback, leading to instability or oscillations in the amplifier.

100
Q

What is a cascade circuit?

A

A cascade circuit is a multistage network designed with stages connected in series with each other, where each stage transmits its output to the input of the next stage in a daisy chain.

101
Q

What types of transistors can be used in cascade circuits?

A

Cascade circuits can use Bipolar Junction Transistors (BJTs) and Field Effect Transistors (FETs).

102
Q

Why are single-stage amplifiers often insufficient in practical applications?

A

Single-stage amplifiers are often insufficient because they do not provide adequate bandwidth. They are replaced by multi-stage transistor amplifiers to achieve the necessary performance.

103
Q

What is cascading in multi-stage amplifiers?

A

Cascading is the process of joining two amplifier stages using a coupling device, such as a capacitor or transformer, to transfer the AC signal from the output of one stage to the input of the next stage while blocking DC.

104
Q

How is the overall gain of a cascade amplifier calculated?

A

The overall gain (AV) of a cascade amplifier is the product of the voltage gains of the individual stages. For example, if AV1 = 5 and AV2 = 5, then the overall gain AV = 25.

105
Q

What is the purpose of a coupling device in a cascade amplifier?

A

The purpose of a coupling device is to transfer AC from the output of one stage to the input of the next stage and to block DC, thereby isolating the DC conditions between stages.

106
Q

What is a push-pull amplifier, and what types of transistors does it use?

A

A push-pull amplifier is a power amplifier that supplies high power to the load and uses both NPN and PNP transistors. One transistor pushes the output on the positive half cycle, and the other pulls on the negative half cycle.

107
Q

What is crossover distortion in a Class AB push-pull amplifier?

A

Crossover distortion occurs because the initial ±0.6 V of the input is lost to overcome the voltage across the base-emitter (Vbe) diode drop. This can be mitigated by adding enough DC bias to each base-emitter junction to bring each device into its active region.

107
Q

What are the two preconditions for the oscillation of an amplifier?

A

The two preconditions are: 1) Displacement of phase must be 0° or 360°, and 2) The product of amplification and feedback must be kv = 1.

108
Q

What are the common waveforms generated by oscillators?

A

The common waveforms generated by oscillators are sine wave, square wave, triangle, and sawtooth.

109
Q

What is the purpose of an amplitude limiter in an oscillator?

A

An amplitude limiter is installed to prevent overdrive in the oscillator circuit, which could otherwise cause the amplifier to operate as a rectangular wave generator.

110
Q

Name three basic types of oscillators based on frequency control components.

A

The three basic types of oscillators are Meissner Oscillator, Hartley Oscillator, and Colpitts Oscillator.

110
Q

What is a multivibrator, and what are its three types?

A

A multivibrator is an electronic circuit used for oscillation or switching purposes. The three types are astable, monostable, and bistable multivibrators.

111
Q

What are the advantages of an RC oscillator over an LC oscillator?

A

The advantages include improved frequency stability, better waveform quality, suitability for low frequencies, and elimination of bulky and expensive inductors.

112
Q

What is the difference between a simple and a clocked SR flip-flop?

A

A simple SR flip-flop changes state immediately based on the inputs, while a clocked SR flip-flop changes state only when a clock pulse is applied, ensuring synchronous operation.

113
Q
A

UKCAA MODULE 4 ELECTRONIC FUNDAMENTALS (5 decks)

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