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PE4505 Flash Cards > Exam 1 - 1.1 to 2.8 > Flashcards

Exam 1 - 1.1 to 2.8 Flashcards

1
Q

How many valance electrons in a semiconductor

A

4

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2
Q

Whats the energy level of an atom’s shell measured in?

A

Electron Volts (eV)

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3
Q

What is a hole?

A

Absence of an electron where one could exist

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4
Q

Whats an Instrinsic semiconductor

A

When it has no impurities

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5
Q

What is Doping?

A

Addition of impurities to the lattice structure

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6
Q

If the added impurity has only 3 electrons what is it called?

A

A Trivalent Impurity

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7
Q

Common Trivalent elements

A
  • Aluminum
  • Boron
  • Gallium
  • Indium
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8
Q

If the added impurity has 5 electrons, whats it called?

A

A pentavalent impurity

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9
Q

Common Pentavalent impurity

A

Antimony
Arsenic
Bismuth
Phosphorus

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10
Q

Whats the Depletion Region?

A

When enough voltage is applied the electrons will fill the holes on the Positive side to create a negative charge and leave a positive on the negative - this moment is when the depletion region develops

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11
Q

What happens to the depletion region when Forward Bias?

A

The Width of the depletion region is reduced and the barrier potential decreases

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12
Q

What happens to the depletion region when Reverse Bias

A

The Width of the depletion region is increased and the barrier potential is increased

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13
Q

What is Reverse Breakdown voltage & effect if current is not limited?

A

Reverse breakdown voltage is the voltage across a reverse bias diode at which avalanche breakdown occurs and the diode conducts heavily

  • If current is not limited the diode will destory itself
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14
Q

What is Reverse/Leakage current

A

As temp increases, the additional thermal energy causes more electrons to break away from the atoms, this creates more electron-hole pairs and more MINORITY CARRIERS

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15
Q

What is forward voltage drop?

A

This is the voltage across the diode when current flows through the diode in forward direction

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16
Q

What is Diode clamping?

A

A Circuit which can set the positive or negative peak of the input AC signal at a required level

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17
Q

Disadvantage of a Half-Wave Rectifier

A

High Ripple voltage

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18
Q

Effects of a Full wave rectifier

A

The output voltage frequency is double that of the input frequency, also has a stable output voltage

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19
Q

Disadvantage of a full wave rectifier?

A

Dependent on the use of a centre tap output transformer

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20
Q

Main use for a half-wave voltage doubler?

A

To provide a second voltage without the use of a transformer

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21
Q

Disadvantage of a Voltage doubler?

A

Hard to regulate
Ripple is hard to filter
The output cap must be able to withstand x2 the input voltage
The PIV is twice the input voltage

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22
Q

What i used to balance current of diodes mounted in parallel

A

Balancing Resistors or inductors are wired in series to equal out the current

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23
Q

Zener Diodes can act?

A

In both reverse or negative bias, plus avalanche breakdown happens at a higher point

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24
Q

What is Avalanche Breakdown?

A

As the reverse bias becomes more and more negative, a point is reached where the few minority carriers have developed enough velocity to liberate additional carriers through ionization

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25
Q

What are the two main categories of how Varactor Diodes are used

A

Tuning and Hormonic Diodes

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26
Q

What is a Varistor?

A

A non linear resistor which has its resistance controlled via applied voltage

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27
Q

If the voltage applied is doubled in a varistor what happens to current? ( Thryrite )

A

The Current is increased 11 times

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28
Q

What is a tunnel diode?

A

A small two terminal semi-conductor containing a single junction formed by heavily doped materials

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29
Q

In a tunnel diode oscillator, where should the operating point be?

A

Closest to the centre of the negative-resistance curve

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30
Q

What happens to the Junction Capacitance in a reverse bias in a Varactor

A

The Junction capacitance decreases due to the depletion region widening

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31
Q

What happens to the Junction Capacitance in a forward bias in a Varactor

A

The Junction capacitance increases due the depletion region shortening

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32
Q

Common use for a varactor?

A

The most common use for a varactor is to allow remote adjustment of the resonant frequency of a tuned circuit

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33
Q

Two Rules of a LED?

A

They Must be connected in the correct polarity
Must not be connected directly across a battery

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34
Q

Two Modes of a Photo-Conductive Diode?

A

Photovoltaic Mode = Measures Voltage
Photoconductive Mode = Measures Current

35
Q

Is a Photo-Conductive Diode used in FWD or REV bias?

A

Reverse Bias

36
Q

What are Photoconductive Diodes constructed of?

A

Selenium, Germanium & Silicon

37
Q

Positives of a Schottky Barrier Diode?

A

Very fast operating at low voltages
Better High Frequency Performance
Very small Reverse Bias to make it stop
Extremely Low reverse current

38
Q

Negatives of a Schottky Barrier Diode?

A

Low Reverse breakdown voltage
The diode cannot withstand large current surges
Heat causes the barrier to form slowing response times

39
Q

What is a Thyristor?

A

A 4 layer 3 terminal semiconductor device

40
Q

Thyristors are trigged by?

A

The application of high voltage
A temp increase
Application of an appropriate gate signal
An increase in light

41
Q

How many Thyristors turn off?

A

Removal of the power supply
Power supply reversal
Application of pulse to the gate

42
Q

What is an SCR & Its use?

A

An SCR is a four layer P-N-P-N Semiconductor
Used in Rectification, Switching & Power Control

43
Q

What is the process / action of turning off a SCR called?

A

Commutation

44
Q

How is an SCR turned off

A

The anode current must be reduced to near zero ( Minimum Value of the holding current has the symbol I*H

45
Q

How is anode current reduced below holding current?

A

Reduce or Disconnect the power supply voltage
Disconnecting the SCR from the supply by means of a switch
Making the anode negative with respect to the cathode
Temporarily short circuiting the anode to the cathode

46
Q

Application of a DIAC?

A

a DIAC is used to drive the TRIAC ensuring both half cycles of the sinewave are used

47
Q

“VCC” stands for?

A

Collector DC supply voltage

48
Q

Is the BASE - EMITTER junction of a transistor FWD or REV bias?

A

Always FWD bias

49
Q

Is the BASE - COLLECTOR junction of a transistor FWD or REV bias?

A

Always REV bias

50
Q

Does a Darlington Transistor create high or low gain>

A

High Gain

51
Q

What makes the Common Emitter transistor configuration unique?

A

Is make the Input 180 degrees out of phase

52
Q

How do you identify the common element in a transistor

A

Identify the input
Identify the output
The Remaining element is the common one

53
Q

Voltage Gain In a Common Emitter?

A

Medium

54
Q

Current Gain in a Common Emitter?

A

Medium

55
Q

Power Gain in a common Emitter?

A

High

56
Q

Input & Output resistance in a common Emitter?

A

Medium

57
Q

Whats the current Gain in a common emitter circuit called?

A

BETA

58
Q

Applications of a common Emitter?

A

Low Noise Amp’s
Phase Shift Amp’s
General Audio Amp’s

59
Q

Most common use for Common Collector?

A

Impedance matching

60
Q

What causes instability in a Transistor?

A

Operation from a different Q point or the Q point drifts up or down the Load line

61
Q

Does a forward bias base-emitter have a neg or pos temp co-efficient?

A

Negative

62
Q

What causes a Bias shfit?

A

As the junction temperature increases, resistance and VBE drops resulting in the shift

63
Q

How do you improve stability in a Base-Emitter Junction?

A

DC Negative ( - ) feedback

64
Q

Characteristics of a UJT?

A

It cannot be used to amplify a signal
It is used as a ON - OFF switch

65
Q

Are UJT’s unidirectional?

A

Yes

66
Q

What are PUT’s?

A

They are Programmable UJT’s

67
Q

How is a PUT’s parameter set?

A

Via external resistors

68
Q

How is a photo transistor activated

A

Via light, current increases as light increases

69
Q

What is a Opto-isolator?

A

Both an infrared LED and a photodetector

70
Q

How can the influence of Beta be reduced?

A

via the addition of emitter resistance

71
Q

What does the symbol ƞ mean in terms of a UJT

A

The intrinsic standoff ratio

72
Q

Most common use for UJT’s

A

Trigging SCR’s
Relaxation Oscillators

73
Q

Is an enhancement mode MOSFET OFF or ON at 0 voltage?

A

OFF

74
Q

Is a Depletion Mode MOSFET, Off or On at 0 voltage

A

ON

75
Q

Do VFETS suffer from thermal runaway?

A

No

76
Q

Why must MOSFETs be handled with care

A

The dielectric acts as a capacitor making it vulnerable to static discharge.

77
Q

What’s makes VFET different to MOSFET

A

Faster switching and ability to handle larger current

78
Q

Difference in bais in JFET and MOSFET

A

JFET is always reverse biased

MOSFET:
Reverse bias - depletion mode
Fwd bias - enhancement mode

79
Q

What region does the JFET operate in as an amplifier

A

Pinch off region

80
Q

How is resistance controlled in a FET

A

Electric field at right angles to current

81
Q

What is the resistance of a FET dependant on

A

Reverse voltage bias

82
Q

What is the resistance of a FET dependant on

A

Reverse voltage bias

83
Q

Advantage of an Opto-Isolator

A

Very small response times: in the megahertz range

84
Q

What is tailored to be identical to permit highest measurement if coupling

A

Wavelength responce

PE4505 Flash Cards (6 decks)

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