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Term 3 - Electronics > PPT #5/6 Notes > Flashcards

PPT #5/6 Notes Flashcards

1
Q

The zener diode acts as a ________-________ by itself or in conjunction with other semi-conductor devices

A

voltage-regulator

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2
Q

Zener diode is often referred to as a?

A

Avalanche diode

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3
Q

The zener diode normally operates in ______-_______ which is why it is referred to as an avalanche diode

A

reverse- breakdown

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4
Q

The overall forward and reverse characteristics of the zener diode are similar to a standard _____ diode.

A

silicon

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5
Q

When source voltage is applied to the zener in the reverse direction, the resistance of the PN junction is _____, as voltage increases, what occurs?

A

high

critical voltage is reached and avalanche occurs

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6
Q

On a zener diode, the PN junction should only produce leaky current in the micro-ampere range. True or False?

A

True

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7
Q

As Zener avalanche current is reached, PN junction resistance becomes ____ and the current increases rapidly. How is the current controlled/limited?

A

low

By a circuit resistor or resistance RL

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8
Q

Is a Zener diode capable of limiting the positive or negative segments of an AC cycle? How?

A

Yes, when it is supplied with AC and connected as a shunt.

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9
Q

A zener diode installed as a voltage regulator is installed in series with a current-limiting _______ and in parallel with the ________

A

resistor (RL)

load (RL)

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10
Q

When the zener is installed in parallel it is called a _____-________

A

shunt-regulator

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11
Q

Total current through the resistor (R1) is the sum of the zener and load (RL) current. True or False?

A

True

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12
Q

As source voltage increases, the current does not increase through R1 and RL because the zener diode acts as a _______-_________

A

voltage regulator

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13
Q

When voltage across the zener diode increases, the resistance of the diode ________

A

decreases

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14
Q

Reducing resistance at the zener diode causes zener current to rise, increasing the _______-_____ across the resistor (r1)

A

voltage drop

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15
Q

The larger the voltage drop across the resistor (R1), lowers the output voltage but keeps the current across RL ________

A

constant

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16
Q

DECREASING voltage across the zener diode causes the current through it to decrease and R1 drops less voltage. This, in turn, raises the output voltage to normal. True or False?

A

True

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17
Q

Lowering the voltage drop creates ________ output voltage

Higher voltage drop creates _______ output

A

steady

lower

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18
Q

As load increases or decreases, the zener diode, acting as a shunt, will draw more or less _________ respectively

A

current

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19
Q

Main purpose of a zener diode is to regulate and maintain a constant output

A

voltage

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20
Q

Zener voltage should not vary more than ___

A

0.1v

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21
Q

Zener diodes are designed to deliver constant voltage ratings ranging from ____ volts to _________ volts

A

few - several-hundred

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22
Q

What is an SCR?

A

Silicon controlled rectifier

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23
Q

An SCR is a member of the ________ family of semi- conductor devices

A

Thyristor

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24
Q

An SCR uses ________-_________

A

regenerative - feedback

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25
Q

When part of the output is returned to the input to reinforce the
input power?

A

Regenerative feedback

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26
Q

How many layers does an SCR have?

A

4

27
Q

The ____ is un-directional and operates based on __________

A

SCR

current

28
Q

An SCR is used to control ___ and ___ power and can also rectify AC

A

Ac and Dc

Ac

29
Q

______-_______ is the current that must be supplied to initiate the SCR

A

latching current

30
Q

________-________ the current that must be maintained for the SCR to remain in conduction

A

holding current

31
Q

________ _____-______ is the forward voltage that will put the SCR into conduction

A

Voltage break-over

32
Q

SCR operates much like a regular diode in _______-____. In forward bias, a certain value of _______ break-over voltage must be reached before the SCR will conduct

A

reverse bias

forward break-over

33
Q

The internal structure of an SCR consists of two PN junctions joined together to form a _____ layer. With reverse bias voltage applied to this layered structure, there is no noticeable current flow due to the formation of _______ ______

A

PNPN

depletion regions

34
Q

Forward blocking state is the normal state for ____

A

SCR

35
Q

The SCR will only conduct if one of the two following conditions apply?

A
  • Exceed forward VBO
  • Apply a gate voltage
36
Q

With forward bias voltage applied to the layered structure, there is no noticeable current flow due to the formation of the _______ depletion region in the center

A

larger

37
Q

Conditions required to “gate on” the SCR

  • Must be positive on the ________
  • Must be negative on the ________
  • Gate must be + compared to the cathode and have a knee voltage of at least
A

anode
cathode
1.4v

38
Q

When gate of the SCR is triggered with a forward bias. The SCR will conduct and continue to conduct so long as ______ is supplied

A

current

39
Q

S1 switch is momentarily closed in order to supply enough gate current through the current-limiting resistor. Once the SCR is conducting, the S1 switch can be open and the gate current can be removed. True or False

A

True

40
Q

How to turn off there SCR?
- install switch on the ________
- install shorting wire from __ to __
- _______ signal on gate (not rec)
- drop golfing current below ______

A
  • anode
  • A to C
  • negative (not rec)
  • L.C.D
41
Q

Shorting wire between anode and cathode momentarily shorts out the SCR bringing volts to __ which brings forward current below holding value

A

0

42
Q

a _______ is essentially a bidirectional version of the SCR (Silicon Controlled Rectifier)

A

Triac

43
Q

Difference between Triacs and SCR?

A

Triacs allow current flow in both directions

44
Q

Triacs can be triggered by a positive or negative voltage to the gate. True or False?

A

True

45
Q

How to turn on the triac?
- __ on T1
- ___ on T2
+ on the ____
at least ___v potential between t1 and t2

A

neg
pos
gate
1.5v

46
Q

How to turn off the triac?

A

drop load current below holding current

47
Q

The characteristics of the triac are based on terminal __ as the voltage reference point. The triac can be triggered into conduction in either direction by a __________ (IG) in either
direction.

A

1

gate current

48
Q

What is the voltage reference point in a triac?

A

terminal 1

49
Q

A ________ ___-___ may be replaced with a triac.

A

mechanical cut-out

50
Q

Can a pair of triacs replace reversing contactors on a PSC motor?

A

Yes

51
Q

Continuity should be seen across a triac when the gate is energized. true or false?

A

true

52
Q

A diac is a _________ device with ___ gate

A

bi-directional
no gate

53
Q

Diac will not conduct until _____ is exceeded and it turns off by dropping load current below ________ current

A

VBO

holding

54
Q

Diacs ensure the Triacs are not turned on by ______ in the line

A

spikes

55
Q

Diac is a triggering device used with ________

A

Triacs

56
Q

When a positive or negative voltage reaches the break over voltage, the diac rapidly switches from a _____ resistive state to a _____ resistive state

A

high

low

57
Q

Testing a Diac should have high resistance in both directions. true or false?

A

true

58
Q

Photocells have _____ resistance when no light is present

A

high

59
Q

photo cells are _______ biased

A

forward

60
Q

Photocells are used when time response is not critical. true or false?

A

true

61
Q

Photocells are commonly used with?

A

pilot lights

62
Q

How do photocells work with gas valves and pilots?

A

No light = high resistance and no current flow to valve

Light = low resistance and current flow to gold gas valve open

63
Q

Photo DIODES are operated in the ______ biased mode and are _______ with a _____ response time

A

reverse
rugged
fast

64
Q

Photo diode is lens added to a semi-conductor that allows light through on the PN junction which excites electrons and allows current to flow. True or False?

A

True

Term 3 - Electronics (6 decks)

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