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CAT B- Mod 4 Electronic Fundamentals > 4.1.1 Semi Conductors > Flashcards

4.1.1 Semi Conductors Flashcards

1
Q

What is a diode?

A

Two terminal electronic components

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2
Q

What does the diode do?

A

Conducts current in a single direction by applying low resistance in one direction and high in the other.

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3
Q

In a schematic symbol for a diode what is the arrow end?

A

Anode

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4
Q

In a schematic symbol for a diode what is the bar end?

A

Cathode

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5
Q

What does a generic diode symbol look like?

A

Line with an arrow and bar.

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6
Q

What does a schottky diode symbol look like?

A

Line with an arrow and ‘s’ bar (tips of s curl round)

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7
Q

What does a shockley diode symbol look like?

A

Line with two bars and a diagonal connecting the two.

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8
Q

What does a constant current diode symbol look like?

A

Line with an arrow and an ‘I’ bar

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9
Q

What does a zener diode symbol look like?

A

Not to be confused with a schottky, it is a line with an arrow and ‘s’ bar but the ends don’t curl.

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10
Q

What does a light emitting diode symbol look like?

A

Line with arrow and bar, surrounded by circle and arrows pointing away.

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11
Q

What does a photo diode symbol look like?

A

Line with arrow and bar, surrounded by circle and arrows pointing towards.

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12
Q

What does a step recovery diode symbol look like?

A

Line with an arrow and ‘L’ shaped bar.

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13
Q

What does a tunnel diode symbol look like?

A

Line with an arrow and backwards ‘c’ bar

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14
Q

What does a varactor diode symbol look like?

A

Line with an arrow and double bar

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15
Q

What does a Pin diode symbol look like?

A

Line with an arrow and bar, between them is a little square.

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16
Q

What does a vacuum tube diode symbol look like?

A

Completely different to the rest, big circle with a load of squiggles.

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17
Q

What are diodes susceptible too?

A

Electro static discharge

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18
Q

What are diodes made of?

A

Semi conductors

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19
Q

What can semiconductors be manufactured as?

A

Single discrete devices- diodes and transistors
Multiple- fully integrated circuits

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20
Q

What is a fundamental semiconductor device?

A

Positive negative junction diode

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21
Q

How are positive negative diodes fabricated?

A

Doping together two sides of a single crystal semiconductor with opposite impurities.

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22
Q

In a positive negative junction diode with side of the junction has an excess of electrons?

A

Negative

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23
Q

Diodes can be thought of as check valves, how do they decide whether to ‘block’ the current or let it through?

A

Depletion layer

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24
Q

What is a depletion layer?

A

When P and N materials are bonded together, electrons migrate to fill holes on the p side, leaving a depletion zone.

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25
Q

What is the depletion zone sometimes referred too as?

A

Barrier region

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26
Q

What is a diode being forward bias doing?

A

Conducting

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27
Q

What is a diode being reverse bias doing?

A

Insulating

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28
Q

If the p type is connected to the plus of the battery what does it do the depletion layer?

A

Narrow, making it function as a conductor

29
Q

What is a the barrier potential or trigger of a diode?

A

High resistance to current flow at the point of switching.

30
Q

What happens when diodes are connected in series?

A

The forward current flowing through each diode is the same. Therefore the current must not exceed a individual diode rating.

31
Q

In series diodes what is the voltage drop?

A

Germanium- 0.3V
Silicon- 0.7V

32
Q

What happens to the current when diodes are in parallel?

A

The current is divided across them.

33
Q

What is the benefit of parallel diodes but the risk too it?

A

They current they can carry can be increased as it shared, but if one were too fail, then the others may be above their rating.

34
Q

Parallel diodes don’t conduct current equally, therefore what kind of diode is required if the same output is required?

A

Identical diodes.

35
Q

What is a thyristors other name?

A

Silicon controlled rectifier

36
Q

How many layers does a thyristor have?

A

4

37
Q

What is a thyristor?

A

Fast electronic switches (up to 400Hz)

38
Q

Due to the way thyristors are constructed how many p-n junctions are formed?

A

3

39
Q

What are the three operating states of thyristors?

A

Reverse blocking
Forward blocking
Forward conducting

40
Q

What is reverse blocking?

A

voltage is applied that would reverse bias an equivalent diode.

41
Q

What is forward blocking?

A

voltage is applied that would forward bias an equivalent diode but the thyristor has not been triggered into conduction.

42
Q

What is the breakdown voltage?

A

The point at which enough voltage is applied to allow the thyristor to conduct

43
Q

What is the benefit of thyristors?

A

Very large currents and high power levels can be switched

44
Q

Why are thyristors used in light dimming systems?

A

used to reduce the average voltage supplied to the lights, by controlling the gate trigger signal position.

45
Q

What does LED stand for?

A

Light emitting diode

46
Q

How do LED’s work?

A

When the electron re-aligns with a hole it emits energy in the form of photons.

47
Q

What is the voltage range of an LED?

A

1.4 to 4.5V (Purple to white)

48
Q

What is the switching time for a red emitting diode?

A

50 nanoseconds

49
Q

What is the switching time for green emitting diodes?

A

400 nanoseconds

50
Q

LEDs in the visible range are manufactured with what?

A

Gallium Arsenide Phosphide (GaAsP)

51
Q

What is used to emit infrared light from LEDs?

A

Gallium Arsenide with zinc and sillicon.

52
Q

What does the junction of a photo conductive diode respond to?

A

Light, and more specifically to longer wavelengths, such as red and infra-red

53
Q

Which way is a photo diode junction biased?

A

Reverse

54
Q

What is the proper name for a varistor?

A

Voltage Dependant Resistors

55
Q

What does the effective semiconductor layer of a VDR consist of?

A

Many small, highly conductive crystal particles, each of which is covered with an extremely thin barrier layer and sintered together.

56
Q

What does the symbol for a varistor look like?

A

Line with a rectangle and a tick through it.

57
Q

What does the U mean on a varistor symbol?

A

EU standard for voltage

58
Q

What is the resistance level of varistors?

A

Inversely proportional to the voltage applied

59
Q

What are varistors used for?

A

Protect against excess voltage, and regulating voltage.

60
Q

Where is a rectifier diode used?

A

used in applications that require high current, such as power supplies

61
Q

What does a rectifier diode do?

A

Convert AC-DC

62
Q

What range of amps can rectifier diodes handle?

A

1-100

63
Q

What make rectifier diodes recognisable?

A

They are cased in metal, acting as a heat sink.

64
Q

How can you tell if a diode is faulty in the open circuit condition?

A

The reading is high resistance in both directions

65
Q

When a multimeter is set to diode test, what voltage does it supply?

A

2.5-3.5V

66
Q

When tested in the forward bias condition what voltage would the diode show?

A

0.6-0.7V

67
Q

When tested in the reverse bias condition what would the multimeter display?

A

OL- Overload, high internal resistance

68
Q

If a diode has failed open circuit, it shows what on the multimeter?

A

Indicates OL in both forward and reverse or internal voltage of the meter.

69
Q

If a diode has failed in the short circuit condition, what does the meter show?

A

Shows 0 in both directions, and makes an audible beep depending on meter type.

CAT B- Mod 4 Electronic Fundamentals (5 decks)

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