Electronics; Recifiers And Battery Chergers- Part A Flashcards
What kind of current flows in only one direction?
Direct current
A DC value can be constant or pulsating but two circuit properties dont change:
direction of current; and polarity of voltage
Give an example of a dc source that supplies a constant value of voltage
Battery
Give an example of a DC source that supplies pulsating DC
Electronic rectifier
What is the average value equal to for a constant output DC source?
Equal to the instantaneous value at any time
What is the average value equal to for a pulsating DC source?
Average value is between the maximum and minimum instantaneous values.
Measured dc values are always understood to be _________ values unless stated otherwise
Average
What kind of current does an alternator produce?
Alternating current
What are 6 terms used to define a sine wave?
Cycle Period Frequency Peak Peak-to-peak Instantaneous Effective and RMS
How many degrees represents one cycle?
360°
How is the period (T) of a sine wave defined? And calculated.
Amount of time required for one complete cycle (milliseconds to complete 360°) T= 1/frequency
How is the frequency (f) of a sine wave defined? And calculated.
Number of cycles that occur in 1 sec. (360° in 1sec) f= 1/T
Why is the sine wave characterized by a single peak value if there are TWO peaks in a complete sine wave?
Because these peaks are equal in magnitude
What is V(pp) and I(pp)?
Peak to peak voltage and peak to peak current
How do you find instantaneous values of voltage and current?
Multiply the peak value by sine of the angle.
What trigonomic functions are associated with each of the following:
Pf
Instantaneous value
Real power
Reactive power
Cos theta
Sin theta
Cos theta (or pf)
Sin theta (or sin of inverse cos pf)
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?
The effective value
How do you determine the effective value of a sine wave?
V(eff) = V(max) x 0.707
Or
V(max)/ squr root of 2
What is another name for effective value?
Root mean square (rms); square root of the mean of all instantaneous values
What is the difference in readings between an ac meter and a DC meter? Ie. What does each measure?
AC measures rms value
DC measures average value
What is the average of a sine wave?
0
Give the “power of 10” value and abbreviation for each of the following prefixes:
Milli Mega Nano Micro Kilo Giga Pico
1) (-3) m
2) (6) M
3) (-9) n
4) (-6) ‘mew’
5) (3) k
6) (9) G
7) (-12) p
When is double subscript notation used?
When you need to determine the polarity of one point in a circuit with respect to a second point
What is a voltage divider calculation used for?
To predict the voltage values across the components in a circuit
How do you find the voltage drop across a resistor in a series circuit?
With the voltage divider rule:
V(resistor)=( R(resistor)/R(total) ) x E
What does an oscilloscope do?
Uses graphic waveforms to display how voltage or current changes over time
What kind of metre do you use to check for continuity and resistance?
Ohmmeter
What’s the first step when using an ohmmeter?
Turn off power to the circuit
What does OL reading indicate on an ohmmeter?
- Indicates too low of a range
- or an open circuit
What does a reading of 0 ohms indicate on an ohmmeter?
- A short circuit
- resistance below the limits of the metre
What is the electrical potential difference between two points?
Voltage
What should you consider When selecting the appropriate range on your voltmeter?
Select a range that is high enough to read the expected voltage. Selecting a range thats lower than measured voltage may cause damage.
What do you do to verify your voltmeter is working?
Test a known voltage
How do you verify your ohmmeter is working?
Touch the leads together to read 0 ohms
What are two types of ammeters that exist?
Clamp-on
Series
What type of ammeter would you use on ranges below 100 milliamps?
Series
What type of ammeter allows you to measure current without disconnecting any wires?
Clamp-on
What is the resistance of an ammeter?
0 ohms
What are the main controls of a multimeter?
Function selector
Range selector
True or false: Voltmeters and ammeters can measure a moment in time.
False. That is what oscilloscopes are for
What is represented on the vertical axis of a graph produced by an oscilloscope?
Amplitude ie. Amount of current or voltage
What is represented on the horizontal axis of a graph produced by an oscilloscope?
Time
What are three applications of an oscilloscope?
Measurement of harmonics, ground-fault test current, and instrumentation signals
What does a transducer do?
Device that converts an input value to a signal the oscilloscope can interpret
What device converts a measured quantity into a voltage signal then displays a graph of this voltage versus time?
Transducer
What operational features are common to all oscilloscopes?
Volts / division selector switch
Time base control switch
AC ground DC switch
Trigger control
How do you decrease the voltage per division setting on an oscilloscope? Increase?
Pressing mV decreases volts/division setting. Pressing V increases it.
What does the time base select on a oscilloscope?
Select time interval that each horizontal division represents.
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?
50
How would you find frequency knowing milliseconds it takes for one cycle?
f = 1/T
If you increase the time base what happens the amount of Cycles displayed?
Higher time base = more time represented = more cycles displayed
True or false: even when measuring known AC waveforms, it is better to keep the scope in DC mode. Why or why not?
True because DC mode displays AC and DC together when they are both present
What does an oscilloscope measure?
Voltage
What kind of oscilloscope has a grounded reference lead?
AC powered bench type scope
When can the reference lead be attached to live parts of a circuit?
When it is a handheld ungrounded oscilloscope.
What is the outermost electron shell of an atom called
Valence shell
What largely determines the ability of a material to act as an insulator or conductor?
The number of valence electrons in the valence shell
Define a free electron
Electrons only Loosely bound to the atom
How many valence electrons would you expect from a good conductor
1, 2, or 3.
How many valence electrons would you expect from an insulator
5 to 8
What do you call a material that is neither good conductor nor a good insulator?
Semiconductor
How many valence electrons would you expect from a semiconductor?
4 tetravalent
What is the most common element used in semiconductor devices?
Silicon
What is another, less commonly used, element used in semiconductor devices?
Germanium
What are electronic devices made from semiconductor material called?
Solid state devices
What is covalent bonding?
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
What is the initial step in the development of semiconductor material?
Manufacturer of pure intrinsic materials
What does covalent bonding mean?
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.
How are intrinsic materials created?
Through covalent bonding
An intrinsic material behaves, at room temperature, like an insulator.
True
What is it called when impurities are added to Pure intrinsic materials?
Doping
What does intrinsic material become after doping?
Extrinsic material
How much impurity is added to intrinsic material during the process of doping?
1 atom for each 12 000 000
What does adding impurities to Intrinsic material do to the material properties?
Reduces the resistance of the material
True or false extrinsic extrinsic semiconductor material is p-type only.
False it is either n-type or p-type
What do you get when doping silicon with pentavalent materials?
N-type
What type of material do you get from doing silicon with trivalent materials?
P-type
What are some examples of trivalent materials?
Boron, aluminum, indium
What are some examples of pentavalent materials?
Arsenic, phosphorus, antimony
What are the majority charge carriers in an type semiconductor material?
Electrons
What are the majority charge carriers in p-type material?
Holes
What materials develop more free electrons in the presence of light? What is their application?
Lead sulfide, indium antimonide, and cadmium sulfide. Making photoconducitve cells called light-dependent resistors (LDR) or photo resistors.
Describe the process that makes a semiconductor material less resistive
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.
What is it called when a material that exhibits a lower resistance when exposed to light energy?
Photoconduction
What is the makeup of a photocell?
Photoconductive material
What is a metal oxide varistor?
Common type of surge suppressor
What is the basic building block of semiconductor devices?
PN Junction
What material is the anode lead connected to on a diode?
P-type
What lead is connected to the end type material on a diode?
Cathode
What is the area depleted of charge carriers in a diode called?
Depletion region
Why does the depletion region exist?
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.
When does a diode allow current to flow?
When the anode is positive with respect to the cathode
What is a barrier potential?
The applied voltage to a PN junction that allows charge carriers to be pushed across the depletion region and current to flow.
What is the barrier potential at room temperature for a germanium PN Junction?
0.3 volts
What is the barrier potential at room temperature for silicon PN Junction?
0.7 volts
What happens when the applied voltage equals the barrier potential?
The depletion region is overcome and conventional current flows from anode to cathode
What is the polarity of the leads in a reverse based situation?
Anode is negative with respect to the cathode.
In which condition is a diode thought of as an open switch
In a reverse biased diode
What is the ideal reverse resistance of a silicon diode?
Infinity
What is the Practical reverse resistance of a silicon diode?
30 megaohms
What are the electrons in the n-material attracted to in a reverse bias diode?
Toward the positive terminal (away from the junction)
What is the safe operating region for a diode?
Within the limits bounded by I(fmax) at one extreme and V(rrm) at the other
What is a forward bias limit labelled on a characteristic curve for a diode?
I(fmax); rated current.
What is the reverse bias limit?
Maximum amount of reverse voltage that can be applied to a diode.
What are other names for the reverse bias limit?
Also called voltage repetitive reverse maximum, peak inverse voltage, or peak reverse voltage.
What is Avalanche current?
The high reverse current that flows as a result of Applied voltage above the safe maximum, causing the diode to break down
What kind of diodes are used in rectifier applications?
Press-fit diodes
Diodes in the 150 amp to 500 amp range are usually what kind of diode type?
Stud mounted with a pigtail
What is the purpose of a heat sink
Dissipate Heat
How do you find the power in Watts dissipated by the diode and heatsink?
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)
What is an important consideration when installing hockey puck style diode in heat sinks?
Clamping Force; applied pressure between anode and cathode. Too loose= not close enough for good heat transfer. Too tight= contorts and surfaces spread apart.
What kind of diodes are used for high currents?
Hockey puck
What are the most important electrical ratings of a diode?
Max forward bias average current
Max instantaneous forward surge current
Repetitive reverse maximum
Forward voltage drop at rated current
Define repetitive reverse maximum V(rrm)
Instantaneous reverse bias voltage that can safely be applied to the diode
What does I(fsm) or I(fm) surge mean?
Current a diode can withstand occasionally but not repetitively
Define forward voltage at rated current
Theoretical voltage drop across a PN junction. Close to 1V under load
What do you need to take into consideration when replacing a diode?
Peak value of ac to be rectified.(voltage repetitive reverse maximum/ voltage peak reverse).
Where do the meter leads go when performing a reverse bias check?
Positive lead to cathode and negative lead to anode
What meter readings do we expect from a diode that failed open?
‘OL’ for both forward and reverse tests
What meter readings do we expect from a diode that shorted out?
Same as when the two leads are touched together.
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
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.
What is the first step in replacing a faulty diode?
Find diode part number. (Usually printed on diode itself or on schematic)
If you dont have a diode part number, how do you find a replacement?
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
When replacing a fast recovery diode, what specs must the replacement meet?
Replacement must have max t(rr) (recovery time) that is equal to or less than the original.
What does “recovery time” mean when talking about a diode?
Time it takes for the diode to complete the transition between on and off states.
What are three common diode types?
Freewheeling
Directional
Rectifier
When switching inductive loads on or off, when do you see the greatest change in current?
When you stop current completely (ie. Open a switch).
Why dont we see greatest current change when switching inductive loads on? (As opposed to off)
The inductance prevents current from rising too quickly.
Why is switching current off from an inductive load problematic?
- 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.
What is the function of a freewheeling diode?
Used to control the destructive effects of Cemf spikes in DC circuits.
Another name for a freewheeling diode
Suppression or protection diode
Why can’t freewheeling diodes be used for ac circuits?
Because the diode would be forward biased every half-cycle.
Another name for directional diodes
Blocking, steering, or isolating.
Common applications of directional diodes?
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
What does the charging current of each battery depend on?
- The batteries terminal voltage
- And its internal resistance.
What is dark current?
The small (negligible) amount of current that flows through a photo diode when no light is applied.
What are LEDs made of?
Gallium arsenic phosphate (GaAsP) or Gallium phosphate (GaP)
What kind of energy are infrared wavelengths are sensed as?
Heat
What kind of wavelengths are sensed as visible light?
Shorter wavelengths, like the ones produced by GaAsP or GaP
What kind of chemical compound produces a red or yellow light?
gallium arsenic phosphate
What kind of chemical compound produces red or green light?
Gallium phosphate
What’s the typical forward operating voltage of LEDs?
1.8 to 2.2 V
What are the typical forward current ratings of LEDs?
15mA to 30mA
What is the maximum power dissipation for LEDs?
80mW to 100mW
What is the most common application of diodes?
Rectifier
Where is the reference lead connected when using an ac powered bench oscilloscope?
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)
What are some precautions to be taken when using an oscilloscope?
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.
Name the four diode packages and approximate available I(fav)
Axial type = up to 5A
Stud mount = up to 600A
Power Module = up to 600A
Hockey Puk = up to 7000A
