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Diodes
and Applications
Prepared by:
Emily France M. Balce
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Semiconductor DiodeAn electronic device that results from thefusion of P-type material and an N-typematerial
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a. Diffusion movement of electrons from a region of high
concentration to lower concentration
b. At the junction, the electrons from then-type and holes from the p-type attract eachother, combine and cancel their net charges
Formation of the Depletion Region
C A
Junction
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c. Due to the cancellation of electrons andholes at the junction, the junction will have no
more carriers so it is called a depleted region
or depletion region.
Depletion region
C A
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Practical diode is a nonlinear device with a
current versus voltage
Barrier potential (0.7 for Si and 0.3 for Ge )
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To simplify the analysis of diode circuits,
diodes are assumed to be Ideal.
Short circuit when forward biased
Open circuit when reverse biased
http://www.google.com.ph/url?url=http://www.patchn.com/index.php/articles/electronics/68-diode-tutorial&rct=j&frm=1&q=&esrc=s&sa=U&ei=QE-hU-r4Co_GuASq94KgDQ&ved=0CBYQ9QEwAQ&usg=AFQjCNGvd1MEQoq7YdcnZF_j2DNri_q8wAhttp://www.google.com.ph/url?url=http://www.patchn.com/index.php/articles/electronics/68-diode-tutorial&rct=j&frm=1&q=&esrc=s&sa=U&ei=QE-hU-r4Co_GuASq94KgDQ&ved=0CBYQ9QEwAQ&usg=AFQjCNGvd1MEQoq7YdcnZF_j2DNri_q8wA
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a. Forward Biased P-type is more positive than the N-type A condition that allows current to flow
through the pn junction
The pn junction narrows
Biasing the PN Junction
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b. Reverse Biased P-type is more negative than the N-type A condition that prevents current to flow
through the pn junction
The pn junction widens
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Half – Wave Rectifier
A rectifier circuit with a single diode that
conducts current during positive ornegative half cycles of input AC signal at arate determined by the input frequency.
Input
Output
Conversion factor = 40.6%Freqoutput = Freqinput
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Full – Wave Rectifier
A rectifier circuit that conducts current
during positive and negative half cycles of input AC signal.
Input
Output
Center – Tapped
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Input
Output
Conversion factor = 81.2%Freqoutput = 2 x Freqinput
Bridge Type
http://www.micro-digital.net/micro/wp-content/uploads/2011/11/Full-Wave-Bridge-Rectifier-Supply-4.jpghttp://www.micro-digital.net/micro/wp-content/uploads/2011/11/Full-Wave-Bridge-Rectifier-Supply-4.jpg
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Half – Wave Center –tapped Bridge Type
Vrms Vpk / 2 Vpk / √2 Vpk / √2
Vave Vpk / ∏ 2Vpk / ∏ 2Vpk / ∏
Irms Ipk / 2 Ipk / √2 Ipk / √2
Iave Ipk / ∏ 2Ipk / ∏ 2Ipk / ∏
PIV Vpk 2Vpk Vpk
Comparison of Rectifiers
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EXAMPLES
1. The average value of a half wave rectifiedvoltage with a peak value of 200 v is
2. When a 60 Hz sinusoidal voltage is appliedto the input of a half wave rectifier, the
output frequency is
3. The average value of a full wave rectifiedvoltage with a peak value of 75 v is
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EXAMPLES
4. When the peak output voltage is 100v, thePIV for each diode in a center tapped fullwave rectifier is
5. If the input voltage to a voltage tripler has
an rms value of 12 v, the DC output voltageis approximately
6. When a 60 Hz sinusoidal voltage is applied
to the input of a full wave rectifier, theoutput frequency is
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Filter
Smoothens the output waveform
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Ripple Factor of a Rectifier
Ratio of the rms value of the AC
component of the signal to the averagevalue of the signal
r = Vr(rms) / Vdc
Vr(rms) = (Vrms exp 2 – Vdc exp 2)exp 1/2
Vr(rms) = 0.385Vpeak for Half wave Rectifier
Vr(rms) = 0.308Vpeak for Full Rectifier
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EXAMPLES
1. A certain power supply filter produces anoutput with a ripple of 100mV peak topeak and a DC value of 20 v. The ripplefactor is
2. Find the ripple factor of sinusoidal signalwith peak ripple of 4 volts on an averagevalue of 30 v.
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Voltage Regulation
Means maintaining the output voltage at
any load
The type of diode used for regulation isZener diode
ID
Avalanche
region
Iz min
Iz max
ZenerRegulation
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Voltage Regulation
Current Regulation
VR = V no load – V full load / V full load x 100%
CR = I no load – I full load / I full load x 100%
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EXAMPLES
1. A DC voltage supply is measured at 50volts and drops to 45 volts when the loadis connected. What is the value of voltageregulation?
2. What is the voltage regulation when the fullload voltage is the same as the no loadvoltage assuming a perfect voltage source?
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2. Clippers
Electronic circuits that have the ability to
clip – off a portion of the input signalwithout distorting the remaining part of the alternating waveform
Other names are limiters, amplitudeselectors and slicers
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Input
Output
Example of Clipper Circuit
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Input
Output
DC signal
Example of Clipper Circuit
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Analysis of Clippers - Short Cut Method
1. Determine the output waveform without the effect of
the diode bya. shorting the diode for series limiterb. opening the diode for parallel limiter.
2. Determine the Clipping Linea. For Series Limiter, the clipping line is at the abscissa.b. For Parallel Limiter, the clipping line is the output
reflection of the voltage source; if there is no voltagesource present, the clipping line is at the abscissa.
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Analysis of Clippers - Short Cut Method
3. Inspect the position of the diode
a. For series limiters, if the arrowhead of the diode isi. pointing to the right, the output waveform is above
the clipping line.ii. Pointing to the left, the output waveform is below
the clipping line
b. For parallel limiters, if the arrowhead of the diode isi. pointing upward, the output waveform is above the
clipping line.
ii. Pointing downward, the output waveform is belowthe clipping line.
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Analysis of Clippers - Short Cut Method
4. For Double Diode Clippers, same procedure for 1 and 2.
The resulting waveforem is between the 2 clippinglines.
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3. Clampers
Circuits that shift the waveform of the
input signal either all above or below thereference voltage
Add or restore a DC level to an electrical
signal
Also known as DC restorer
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Clamping circuit is often used in television
receivers as dc restorer. Incomingcomposite video signal is normallyprocessed through capacitively coupledamplifiers that eliminate the dccomponent losing the reference levelswhich must be restored using clampingcircuits before applying to the picture tube.
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Example of Clamper CircuitInput
Output
Vpk
2Vpk
Positive Clamper
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Analysis of Clampers - Short Cut Method
1. Determine the Clamping Line as given by the output
reflection of the voltage source. If there is no voltagesource present, the clamping line is at the abscissa.
Note: There should be no part of the waveform to be
either above or below the clamping line.
2. Determine where the arrowhead of the diode ispointing
a. upward, the waveform is above the clamping line.b. downward, the waveform is below the clampingline.
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4. Voltage Multiplier
Circuit which produces a greater DC output
voltage than AC input voltage to therectifiers
Uses clamping action to increase peakrectified voltages without the necessity of increasing the input’s transformers voltagerating
Used in high – voltage, low current
applications such as TV receivers
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Voltage Doubler
A voltage multiplier with a multiplication
factor of 2
C1
C2D1
D2
Vp Vo
At the first negative half cylcleD1 = forward biasD2 = reverse biasVC
1= V
pVC2 = 2Vp
At the first positivehalf cylcleD1 = reverse biasD2 = forward biasVC
1= V
pVo = VC2 = 2Vp
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Voltage Tripler
Addition of another diode – capacitor
section to the half wave voltage doublercreates voltage tripler
The PIV of each diode is 2Vp
3Vp
Vp
C1
D2 D2 D3
C3
C2
+ -
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Voltage Quadrupler
The addition of still another diode –
capacitor section in a voltage tripler circuit
The PIV of each diode is 2Vp
C1 C3
C2 C4
Vp D1 D2 D3 D4
4Vp
+-
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II. Special Purpose Diodes
1. Zener Diode Symbol
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Diode designed to operate in the reverse
breakdown region
a. Zener breakdown When the breakdown voltage is
below 5V
b. Avalanche breakdown
When the breakdown voltage isabove 5V
2. Zener Diode
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Typical breakdown voltages of 1.8V to200V with specified tolerances from 1% to20%
With very stable voltage drop
Useful as voltage regulator
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2. Point Contact Diode
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Semiconductor diode having fine wirewhose point is permanent contact with thesurface of a wafer of a semiconductormaterial such as silicon, germanium orgallium arsenide
The fine wire is called cat - whisker
For signal mixing and detection
2. Point Contact Diode
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Also known as Surface Barrier Diode
Also known as Hot - Carrier Diode
This type of diode has no depletion layer
which eliminates the stored charges in the junction
A rectifying metal semiconductor junction
such as gold, silver and platinum
3. Schottky Diode
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Construction of Schottky Diode
cathode anode
Metal Silicon Junction
Typical forward voltage drop is typicallyaround 0.25V to 0.3V
Can rectify frequencies up to 300 MHz
ESBAR (Epitaxial Schottky Barrier)
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4. Varactor (varicap)
V l i bl i
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Voltage-variable capacitor
When this diode is reverse bias, the width
of the depletion layer increases with thereverse voltage
Used for electronic tuning, harmonicgenerator and parametric amplifier
Symbol
where
f = frequencyRs = series resistanceCt = total diode
capacitance
http://www.google.com.ph/url?url=http://electrical-info.com/varactor-diode/varactor-diode-symbol-3/&rct=j&frm=1&q=&esrc=s&sa=U&ei=ib5NVL6tK8bDmAWlioLwAw&ved=0CBQQ9QEwAA&usg=AFQjCNGvlL8KcGtTcVXQv2-vN78A9ttaKwhttp://www.google.com.ph/url?url=http://electrical-info.com/varactor-diode/varactor-diode-symbol-3/&rct=j&frm=1&q=&esrc=s&sa=U&ei=ib5NVL6tK8bDmAWlioLwAw&ved=0CBQQ9QEwAA&usg=AFQjCNGvlL8KcGtTcVXQv2-vN78A9ttaKw
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5. Tunnel Diode
Symbol
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5. Tunnel Diode
Also known as Esaki diode
Type of diode that exhibits thephenomenon known as negativeresistance
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Negative resistance implies that anincrease in forward voltage produces a
decrease in forward current for a certainpart
Utilizes a heavily doped material andtherefore have so many electrons
Has a very thin depletion layer
The extremely narrow depletion region
emits electrons to “tunnel” through the pn junction at very low forward bias voltage
Used for oscillators and amplifiers
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6. Backward Diode
Symbol
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6. Backward Diode
Conducts better in the reverse (-0.1V) thanin the forward (+0.7V) direction
Designed such that its high current flowtakes place when the junction is reverse
bias
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7. PIN Diode
Positive – intrinsic Negative Diode
The intrinsic material between the P and N
layer offers impedance at microwavefrequencies being controlled by lowfrequency signals
Used in microwave switches
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8. Light Emitting Diode (LED)
Symbol
http://www.google.com.ph/url?url=http://www.mds975.co.uk/Content/components01.html&rct=j&frm=1&q=&esrc=s&sa=U&ei=McNNVLaVGIaX8QXy_oCACA&ved=0CB4Q9QEwBQ&usg=AFQjCNEoasokpsGdkFw6vMuZmpMAukuc9whttp://www.google.com.ph/url?url=http://www.mds975.co.uk/Content/components01.html&rct=j&frm=1&q=&esrc=s&sa=U&ei=McNNVLaVGIaX8QXy_oCACA&ved=0CB4Q9QEwBQ&usg=AFQjCNEoasokpsGdkFw6vMuZmpMAukuc9w
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8. Light Emitting Diode (LED)
In a forward biased LED, free electronscross the junction and fall into holes. Asthese electrons fall from higher to a lowerenergy level, they radiate energy whichgoes off in the form of heat. But in an LED,
the energy is being radiated as light.
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Commonly used Gallium Arsenide,Gallium Arsenide Phosphide, and GalliumPhosphide
GaAs LEDs emit infrared (IR) radiation
which is non visible, GaAsP produceseither red or yellow visible light and GaPemits red or green visible light
Red is the most common color of LEDs
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Electroluminescence is the processinvolved when large surface area on onelayer of one semiconductive material
permits the photons to be emitted asvisible light
Metal contact Metal contact
P N
Emitted Visible Light
(–)
(+)
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Irradiance is the power per unit area at agiven distance from an LED sourceexpressed in mW/cm2.
Typical voltage drop: 1.5V to 2.5V for
currents between 10mA and 50mA
Nominal Voltage drop: 2V
Reverse Breakdown: 3V – 10V
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9. LASER Diode
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The term LASER stands for LightAmplification by Stimulated Emission of Radiation
LASER light is monochromatic meaning it
consists of a single color and not a mixtureof colors
LASER light is also a coherent light
meaning a single wavelength
9. LASER Diode
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LASER Light (coherent and monochromatic)
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LASER diode pn junction is formed by twolayers of doped gallium arsenide
It is forward biased
LASER diodes and photodiodes are used inthe pick – up system of compact disk (CD)layers. Audio information is digitallyrecorded in stereo on the surface of a
compact disk in the microscopic “pits andflats”
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10. Photodiode
Symbol
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10. Photodiode
Operated in reverse bias condition
Is one that is optimized for its sensitivity tolight
A window let light to pass through thepackage of the junction. The incoming lightproduces free electrons and holesproducing larger reverse current.
Dark current is the reverse current flowingthrough the photodiode when there is noincident light.
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Review Questions
Diodes and Applications
1. The arrow in the schematic symbol for a diodepoints which way
a. towards the cathodeb. in the direction of the current flow
c. towards the anoded. towards magnetic north
a. towards the cathode
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Review Questions
Diodes and Applications
2. The anode of a semiconductor diode indicatesa __________ charge during conduction
a. positiveb. either, depending on the design
c. neutrald. negative
a. positive
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Review Questions
Diodes and Applications
3. A point in the characteristic curve of a diodewhere the current suddenly rises
a. peak voltageb. knee voltage
c. valley voltaged. trigger voltage
b. knee voltage
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Review Questions
Diodes and Applications
5. In order to simplify a circuit, in analysis andcomputation, the diode is normally assumedas __________.
a. zero
b. idealc. imaginaryd. infinite
b. ideal
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Review Questions
Diodes and Applications
6.An external voltage applied to a junctionreduces its barrier and aid current to flowthrough the junction
a. reverse biasb. external bias
c. junction biasd. forward bias
d. forward bias
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Review Questions
Diodes and Applications
7. How does an ohmmeter behave if its positivelead is connected to the cathode of a diodewhile negative to anode?
a. has infinite high resistanceb. has unstable resistance
c. has very low resistanced. has decreasing resistance
a. has infinite high resistance
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Review Questions
Diodes and Applications
8. It is the maximum permissible reverse voltagefor the diode
a. peak reverse voltageb. barrier voltage
c. maximum voltaged. tolerable voltage
a. peak reverse voltage
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Review Questions
Diodes and Applications
9. Circuit that is used to eliminate or portions of the input waveform above or below aspecified level
a. clamperb. clipper
c. DC restorerd. multiplierb. clipper
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Review Questions
Diodes and Applications
10. Which is not an application of clipper?a. circuit transient protectionb. changing the shape of the waveformc. detection
d. oscillation
d. oscillation
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Review Questions
Diodes and Applications
11. What is another name for clamper?a. slicerb. limiterc. clipper
d. DC restorer
d. DC restorer
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Diodes and Applications
12. Circuit that is used to produce a DC outputvoltage that is some integral multiple of thepeak of the AC input voltage
a. integratorb. restorer
c. differentiatord. multiplier
d. multiplier
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Review Questions
Diodes and Applications
13. What is the process by which AC is convertedto pulsating DC?
a. chargingb. rectification
c. filteringd. clipping
b. rectification
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Review Questions
Diodes and Applications
14. _________ is the output of a half – waverectifier
a. half – wave rectified signalb. square wave signalc. 100%AC signald. sinusoidal signal
a. half – wave rectified signal
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Review Questions
Diodes and Applications
15. How many diodes will you use to have abasic half – wave rectifier?
a. threeb. fourc. twod. one
d. one
i i
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Review Questions
Diodes and Applications
16. The four basic circuit blocks that make up apower supply are
a. transformer, clipper, filter, regulatorb. rectifier, clamper, filter, regulatorc. transformer, rectifier, inverter, regulatord. transformer, rectifier, filter, regulator
d. transformer, rectifier, filter, regulator
R i Q i
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Diodes and Applications
17. What is the ideal voltage regulation of apower supply?
a. 0%b. 50%c. 100%d. 1%
a. 0%
R i Q i
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Diodes and Applications
18. It is a type of transformer whose secondaryvoltage is equal to the primary voltage andused to isolate electrically the power supplyfrom the AC power line thus protecting thepower supply and the technician who is
working on ita. autotransformerb. step – down transformerc. step – up transformerd. isolation transformer
d. isolation transformer
R i Q ti
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Review Questions
Diodes and Applications
19. Find the direct current voltage from a full –wave rectifier with 120V peak rectifiedvoltage
a. 60Vb. 7.639V
c. 76.39Vd. 6.0V
c. 76.39V
R i Q ti
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Diodes and Applications
20. What is the maximum efficiency of a half –wave rectifier?
a. 50%b. 40.6%c. 81.2%d. 100%
b. 40.6%
R i Q ti
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Diodes and Applications
21. A half – wave rectifier circuit utilizing onehalf of an AC input cycle have a ripplefrequency in its output equivalent to
a. 60 cpsb. 120 cps
c. 110 cpsd. 240 cps
a. 60 cps
Re ie Q estions
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Diodes and Applications
22. Find the ripple factor (kr) of sinusoidal signalwith peak ripple of 4V on an average of 30
a. 0.094b. 0.013c. 0.130d. 0.940
a. 0.094
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Diodes and Applications
23. It the remaining variation in the output of apower supply filter
a. residual voltageb. ripplec. offset voltaged. persistent voltage
b. ripple
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Diodes and Applications
24. A DC voltage supply is measured at 50V anddrops to 45V when the load is connected.What is the value of “voltage regulation”?
a. 5%b. 50%
c. 60%d. 11.11%
d. 11.11%
Review Questions
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Diodes and Applications
25. How much voltage regulation doescommercial power supply have?
a. 10%b. 10% and abovec. 15% and aboved. within 1%
d. within 1%
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Diodes and Applications
26. What is the voltage regulation when the fullload voltage is the same as no – load voltageassuming a perfect voltage source?
a. 100%b. 0%
c. 1%d. 10%
b. 0%
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Diodes and Applications
27. _________ is a type of linear voltage used inapplication where the load on theunregulated voltage source must be keptconstant
a. a series regulator
b. a constant current sourcec. a shunt current sourced. a shunt regulator
d. a shunt regulator
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Diodes and Applications
28. __________ is a type of linear regulator usedin applications requiring efficient utilizationof the primary power source
a. a series regulatorb. a shunt regulator
c. a constant current sourced. a shunt current source
a. a series regulator
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Diodes and Applications
29. It is the sudden current and voltage spikethat has a small duration
a. transientb. Vrmsc. peak voltaged. VDC
a. transient
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Diodes and Applications
30. It is the component that is used to provide adischarge path for the capacitor in a voltagemultiplier if the load opens
a. discharging pathb. tuned circuit
c. inductive pathd. bleeder resistor
d. bleeder resistor
Review Questions
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Diodes and Applications
31. How do you determine if a diode isdefective?
a. diode resistance is very low or very high on eitherdirection
b. high current
c. very low currentd. high voltage
a. diode resistance is very low orvery high on either direction
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Diodes and Applications
32. The term used to describe sudden reverse
conduction of an electronic componentcause by excess reverse voltage across thedevice
a. cut – off
b. saturationc. avalanched. reversion
c. avalanche
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34. __________ is a PN junction semiconductor
device that emits non coherent opticalradiation when biased in the forwarddirection, as a result of a recombinationeffect.
a. LASER
b. JUGPETc. LEDd. optical cavity
c. LED
Review Questions
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Diodes and Applications
35. What type of bias is required for an LED toproduce luminescence?
a. reverse biasb. zero biasc. forward biasd. inductive bias
c. forward bias
Review Questions
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e e Quest o s
Diodes and Applications
36. What special type of diode is capable of bothamplification and oscillation?
a. point contact diodeb. junction diodec. zener dioded. tunnel diode
d. tunnel diode
Review Questions
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Diodes and Applications
37. Which is the principal characteristic of atunnel diode?
a. a very high PIVb. a high forward current ratingc. a high forward resistanced. a negative resistance region
d. a negative resistance region
Review Questions
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Diodes and Applications
38. A high – speed diode with very small junctioncapacitance
a. silicon diodeb. schottkyc. germanium dioded. tunnel
b. schottky
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39. Which is the principal characteristic of avaractor diode?
a. it has a very high PIVb. it has a negative regionc. its internal capacitance varies with the applied
voltaged. it has a constant voltage under conditions of
varying current
c. its internal capacitance varies with
the applied voltage
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41. A varactor diode with a high capacitanceratio can be used in
a. tuning forkb. coarse tuningc. phase tuningd. fine tuning
b. coarse tuning
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42. It is a kind of a tuning circuit that is used tovary the value of the resonant frequencyover a wide range of frequencies
a. resonant circuitb. band wide circuit
c. fine tuning circuitd. coarse tuning circuit
d. coarse tuning circuit
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43. It is a diode whose central material is madeup of intrinsic silicon sandwiched by p and ntype materials
a. PINb. zener
c. schottkyd. tunnel
a. PIN
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44. Type of diode that is made of metal whiskertouching a very small semiconductor die
a. a junction diodeb. varactor diodec. point contact dioded. zener diode
c. point contact diode
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45. It is a circuit that uses two diodes to provideDC output voltage equal to twice the ACvoltage
a. voltage doublerb. voltage regulator
c. voltage multiplierd. all of these
a. voltage doubler
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47. The main job of a voltage regulator is toprovide a nearly __________ output voltage
a. sinusoidalb. constantc. smooth
d. fluctuating
b. constant
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48. The average value of a half – wave rectifiedvoltage with a peak value of 200V is
a. 63.7Vb. 127.3Vc. 141V
d. 0V
a. 63.7V
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49. When the peak output voltage is 100V thePIV for each diode in the center – tapped full– wave rectifier is (neglecting the diode drop)
a. 100Vb. 200V
c. 141Vd. 50V
b. 200V
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50. When the rms output voltage of a full –wave
bridge rectifier is 20V, the peak inversevoltage across the diodes is (neglecting thediode drop)
a. 20Vb. 40Vc. 28.3Vd. 56.6Vc. 28.3V
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51. If the input voltage to a voltage tripler has anrms value of 12V, the DC output voltage isapproximately
a. 36Vb. 50.9V
c. 33.9Vd. 32.4V
b. 50.9V
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52. A transformer giving secondary voltage of 9Vrms is used in a half – wave rectifier circuit.The peak inverse voltage across the diodes is
a. 9Vb. 13V
c. 18Vd. 26Vb. 13V
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53. A certain power supply filter produces an
output with a ripple of 100mV peak – to –peak and a DC value of 20V. The ripple factoris
a. 0.05b. 0.005c. 0.00005d. 0.02b. 0.005
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54. The ripple of a filter output voltage with thefollowing output signal measurement of VDC = 30V and Vrms = 1.5V is
a. 9.5%b. 95%
c. 5%d. 50%
c. 5%
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55. Find the voltage regulation giving a DC
voltage of 67V without load and with fullload current drawn the output voltage dropsto 42V.
a. 59.5%b. 62.7%c. 15.9%d. 32.5%
a. 59.5%