ElEctronic DEvicEs

Vayu Education of India2/25, Ansari Road, Darya Ganj, New Delhi-110 002

(An ISO 9001:2008 Certified Company)

Prof. Rajeshwar SinghDean

Gateway Institute of Engineering and Technology,Sonipat, NCR Delhi.

Electronic Devices

Copyright ©VAYU EDUCATION OF INDIA

ISBN: 978-93-83137-86-2

First Edition: 2013

Price: 150/-

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contents

1. Component and diodes .......................................................................... 1-43 1.1 Introduction ......................................................................................................................... 1 1.2 History and Evolution ........................................................................................................... 1 1.3 Electronic Circuit Components ............................................................................................. 4 1.3.1 Resistors ................................................................................................................... 4 1.4 Diodes as Rectifier ............................................................................................................... 10 1.5 Voltage waveforms in a single diode rectifier circuit ............................................................. 11 1.6 performance Parameters of rectifiers .................................................................................... 11 1.6.1 DC Voltage or Current ........................................................................................... 11 1.6.2 Ripple Factor .......................................................................................................... 12 1.6.3 Diode Approximate Equivalent Circuit ................................................................... 13 1.6.4 Three Segment Piecewise Linear Approximation ..................................................... 13 1.6.5 Efficiency ................................................................................................................ 14 1.6.6 Regulation .............................................................................................................. 15 1.6.7 Rectifier Applications .............................................................................................. 15 1.6.8 Transformer Utilization Factor (TUF) .................................................................... 15 1.7 Types of rectifier circuits ...................................................................................................... 15 1.7.1 Single Phase Half Wave Rectifier (with resistive load) ............................................. 15 1.7.2 Single Phase Full Wave Rectifier Circuits ................................................................ 22 1.7.3 Three Phase Rectifier Circuits ................................................................................. 35 1.8 Rectifier applications ........................................................................................................... 35 1.9 Filters .................................................................................................................................. 35 1.9.1 Capacitor Filter ....................................................................................................... 36 1.9.2 Inductor Filter ........................................................................................................ 41 1.9.3 L-C Filter................................................................................................................ 42 1.9.4 L-C p Filter ............................................................................................................ 42 1.9.5 R-C p Filter ............................................................................................................ 42 1.9.6 Combination or Multisection Filters ....................................................................... 43

Questions ............................................................................................................................ 43

2. Bipolar JunCtion transistors ......................................................... 44-67 2.1 Bipolar junction transistor (BJT) ........................................................................................... 44 2.2 Transistor action .................................................................................................................. 45 2.2.1 Current Across the Collector Junction .................................................................... 47 2.2.2 Total Components of Currents in NPN Transistor.................................................. 48 2.2.3 Generalized Collector Current Expression .............................................................. 48 2.2.4 Inverted Operation of a BJT ................................................................................... 49 2.2.5 Current Gain of a Transistor ................................................................................... 49

iv Electronic Devices

2.3 Transistor amplifier configuration ....................................................................................... 50 2.3.1 Common Base (CB) Configuration ........................................................................ 50 2.3.2 Common Emitter (CE) Configuration ................................................................... 52 2.3.3 Common Collector (CC) Configuration ................................................................ 52 2.4 Bjt characteristics ................................................................................................................ 55 2.4.1 Transistor Characteristics in CB Configuration ....................................................... 58 2.4.2 Transistor Characteristics in CE Configuration ....................................................... 59 2.4.3 Transistor Characteristics in CC Configuration ...................................................... 59 2.4.4 Limiting Values in Transistor Operation ................................................................. 59 2.4.5 Early Effect ............................................................................................................. 61 2.4.6 Non-linearity in the Transistor Characteristics ........................................................ 61 2.5 Feedback amplifiers ............................................................................................................... 61 2.6 Analysis of Feedback Amplifiers .......................................................................................... 61 2.7 Positive Feedback .................................................................................................................. 62 2.8 Negative Feedback ............................................................................................................... 62 2.9 Effect of Positive And Negative Feedback ............................................................................ 62 2.9.1 Effect of –ve Feedback on Distortion and Noise .................................................................... 63 2.9.2 Effect of –ve Feedback on Bandwidth .................................................................................... 63 2.10 Types of Feedback ................................................................................................................. 64 2.10.1 Voltage Series Feedback or Voltage Sampled Voltage Feedback Amplifier ................ 64 2.10.2 Voltage Shunt Feedback or Trans-resistance Amplifier ............................................. 65 2.10.3 Current Series Feedback or Transconductance Amplifier ......................................... 65 2.10.4 Current Shunt Feedback or Current Sampled Current Feedback Amplifier ............. 66

Questions .............................................................................................................................. 67

3. transistor osCillators and Fet, uJt ...........................................68-87 3.1 Oscillators and Criteria for Oscillations ................................................................................. 68 3.2 RC Oscillators ..................................................................................................................... 68 3.3 LC Oscillators ..................................................................................................................... 68 3.4 Phase Shift Oscillator .......................................................................................................... 69 3.5 Wien Bridge Oscillator ........................................................................................................ 70 3.6 Colpitts Oscillator ................................................................................................................. 72 3.7 Hartley Oscillator .................................................................................................................. 73 3.8 Crystal Oscillator .................................................................................................................. 74 3.9 Field Effect Transistors (FFT) ................................................................................................ 75 3.9.1 Junction Field Effect Transistor (JFET) ................................................................... 76 3.9.2 Operation on JFET ................................................................................................ 77 3.9.3 Characteristics ........................................................................................................ 79 3.10 UJT and Its Operation .......................................................................................................... 81

Questions ............................................................................................................................ 87

4. thyristors ..........................................................................................88-104 4.1 PN-Pn Diode: Thyristor or Scr (silicon controlled rectifier) ................................................. 88 4.2 Bi-lateral Device: Diac ........................................................................................................... 91 4.3 Triac ...................................................................................................................................... 92

contents v

4.3.1 Power Control ........................................................................................................ 93 4.4 GTO ..................................................................................................................................... 94 4.4.1 Saw Tooth Generator .............................................................................................. 94 4.5 I GBT ................................................................................................................................... 95 4.6 IGB Ts Switching Characteristics........................................................................................... 96 4.6.1 Turn-on Transients .................................................................................................. 97 4.6.2 Turn-off Transients ................................................................................................. 98 4.6.3 IGBT Safe Operating Area...................................................................................... 99 4.7 MESFETs – Metal – Semiconductor ................................................................................... 100 4.8 MISFET ............................................................................................................................. 102 4.9 Metal oxide semiconductor fet ............................................................................................ 102

Questions .......................................................................................................................... 104

5. opto eleCtroniC deviCes and Wave shaping CirCuits .............. 105-123 5.1 Light Dependent Resistors (LDR) ....................................................................................... 105 5.2 Light emitting diodes (LEDs) ............................................................................................ 105 5.2.1 7-Segment Displays .............................................................................................. 106 5.2.2 14-Segment Display .............................................................................................. 107 5.2.3 16-Segment Display .............................................................................................. 107 5.2.4 Dot Matrix Display .............................................................................................. 108 5.3 LCDs (Liquid Crystal Displays) .......................................................................................... 108 5.3.1 Introduction ......................................................................................................... 108 5.3.2 Principle of Operation and Construction .............................................................. 108 5.3.3 Dynamic Scattering Type LCD ............................................................................. 108 5.3.4 Field Effect Type LCD .......................................................................................... 109 5.3.5 Advantages and Disadvantages of LCD Display .................................................... 109 5.3.6 Applications .......................................................................................................... 109 5.4 Diode wave shaping circuits .............................................................................................. 109 5.4.1 Clipper Circuits .................................................................................................... 110 5.4.2 Diode Clamping Circuits...................................................................................... 113 5.5 Voltage Multiplier Circuits ............................................................................................... 116 5.6 Flip-Flops ............................................................................................................................ 116 5.6.1 Combinational Logic ............................................................................................ 116 5.6.2 Sequential Logic ................................................................................................... 116 5.6.3 SR Flip-Flop-Active High ..................................................................................... 116 5.6.4 SR Flip-flop-Active-Low ....................................................................................... 117 5.6.5 Level Clocked SR Flip-Flop .................................................................................. 118 5.6.6 D-Flip-Flop (Data Flip-Flop) ................................................................................ 119 5.6.7 Level Clocked JK Flip-Flops ................................................................................. 120 5.6.8 Edge Triggered JK Flip-flop .................................................................................. 121 5.6.9 T-Flip-flop ............................................................................................................ 122

Questions .......................................................................................................................... 123

Index ............................................................................................................................125-126

1.1 INTRODUCTION Whether there is an electrical system or electronic system, both deal with electrical parameters likeelectric charge, current, voltage, frequency, resistance, inductance, capacitance etc. Then what is thedifference?

They can be differentiated in so many ways, like, electronic circuits or systems are those whichinclude devices in which the flow (drift) of electronic charge carriers takes place through vacuum, gasor semiconductor, while in electrical circuits or systems the current flow is through metals or liquids.But more precise definition which clearly differentiates electronics from electrical is that an electronicsystem deals or concerns with signals which carry some information, the electrical quantities involvedare just the medium. Thus an electronic circuit may be for generating, receiving, transmitting,transforming, processing or evaluating some signals. These signals may be for some display, control orcommunication. There is always some amount of electrical energy consumed in electronic systemsalso, but, this energy is not the purpose. So least is the energy consumed the best it is, but the informationshould be dealt with most faithfully. On the contrary, electrical systems deal with energy. So an electricaldevice or system may be for the generation, transmission, or utilization of electrical energy. In electricaldevices current is due to drift of electrons while in electronic devices, especially active electronicdevices, current is due to movement of electrons or holes or both.

By using any of the above statements differentiating electronics from electrical, one can easily saywhich system is electronic and which is electrical. But in some cases there may still be overlapping; thesame system one person may call it electronic and other person may call it electrical.

1.2 HISTORY AND EVOLUTIONBoth electrical and electronic systems basically involve charge carriers or electricity. Thousands ofyears ago when Greeks discovered artificially produced electricity by rubbing some materials, that wasthe birth of electrical or electronic science. Natural electricity has always existed in the form of lightningetc. But the application of electricity produced by friction was restricted merely to stage presentationsas the manifestations of some magical or divine phenomenon. It was in the later part of the 18th centurywhen the discovery of current electricity was first made by an Italian doctor Aloisio Luigi Galvani,while experimenting with frog-legs. That led to the development of first electrical cell. Then various

Component and Diodes

CHAPTER

1

2 Electronic Devices

discoveries in the field of electric power engineering took place like the development of electromagneticgenerators and motors, electric lamp etc. in the 19th century. Most of the historical discoveries whichhave led to the development of electronics of today’s stage have been listed in chronological order asfollows:

Year Event1837 Gauss and Weber invented telegraph in Germany1843 Wheatstone bridge was invented1856 Transoceanic telegraph cable laid1860 Plante developed a lead storage battery1864 Maxwell postulated electromagnetic waves1868 Leclanche invented the famous cell1875 Graham Bell invented the telephone1878 Hughes demonstrated the microphone1887 Hellesen developed the first commercial dry cell1887 Photo electric effect observed by Hertz1888 Heinrisch Hertz discovered the electromagnetic waves1895 Marconi transmitted the first radio signals over one kilometer.1895 Conrad Roentgen discovered X-rays1897 J.J. Thomson discovers the electron1900 Wireless first installed on merchant ships1900 Quantum Theory developed by the Max Planck1902 Cooper Hewitt developed Mercury Arc rectifier1904 Thermioinic Diode (Vacuum tube diode) was invented by Fleming1906 International Electro Technical Commission (IEC) founded1913 Niels Bohr postulated the modified structure of atom1914–18 Valve amplifiers were introduced on telephone networks1922 Cathode Ray Oscilloscope produced1925 Pauli’s exclusion Principle proclaimed1927 Television appeared1929 Thyratron introduced1931 Classical exposition on semiconductors by Wilson1946 The first electronic computer (ENIAC) employing 18000 vacuum tubes produced

at the university of Pennsylvania1948 Bardeen, Brattain and Shockley fabricated and demonstrated in Bell Telephone

laboratories the amplifying action of a semiconductor transfer resister (whichwas named later on Transistor). This is considered as the most important historicalevent or the evolutionary event in the progress history of electronics.

1956 Thyristor was produced in General Electric company1959 Fairchild Semiconductor corporation developed the planar process for diffusing

the semiconductor layers.

Component and Diodes 3

1961 Fairchild introduced the first monolithic integrated circuit, an RTL flip-flop IC,for commercial use.

1971 The first 4-bit microprocessor introduced by Intel corporation.1980s From 1980 onwards, has been a glut of higher and higher order microprocessors

incorporated as CPUs in modern computers.1990s 1990s and start of 21st century is the era of satellite and mobile communication.With the progress of IC technology, component densities on the silicon chip increased so rapidly,

that large circuits could be put on a single small silicon chip, so the costs and sizes decreased tremendouslyand the performances increased. That led to very fast spread of electronics, especially digital electronics,computers and then the software technology and spurt of communication technologies. So today we findelectronics and electronics all around us. Information technology is developing with mind boggling pace.

1948 is the historical year in the growth of electronics, because the semiconductor transistor amplifiertook birth in this year, which heralded the start of the solid slate electronics. So fast and so vast spreadof electronics owe to it. Before that it was mostly all vacuum tube electronics. In 1950s and 1960s moreand more semiconductor discrete components and ICs were produced. At first the circuits were beingdesigned and assembled using discrete solid state components, then mixed with ICs. In this period andafterwards tremendous miniturization of electronic systems took place, costs went down, so the productionof vacuum tubes also gradually reduced and by about 1970 there was vacuum tube production only forspecial applications.

Now the field of electronics engineering is so large that no body can master it wholly in onelifetime. Not only that, it is still expanding. So, for the specialization, electronics now has so manybranches and sub-branches like-

1. Communication Engineering(a) Radio Communication(b) Microwave Communication(c) Satellite Communication(d) Radar Engineering(e) Mobile or Cellular Communication(f) Cable Communication(g) Digital Communication and Internet(h) Optical Communication(i) ISDN, etc.

2. Consumer Electronics3. Industrial Electronics4. Television Engineering5. Electronic Instrumentation and Control6. Biomedical Electronics and Instrumentation7. Computer Engineering8. Power Electronics9. Microprocessor based control systems

10. VLSI/Microelectronics/Nano electronics11. Defence Electronics

4 Electronic Devices

12. Signal Processing13. Industrial automation and process control14. Robotic Engineering, and so on.

1.3 ELECTRONIC CIRCUIT COMPONENTSAn electronic circuit comprises of active and passive components. Active components are the voltageor current source in the circuit and those components which shape the given input signal into a desiredoutput. So a power supply to the circuit and any semiconductor device like a diode, transistor, thyristoretc. are all active devices. The three possible circuit parameters in any electrical or electronic circuitviz. resistances capacitances and inductances are called passive parameters; these devices are termedas passive components. Any one or more of these three components are essentially present in a circuitwith single unit or multiple units of them. They simply control the value of current or change of voltageor change of current across or through them. The behavour construction, characteristics and applicationof the active components is to be discussed in the following chapters. The characteristics of resistances,capacitances and inductances has already been learnt by you in your earlier courses. Only certainrelevant practical points regarding them are presented here.

Any wire or terminal has besides its resistance, some capacitance and some inductance. But theirvalues are generally so small that they are insignificant in the circuit and are neglected except in somespecial critical cases. Majority of the electronic circuits are designed today based on ICs. In ICs all theactive and passive components are fabricated and their connections made within a small silicon chip.So the user need not bother for the assembly of the circuit. Still some discrete components may haveto be added to the IC for achieving some special functions. Besides the large current or voltagecomponents, large values of resistances and capacitances and significant values of inductances aredifficult to fabricate in an IC. So such components are used discretely. Use of inductances is generallyminimized in electronic design. When an inductance has to be used it is in discrete form.

All the circuits are not and cannot be available in IC form. A circuit in IC form is available onlywhen it is to the used in large quantity, generally millions of chips. Because larger is the number of ICsfabricated for a given circuit lesser is the cost of one IC. If you design a small circuit which is to theused only at ten places i.e. only ten number of the circuit boards are to the fabricated. If it is already notavailable in IC form then you may get them using discrete components and spend few hundreds ofrupees. But if you try to get 10 pieces of IC of this circuit, it may cost you millions of rupees per IC.If millions of ICs of one circuit are ordered then it may cost only few rupees per IC. That is why stilltoday a lot of discrete components are produced and used. Bigger new circuits or systems to be usedonly at few places, are generally designed using standard ICs for different functions/sub-functions inthe system. A large number of standard ICs are now available for most of the electronic functions.

1.3.1 ResistorsResistors can be classified into three main groups:

1. Fixed resistors2. Manually variable resistors3. Automatically variable resistors (sensors/transducers)

1.3.1.1 Fixed resistorsFollowing types of fixed resistors are used as shown in Fig. 1.1.

Component and Diodes 5

Fig. 1.1

Film Resistors: Electronic circuits generally need higher ohmic value and low wattage resistors.Carbon or metal film resistors are widely used (refer Fig. 1.1), since they satisfy the requirement andare very cheap. In case of carbon film resistors a layer of 0.001 µm to 10 µm, as required, is depositedon a base of porcelain. Coils are cut and finally varnished.

Metal film resistors are produced by either of the two processes. In thick film process, a paste ofmetals, metal components and powdered glass is spread on to a ceramic base and then baked. In thinfilm process, the metals are vapour deposited through a mask and a film as thin as 0.05 µm can beobtained.

All film resistors are coated with synthetic resin to protect them against mechanical and climaticinfluences. It is therefore difficult to distinguish them from each other externally. Metal film resistorsare slightly superior to carbon film resistors as they have slightly better temperature stability andslightly larger power dissipation capacity. These metal film resistors are available from a few ohms toa few mega ohms values. Only standard nominal values with standard tolerances as specified by IECare manufactured. Film resistors are manufactured for various wattages from 50 mW to ½ W. Also theresistors of I W and 2 W are available.

Wire Wound Resistors: Only in some special cases low ohmic value and large wattage resistancesare needed in electronic circuits, then wire wound resistors are used. In electric circuits usually wirewound resistor are used. These resistors are wound from insulated or oxidized resistance wires thenvarnished, cemented, glazed or coated with ceramic.

Resistor Specifications: Following are the most important specifications of a resistor:1. Nominal ohmic value2. Tolerance limits of the nominal value3. Wattage or loading capacity

Besides the above specifications some other characteristics of resistors may also have to beconsidered sometimes, like temperature coefficient, voltage coefficient , high frequency characteristics,electrical noises etc.

Resistors are manufactured of nominal ohmic values and tolerance specified by IEC as follows:(i) Serieses have been fixed with number of values for each decade as shown in Table 1.1.

(ii) The nominal values have been so chosen that the maximum tolerance limits between neighboringvalues result in small overlaps.

6 Electronic Devices

Table 1.1: IEC – specified resistance serieses

E 6 E 12 E 24± 20% ± 10% ± 5%

1.0 1.0 1.01.1

1.2 1.21.3

1.5 1.5 1.51.6

1.8 1.82.0

2.2 2.2 2.22.4

2.7 2.73.0

3.3 3.3 3.33.6

3.9 3.94.3

4.7 4.7 4.75.1

5.6 5.66.2

6.8 6.8 6.87.5

8.2 8.2

9.1

Table 1.2: Standard colour code for resistors (also for capacitors if used)

Value of resistor in Tolerance Voltage ratingCharacteristic in case of

colour capacitors

1st band 2nd band 3rd band 4thband

none - - - ± 20% 500(v)silver - - 10-2 ± 10% 2000gold - - 10-1 ± 5% 1000black - 0 100 = 1 - -brown 1 1 101 ± 1% 100red 2 2 102 ± 2% 200orange 3 3 103 - 300yellow 4 4 104 - 400green 5 5 105 ± 0.5% 500

Component and Diodes 7

blue 6 6 106 ± 0.25% 600violet 7 7 107 ± 0.1% 700grey 8 8 108 - 800white 9 9 109 - 900

Table 1.3

Rated Value Characterisation

0.33 R333.3 3R333 33R330 330R0.33 k K333.3 k 3K333 k 33K330 k 330K0.33 M M333.3 M 3M333 M 33M330 M 330M

The nominal value of resistance and the tolerance is usually provided on the round surface of theresistor with the help of the four colour bands (rings) as shown in Fig.1.2. The standard colour codeis provided in Table 1.2

Fig. 1.2: 4-ring colour code of resistors. Fig. 1.3: 5-ring colour code of resistors.

The nominal ohmic value of a resistor can be found by the Eq. 1.1R = (AB) × 10c ± D% ...(1.1

Sometimes a manufacturer provides five colour bands on the resistor ad depicted in Fig. 1.3.Then the first three of these bands provide the IEC number for the resistance value, the 4th band givesthe multiplier and the 5th band gives the tolerance. Sometimes resistors are specified for their resistancevalue by an alphanumeric code as depicted by Table 1.3.

8 Electronic Devices

EXAMPLE 1.1

A resistor has 4 colour bands : 1st band brown, 2nd band blue, 3rd yellow and 4th gold. Determine itsnominal value of resistance and tolerance value.Solution: From Eq. 1.1 (using table 1.2) we have:

R = (16) × 104 ± 5%Hence the nominal value of the resistance 160 k .

Tolerance Value:5160

100 = ± 8 k

1.3.1.2 Manually variable resistorssThese are generally called potentiometers or pots. The resistance value can be manually changed asdesired within the limits. These are classified as per the method of adjustment: Some of the types ofpots are depicted in Figs. 1.4, 1.5 and 1.6.

Trimmer potentiometers are resistors whose ohmic value can be adjusted with the help of a tool(e.g. screw driver).

Fig.1.4: Trimmer pots.

Fig.1.5: Rotary pots.

Fig. 1.6: Sliding potentiometers.

Component and Diodes 9

1.3.1.3 Automatic variable resistors (resistor sensors/transducers)There are special resistors in use in electronic circuits whose ohmic value is dependent upon the valueof the particular physical quantity they sense like voltage, temperature, light, pressure, etc.Such resistorsare produced using special materials. For instance, a resistor which is made from such material whichis effected substantially when light falls on it, is called a light dependent resistor. Some such specialpurpose resistors are described in brief here:

1. Light Dependent Resistors (LDR): They are also sometimes termed as photoconductors.Their resistance falls with increasing intensity of illumination. The light energy sets free somemore electrons in the material of the resistor. Thus the conductivity increases. Symbol is givenin Fig. 1.7 (a)

2. Voltage Dependent Resistors (VDR):They are also known as varistors. Their resistancefalls with increasing voltage. The explanation given is this that the component is made up ofvery large number of small grains. These may be conceived of as a complicated network ofvery small resistors. Due to the applied voltage, the contact resistance between them reduces,so the material conducts better. Fig. 1.7(b) depicts the symbol. Usually VDR is constructedusing materials like silicon carbide, zinc oxide or ceramic mixtures.

3. Pressure Dependent Resistors: In these components, the resistance increases with risingpressure. More pressure reduces the distance between the atoms and the frequency of collisionswith the free electrons increases, so the resistance increases. The symbol is depicted in Fig. 1.7(c).

4. Temperature Dependent Resistors: All metals increase their resistance with increase intemperature. But their temperature coefficient of resistance is very small. In case of semi conductingmaterials the temperature coefficient of resistance is quite substantial. Normally temperaturedependent resistors are made of the semi-conducting materials. Such resisters are calledThermistors. Generally the resistance of thermistors decreases with the increase in temperature;such resistors are called NTC (Negative Temperature Coefficient) type thermistors. But certainsemi-conducting materials resistors are manufactured whose resistance increases with increasein temperature. Such resistors are called PTC (Positive Temperature Coefficient) type thermistors.Fig. 1.7(d) depicts an NTC type of temperature dependent resistor. In case of PTC type, thearrows are drawn both vertically upward depicting rise of resistance with rise in temperature.Usually thermistors are made from the mixtures of metallic oxides like MnO2 and NiOwhich possesssemi-conducting properties. Thermistors are more commonly used for temperature sensingbecause they are available in all shapes and sizes and sufficient values of resistances.

5. Magnetic Field Dependent Resistors: These are also termed as field plates. As magneticfield increases their resistance also increases. This phenomenon can be explained as follows:Due to the presence of magnetic field, the electrons are deflected to one side in their passagethrough the resistor. Thus they have to traverse a longer path and so increase in resistance.

10 Electronic Devices

Fig. 1.7: Symbols of special purpose resistors.

1.4 DIODES AS RECTIFIERDiodes are used commonly in electronic circuits to block the flow of current in a particular direction,as they possess the property of unidirectional conduction. This very property gives them very usefulapplication of rectification i.e converting an AC to DC as depicted in Fig. 1.8. When a diode is connectedbetween an AC supply and a load, the load receives a DC i.e a unidirectional supply. The supply is ACmeans, the input of terminals, each one of them T1 and T2 gets alternately the +ve and –ve polarities ofthe supply voltage. When T1 is +ve, T2 is –ve and vice versa. As long as T1 is +ve, the anode terminalof the diode D (P side of the P-N junction) is +ve with respect to the cathode (N side of the P-Njunction of the diode), the diode conducts i.e., it behaves like a closed switch as depicted in Fig. 1.8(b)so the input voltage passes on to the load RL, the output voltage v0 is nearly the same as the inputvoltage vi.

Fig. 1.8: Diode as a rectifier.

Electronic Devices By Prof. Rajeshwar Rai

Publisher : Vayu Education ISBN : 9789383137862 Author : Prof . RajeshwarRai

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