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

Exam 1 - 1.1 to 2.8 Flashcards

(84 cards)

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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
What are the two main categories of how Varactor Diodes are used
Tuning and Hormonic Diodes
26
What is a Varistor?
A non linear resistor which has its resistance controlled via applied voltage
27
If the voltage applied is doubled in a varistor what happens to current? ( Thryrite )
The Current is increased 11 times
28
What is a tunnel diode?
A small two terminal semi-conductor containing a single junction formed by heavily doped materials
29
In a tunnel diode oscillator, where should the operating point be?
Closest to the centre of the negative-resistance curve
30
What happens to the Junction Capacitance in a reverse bias in a Varactor
The Junction capacitance decreases due to the depletion region widening
31
What happens to the Junction Capacitance in a forward bias in a Varactor
The Junction capacitance increases due the depletion region shortening
32
Common use for a varactor?
The most common use for a varactor is to allow remote adjustment of the resonant frequency of a tuned circuit
33
Two Rules of a LED?
They Must be connected in the correct polarity Must not be connected directly across a battery
34
Two Modes of a Photo-Conductive Diode?
Photovoltaic Mode = Measures Voltage Photoconductive Mode = Measures Current
35
Is a Photo-Conductive Diode used in FWD or REV bias?
Reverse Bias
36
What are Photoconductive Diodes constructed of?
Selenium, Germanium & Silicon
37
Positives of a Schottky Barrier Diode?
Very fast operating at low voltages Better High Frequency Performance Very small Reverse Bias to make it stop Extremely Low reverse current
38
Negatives of a Schottky Barrier Diode?
Low Reverse breakdown voltage The diode cannot withstand large current surges Heat causes the barrier to form slowing response times
39
What is a Thyristor?
A 4 layer 3 terminal semiconductor device
40
Thyristors are trigged by?
The application of high voltage A temp increase Application of an appropriate gate signal An increase in light
41
How many Thyristors turn off?
Removal of the power supply Power supply reversal Application of pulse to the gate
42
What is an SCR & Its use?
An SCR is a four layer P-N-P-N Semiconductor Used in Rectification, Switching & Power Control
43
What is the process / action of turning off a SCR called?
Commutation
44
How is an SCR turned off
The anode current must be reduced to near zero ( Minimum Value of the holding current has the symbol I*H
45
How is anode current reduced below holding current?
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
Application of a DIAC?
a DIAC is used to drive the TRIAC ensuring both half cycles of the sinewave are used
47
"VCC" stands for?
Collector DC supply voltage
48
Is the BASE - EMITTER junction of a transistor FWD or REV bias?
Always FWD bias
49
Is the BASE - COLLECTOR junction of a transistor FWD or REV bias?
Always REV bias
50
Does a Darlington Transistor create high or low gain>
High Gain
51
What makes the Common Emitter transistor configuration unique?
Is make the Input 180 degrees out of phase
52
How do you identify the common element in a transistor
Identify the input Identify the output The Remaining element is the common one
53
Voltage Gain In a Common Emitter?
Medium
54
Current Gain in a Common Emitter?
Medium
55
Power Gain in a common Emitter?
High
56
Input & Output resistance in a common Emitter?
Medium
57
Whats the current Gain in a common emitter circuit called?
BETA
58
Applications of a common Emitter?
Low Noise Amp's Phase Shift Amp's General Audio Amp's
59
Most common use for Common Collector?
Impedance matching
60
What causes instability in a Transistor?
Operation from a different Q point or the Q point drifts up or down the Load line
61
Does a forward bias base-emitter have a neg or pos temp co-efficient?
Negative
62
What causes a Bias shfit?
As the junction temperature increases, resistance and VBE drops resulting in the shift
63
How do you improve stability in a Base-Emitter Junction?
DC Negative ( - ) feedback
64
Characteristics of a UJT?
It cannot be used to amplify a signal It is used as a ON - OFF switch
65
Are UJT's unidirectional?
Yes
66
What are PUT's?
They are Programmable UJT's
67
How is a PUT's parameter set?
Via external resistors
68
How is a photo transistor activated
Via light, current increases as light increases
69
What is a Opto-isolator?
Both an infrared LED and a photodetector
70
How can the influence of Beta be reduced?
via the addition of emitter resistance
71
What does the symbol ƞ mean in terms of a UJT
The intrinsic standoff ratio
72
Most common use for UJT's
Trigging SCR's Relaxation Oscillators
73
Is an enhancement mode MOSFET OFF or ON at 0 voltage?
OFF
74
Is a Depletion Mode MOSFET, Off or On at 0 voltage
ON
75
Do VFETS suffer from thermal runaway?
No
76
Why must MOSFETs be handled with care
The dielectric acts as a capacitor making it vulnerable to static discharge.
77
What's makes VFET different to MOSFET
Faster switching and ability to handle larger current
78
Difference in bais in JFET and MOSFET
JFET is always reverse biased MOSFET: Reverse bias - depletion mode Fwd bias - enhancement mode
79
What region does the JFET operate in as an amplifier
Pinch off region
80
How is resistance controlled in a FET
Electric field at right angles to current
81
What is the resistance of a FET dependant on
Reverse voltage bias
82
What is the resistance of a FET dependant on
Reverse voltage bias
83
Advantage of an Opto-Isolator
Very small response times: in the megahertz range
84
What is tailored to be identical to permit highest measurement if coupling
Wavelength responce

PE4505 Flash Cards (6 decks)

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