Semiconductor Physics Semiconductors And DiodesSemiconductors And .
EET1240/ET212 ElectronicsOutline Semiconductor Physics The PN junction Biasing the PN junction The diode Trouble ShootingSemiconductors and DiodesElectrical and TelecommunicationsEngineering Technology DepartmentProfessor JangKey Words: Semiconductor, Silicon, PN Junction, Forward Bias, Reverse Bias, DiodePrepared by textbook based on “Electronics Devices”by Floyd, Prentice Hall, 7th edition.ET212 Electronics – SemiconductorsIntroductionFloyd2Bohr model of an atomThe basic function of a diode is to restrict current flow to one direction.As seen in thismodel, electronscircle the nucleus.Atomic structure ofa materialdetermines it’sability to conductor insulate.Forward biasReverse BiasCurrent flowsNo current flowET212 Electronics – SemiconductorsFloydFIGURE 1 The Bohr model of an atom showing electrons in orbits and around the nucleus,which consists of protons and neutrons. The “tails” on the electrons indicate motion.3ET212 Electronics – SemiconductorsFloyd41
The two simplest atomsConductors, Insulators, and SemiconducSemiconductors¾ The ability of a material to conduct current isbased on its atomic structure.¾ The orbit paths of the electrons surrounding thenucleus are called shells.¾ Each shell has a defined number of electrons itwill hold. This is a fact of nature and can bedetermined by the formula, Ne 2n2.¾ The outer shell is called the valence shell.¾ The less complete a shell is filled to capacity themore conductive the material is.FIGURE 2 The two simplest atoms, hydrogen and helium.ET212 Electronics – SemiconductorsFloyd5Atomic numbernumber,, Electron s, and IonizaIonizationtionFloydFloyd6Electron shells and Orbits All elements are arranged in the periodic table of theelements in order according to their atomic number.The atomic number equals the number of protons in thenucleus, which is the same as the number electrons. Electron shells and Orbits The outmost shell is known as the Valence shell andelectrons in this shell are called valence electrons. The process of losing a valence electron is known asionization (i.e. positive ion and negative ion).ET212 Electronics – SemiconductorsET212 Electronics – Semiconductors7FIGURE 3 Energy levels increase as the distance from the nucleus increases.ET212 Electronics – SemiconductorsFloyd82
Energy BandsConductors, Insulators,Insulators,and Semiconductors A conductor is a material that easily conductselectrical current. The best conductors are singleelement material, such as copper, gold, and aluminum,which are characterized by atoms with only one valenceelectron very loosely bound to the atom. An insulator is a material that does not conductelectrical current under normal conditions. Valenceelectrons are tightly bound to the atoms. A semiconductor is a material that is betweenconductors and insulators in its ability to conductelectrical current. The most common single –elementsemiconductors are silicon, germanium, and carbon.ET212 Electronics – Semiconductors9FloydET212 Electronics – Semiconductors10FloydCovalent BondingConductors, Insulators, and SemiconductorsThe valence shell determines the ability of material to conduct current.A Silicon atom has 4 electrons inits valence ring. This makes it asemiconductor. It takes 2n2electrons or in this case or 18electrons to fill the valence shell.FIGURE 4 Energy band diagram for a pure (intrinsic) silicon crystal with unexcitedatoms. There are no electrons in the conduction band.A Copper atom has only 1 electronin it’s valence ring. This makes it agood conductor. It takes 2n2electrons or in this case 32electrons to fill the valence shell.Covalent bonding is a bonding of two or more atoms by the interactionof their valence electrons.FIGURE 5Diagrams of thesilicon andcopper atoms.ET212 Electronics – SemiconductorsFloyd11ET212 Electronics – SemiconductorsFloydFIGURE 6123
Conduction in SemiconductorsSemiconductorsSilicon and GermaniumFIGURE 9 Energy band diagram for a pure (intrinsic) silicon crystal withunexcited atoms. There are no electrons in the conduction band.FIGURE 7 Diagrams of the silicon and germanium atoms.ET212 Electronics – SemiconductorsFloyd13ET212 Electronics – SemiconductorsThe Depletion RegionN-type and PP-type Semiconductorsp regionThe process of creating N and P type materials is called doping.Other atoms with 5 electrons(pentavalent atom) such asAntimony are added to Siliconto increase the free electrons.N-typen re gionp regionn regionOther atoms with 3 electrons(trivalent atoms) such as Boron areadded to Silicon to create a deficiencyof electrons or hole charges.P-typeWith the formation of the p andn materials combination ofelectrons and holes at thejunction takes place.ET212 Electronics – Semiconductors14FloydFloyd15ET212 Electronics – SemiconductorsThis creates the depletion regionand has a barrier potential. Thispotential cannot be measured witha voltmeter but it will cause asmall voltage drop.Floyd164
Biasing the Diode : Forward and Reverse BiasForward BiasVoltage source or bias connections are to the p material and – to the nmaterialBias must be greater than .3 V forGermanium or .7 V for Silicon diodes.The depletion region narrows.Reverse BiasVoltage source or bias connections are –to the p material and to the n material.Bias must be less than the break downvoltage.Current flow is negligible in most cases.Floyd17Reverse BiasFloyd18In this case with thevoltage applied is lessthan the barrierpotential so the diodefor all practicalpurposes is still in anon-conducting state.Current is very small.voltage is applied.FloydET212 Electronics – SemiconductorsForward Bias Measurements With SmallVoltage AppliedFIGURE 11 The diode during the short transition time immediately after reverse-biasET212 Electronics – SemiconductorsFIGURE 10 A forward-biased diode showing the flow of majority carriers and thevoltage due to the barrier potential across the depletion region.The depletion region widens.ET212 Electronics – SemiconductorsForward Bias19ET212 Electronics – SemiconductorsFloyd205
Ideal Diode Characteristic CurveForward Bias Measurements With AppliedVoltage Greater Than the Barrier Voltage.Voltage.With the applied voltageexceeding the barrierpotential the now fullyforward biased diodeconducts. Note that theonly practical loss is the.7 Volts dropped acrossthe diode.ET212 Electronics – SemiconductorsIn this characteristiccurve we do notconsider the voltagedrop or the resistiveproperties. Currentflow proportionallyincreases withvoltage.Floyd21V-I Characteristic for Forward Bias(a) V-I characteristic curve for forward bias. Part (b) illustrates how the dynamic resistancer’d decreases as you move up the curve (r’d VF/ IF).ET212 Electronics – SemiconductorsFloyd23ET212 Electronics – SemiconductorsFloyd22V-I Characteristic for Reverse BiasV-I characteristic curve for reverse-biased diode.ET212 Electronics – SemiconductorsFloyd246
The complete V-I characteristic curve for a diodeForward-bias and reverse-bias connectionsshowing the diode symbol.ET212 Electronics – SemiconductorsFloyd25ET212 Electronics – Semiconductors26FloydThe Ideal Diode ModelPractical Diode Characteristic CurveIn most cases weconsider only the forwardbias voltage drop of adiode. Once this voltageis overcome the currentincreases proportionallywith voltage.This drop isparticularly important toconsider in low voltageapplications.VF 0 VIF VBIASRLIMITIR 0 AVR VBIASET212 Electronics – SemiconductorsFloyd27ET212 Electronics – SemiconductorsFloyd287
The Practical Diode ModelThe Complete Diode ModelVF 0.7 V (silicon)VF 0.3 V (germanium)VF 0.7 I F rd'V BIAS V F V R LIMIT 0V R LIMIT I F R LIMITIF V VFI F BIASRLIMITET212 Electronics – Semiconductors29FloydET212 Electronics – SemiconductorsV BIAS 0.7RLIMIT rd'Floyd30TroubleshootingTroubleshooting DiodDiodesTroubleshooting DiodesOpen DiodeTesting a diode is quite simple, particularly if the multimeter used hasa diode check function. With the diode check function a specificknown voltage is applied from the meter across the diode.In the case of an open diode no currentflows in either direction which isindicated by the full checking voltagewith the diode check function or highresistance using an ohmmeter in bothforward and reverse connections.With the diode check function agood diode will showapproximately .7 V or .3 Vwhen forward biased.Shorted DiodeWhen checking in reverse biasthe full applied testing voltagewill be seen on the display.KET212 Electronics – SemiconductorsFloydAIn the case of a shorted diode maximumcurrent flows indicated by a 0 V withthe diode check function or lowresistance with an ohmmeter in bothforward and reverse connections.A K31ET212 Electronics – SemiconductorsFloyd328
OutlinesEET1240/ET212 Electronics¾ Half Wave Rectifiers¾ Full Wave RectifierDiode Applications¾ DC Power Supply Filter and Regulator¾ IC RegulatorElectrical and TelecommunicationsEngineering Technology Department¾ Zener Diode¾ TroubleshootTroubleshootProfessor JangKey Words: Half Wave, Full Wave, Rectifier, Power Supply, Regulator, ZenerPrepared by textbook based on “Electronics Devices”by Floyd, Prentice Hall, 7th edition.ET212 Electronics – Diodes and ApplicationsIntroduction2Half Wave RectifierThe basic function of a DC power supply is to convert an ACvoltage (110 V, 60 Hz) to a smooth DC voltage.A half wave rectifier(ideal) allows conduction for only 180 or half of a complete cycle.The output frequency is the same as the input. The average VDC or VAVG Vp/πThe rectifier can be either a half- or Full-waverectifier. The rectifier convert the ac inputvoltage to a pulsating dc voltage.The filter eliminates the fluctuationin the rectified voltage and produces arelatively smooth dc voltage.The regulator is a circuit thatmaintains a constant dc voltage forvariations in the input power linevoltage or in the load.ET212 Electronics – Diodes and ApplicationsFloydFloyd3When the sinusoidal input voltage (Vin)goes positive, the diode is forwardbiased and conducts current through theload resistor. The current produces anoutput voltage across the load RL.When the input voltage goes negativeduring the second half of its cycle, thediode reversed-biased. There is nocurrent, so the voltage across the loadresistor is 0 V.The net result is that only the positivehalf-cycles of the ac input voltageappear across the load. Since the outputdoes not change polarity, it is pulsatingdc voltage with a frequency of 60 Hz.ET212 Electronics – Diodes and ApplicationsFloyd41
Average value of the half-wave rectified signalv VpV AVGEx 2-1 What is the average value of the half-waverectified voltage in Figure?sin θarea2π 12ππ Vpsin θ d θ 0 ET212 Electronics – Diodes and ApplicationsVp2πVp2π[ cos π ( cos 0)][ ( 1) ( 1)] FloydVp2πVAVG ( 2) Vpπ5Vpπ ET212 Electronics – Diodes and Applications 31.8VFloyd6voltage, as shown in Figure. The IN4001 and IN4003 are specific rectifier diodes.The peak output voltage for circuit (a) isVp(out) Vp(in) – 0.7 V 5 V – 0.7 V 4.30 VThe effect of the barrier potential on the half-wave rectified output voltageis to reduce the peak value of the input by about 0.7 V.FloydπEx 2-2 Sketch the output voltages of each rectifier for the indicated inputEffect of the Barrier Potential on theHalf-Wave Rectified OutputET212 Electronics – Diodes and Applications1007ET212 Electronics – Diodes and ApplicationsThe peak output voltage for circuit (b) isVp(out) Vp(in) – 0.7 V 100 V – 0.7 V 99.30 V82
Half Wave Rectifier - Peak Inverse Voltage (PIV)Half Wave Rectifier with Transformer-Coupled Input VoltagePeak inverse voltage is the maximum voltage across the diode when it isin reverse bias. The diode must be capable of withstanding this amountof voltage. PIV Vp(in)Transformer coupling provides two advantages. First, it allows the sourcevoltage to be stepped up or stepped down as needed. Second, the ac sourceis electrically isolated from the rectifier, thus preventing a shock hazard inthe secondary circuit.Vsec nVpriwhere n Nsec/NpriIf n 1, stepped uptransformerIf n 1, Stepped downtransformerVp(out) Vp(sec) – 0.7 VThe PIV occurs at the peak of each half-cycle of the input voltage when the diode isreverse-biased. In this circuit, the PIV occurs at the peak of each negative half-cycle.ET212 Electronics – Diodes and ApplicationsFloydFigure Half-wave rectifier with transformer-coupled input voltage.9ET212 Electronics – Diodes and ApplicationsFloyd10Full-Wave RectifiersEx 2-3 Determine the peak value of the output voltagefor Figure if the turns ratio is 0.5.A full-wave rectifier allows current to flow during both the positive andnegative half cycles or the full 360º. Note that the output frequency is twicethe input frequency.V AVG 2V pπVp(pri) Vp(in) 156 VThe peak secondary voltage isVp(sec) nVp(pri) 78 VThe rectified peak output voltage isVp(out) Vp(sec) – 0.7 V 78 V – 0.7 V 77.3 VET212 Electronics – Diodes and ApplicationsFloyd11ET212 Electronics – Diodes and ApplicationsFloyd123
The Center-Tapped Full-Wave RectifierEx 2-4 Find the average value of the full-wave rectifiedvoltage in Figure.This method of rectification employs two diodes connected to acenter-tapped transformer. The peak output is only half of thetransformer’s peak secondary voltage.VAVG 2V pπ 2(15)π 9.55 VET212 Electronics – Diodes and ApplicationsFloyd13ET212 Electronics – Diodes and ApplicationsFloydFull-Wave Center Tapped14Center-tapped fullwave rectifier with atransformer turnsratio of 1. Vp(pri) isthe peak value of theprimary voltage.Note the current flow direction during both alternations. Being that itis center tapped, the peak output is about half of the secondarywindings total voltage. Each diode is subjected to a PIV of the fullsecondary winding output minus one diode voltage dropPIV 2Vp(out) 0.7VCenter-tapped fullwave rectifier with atransformer turnsratio of 2.ET212 Electronics – Diode ApplicationsProf. Jang15ET212 Electronics – Diodes and ApplicationsFloyd164
Full Wave Rectifier - Peak Inverse Voltage (PIV)Ex 2-5 Show the voltage waveforms across each half of the secondarywinding and across RL when a 100 V peak sine wave is applied to the primarywinding in Figure. Also, what minimum PIV rating must the diodes have?The peak inverse voltage across D2 isPIV ( V p (sec)2V p (sec) 0 .7 ) ( V p (sec)22 V p (sec) 0 .7V V p (sec)2) 0 .7VVp(out) Vp(sec)/2 – 0.7 VVp(sec) nVp(pri) 0.5(100 V) 50 VThere is a 25 V peak across each half of thesecondary with respect to ground. The outputload voltage has a peak value of 25 V, less the0.7 V drop across the diode.PIV Vp(sec) – 0.7 V 50 V – 0.7 V 49.3 VVp(sec) 2Vp(out) 1.4 VPIV 2Vp(out) 0.7 VET212 Electronics – Diodes and ApplicationsThe Full-Wave Bridge RectifierFloyd18The Full-Wave Bridge Rectifier-Peak Inverse VoltageThe full-wave bridge rectifier takes advantage of the full output of thesecondary winding. It employs four diodes arranged such that currentflows in the direction through the load during each half of the cycle.When the input cycle is positive as in part (a),diode D1 and D2 are forward-biased andconduct current in the direction shown. Avoltage is developed across RL which lookslike the positive half of the input cycle.During this time, diodes D3 and D4 arereverse-biased.Bridge Output Voltage:Vp(out) Vp(sec)Vp(out) Vp(sec) - 1.4 VWhen the input cycle is negative as in part(b), diode D3 and D4 are forward-biased andconduct current in the same direction throughRL as during the positive half-cycle. Duringnegative half-cycle, D1 and D2 are reversebiased. A full-wave rectified output voltageappears across RL as a result of this action.ET212 Electronics – Diodes and ApplicationsFloyd19ET212 Electronics – Diodes and ApplicationsFloyd205
Ex 2-6 Determine the peak output voltage for the bridge rectifier in Figure.Assuming the practical model, what PIV rating is required for the diodes?The transformer is specified to have a 12 Vrms secondary voltage for thestandard 110 V across the primary.The Full-Wave Bridge RectifierThe PIV for a bridge rectifier is approximately half the PIVfor a center-tapped rectifier.PIV Vp(out) 0.7VVp(sec) 1.414Vrms 1.414(12 V) 17 VVp(out) Vp(sec) - 1.4 V 17 V – 1.4 V 15.6 VNote that in most cases we take the diode drop into account.ET212 Electronics – Diodes and ApplicationsFloydPIV Vp(out) 0.7 V 15.6 V 0.7 V 16.3 V21Floyd22Power Supply Filters and RegulatorsPower Supply Filters And RegulatorsAs we have seen, the output of a rectifier is a pulsating DC. Withfiltration and regulation this pulsating voltage can be smoothedout and kept to a steady value.Figure illustrates the filtering concept showing a nearly smooth dc output voltagefrom filter. The small amount of fluctuation in the filter output voltage is calledET212Electronics – Diodes and ApplicationsFloydripple.ET212 Electronics – Diodes and ApplicationsA capacitor-inputfilter will charge anddischarge such that itfills in the “gaps”between each peak.This reducesvariations of voltage.This voltage variationis called ripplevoltage.23ET212 Electronics – Diodes and ApplicationsFloyd246
Power Supply Filters And RegulatorsRipple FactorThe advantage of a full-wave rectifier over a half-wave is quiteclear. The capacitor can more effectively reduce the ripple whenthe time between peaks is shorter.The ripple factor (r) is an indication of theeffectiveness of the filter and defined asr Vr(pp) / VDCVr ( pp ) (1)V p ( rect )fRL CVDC (1 ET212 Electronics – Diodes and Applications25Surge Current in the Capacitor-Input Filter1)V p ( rect )2 fRL CET212 Electronics – Diodes and ApplicationsFloyd26IC RegulatorsBeing that the capacitor appears as a short during the initial charging, thecurrent through the diodes can momentarily be quite high. To reduce riskof damaging the diodes, a surge current limiting resistor is placed inseries with the filter and load.ET212 Electronics – Diode ApplicationsProf. Jang27The –7800three-terminal fixedProf.positiveET212 ElectronicsDiodeseriesApplicationsJangvoltage regulators.287
Power Supply Filters And RegulatorsPower Supply Filters and RegulatorsRegulation is the last step in eliminating the remaining ripple andmaintaining the output voltage to a specific value. Typically this regulationis performed by an integrated circuit regulator. There are many differenttypes used based on the voltage and current requirements.How well the regulation is performed by a regulator is measuredby its regulation percentage. There are two types of regulation,line and load. Line and load regulation percentage is simply aratio of change in voltage (line) or current (load) stated as apercentage.Line Regulation ( VOUT/ VIN )100%Load Regulation ((VNL – VFL )/ VFL)100%Load Regulation (ET212 Electronics – Diodes and ApplicationsFloyd29V NL VFL5.185V 5.152V)100 % ()100 % 0.64 %VFL5.152VET212 Electronics – Diodes and ApplicationsFloyd30Ex 2-7 What would you expect to see displayed on an oscilloscopeconnected across RL in the limiter shown in Figure.Diode LimitersLimiting circuits limit the positive or negative amount of an inputvoltage to a specific value.Vout (ET212 Electronics – Diodes and ApplicationsFloydRL)VinR1 RL31V p ( out ) (RL1.0 kΩ)V p ( in ) ()10V 9.09VR1 RL1.1 kΩET212 Electronics – Diodes and Applications328
Ex 2-8 Figure shows a circuit combining a positiveEx 2-9 Describe the output voltage waveform for thediode limiter in Figure.limiter. Determine the output voltage waveform.VBIAS (R3)VSUPPLYR2 R3220Ω)12 V100Ω 220Ω 8.25V (ET212 Electronics – Diodes and ApplicationsFloyd33Floyd34Zener DiodesIntroduction – Zener DiodeThe zener diode is a silicon pn junction devices that differs fromrectifier diodes because it is designed for operation in the reversebreakdown region. The breakdown voltage of a zener diode is set bycarefully controlling the level during manufacture. The basic functionof zener diode is to maintain a specific voltage across its terminalswithin given limits of line or load change. Typically it is used forproviding a stable reference voltage for use in power supplies and otherequipment.This particularzenercircuitwill work to maintain 10V acrossET212 Electronics– SpecialPurposeDiodesProf.Jang the load.ET212 Electronics – Diodes and ApplicationsA zener diode is much like a normal diode. The exception being is that it isplaced in the circuit in reverse bias and operates in reverse breakdown. Thistypical characteristic curve illustrates the operating range for a zener. Notethat its forward characteristics are just like a normal diode.35Volt-ampere characteristic is shown in this Figure with normal operating regions forrectifier diodes and for zener diodes shown as shaded areas.369
Zener BreakdownBreakdown CharacteristicsZener diodes are designed to operate in reverse breakdown. Two typesof reverse breakdown in a zener diode are avalanche and zener. Theavalanche break down occurs in both rectifier and zener diodes at asufficiently high reverse voltage. Zener breakdown occurs in a zenerdiode at low reverse voltages.Figure shows the reverse portion of a zener diode’s characteristic curve.As the reverse voltage (VR) is increased, the reverse current (IR) remainsextremely small up to the “knee” of the curve. The reverse current is alsocalled the zener current, IZ. At this point, the breakdown effect begins;the internal zener resistance, also called zener impedance (ZZ), begins todecrease as reverse current increases rapidly.A zener diode is heavily doped to reduced the breakdown voltage. Thiscauses a very thin depletion region. As a result, an intense electric fieldexists within the depletion region. Near the zener breakdown voltage(Vz), the field is intense enough to pull electrons from their valencebands and create current. The zener diodes breakdown characteristicsare determined by the doping processLow voltage zeners less than 5V operate in the zener breakdown range.Those designed to operate more than 5 V operate mostly in avalanchebreakdown range. Zeners are commercially available with voltagebreakdowns of 1.8 V to 200 V.ET212 Electronics – Diodes and ApplicationsFloyd37Zener Equivalent CircuitET212 Electronics – Diodes and ApplicationsZZ VZ I Z38Ex 2-10 A zener diode exhibits a certain change in VZ for a certainchange in IZ on a portion of the linear characteristic curve betweenIZK and IZM as illustrated in Figure. What is the zener impedance?Figure (b) represents the practical model of a zener diode, where thezener impedance (ZZ) is included. Since the actual voltage curve is notideally vertical, a change in zener current ( IZ) produces a small changein zener voltage ( VZ), as illustrated in Figure (c).ZZ Floyd VZ I Z50 mV5 mV 10 ΩZener diode equivalent circuit models andthe characteristic curve illustrating ZZ.39ET212 Electronics – Diodes and ApplicationsFloyd4010
Ex 2-11 Figure shows a zener diode regulator designed to hold 10 V at the output.Assume the zener current ranges from 4 mA maximum (IZK) to 40 mA maximum(IZM). What are the minimum and maximum input voltages for these current?.Zener diode Data Sheet InformationAs with most devices,zener diodes have givencharacteristics such astemperature coefficientsand power ratings thathave to be considered.The data sheet providesthis information.For minimum current,The voltage across the1.0 kΩ resistor isVR IZK · R (4 mA)(1 kΩ) 4 VSince VR VIN – VZ,VIN VR VZ 4 V 10 V 14 VVZ: zener voltageIZT: zener test currentZZT: zener ImpedanceIZK: zener knee currentIZM: maximum zenercurrentFor the maximum zener current, the voltage across the 1.0 kΩ resistor isVR (40 mA)(1.0 kΩ) 40 VTherefore,VIN 40 V 10 V 50 VET212 Electronics – Diodes and ApplicationsFloyd41Zener Diode Applications – ZenerRegulation with a Varying Input VoltagePartialdatasheet for the1N4728-1N4764series 1 W zener diodes. FloydET212Electronics– Diodesand Applications42TroubleshootingAlthough precise power supplies typically use IC type regulators,zener diodes can be used alone as a voltage regulator. As with alltroubleshooting techniques we must know what is normal.A properly functioning zener will work to maintain the output voltage withincertain limits despite changes in load.ET212 Electronics – Diodes and ApplicationsFloyd43ET212 Electronics – Diodes and ApplicationsFloyd4411
OutlinesEET1240/ET212 Electronics¾ Introduction to Zener Diode¾ Voltage regulation and limitingSpecial Purpose Diodes¾ The varactor diode¾ LEDs and photodiodesElectrical and TelecommunicationsEngineering Technology Department¾ Special DiodesProfessor JangKey Words: Zener Diode, Voltage Regulation, LED, Photodiode, Special DiodePrepared by textbook based on “Electronics Devices”by Floyd, Prentice Hall, 7th edition.ET212 Electronics – Special Purpose DiodesIntroductionThis particular zener circuit will work to maintain 10 V across the load.Floyd2Zener DiodesThe zener diode is a silicon pn junction devices that differs from rectifierdiodes because it is designed for operation in the reverse-breakdownregion. The breakdown voltage of a zener diode is set by carefullycontrolling the level during manufacture. The basic function of zener diodeis to maintain a specific voltage across it’s terminals within given limits ofline or load change. Typically it is used for providing a stable referencevoltage for use in power supplies and other equipment.ET212 Electronics – Special Purpose DiodesFloyd3A zener diode is much like a normal diode. The exception being is that it isplaced in the circuit in reverse bias and operates in reverse breakdown. Thistypical characteristic curve illustrates the operating range for a zener. Notethat it’s forward characteristics are just like a normal diode.Volt-ampere characteristic is shown in this Figure with normal operating regions forrectifier diodes and for zener diodes shown as shaded areas.41
Zener BreakdownBreakdown CharacteristicsZener diodes are designed to operate in reverse breakdown. Two typesof reverse breakdown in a zener diode are avalanche and zener. Theavalanche break down occurs in both rectifier and zener diodes at asufficiently high reverse voltage. Zener breakdown occurs in a zenerdiode at low reverse voltages.Figure shows the reverse portion of a zener diode’s characteristic curve.As the reverse voltage (VR) is increased, the reverse current (IR) remainsextremely small up to the “knee” of the curve. The reverse current is alsocalled the zener current, IZ. At this point, the breakdown effect begins;the internal zener resistance, also called zener impedance (ZZ), begins todecrease as reverse current increases rapidly.A zener diode is heavily doped to reduced the breakdown voltage. Thiscauses a very thin depletion region. As a result, an intense electric fieldexists within the depletion region. Near the zener breakdown voltage(Vz), the field is intense enough to pull electrons from their valencebands and create current. The zener diodes breakdown characteristicsare determined by the doping processLow voltage zeners less than 5V operate in the zener breakdown range.Those designed to operate more than 5 V operate mostly in avalanchebreakdown range. Zeners are commercially available with voltagebreakdowns of 1.8 V to 200 V.ET212 Electronics – Special Purpose DiodesFloyd5 VZZ Z I ZFloyd6IZ on a portion of the linear characteristic curve between IZK and IZM asillustrated in Figure. What is the zener impedance?Figure (b) represents the practical model of a zener diode, where the zenerimpedance (ZZ) is included. Since the actual voltage curve is not ideallyvertical, a change in zener current ( IZ) produces a small change in zenervoltage ( VZ), as illustrated in Figure (c).ET212 Electronics – Special Purpose DiodesFloydEx 33-1 A zener diode exhibits a certain change in VZ for a certain change inZener Equivalent CircuitZenealent circtrattingZZZ.Zenerr diodiode equivequivaircuitmodmodelsaand thethe chacharacterististiccucurverve illusillustraET212 Electronics – Special Purpose Diodes7ZZ VZ 50mV 10Ω I Z5mVET212 Electronics – Special Purpose DiodesFloyd82
Zener diodediode Data SheetSheet InformaInformationEx 33-2 A IN4736 zener diode has a ZZT of 3.5 Ω. The data sheet gives VZT As with most devices,zener diodes have givencharacteristics such astemperature coefficientsand power ratings thathave to be considered.The data sheet providesthis information.6.8 V at IZT 37 mA and IZK 1 mA. What is the voltage across the zenerterminals when the current is 50 mA? When the current is 25 mA? IZ IZ – IZT 13 mA VZ IZ ZZT (13 mA)(3.5 Ω) 45.5mVVZ 6.8 V VZ 6.8 V 45.5 mV 6.85VVZ: zener voltageIZT: zener test currentZZT: zener ImpedanceIZK: zener knee currentIZM: maximum zenercurrent IZ - 12 mA VZ IZ ZZT (-12 mA)(3.5 Ω) - 42 mVVZ 6.8 V - VZ 6.8 V - 42 mV 6.76VPartial da28-1N4764 sedata shsheet foforththe 1N471N4728-1N4764serieries11WW zenerzener diodediodess.ET212 Electronics – Special Purpose DiodesFloyd9The temperature coefficient specifies the percent change in zenervoltage for each oC change in temperature. For example, a 12 V zenerdiode with a positive temperature coefficient of 0.01%/oC will exhibit a1.2 mV increase in VZ when the junction temperature increases oneCelsius degree. VZ VZ TC T25 oC) has a positive temperaturecoefficient of 0.05 %/oC. What is the zener voltage at 60 oC?The change in zener voltage isEx 33-4 A certain zener diode has a maximum power rating of 400 mW at 50ΔVZ VZ TC ΔT (8.2 V)(0.05 %/oC)(60 oC – 25 oC)oC and a derating factor of 3.2 mW/oC. Determine the maximum power the zenercan dissipate at a temperature of 90 oC. 144 mVPD(derated) PD(max) – (mW/oC) T 400 mW – (3.2 mW/oC)(90oC – 50 oC) 400 mW – 128 mW 272 mWNotice that 0.05%/oC was converted to 0.0005/oC. The zener voltage at 60 oC isVZ ΔVZ 8
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Physics 20 General College Physics (PHYS 104). Camosun College Physics 20 General Elementary Physics (PHYS 20). Medicine Hat College Physics 20 Physics (ASP 114). NAIT Physics 20 Radiology (Z-HO9 A408). Red River College Physics 20 Physics (PHYS 184). Saskatchewan Polytechnic (SIAST) Physics 20 Physics (PHYS 184). Physics (PHYS 182).
The Physics of Semiconductors – Grundmann . Basic Semiconductors Physics - Hamaguchi . Introduction 2. Crystal and Energy Band structure 3. Semiconductor Statistics 4. Defects and Impurities . Lecture Ivan Ivanov, IFM Lecture Micheal Re
ADEKA SUPER TEOS PRODUCT NAME Si(OC 2H5)4 CHEMICAL FORMULA APPLICATION Dielectric film/Semiconductor ADEKA HIGH-PURITY TEOP PO(OC 2H5)3 Dopant/Semiconductor ADEKA HIGH-PURITY TEB B(OC 2H5)3 Dopant/Semiconductor ADEKA HIGH-PURITY TiCl4 TiCl4 Electrode/Semiconductor ADEKA SUPER TMA Al(CH 3)3 High-k material/Semiconductor ADEKA ORCERA TDMAH Hf[N(CH 3)2]4 High-k material/Semiconductor
8 Annual Book of ASTM Standards, Vol 14.02. 9 Annual Book of ASTM Standards, Vol 03.03. 10 Annual Book of ASTM Standards, Vol 03.06. 11 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036. 12 Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, Three Park Ave., New York, NY 10016-5990. 13 .
