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4th Year Electrical > Electronics; Recifiers And Battery Chergers- Part A > Flashcards

Electronics; Recifiers And Battery Chergers- Part A Flashcards

1
Q

What kind of current flows in only one direction?

A

Direct current

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2
Q

A DC value can be constant or pulsating but two circuit properties dont change:

A

direction of current; and polarity of voltage

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3
Q

Give an example of a dc source that supplies a constant value of voltage

A

Battery

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4
Q

Give an example of a DC source that supplies pulsating DC

A

Electronic rectifier

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5
Q

What is the average value equal to for a constant output DC source?

A

Equal to the instantaneous value at any time

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6
Q

What is the average value equal to for a pulsating DC source?

A

Average value is between the maximum and minimum instantaneous values.

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7
Q

Measured dc values are always understood to be _________ values unless stated otherwise

A

Average

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8
Q

What kind of current does an alternator produce?

A

Alternating current

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9
Q

What are 6 terms used to define a sine wave?

A 
Cycle
Period
Frequency
Peak
Peak-to-peak
Instantaneous 
Effective and RMS
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10
Q

How many degrees represents one cycle?

A

360°

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11
Q

How is the period (T) of a sine wave defined? And calculated.

A

Amount of time required for one complete cycle (milliseconds to complete 360°) T= 1/frequency

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12
Q

How is the frequency (f) of a sine wave defined? And calculated.

A

Number of cycles that occur in 1 sec. (360° in 1sec) f= 1/T

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13
Q

Why is the sine wave characterized by a single peak value if there are TWO peaks in a complete sine wave?

A

Because these peaks are equal in magnitude

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14
Q

What is V(pp) and I(pp)?

A

Peak to peak voltage and peak to peak current

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15
Q

How do you find instantaneous values of voltage and current?

A

Multiply the peak value by sine of the angle.

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16
Q

What trigonomic functions are associated with each of the following:

Pf
Instantaneous value
Real power
Reactive power

A

Cos theta
Sin theta
Cos theta (or pf)
Sin theta (or sin of inverse cos pf)

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17
Q

What’s the heating effect of ac voltage across a certain value of resistance compared to the effect of a DC voltage applied to the same resistance?

A

The effective value

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18
Q

How do you determine the effective value of a sine wave?

A

V(eff) = V(max) x 0.707
Or
V(max)/ squr root of 2

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19
Q

What is another name for effective value?

A

Root mean square (rms); square root of the mean of all instantaneous values

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20
Q

What is the difference in readings between an ac meter and a DC meter? Ie. What does each measure?

A

AC measures rms value

DC measures average value

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21
Q

What is the average of a sine wave?

A

0

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22
Q

Give the “power of 10” value and abbreviation for each of the following prefixes:

Milli
Mega
Nano
Micro
Kilo
Giga
Pico
A

1) (-3) m
2) (6) M
3) (-9) n
4) (-6) ‘mew’
5) (3) k
6) (9) G
7) (-12) p

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23
Q

When is double subscript notation used?

A

When you need to determine the polarity of one point in a circuit with respect to a second point

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24
Q

What is a voltage divider calculation used for?

A

To predict the voltage values across the components in a circuit

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25
Q

How do you find the voltage drop across a resistor in a series circuit?

A

With the voltage divider rule:

V(resistor)=( R(resistor)/R(total) ) x E

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26
Q

What does an oscilloscope do?

A

Uses graphic waveforms to display how voltage or current changes over time

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27
Q

What kind of metre do you use to check for continuity and resistance?

A

Ohmmeter

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28
Q

What’s the first step when using an ohmmeter?

A

Turn off power to the circuit

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29
Q

What does OL reading indicate on an ohmmeter?

A
  • Indicates too low of a range

- or an open circuit

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30
Q

What does a reading of 0 ohms indicate on an ohmmeter?

A
  • A short circuit

- resistance below the limits of the metre

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31
Q

What is the electrical potential difference between two points?

A

Voltage

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32
Q

What should you consider When selecting the appropriate range on your voltmeter?

A

Select a range that is high enough to read the expected voltage. Selecting a range thats lower than measured voltage may cause damage.

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33
Q

What do you do to verify your voltmeter is working?

A

Test a known voltage

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34
Q

How do you verify your ohmmeter is working?

A

Touch the leads together to read 0 ohms

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35
Q

What are two types of ammeters that exist?

A

Clamp-on

Series

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36
Q

What type of ammeter would you use on ranges below 100 milliamps?

A

Series

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37
Q

What type of ammeter allows you to measure current without disconnecting any wires?

A

Clamp-on

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38
Q

What is the resistance of an ammeter?

A

0 ohms

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39
Q

What are the main controls of a multimeter?

A

Function selector

Range selector

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40
Q

True or false: Voltmeters and ammeters can measure a moment in time.

A

False. That is what oscilloscopes are for

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41
Q

What is represented on the vertical axis of a graph produced by an oscilloscope?

A

Amplitude ie. Amount of current or voltage

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42
Q

What is represented on the horizontal axis of a graph produced by an oscilloscope?

A

Time

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43
Q

What are three applications of an oscilloscope?

A

Measurement of harmonics, ground-fault test current, and instrumentation signals

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44
Q

What does a transducer do?

A

Device that converts an input value to a signal the oscilloscope can interpret

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45
Q

What device converts a measured quantity into a voltage signal then displays a graph of this voltage versus time?

A

Transducer

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46
Q

What operational features are common to all oscilloscopes?

A

Volts / division selector switch
Time base control switch
AC ground DC switch
Trigger control

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47
Q

How do you decrease the voltage per division setting on an oscilloscope? Increase?

A

Pressing mV decreases volts/division setting. Pressing V increases it.

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48
Q

What does the time base select on a oscilloscope?

A

Select time interval that each horizontal division represents.

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49
Q

If one cycle of a sine wave is 5 divisions of the scope and the seconds per division setting is set to 10 milliseconds how many milliseconds does it take for one cycle?

A

50

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50
Q

How would you find frequency knowing milliseconds it takes for one cycle?

A

f = 1/T

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51
Q

If you increase the time base what happens the amount of Cycles displayed?

A

Higher time base = more time represented = more cycles displayed

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52
Q

True or false: even when measuring known AC waveforms, it is better to keep the scope in DC mode. Why or why not?

A

True because DC mode displays AC and DC together when they are both present

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53
Q

What does an oscilloscope measure?

A

Voltage

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54
Q

What kind of oscilloscope has a grounded reference lead?

A

AC powered bench type scope

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55
Q

When can the reference lead be attached to live parts of a circuit?

A

When it is a handheld ungrounded oscilloscope.

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56
Q

What is the outermost electron shell of an atom called

A

Valence shell

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57
Q

What largely determines the ability of a material to act as an insulator or conductor?

A

The number of valence electrons in the valence shell

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58
Q

Define a free electron

A

Electrons only Loosely bound to the atom

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59
Q

How many valence electrons would you expect from a good conductor

A

1, 2, or 3.

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60
Q

How many valence electrons would you expect from an insulator

A

5 to 8

61
Q

What do you call a material that is neither good conductor nor a good insulator?

A

Semiconductor

62
Q

How many valence electrons would you expect from a semiconductor?

A

4 tetravalent

63
Q

What is the most common element used in semiconductor devices?

A

Silicon

64
Q

What is another, less commonly used, element used in semiconductor devices?

A

Germanium

65
Q

What are electronic devices made from semiconductor material called?

A

Solid state devices

66
Q

What is covalent bonding?

A

Each atom shares its four valence electrons with the adjoining Adams, causing the material to act as if each atom had eight electrons in the outer shell

67
Q

What is the initial step in the development of semiconductor material?

A

Manufacturer of pure intrinsic materials

68
Q

What does covalent bonding mean?

A

Each atom shares its 4 valence electrons with the adjoining atoms, causing the material to act as though each atom had 8 electrons in the outer shell.

69
Q

How are intrinsic materials created?

A

Through covalent bonding

70
Q

An intrinsic material behaves, at room temperature, like an insulator.

A

True

71
Q

What is it called when impurities are added to Pure intrinsic materials?

A

Doping

72
Q

What does intrinsic material become after doping?

A

Extrinsic material

73
Q

How much impurity is added to intrinsic material during the process of doping?

A

1 atom for each 12 000 000

74
Q

What does adding impurities to Intrinsic material do to the material properties?

A

Reduces the resistance of the material

75
Q

True or false extrinsic extrinsic semiconductor material is p-type only.

A

False it is either n-type or p-type

76
Q

What do you get when doping silicon with pentavalent materials?

A

N-type

77
Q

What type of material do you get from doing silicon with trivalent materials?

A

P-type

78
Q

What are some examples of trivalent materials?

A

Boron, aluminum, indium

79
Q

What are some examples of pentavalent materials?

A

Arsenic, phosphorus, antimony

80
Q

What are the majority charge carriers in an type semiconductor material?

A

Electrons

81
Q

What are the majority charge carriers in p-type material?

A

Holes

82
Q

What materials develop more free electrons in the presence of light? What is their application?

A

Lead sulfide, indium antimonide, and cadmium sulfide. Making photoconducitve cells called light-dependent resistors (LDR) or photo resistors.

83
Q

Describe the process that makes a semiconductor material less resistive

A

When energy is applied to a semiconductor material some of the electrons break their covalent bonds. As more energy is applied more electrons break their bonds.

84
Q

What is it called when a material that exhibits a lower resistance when exposed to light energy?

A

Photoconduction

85
Q

What is the makeup of a photocell?

A

Photoconductive material

86
Q

What is a metal oxide varistor?

A

Common type of surge suppressor

87
Q

What is the basic building block of semiconductor devices?

A

PN Junction

88
Q

What material is the anode lead connected to on a diode?

A

P-type

89
Q

What lead is connected to the end type material on a diode?

A

Cathode

90
Q

What is the area depleted of charge carriers in a diode called?

A

Depletion region

91
Q

Why does the depletion region exist?

A

Because when the junction is first formed some of the free electrons in the end type material are attracted across the junction to the holes within the p-type material. So they f**** equalize each other or something.

92
Q

When does a diode allow current to flow?

A

When the anode is positive with respect to the cathode

93
Q

What is a barrier potential?

A

The applied voltage to a PN junction that allows charge carriers to be pushed across the depletion region and current to flow.

94
Q

What is the barrier potential at room temperature for a germanium PN Junction?

A

0.3 volts

95
Q

What is the barrier potential at room temperature for silicon PN Junction?

A

0.7 volts

96
Q

What happens when the applied voltage equals the barrier potential?

A

The depletion region is overcome and conventional current flows from anode to cathode

97
Q

What is the polarity of the leads in a reverse based situation?

A

Anode is negative with respect to the cathode.

98
Q

In which condition is a diode thought of as an open switch

A

In a reverse biased diode

99
Q

What is the ideal reverse resistance of a silicon diode?

A

Infinity

100
Q

What is the Practical reverse resistance of a silicon diode?

A

30 megaohms

101
Q

What are the electrons in the n-material attracted to in a reverse bias diode?

A

Toward the positive terminal (away from the junction)

102
Q

What is the safe operating region for a diode?

A

Within the limits bounded by I(fmax) at one extreme and V(rrm) at the other

103
Q

What is a forward bias limit labelled on a characteristic curve for a diode?

A

I(fmax); rated current.

104
Q

What is the reverse bias limit?

A

Maximum amount of reverse voltage that can be applied to a diode.

105
Q

What are other names for the reverse bias limit?

A

Also called voltage repetitive reverse maximum, peak inverse voltage, or peak reverse voltage.

106
Q

What is Avalanche current?

A

The high reverse current that flows as a result of Applied voltage above the safe maximum, causing the diode to break down

107
Q

What kind of diodes are used in rectifier applications?

A

Press-fit diodes

108
Q

Diodes in the 150 amp to 500 amp range are usually what kind of diode type?

A

Stud mounted with a pigtail

109
Q

What is the purpose of a heat sink

A

Dissipate Heat

110
Q

How do you find the power in Watts dissipated by the diode and heatsink?

A

Multiply the average current by the average forward bias voltage of the diode. Assume the diode is operating close to its rated current (1V used instead of 0.7V)

111
Q

What is an important consideration when installing hockey puck style diode in heat sinks?

A

Clamping Force; applied pressure between anode and cathode. Too loose= not close enough for good heat transfer. Too tight= contorts and surfaces spread apart.

112
Q

What kind of diodes are used for high currents?

A

Hockey puck

113
Q

What are the most important electrical ratings of a diode?

A

Max forward bias average current
Max instantaneous forward surge current
Repetitive reverse maximum
Forward voltage drop at rated current

114
Q

Define repetitive reverse maximum V(rrm)

A

Instantaneous reverse bias voltage that can safely be applied to the diode

115
Q

What does I(fsm) or I(fm) surge mean?

A

Current a diode can withstand occasionally but not repetitively

116
Q

Define forward voltage at rated current

A

Theoretical voltage drop across a PN junction. Close to 1V under load

117
Q

What do you need to take into consideration when replacing a diode?

A

Peak value of ac to be rectified.(voltage repetitive reverse maximum/ voltage peak reverse).

118
Q

Where do the meter leads go when performing a reverse bias check?

A

Positive lead to cathode and negative lead to anode

119
Q

What meter readings do we expect from a diode that failed open?

A

‘OL’ for both forward and reverse tests

120
Q

What meter readings do we expect from a diode that shorted out?

A

Same as when the two leads are touched together.

121
Q

What forward bias voltage would we expect from a smaller diode with an I(fmax) rating of less than 1A vs. A larger diode with an I(fmax) rating of more than 100A

A

As high as 0.7V for smaller diode vs. As low as 0.4V for the larger. Larger has less resistance so 0.5mA flows when only small voltage is applied.

122
Q

What is the first step in replacing a faulty diode?

A

Find diode part number. (Usually printed on diode itself or on schematic)

123
Q

If you dont have a diode part number, how do you find a replacement?

A 
Rated I(fav) must be equal to or greater than original.
Rated V(rrm) must be equal to or greater than original.
Rated I(fsm) must be equal to or greater than original
124
Q

When replacing a fast recovery diode, what specs must the replacement meet?

A

Replacement must have max t(rr) (recovery time) that is equal to or less than the original.

125
Q

What does “recovery time” mean when talking about a diode?

A

Time it takes for the diode to complete the transition between on and off states.

126
Q

What are three common diode types?

A

Freewheeling
Directional
Rectifier

127
Q

When switching inductive loads on or off, when do you see the greatest change in current?

A

When you stop current completely (ie. Open a switch).

128
Q

Why dont we see greatest current change when switching inductive loads on? (As opposed to off)

A

The inductance prevents current from rising too quickly.

129
Q

Why is switching current off from an inductive load problematic?

A
  • As the magnetic field collapses they induce a high voltage (Cemf spike)
  • in attempt to maintain current the inductor arcs across the opening switch.
  • cemf spike is opposite polarity as source and can damage electronic circuits.
130
Q

What is the function of a freewheeling diode?

A

Used to control the destructive effects of Cemf spikes in DC circuits.

131
Q

Another name for a freewheeling diode

A

Suppression or protection diode

132
Q

Why can’t freewheeling diodes be used for ac circuits?

A

Because the diode would be forward biased every half-cycle.

133
Q

Another name for directional diodes

A

Blocking, steering, or isolating.

134
Q

Common applications of directional diodes?

A

1) In a dc generator charging batteries to prevent current from cycling between batteries. (Ie. Isolating kit)
2) in low voltage switching circuits to decrease amount of wire needed for install (also called steering diodes in this application)
3) fire alarm bells

135
Q

What does the charging current of each battery depend on?

A
  • The batteries terminal voltage

- And its internal resistance.

136
Q

What is dark current?

A

The small (negligible) amount of current that flows through a photo diode when no light is applied.

137
Q

What are LEDs made of?

A 
Gallium arsenic phosphate (GaAsP) or
Gallium phosphate (GaP)
138
Q

What kind of energy are infrared wavelengths are sensed as?

A

Heat

139
Q

What kind of wavelengths are sensed as visible light?

A

Shorter wavelengths, like the ones produced by GaAsP or GaP

140
Q

What kind of chemical compound produces a red or yellow light?

A

gallium arsenic phosphate

141
Q

What kind of chemical compound produces red or green light?

A

Gallium phosphate

142
Q

What’s the typical forward operating voltage of LEDs?

A

1.8 to 2.2 V

143
Q

What are the typical forward current ratings of LEDs?

A

15mA to 30mA

144
Q

What is the maximum power dissipation for LEDs?

A

80mW to 100mW

145
Q

What is the most common application of diodes?

A

Rectifier

146
Q

Where is the reference lead connected when using an ac powered bench oscilloscope?

A

A grounded point. Unless the cct under test is ungrounded, then you can attach the reference lead anywhere (this will ground the cct at that point)

147
Q

What are some precautions to be taken when using an oscilloscope?

A

1) never connect 2 reference leads to two different voltages (use only one reference lead)
2) never connect a grounded reference lead to a grounded circuit except to attach it to ground.

148
Q

Name the four diode packages and approximate available I(fav)

A

Axial type = up to 5A
Stud mount = up to 600A
Power Module = up to 600A
Hockey Puk = up to 7000A

4th Year Electrical (24 decks)

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