diodes and applications final

8/16/2019 Diodes and Applications Final

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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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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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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

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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

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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


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


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


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


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


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


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


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


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


11. What is another name for clamper?a. slicerb. limiterc. clipper

d. DC restorer

d. DC restorer


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Review Questions


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


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


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


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


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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Review Questions


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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Review Questions


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


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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Review Questions


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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Review Questions


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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Review Questions


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

Review Questions


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Review Questions


23. It the remaining variation in the output of apower supply filter

a. residual voltageb. ripplec. offset voltaged. persistent voltage

b. ripple

Review Questions


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Review Questions


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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Review Questions


25. How much voltage regulation doescommercial power supply have?

a. 10%b. 10% and abovec. 15% and aboved. within 1%

d. within 1%

Review Questions


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Review Questions


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%

Review Questions


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Review Questions


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

Review Questions


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Review Questions


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

Review Questions


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Review Questions


29. It is the sudden current and voltage spikethat has a small duration

a. transientb. Vrmsc. peak voltaged. VDC

a. transient

Review Questions


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Review Questions


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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Review Questions


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

Review Questions


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Review Questions


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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Review Questions


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Review Questions


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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Review Questions


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


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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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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38. A high – speed diode with very small junctioncapacitance

a. silicon diodeb. schottkyc. germanium dioded. tunnel

b. schottky

Review Questions


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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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Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions


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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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Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions


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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

Review Questions

i d d li i


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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

Review Questions

i d d li i


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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%

Review Questions

i d d li i


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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%

diodes and applications final

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