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

PPT #5/6 Notes Flashcards

(64 cards)

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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
When part of the output is returned to the input to reinforce the input power?
Regenerative feedback
26
How many layers does an SCR have?
4
27
The ____ is un-directional and operates based on __________
SCR current
28
An SCR is used to control ___ and ___ power and can also rectify AC
Ac and Dc Ac
29
______-_______ is the current that must be supplied to initiate the SCR
latching current
30
________-________ the current that must be maintained for the SCR to remain in conduction
holding current
31
________ _____-______ is the forward voltage that will put the SCR into conduction
Voltage break-over
32
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
reverse bias forward break-over
33
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 _______ ______
PNPN depletion regions
34
Forward blocking state is the normal state for ____
SCR
35
The SCR will only conduct if one of the two following conditions apply?
- Exceed forward VBO - Apply a gate voltage
36
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
larger
37
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
anode cathode 1.4v
38
When gate of the SCR is triggered with a forward bias. The SCR will conduct and continue to conduct so long as ______ is supplied
current
39
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
True
40
How to turn off there SCR? - install switch on the ________ - install shorting wire from __ to __ - _______ signal on gate (not rec) - drop golfing current below ______
- anode - A to C - negative (not rec) - L.C.D
41
Shorting wire between anode and cathode momentarily shorts out the SCR bringing volts to __ which brings forward current below holding value
0
42
a _______ is essentially a bidirectional version of the SCR (Silicon Controlled Rectifier)
Triac
43
Difference between Triacs and SCR?
Triacs allow current flow in both directions
44
Triacs can be triggered by a positive or negative voltage to the gate. True or False?
True
45
How to turn on the triac? - __ on T1 - ___ on T2 + on the ____ at least ___v potential between t1 and t2
neg pos gate 1.5v
46
How to turn off the triac?
drop load current below holding current
47
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.
1 gate current
48
What is the voltage reference point in a triac?
terminal 1
49
A ________ ___-___ may be replaced with a triac.
mechanical cut-out
50
Can a pair of triacs replace reversing contactors on a PSC motor?
Yes
51
Continuity should be seen across a triac when the gate is energized. true or false?
true
52
A diac is a _________ device with ___ gate
bi-directional no gate
53
Diac will not conduct until _____ is exceeded and it turns off by dropping load current below ________ current
VBO holding
54
Diacs ensure the Triacs are not turned on by ______ in the line
spikes
55
Diac is a triggering device used with ________
Triacs
56
When a positive or negative voltage reaches the break over voltage, the diac rapidly switches from a _____ resistive state to a _____ resistive state
high low
57
Testing a Diac should have high resistance in both directions. true or false?
true
58
Photocells have _____ resistance when no light is present
high
59
photo cells are _______ biased
forward
60
Photocells are used when time response is not critical. true or false?
true
61
Photocells are commonly used with?
pilot lights
62
How do photocells work with gas valves and pilots?
No light = high resistance and no current flow to valve Light = low resistance and current flow to gold gas valve open
63
Photo DIODES are operated in the ______ biased mode and are _______ with a _____ response time
reverse rugged fast
64
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?
True

Term 3 - Electronics (6 decks)

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