5-Types of Diodes

8/13/2019 5-Types of Diodes

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Types of DiodesTypes of Diodes

ZenerZener DiodesDiodesPP--N Junction DiodesN Junction Diodes

PP--N JUNCTION DIODEN JUNCTION DIODE

SchottkySchottky DiodesDiodes Shockley DiodesShockley Diodes

Photosensitive Diodes

Varactor Diodes

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PhotodiodesPhotodiodes

Photo voltaic cells

Light Emitting Diode LED

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Types of Diodes and Their UsesTypes of Diodes and Their Uses

11.P.P--N Junction Diodes:N Junction Diodes:


The characteristics of a regular P- junction diode show that it is designed

primarily for operation in the forward direction.

rere useuse toto a ow a ow currentcurrent toto ow ow nn oneone rect onrect on w ew e oc ngoc ng currentcurrentflowflow inin thethe oppositeopposite directiondirection..

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Schematic Symbol for a PN JunctionSchematic Symbol for a PN Junction

DiodeDiode

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The Zener diode is aheavily doped diodewhich, as a result of doping,has

a very narrow depletion region. This allows the diode to be operated in

the reverse biased region of the characteristic curve without damaging

the P junction.


22.Zener Diodes:.Zener Diodes:

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AreAre specificallyspecifically designeddesigned toto operateoperate underunder reversereverse breakdownbreakdown

conditions,conditions, havehave aa higherhigher resistanceresistance toto currentcurrent flowflow.. TheseThese diodesdiodes havehave

aa veryvery accurateaccurate andand specificspecific reversereverse breakdownbreakdown voltagevoltage.. DoesDoes notnot obeyobey

OhmsOhms lawlaw


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Schematic Symbol for aSchematic Symbol for a ZenerZener

DiodeDiode

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Figure shows a

representative zener

diode regulator

circuit.

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the circuit contains a series resistor, zener diode, load device, and a dc power supply.

The primary function of this circuit is to maintain the load voltage at a constant 15 V.

With 25 V applied, current through RS will cause a voltage drop of 10 V.


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The output voltage or VZ across the diode is therefore 15 V. An increase in

the supply voltage to 30 V would simply cause the zener to conduct more

current. The voltage drop across RS would therefore increase to 15 V. This

in turn would cause VZ and the load voltage to remain at 15 V. A decrease

in supply voltage to 20 V would cause a reduction in total current. The


S .

across the diode would continue to be 15 V.

This means that the regulated output will remain at 15 V for a change in

supply voltage from 20 to 30 V. Voltage regulation is an important function

of many electronic circuits today.7


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33.Schottky Diodes:.Schottky Diodes:

TheseThese diodesdiodes areare designeddesigned toto havehave aa veryvery fastfast switchingswitching timetime

whichwhich makesmakes themthem aa greatgreat diodediode forfor digitaldigital circuitcircuit

applicationsapplications.. TheyThey areare veryvery commoncommon inin computerscomputers becausebecause ofof

theirtheir abilityability toto bebe switchedswitched onon andand offoff soso quicklyquickly..


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Schematic Symbol for aSchematic Symbol for a

SchottkySchottky DiodeDiode

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44..Shockley Diodes:Shockley Diodes:

TheThe ShockleyShockley diodediode isis aa fourfour--layerlayer diodediodewhilewhile otherother diodesdiodes

areare normallynormally mademade withwith onlyonly twotwo layerslayers.. TheseThese typestypes ofof

diodesdiodes areare generallygenerally usedused toto controlcontrol thethe averageaverage powerpower


..

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Schematic Symbol for a fourSchematic Symbol for a four--

layer Shockley Diodelayer Shockley Diode

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PP--N JUNCTION DIODEN JUNCTION DIODE55.. VaractorVaractor Diodes:Diodes:

Varactors have a very light dose of impurities near the junction.

Moving away from the junction the impurity level increases.

This type of construction produces a much steeper voltage-

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capacitance relationship.

Varactor diodes are normally operated in the reverse bias

direction. With an increase in reverse biasing the depletion

region increases.


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A decrease in reverse bias voltage causes a corresponding

increase in capacitance. In effect, the capacitance of a diode

varies inversely with its bias voltage.

55.. VaractorVaractor Diodes:Diodes:

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arac or o es are use pr mar y n resonan c rcu s w eresome level of tuning or frequency control is desired.

Schematic Symbols for PhotodiodesSchematic Symbols for Photodiodes


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PhotodiodesPhotodiodesLight Emitting Diode LED


Photo voltaic cells Varactor Diodes

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a.Lighta.Light Emitting Diode: LEDEmitting Diode: LED

LightLight--emittingemitting diodesdiodes areare semiconductorsemiconductor diodesdiodes whichwhich emitemit

lightlight whenwhen currentcurrent passespasses throughthrough themthem..


It contains a P- junction that emits light when passing

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forward current

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Schematic Symbol for aSchematic Symbol for a

LightLight--Emitting DiodeEmitting Diode


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What is an LED?What is an LED? LightLight--emitting diodeemitting diode

SemiconductorSemiconductor

Has polarityHas polarity


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LED: How It WorksLED: How It Works WhenWhen currentcurrent flowsflows

acrossacross aa diodediode


oneone wayway andand positivepositive holesholes

movemove thethe otherother wayway

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LED: How It WorksLED: How It Works This energy is emittedThis energy is emitted

in a form of a photon,in a form of a photon,which causes lightwhich causes light


The color of the light isThe color of the light is

determined by the fall ofdetermined by the fall of

the electron and hencethe electron and henceenergy level of theenergy level of the

photonphoton

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Inside a Light Emitting DiodeInside a Light Emitting Diode

1.1. Transparent Plastic CaseTransparent Plastic Case


2.2. Terminal PinsTerminal Pins

3.3. DiodeDiode

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Kinds of LEDsKinds of LEDs


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How to Connect a LED:How to Connect a LED:

RequiresRequires 11..55~~22..55V andV and 1010 mAmA

To prevent overloading, use resistorTo prevent overloading, use resistor 470470


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b.b. Photodiodes:Photodiodes:

WhileWhile LEDsLEDs emitemit light,light, PhotodiodesPhotodiodes areare sensitivesensitive toto receivedreceived

lightlight.. TheyThey areare constructedconstructed soso theirtheir PP--NN junctionjunction cancan bebe

exposedexposed toto thethe outsideoutside throughthrough aa clearclear windowwindow oror lenslens..


This device is designed for operation in the reverse

bias direction. An external voltage source is

required to reverse bias the device.


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InIn PhotoconductivePhotoconductive modemode thethe saturationsaturation currentcurrent increasesincreases inin

proportionproportion toto thethe intensityintensity ofof thethe receivedreceived lightlight.. ThisThis typetype ofof

diodediode isis usedused inin CDCD playersplayers..

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Schematic Symbols for PhotodiodesSchematic Symbols for Photodiodes22


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c.c. Photovoltaic Cells:Photovoltaic Cells:

WhenWhen thethe PP--NN junctionjunction isis exposedexposed toto aa certaincertain wavelengthwavelength ofof

light,light, thethe diodediode generatesgenerates voltagevoltage andand cancan bebe usedused asas anan energyenergy

sourcesource..


o outside source of electricity is needed to produce current.

, .

Photocurrent (IPH) will flow in the circuit because of the photovoltage

(VPH) that is developed across the junction.

VPH is due to the generation of new electron-hole pairs in the depletion

region.


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c.c. Photovoltaic Cells:Photovoltaic Cells: PP--N JUNCTION DIODEN JUNCTION DIODE

This action causes the material to immediately take on a negative charge

and the P material to take on a positive charge. The P- junction therefore

Electrons move into the material because of its normal positive ion

concentration. Holes are likewise swept into the P material because of its

negative-ion content

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Schematic Symbols for PhotodiodesSchematic Symbols for Photodiodes

ThisThis typetype ofof diodediode isis usedused inin thethe productionproduction ofof solarsolar powerpower..

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responds as a small voltage cell.

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5-Types of Diodes