UNIT 1

SUBJECT- BASIC ELECTRONICS SEM- 3rdBRANCH- EEE

Created by: Ritwik Tripathi (Lecturer)Dept. of EEEDr. C.V.Raman universityBilaspur(C.G)

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UNIT IDIODESDept. Of EEE Dr. C. V. Raman University

TRANSPORT PHENOMENONApn junctionis a boundary or interface between two types of semiconductor material, p and n type.

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PROPERTIES OF P-N JUNCTION

pn junctions are commonly used asdiodes: circuit elements that allow a flow ofelectricityin one direction but not in the other (opposite) direction.Biasis the application of a voltage across a pn junction;forward biasis in the direction of easy current flow, andreverse biasis in the direction of little or no current flow.

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VI - CHARCTERISTICS

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TEMPERATURE DEPENDENCE P-N CHARACTERISTICSThe cut-in voltage decreases as the temperature increases. The diode conducts at smaller voltage at large temperature.The reverse saturation current increases as temperature increases.This increases in reverse current Iois such that it doubles at every 10oC rise in temperature. Mathematically,where Io2= Reverse current at T2oC Io1= Reverse current at T1C T = (T2- T1)

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IDEAL DIODE

An ideal diode is a diode that acts like a perfect conductor when voltage is applied forward biased and like a perfect insulator when voltage is applied reverse biased.

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DIODE EQUATIONDiode equationThe following equation is called theShockley ideal diode equationwhenn, the ideality factor, is set equal to 1:

Iis the diode current, ISis the reverse biassaturation current (or scale current.

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DIODE EQUATIONVDis the voltage across the diode,VTis thethermal voltage , andnis theideality factor, also known as thequality factor

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CAPACITANCE

Transition and Diffusion capacitanceTransition capacitances:When P-N junction is reverse biased the depletion region act as an insulator or as a dielectric medium and the p-type an N-type region have low resistance and act as the plates.

CT = dQ/dVDept. Of EEE Dr. C. V. Raman University

CAPACITANCE

Where dQ is the increase in charge and dV is the change or increase in voltage.

The depletion region increases with the increase in reverse bias potential the resulting transition capacitance decreases.

The formula for transition capacitance is given as CT = A/W, where A is the cross sectional area of the region, and W is the width.

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CAPACITANCE

Diffusion capacitance:1. When the junction is forward biased, a capacitance comes into play , that is known as diffusion capacitance denoted as CD. It is much greater than the transition capacitance.2. During forward biased the potential barrier is reduced. The charge carriers moves away from the junction and recombine.

3. The density of the charge carriers is high near the junction and reduces or decays as the distance increases.Dept. Of EEE Dr. C. V. Raman University

CAPACITANCE

4.Thus in this case charge is stored on both side of the junction and varies with the applied potential. So as per definition change in charge with respect to applied voltage results in capacitance which here is called as diffusion capacitance.5. The formula for diffusion capacitance is CD = ID / VT , where is the mean life time of the charge carrier, ID is the diode current and VT is the applied forward voltage, and is generation recombination factor.Dept. Of EEE Dr. C. V. Raman University

UNIT IIRECTIFYING CKT. AND DC POWER SUPPLYDept. Of EEE Dr. C. V. Raman University

LOAD LINELoad line analysis of diode circuit Aload lineis used in graphical analysis ofnonlinearelectronic circuits, representing the constraint other parts of the circuit place on anon-lineardeviceIt is usually drawn on a graph of thecurrentvs thevoltagein the nonlinear device, called the device'scharacteristic curve.

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LOAD LINE

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HALF WAVE RECTIFIER

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FULL WAVE RECTIFIERFull Wave Rectifier Circuitproduces an output voltage or current which is purely DC or has some specified DC component. Full wave rectifiers have some fundamental advantages over their half wave rectifier counterparts.In aFull Wave Rectifiercircuit two diodes are now used

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FULL WAVE RECTIFIER

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The Full Wave Bridge Rectifier

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OPERATION The four diodes labelledD1toD4are arranged in series pairs with only two diodes conducting current during each half cycle. During the positive half cycle of the supply, diodesD1andD2conduct in series while diodesD3andD4are reverse biased and the current flows through the load as shown below.

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FILTER CKTS

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FILTER

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FILTER

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UNIT IIITRANSISITORDept. Of EEE Dr. C. V. Raman University

BJTTransistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistors ability to change between these two states enables it to have two basic functions: switching (digital electronics) or amplification (analog electronics).Dept. Of EEE Dr. C. V. Raman University

Bipolar TransistorsThenBipolar Transistorshave the ability to operate within three different regions:Active Region the transistor operates as an amplifier andIc=.IbSaturation the transistor is Fully-ON operating as a switch andIc=I(saturation)Cut-off the transistor is Fully-OFF operating as a switch andIc=0

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BJT

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BJTCommon Base

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BJTCommon Collecter

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BJTCommon Emitter

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EQUATIONSRelationship between DC Currents and Gains

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CharacteristicCommonBaseCommonEmitterCommonCollectorInput ImpedanceLowMediumHighOutput ImpedanceVery HighHighLowPhase Angle0o180o0oVoltage GainHighMediumLowCurrent GainLowMediumHighPower GainLowVery HighMedium

TABLEDept. Of EEE Dr. C. V. Raman University

EARLY EFFECTTheEarly effect is the variation in the width of the base in abipolar junction transistor(BJT) due to a variation in the applied base-to-collector voltage. Increases the collectorbasedepletion width, decreasing the width of the charge carrier portion of the base.

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EARLY EFFECTEBERS moll model

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UNIT IV

TRANSISTOR BIASING AND THERMAL STABILIZATIONDept. Of EEE Dr. C. V. Raman University

OPERATING POINT AND BIAS STABILITYIn order to produce distortion free output in amplifier circuits, the supply voltages and resistances establish a set of dc voltage VCEQ and ICQ to operate the transistor in the active region.These voltages and currents are called quiescent values which determine the operating point or Q-point for the transistor. The process of giving proper supply voltagesand resistances for obtaining the desired Q-Point is called Biasing.Q-point should be stable.Dept. Of EEE Dr. C. V. Raman University

THERMAL RUN AWAYCollector current IC = IB + ( +1) ICBOIB, ICBO all increases with temperatureICBO doubles for every 10 C rise in temperatureCollector current causes junction temperature to rise, which in term rises ICBO rise in Ic. This cumulative process leads to collector current to increase further and transistor may be destroyed. This phenomenon is called thermal run away.Dept. Of EEE Dr. C. V. Raman University

The extent to which the collector current IC is stabilized with varying Ico is measuredby stability factor S.It is defined as the rate of change of collector current to the change in Ico, keeping IBand B as constant., & CBCOIS IIConstant Or CcodISdICollector current Ic = IB + ( +1) ICODept. Of EEE Dr. C. V. Raman University

METHODS OF TRANSISTOR BIASING

For BJT amplifiersFive common biasing circuits are used with bipolar transistor amplifier1 Fixed Bias or base resistor Bias2 Emitter-feedback bias3 Collector to Base bias or collector feet back bias4 Collector-emitter feedback bias5 Self-bias or emitter bias or potential divider Bias.Dept. Of EEE Dr. C. V. Raman University

FIXED BIAS

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EMITTER FEEDBACK BIAS

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COLLECTOR TO BASE BIAS

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COLLECTOR TO EMITTER FEEDBACK BIAS

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VOLTAGE DIVIDER BIAS

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BIAS COMPENSATIONVarious Types Of Diode Compensations.Diode bias compensationSensistor Bias compensationThermistor Bias compensation

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UNIT VFIELD EFFECT TRANSISTORDept. Of EEE Dr. C. V. Raman University

FET ( Field Effect Transistor)1.Unipolar device i. e. operation depends on only one type of charge carriers (h or e) 2.Voltage controlled Device (gate voltage controls drain current)3.Very high input impedance (109-1012 )4.Low Voltage Low Current Operation is possible (Low-power consumption)5.Less Noisy as Compared to BJT.

Advantages of FET over conventional TransistorsDept. Of EEE Dr. C. V. Raman University

TYPES OF FIELD EFFECT TRANSISTORS (THE CLASSIFICATION) JFETMOSFET (IGFET)n-Channel JFETp-Channel JFET

n-Channel EMOSFET p-Channel EMOSFET

Enhancement MOSFETDepletion MOSFETn-Channel DMOSFET p-Channel DMOSFET

FET

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Figure: n-Channel JFET.

THE JUNCTION FIELD EFFECT TRANSISTORDept. Of EEE Dr. C. V. Raman University

GateDrainSourceSYMBOLSn-channel JFET

GateDrainSource

n-channel JFETOffset-gate symbol

GateDrainSource

p-channel JFETDept. Of EEE Dr. C. V. Raman University

Figure: n-Channel JFET and Biasing Circuit.

BIASING THE JFETDept. Of EEE Dr. C. V. Raman University

PP

+-DC Voltage Source

+-+-NNOperation of a JFETGateDrainSourceDept. Of EEE Dr. C. V. Raman University

Figure: Circuit for drain characteristics of the n-channel JFET and its Drain characteristics.

Non-saturation (Ohmic) Region:

The drain current is given by

Where, IDSS is the short circuit drain current, VP is the pinch off voltageOutput or Drain (VD-ID) Characteristics of n-JFETSaturation (or Pinchoff) Region:

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Figure: n-Channel FET for vGS = 0.

Simple Operation and Break down of n-Channel JFETDept. Of EEE Dr. C. V. Raman University

Figure: If vDG exceeds the breakdown voltage VB, drain current increases rapidly.

Break Down RegionN-Channel JFET Characteristics and BreakdownDept. Of EEE Dr. C. V. Raman University

Figure: Typical drain characteristics of an n-channel JFET.

VD-ID Characteristics of EMOS FETSaturation or Pinch off Reg.

Locus of pts where

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Figure: Transfer (or Mutual) Characteristics of n-Channel JFET

IDSSVGS (off)=VP

Transfer (Mutual) Characteristics of n-Channel JFETDept. Of EEE Dr. C. V. Raman University

Figure: n-Channel Enhancement MOSFET showing channel length L and channel width W.

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