EContent_3_2024_09_15_21_08_05_CH01DiodeTheoryandApplications_R1pdf__2024_08_03_09_58_51 (1).pdf
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Diode theory and applications: Department of Energy Band Diagram of conductor, semiconductor and Electrical Engineering insulator; Crystal Structure of Semiconductor Materials, Intrinsic and Extrinsic Semiconductor Materials, Unit no 1 Symbol and Construc...
Diode theory and applications: Department of Energy Band Diagram of conductor, semiconductor and Electrical Engineering insulator; Crystal Structure of Semiconductor Materials, Intrinsic and Extrinsic Semiconductor Materials, Unit no 1 Symbol and Construction, Operating Characteristics in Unit title: Subject name and Forward and Reverse Bias, Applications of Diode as code : BEEE Switch, Clipper, Clamper and Rectifier, Special Purpose Diodes : Zener Diode, Optical Diodes like LED, Photo Diode, Seven Segment Display The material can be classified according to their resistivity range as – Conductors (1.6 X 10-8 to 10-6 ohm-m) Semiconductors (10-4 to 106 ohm-m) Insulators (107 to 1016 ohm-m) Semiconductors are the materials whose resistivity (and hence the Introduction conductivity) lies between those of conductors and insulator The semiconductor devices are highly compact, efficient, more reliable, low power consuming, free from mechanical noise and are cheap. Most commonly used semiconductors are Si, Ge, GaAs, InP etc. Introduction Properties of Semiconductors – 1. Usually high resistivity. Electron 2. Semiconductors are unipolar. Energy States 3. They have negative temperature coefficient. of an isolated 4. They are metallic in nature. Atom 5. At 0K they behaves like insulators. 6. Both electrons and holes can be charge carrier. Types of Semiconductors 1. Elemental and compound semiconductors 2. Direct and indirect bandgap semiconductors Electron 3. Intrinsic and Extrinsic semiconductors Energy States of an isolated Atom Intrinsic or pure semiconductors – Silicon and germanium have crystalline structure. Their atoms are arranged in an ordered array known as the crystal lattice. Intrinsic semiconductor There material are tetravalent i.e. with four valence electrons in the outermost shell. The neighboring atoms form covalent bonds by sharing four electrons with each other so as to achieve stable structure. Crystal lattice structure and band gap diagram of pure germanium Energy gap – 0.72 eV for Ge. Valence Band remains full and conduction band is empty and material behaves as insulator. Intrinsic At room temp, valence band electrons acquire thermal energy semiconductor greater than Eg and hence they can jump to the higher energy conduction band. They are free now and can move under the influence of small applied field. The absence of electrons in valence band is known as hole. Hence in semiconductor there are 2 types of charge carriers. The total current is the sum of electron and holes currents. At any given temperature, Intrinsic no of electrons = no of holes in valence band are same. semiconductor With the rise in temperature, more and more electrons hole pairs are formed and more charge carriers are available for conduction. Hence the conductivity of intrinsic semiconductors increases with rise in temperature. The intrinsic semiconductor have low conductivity. Doped or Extrinsic Semiconductors – Doping is the process of adding a controlled quantity of impurity to an intrinsic semiconductor, so as to increase its conductivity. A semiconductor doped with impurity atoms is called an extrinsic semiconductor. The impurity is added by melting Ge or Si, then the crystal is Extrinsic grown in which the impurities are incorporated. semiconductor The impurity atoms occupy lattice positions which were occupied by Ge atoms in pure metal. Doping element is from III and V group elements. Two types of extrinsic semiconductors are produced depending upon the group of impurity atom. N-type Semiconductors – The pentavalent impurities is added in Ge crystal lattice. It forms four covalent bonds with four neighboring Ge atoms. The 5th electron, not used in bonding, it loosely bound & with supply little energy, it can be made free leaving behind a positively charged immobile ion. Extrinsic The impurity atoms donate free electrons to the crystal thereby semiconductor increasing the conductivity of material. Hence they are called the donor impurities. The conductivity is due to negatively charged electrons. Hence the material is called N-type semiconductor. Example - Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi) Electron-hole pairs are generated in Ge due to thermal energy. For n-type the concentration of free electrons is far greater Extrinsic than concentration of holes. semiconductor Addition of donor impurities generates new energy levels in the band picture. The energy levels ED of neutral donor atoms lie very close to the lowed edge of EC of conduction band. With the supply of little energy (0.01eV for Ge and Extrinsic 0.04eV for Si) the neutral donor atom loses fifth electron semiconductor for conduction and itself gets positively charged. P-type Semiconductors – The trivalent impurities is added in Ge crystal lattice. Trivalent is one electron short of being able to complete the stable structure. The absence of electron in one of these bonds is a hole. Extrinsic With the small amount of energy, it can accept an electron semiconductor from the neighboring Ge atom and vacancy shifts there. The impurity atom becomes a negative charged ion on accepting the electron. Thus impurity atom supply holes which are ready to accept electrons. Hence it’s a acceptor impurity. The holes concentration is much more than the electron concentration. The conductivity is due to the positively charged holes. Hence the semiconductor is called P-type semiconductor. The addition of impurity introduces additional energy Extrinsic levels EA, in the band picture, slightly above the top of the semiconductor valence band. With supply of little energy these vacancies can be occupied by electrons in VB and thus increasing the holes in VB. The extrinsic materials are electrically neutral at any given temperature. Extrinsic semiconductor If a single piece of germanium doped with P-type material from one side and the other half is doped with N-type material, then the Ge is dividing into two zones forms a P- N junction. the P-N junction is the basic element for semiconductor diodes. A Semiconductor diode facilitates the flow of electrons completely in one direction only – which is the P-N Junction main function of semiconductor diode. It can also be used as a Rectifier. There are two operating regions: P-type and N-type. And based on the applied voltage, there are three possible “biasing” conditions for the P-N Junction Diode, which are as follows: Zero Bias – No external voltage is applied to the PN junction diode. P-N Junction Forward Bias– The voltage potential is connected positively to the P-type terminal and negatively to the N- type terminal of the Diode. Reverse Bias– The voltage potential is connected negatively to the P-type terminal and positively to the N- type terminal of the Diode. There are two operating regions: P-type and N-type. And based on the applied voltage, there are three possible “biasing” conditions for the P-N Junction Diode, which are as follows: P-N Junction – Zero Bias – No external voltage is applied to the PN junction diode. Zero Bias In this case, no external voltage is applied to the P-N junction diode; and therefore, the electrons diffuse to the P-side and simultaneously holes diffuse towards the N-side through the junction, and then combine with each other. Due to this an electric field is generated by these charge carriers. When a p-n junction is formed, some of the free electrons in the n-region diffuse across the junction and combine with holes to form negative ions. In so doing they leave behind positive ions at the donor impurity sites. P-N Junction – Zero Bias P-N Junction In the forward bias condition, the negative terminal of the P-N Junction – battery is connected to the N-type material and the positive terminal of the battery is connected to the P-Type Forward Bias material. This connection is also called as giving positive voltage. Electrons from the N-region cross the junction and enters the P-region. Due to the attractive force that is generated in the P-region the electrons are attracted and move towards the positive terminal. Simultaneously the holes are attracted to the negative terminal of the battery. By the movement of electrons and holes current flows. In this condition, the width of the depletion region decreases due to the reduction in the number of positive and negative ions. In the forward bias condition, the negative terminal of the battery is connected to Forward Bias the N-type material and the positive terminal of the battery is connected to the P- Condition Type material. This connection is also called as giving positive voltage. Electrons from the N-region cross the junction and enters the P-region. Due to the attractive force that is generated in the P-region the electrons are attracted and move towards the positive terminal. Simultaneously the holes are attracted to the negative terminal of the battery. By the movement of electrons and holes current flows. In this condition, the width of the depletion region decreases due to the reduction in the number of positive and negative ions. 22 Forward Bias– The voltage potential is connected positively to the P-type terminal and negatively to the N-type terminal of the Diode. P-N Junction Diode 23 In the Reverse bias condition, the negative terminal of the P-N Junction – battery is connected to the P-type material and the positive terminal of the battery is connected to the N-type material. Reverse Bias Hence, the electric field due to both the voltage and depletion layer is in the same direction. This makes the electric field stronger than before. Due to this strong electric field, electrons and holes want more energy to cross the junction so they cannot diffuse to the opposite region. Hence, there is no current flow due to the lack of movement of electrons and holes. Reverse Bias– The voltage potential is connected positively to the N- type terminal and negatively to the P-type terminal of the Diode. P-N Junction Diode 25 V-I Characteristics 26 P-N Junction – Characteristics Definition: The approximation technique that helps in analyzing the various initial criteria of the diode can be defined as Diode Approximations. Each approximates relates from assuming ideal conditions to reaching practical ones. Diode There are three (3) Diodes Approximations: Approximations Ideal Diode (1st Approximation) Second Approximation Third Approximation 28 Ideal (1st-Approximation) - For the 1st-approx. assume the diode drop voltage is zero (Perfect closed switch) Second approximation - For the 2nd-approx. assume the diode drop voltage of 0.7 volts Diode Third Approximation - For the 3rd –approx. assume the diode drop Approximations voltage of 0.7 volt and consider the forward bulk resistance of the diode: Vd = 0.7 V + Id x Rb Ignore bulk resistance of the diode if Rb < 0.01 Rth 29 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. So when positive voltage is applied across the anode to the cathode, the diode conducts forward current instantly. Ideal Diode When voltage is applied in reverse, the diode conducts no current at all. This diode operates like a switch. Forward Bias – Closed switch, Reverse Bias – Open Switch 30 Zero Resistance Characteristics of Ideal Diode - An ideal diode does not offer any resistance to the flow of Forward Biased current through it when it is in forward biased mode. This means that the ideal diode will be a perfect conductor when forward biased. From this property of the ideal diode, one can infer that the ideal diode does not have any barrier potential. 31 Infinite Amount of Current Characteristics of Ideal Diode - This property of the ideal diode can be directly implied from its Forward Biased previous property which states that the ideal diodes offer zero resistance when forward biased. The reason can be explained as follows. In electronic devices, the relationship between the current (I), voltage (V) and resistance (R) is expressed by Ohm’s law which is stated as I = V/R. Now, if R = 0, then I = ∞. This indicates that there is no higher limit for the current which can flow through the forward-biased ideal diode 32 Zero Threshold Voltage Characteristics of Ideal Diode - Even this characteristic of the ideal diode under the forward biased Forward Biased state can be referred from its first property of possessing zero resistance. This is because threshold voltage is the minimum voltage which is required to be provided to the diode to overcome its barrier potential and to start conducting. Now, if the ideal diode is void of depletion region itself, then the question of threshold voltage does not arise at all. This property of the ideal diode makes them conduct right at the instant of being biased, leading to the green-curve of diode characteristics 33 Infinite Resistance Characteristics of Ideal Diode An ideal diode is expected to fully inhibit the flow of current when Reverse through it under reverse biased condition. Biased In other words it is expected to mimic the behavior of a perfect insulator when reverse biased. 34 Zero Reverse Leakage Current Characteristics of Ideal Diode This property of the ideal diode can be directly implied from when Reverse its previous property which states that the ideal diodes possess Biased infinite resistance when operating in reverse biased mode. The reason can be understood by considering the Ohm’s law again which now takes the form Thus it means that there will be no current flowing through the ideal diode when it is reverse biased, no matter how high the reverse voltage applied be. 35 No Reverse Breakdown Voltage Characteristics Reverse breakdown voltage is the voltage at which the reverse biased diode of Ideal Diode fails and starts to conduct heavy current. Now, from the last two properties when Reverse of the ideal diode, one can conclude that it will offer infinite resistance Biased which completely inhibits the current flow through it. This statement holds good irrespective of the magnitude of the reverse voltage applied to it. When the condition is so, the phenomenon of reverse breakdown can never occur due to which there will be no question of its corresponding voltage, the reverse breakdown voltage. Due to all these properties, an ideal diode is seen to behave as a perfect semiconductor switch which will be open when the reverse biased and closed when forward biased. 36 Characteristics of Ideal Diode 37 In the second approximation, the diode is considered as a forward-biased diode in series with a battery to turn on the device. Second For a silicon diode to turn on, it needs 0.7V. A voltage of Approximation 0.7V or greater is fed to turn on the forward-biased diode. The diode turns off if the voltage is less than 0.7V. 38 Second Approximation 39 The third approximation of a diode includes voltage across the diode and voltage across bulk resistance, RB. The bulk resistance is low, such as less than 1 ohm. almost always less than 10Ω. Third The bulk resistance, RB corresponds to the resistance of p and n Approximation materials. This resistance changes based on the amount of forwarding voltage and the current flowing through the diode at any given time. The voltage drop across the diode is calculated using the formula 𝑉𝑑 = 0.7 + 𝐼𝑑 × 𝑅𝐵 40 Third Approximation 41 The Bulk Resistance, RB, of a diode is the approximate resistance across the terminals of the diode when a forward voltage and current are applied across the diode. The bulk resistance represents the resistance of the p and n Third materials of the p-n junction of the diode. Approximation Its value is dependent on the doping level and the size of the p and n materials. The bulk resistance is not a fixed resistance but a dynamic one. It changes according to the amount of forward voltage and current going through the diode at any particular time. 42 The bulk resistance of a diode can be calculated at any given time by ohm's law: ∆𝑉𝐹 𝑅𝐵 = ∆𝐼𝐹 Where, ∆𝑉𝐹 is forward voltage drop and ∆𝐼 𝐹 is forward current Bulk Resistance flowing through diode. of Diode 43 Use the second approximation of diode and find the current flowing through the diode. Numerical related to Diode Approximation 44 Look at both of the circuits and calculate using the third approximation method of diode Numerical related to Diode Approximation 45 A rectifier is a device that simply converts alternating current (AC) into direct current (DC). The way a rectifier changes AC to DC is by the use of a diode, or multiple diodes. Diodes only allow electrons to flow in one direction through them. Rectifier When the voltage on the anode is more positive than the voltage on the cathode, current will flow through the diode. If the voltage is reversed, making the cathode more positive, then current will not flow through the diode. (unless the peak reverse voltage rating is exceeded). 46 Rectification is the process of conversion of the alternating current (which periodically changes direction) into direct current (flow in a single direction). Types of Rectifiers – 1. Half Wave Rectifier Rectifier 2. Full wave rectifier 1. Center Tapper Rectifier 2. Bridge rectifier Half Wave Rectifier: - A Type of rectifier that converts only the half cycle of the alternating current (AC) into direct current (DC) is known as half wave rectifier 47 Working – Positive Half wave - During the positive half cycle, the diode terminal anode will become positive and the cathode will become negative known as forward bias. And it will allow the positive cycle to flow through. Half Wave Rectifier – Working 48 Working – Negative Half wave - During the negative half cycle, the diode terminal anode will become negative and the cathode will become positive known as Reverse bias. And it will block the negative cycle to flow through. Half Wave Rectifier – Working 49 Waveforms – Input voltage, output voltage and output current. Half Wave Rectifier – Waveform 50 A Rectifier circuit that rectifies both the positive and negative half cycles can be termed as a full wave rectifier as it rectifies the complete cycle. The construction of a full wave rectifier can be made in two types. There are two types of full wave rectifier Full Wave 1. Center-tapped Full wave rectifier Rectifier 2. Bridge full wave rectifier 51 A rectifier circuit whose transformer secondary is tapped to get the desired output voltage, using two diodes alternatively, to rectify the complete cycle is called as a Center-tapped Full wave rectifier circuit. Center-tapped Full-Wave The transformer is center tapped here unlike the other cases. Rectifier The center-tapped transformer with two rectifier diodes is used in the construction of a Center-tapped full wave rectifier. 52 The circuit diagram of a center tapped full wave rectifier is as shown below. Center-tapped Full-Wave Rectifier 53 The working of a center-tapped full wave rectifier can be understood by the above figure. When the positive half cycle of the input voltage is applied, the point M at CT – FWR – the transformer secondary becomes positive with respect to the point N. Working in This makes the diode D1 forward biased. positive half Hence current flows through the load resistor from A to B. cycle We now have the positive half cycles in the output 54 CT – FWR – Working in positive half cycle 55 When the negative half cycle of the input voltage is applied, the point M at the transformer secondary becomes negative with respect to the point N. This makes the diode D2 forward biased. CT – FWR – Hence current flows through the load resistor from A to B. Working in We now have the positive half cycles in the output, even during the negative half negative half cycles of the input. cycle 56 CT – FWR – Working in negative half cycle 57 CT – FWR – Waveforms 58 A bridge rectifier is a type of full wave rectifier which uses four or more diodes in a bridge circuit configuration to Bridge efficiently convert the Rectifier Alternating Current (AC) into Direct Current (DC) 59 The bridge rectifier is made up of four diodes namely D1, D2, D3, D4 and load resistor RL. The four diodes are connected in a closed loop (Bridge) configuration to efficiently convert the Alternating Current (AC) into Direct Current (DC). Bridge The main advantage of this bridge circuit configuration is that we do not Rectifier - require an expensive center tapped transformer, thereby reducing its cost Construction and size. The input AC signal is applied across two terminals A and B and the output DC signal is obtained across the load resistor RL which is connected between the terminals C and D. 60 The four diodes D1, D2, D3, D4 are arranged in series with only two diodes allowing electric current during each half cycle. For example, diodes D1 and D3 are considered as one pair which allows electric current during the positive half cycle whereas diodes D2 and D4 are Bridge considered as another pair which allows electric current during the negative Rectifier - half cycle of the input AC signal. Construction 61 During the positive half cycle, the terminal A becomes positive while the terminal B becomes negative. Bridge This causes the diodes D1 and D3 Rectifier – forward biased and at the same Working time, it causes the diodes D2 and D4 positive half reverse biased. cycle The current flow direction during the positive half cycle is shown in the fig. (i.e. A to D to C to B). 62 During the negative half cycle, the terminal B becomes positive while the terminal A becomes negative. Bridge This causes the diodes D2 and D4 Rectifier – forward biased and at the same Working time, it causes the diodes D1 and D3 negative half reverse biased. cycle The current flow direction during negative half cycle is shown in the figure B (I.e. B to D to C to A). 63 From the above two figures (A and B), we can observe that the direction of current flow across load resistor RL is same during the positive half cycle and negative half cycle. Bridge Therefore, the polarity of the output DC signal is same for both positive and Rectifier – negative half cycles. Working The output DC signal polarity may be either completely positive or negative half negative. In our case, it is completely positive. cycle If the direction of diodes is reversed then we get a complete negative DC voltage. 64 Bridge Rectifier – Waveforms 65 The rectifier converts the Alternating Current (AC) into Direct Current (DC).But the obtained Direct Current (DC) at the output is not a pure Direct Current (DC). It is a pulsating Direct Current (DC). The pulsating Direct Current (DC) is not constant. It fluctuates with respect to time. When this fluctuating Direct Current (DC) is applied to Filter any electronic device, the device may not work properly. Sometimes the device may also be damaged. So the fluctuating Direct Current (DC) is not useful in most of the applications. Therefore, we need a Direct Current (DC) that does not fluctuate with respect to time. The only solution for this is smoothing the fluctuating Direct Current (DC). This can be achieved by using a device called filter. 66 A filter circuit is an electronic device which blocks the ac component present in the rectified output and allows the dc component to reach the load. The following figure shows the functionality of a filter circuit. A filter circuit is constructed using two main components, inductor and capacitor An inductor allows dc and blocks ac. Filter A capacitor allows ac and blocks dc. 67 As an inductor allows dc and blocks ac, a filter called Series Inductor Filter can be constructed by connecting the inductor in series, between the rectifier and the load. The figure below shows the circuit of a series inductor filter. The rectified output when passed through this filter, the inductor blocks the ac Series Inductor components that are present in the signal, in order to provide a pure dc. This Filter is a simple primary filter. 68 As a capacitor allows ac through it and blocks dc, a filter called Shunt Capacitor Filter can be constructed using a capacitor, connected in shunt, as shown in the following figure. The rectified output when passed through this filter, the ac components Shunt present in the signal are grounded through the capacitor which allows ac Capacitor components. The remaining dc components present in the signal are Filter collected at the output. 69 A filter circuit can be constructed using both inductor and capacitor in order to obtain a better output where the efficiencies of both inductor and capacitor can be used. The figure below shows the circuit diagram of a LC filter. The rectified output when given to this circuit, the inductor allows dc components to pass through it, blocking the ac components in the signal. Now, from that signal, few more ac components if any present are grounded so that we get a pure dc output. This filter is also called as a Choke Input Filter as the input signal first enters LC Filter the inductor. The output of this filter is a better one than the previous ones. 70 This is another type of filter circuit which is very commonly used. It has capacitor at its input and hence it is also called as a Capacitor Input Filter. Here, two capacitors and one inductor are connected in the form of pi shaped network. A capacitor in parallel, then an inductor in series, followed by another capacitor in parallel makes this circuit. ∏ Filter If needed, several identical sections can also be added to this, according to the requirement. The figure below shows a circuit for p filter Pi-filter 71 Working of a Pi filter In this circuit, we have a capacitor in parallel, then an inductor in series, followed by another capacitor in parallel. Capacitor C1 This filter capacitor offers high reactance to dc and low reactance to ac signal. After grounding the ac components present in the signal, the signal passes to the inductor for further filtration. ∏ Filter Inductor L This inductor offers low reactance to dc components, while blocking the ac components if any got managed to pass, through the capacitor C1 Capacitor C2 Now the signal is further smoothened using this capacitor so that it allows any ac component present in the signal, which the inductor has failed to block. 72 A Zener Diode, also known as a breakdown diode, is a heavily doped semiconductor device that is designed to operate in the reverse direction. When the voltage across the terminals of a Zener diode is Zener Diode reversed and the potential reaches the Zener Voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener Effect. 73 Clarence Melvin Zener was the first person to describe the History of electrical properties of Zener Diode. Zener Diodes Clarence Zener was a theoretical physicist who worked at Bell Labs. As a result of his work, the Zener diode was named after him. He first postulated the breakdown effect that bears his name in a paper that was published in 1934 74 A Zener diode operates just like a normal diode when it is forward- biased. However, when connected in reverse biased mode, a small leakage current flows through the diode. Zener Working As the reverse voltage increases to the predetermined breakdown voltage (Vz), current starts flowing through the diode. The current increases to a maximum, which is determined by the series resistor, after which it stabilizes and remains constant over a wide range of applied voltage. 75 There are two types of breakdowns for a Zener Diode: Avalanche Breakdown Breakdown Zener Breakdown 76 Avalanche breakdown occurs both in normal diode and Zener Diode at high reverse voltage. When a high value of reverse voltage is applied to the PN junction, the Avalanche free electrons gain sufficient energy and accelerate at high velocities. Breakdown in These free electrons moving at high velocity collides other atoms and Zener Diode knocks off more electrons. 77 Due to this continuous collision, a large number of free electrons are generated as a result of electric current in the diode rapidly increases. This sudden increase in electric current may permanently destroy the Avalanche normal diode, however, a Zener diode is designed to operate under Breakdown in avalanche breakdown and can sustain the sudden spike of current. Zener Diode Avalanche breakdown occurs in Zener diodes with Zener voltage (Vz) greater than 6V. 78 Avalanche Breakdown When the applied reverse bias voltage reaches closer to the Zener voltage, the electric field in the depletion region gets strong enough to pull electrons from their valence band. Zener The valence electrons that gain sufficient energy from the strong Breakdown in electric field of the depletion region break free from the parent atom. Zener Diode At the Zener breakdown region, a small increase in the voltage results in the rapid increase of the electric current. 80 The Zener effect is dominant in voltages up to 5.6 volts and the avalanche effect takes over above that. They are both similar effects, the difference being that the Zener Avalanche effect is a quantum phenomenon and the avalanche effect is the Breakdown vs Zener movement of electrons in the valence band like in any electric Breakdown current. Avalanche effect also allows a larger current through the diode than what a Zener breakdown would allow. 81 There are many ways in which a Zener diode is packaged. Circuit Symbol Some are used for high levels of power dissipation and the others are contained with surface mount formats. The most common type of Zener diode is contained within a small glass encapsulation. It has a band around one end marking the cathode side of the diode. 82 V-I Characteristics 83 The V-I characteristics of a Zener diode can be divided into two parts as follows: (i) Forward Characteristics (ii) Reverse Characteristics Characteristics Forward Characteristics The first quadrant in the graph represents the forward characteristics of a Zener diode. From the graph, we understand that it is almost identical to the forward characteristics of any other P-N junction diode. 84 When a reverse voltage is applied to a Zener voltage, initially a small reverse saturation current Io flows across the diode. This current is due to thermally generated minority carriers. Reverse As the reverse voltage is increased, at a certain value of reverse Characteristics voltage, the reverse current increases drastically and sharply. This is an indication that the breakdown has occurred. We call this voltage breakdown voltage or Zener voltage and it is denoted by Vz. 85 Some commonly used specifications for Zener diodes are as follows: Zener/Breakdown Voltage – The Zener or the reverse breakdown voltage ranges from 2.4 V to 200 V, sometimes it can go up to 1 kV while the maximum for the surface-mounted device is 47 V. Zener Diode Current Iz (max) – It is the maximum current at the rated Zener Specifications Voltage (Vz – 200μA to 200 A) Current Iz (min) – It is the minimum value of current required for the diode to breakdown. 86 Some commonly used specifications for Zener diodes are as follows: Power Rating – It denotes the maximum power the Zener diode can dissipate. It is given by the product of the voltage of the diode and the current flowing through it. Zener Diode Temperature Stability – Diodes around 5 V have the best stability Specifications Voltage Tolerance – It is typically ±5% Zener Resistance (Rz) – It is the resistance to the Zener diode exhibits. 87 Zener diode as a voltage regulator Application Zener diode in over-voltage protection Zener diode in clipping circuits 88 It is well known that a diode is expected to operate as a unidirectional device (i.e. only permit current flow in one direction). These are expected to offer very low resistance for the flow of current under the forward biased condition and a very high resistance under the Testing of reverse bias condition. Diode by This important property of the diode can be exploited effectively to test Multimeter the diode with an intention of knowing whether it is working fine or not. In other words, one can undertake diode testing by measuring the resistance across its terminals by using a piece of equipment such as a digital multimeter. 89 The Diode Test Mode is the best way to test a diode as it relies on the characteristics of the Diode. In this method, the diode is put in forward bias and the voltage drop across the diode is measured, using a Multimeter. A normally working diode will allow current to flow in Testing of forward bias and must have voltage drop. Diode by In the Resistance Mode Test of the diode, both the forward and reverse Multimeter bias resistances of the diode are measured. For a good diode, the forward bias resistance should be few hundreds of Ohms to few Kilo Ohms and the reverse bias resistance should be very high (usually indicated as OL – open loop in a multimeter). 90 Identify the anode and cathode terminals of the diode. Keep the Digital Multimeter (DMM) in diode checking mode by rotating the central knob to the position where the diode symbol is indicated. In this mode, the multimeter is capable to supply a current of approximately 2mA between the test leads. Diode Mode Connect the red probe of the multimeter to the anode and black probe to the cathode. This means the diode is forward-biased. Testing of Observe the reading on multimeter’s display. If the displayed voltage Diode by value is in between 0.6 to 0.7 (for a Silicon Diode), then the diode is healthy and perfect. For Germanium Diodes, this value is in between 0.25 Multimeter to 0.3. Now, reverse the terminals of the meter i.e., connect the red probe to cathode and black to anode. This is the reverse biased condition of the diode where no current flows through it. Hence, the meter should read OL or 1 (which is equivalent to open circuit) if the diode is healthy. 91 If the meter shows irrelevant values to the above two conditions, then the diode is defective. The defect in the diode can be either open or short. Open diode means the diode behaves as an open switch in both reverse Diode Mode and forward biased conditions. So, no current flows through the diode in either bias condition. Therefore, the meter will indicate OL (or 1) in both Testing of reverse and forward-biased conditions. Diode by Multimeter Shorted diode means diode behaves as a closed switch, so the current flows through it irrespective of the bias and the voltage drop across the diode will be between 0V to 0.4V. Therefore, the multimeter will indicate zero voltage value, but in some cases it will display a very little voltage as the voltage drop across the diode. 92 Diode Mode Testing of Diode by Multimeter 93 Clipper circuits are the circuits that clip off or removes a portion of an input signal, without causing any distortion to the remaining part of the waveform. These are also known as clippers, clipping circuits, limiters, slicers etc. Clippers are basically wave shaping circuits that control the shape of an Clippers output waveform. It consists of linear and non-linear elements but does not contain energy storing elements The basic operation of a diode clipping circuits is such that, in forward biased condition, the diode allows current to pass through it, clamping the voltage. But in reverse biased condition, no any current flows through the diode, and thus voltage remains unaffected across its terminals. 94 Clipper circuits are basically termed as protection devices. As electronic devices are voltage sensitive and voltage of large amplitude can permanently destroy the device. So, in order to protect the device clipper circuits are used. Usually, clippers employ resistor–diode combination in its circuitry. Clippers Although the input voltage to diode clipping circuits can have any waveform shape, we will assume here that the input voltage is sinusoidal. 95 Classification of Clipper Circuit. 96 1. Series Positive Clipper Circuit. Series Clipper Circuits 97 1. Series Positive Clipper Circuit. Let’s have a look at the circuit diagram of a series positive clipper. Here, the diode is connected in series with the output thus it is named so. The positive half of the input waveform reverse biases the diode. Thus it acts as an open switch and all the applied input voltage drops across the diode. Resultantly providing no output voltage for positive half of the Series Clipper input waveform Circuits For the negative half of the input waveform, the diode is in the forward biased state. Thus it acts as a closed switch causing no any voltage drop at the diode. Hence input voltage will appear across the resistor, ultimately at the output of the circuit 98 2. Series Negative Clipper Circuit. Series Clipper Circuits 99 2. Series Negative Clipper Circuit. Here, during the positive half cycle of input waveform, the diode becomes forward biased, thus ensuring a closed circuit. Due to which current appears across the resistor of the circuit. Series Clipper For negative half of the input waveform, the diode now becomes reverse Circuits biased acting as an open switch. This causes no current to flow through the circuit. Resultantly providing no output for negative half of the input waveform. 100 3. Series Positive Clipper Circuit with Bias Series Positive Clipper Circuit with Positive Bias Series Clipper Circuits 101 Series Positive Clipper Circuit with Positive Bias Here in the circuit shown above, we can see that the diode is in forward bias condition concerning the battery. But positive half of the input waveform puts the diode in reverse biased condition. The diode will conduct until the supply voltage is less than the battery potential. As battery potential dominates the supply voltage, the signal Series Clipper appears at the positive half of output waveform. But as the supply voltage Circuits exceeds the battery potential, the diode is now reverse biased. Resultantly no further current will flow through the diode For the negative half cycle of the input waveform, the diode is forward biased concerning both supply voltage and battery potential. Hence, we achieve a complete negative half cycle at the output waveform. 102 3. Series Positive Clipper Circuit with Bias Series Positive Clipper Circuit with Negative Bias Series Clipper Circuits 103 Series Positive Clipper Circuit with Negative Bias During positive half cycle: During the positive half cycle, the diode D is reverse biased by both input supply voltage Vi and battery voltage VB. So no signal appears at the output during the positive half cycle. Therefore, the complete positive half cycle is removed. Series Clipper During negative half cycle: Circuits During the negative half cycle, the diode is forward biased by the input supply voltage Vi and reverse biased by the battery voltage VB. However, initially, the battery voltage VB dominates the input supply voltage Vi. So the diode remains to be reverse biased until the Vi becomes greater than VB. When the input supply voltage Vi becomes greater than the battery voltage VB, the diode is forward biased by the input supply voltage Vi. So the signal appears at the output. 104 4. Series Negative Clipper Circuit with Bias Series Negative Clipper Circuit with Positive Bias Series Clipper Circuits 105 Series Negative Clipper Circuit with Positive Bias During positive half cycle: During the positive half cycle, terminal A is positive and terminal B is negative. That means the positive terminal A is connected to p-side and the negative terminal B is connected to n-side. As we already know that if the positive terminal is connected to p-side and the negative terminal is Series Clipper connected to n-side then the diode is said to be forward biased. However, we are also supplying the voltage from another source called battery. As Circuits shown in the figure, the positive terminal of the battery is connected to n- side and the negative terminal of the battery is connected to p-side of the diode. That means the diode is forward biased by input supply voltage Vi and reverse biased by battery voltage VB. Initially, the battery voltage is greater than the input supply voltage. Hence, the diode is reverse biased and does not allow electric current. Therefore, no signal appears at the output. 106 Series Negative Clipper Circuit with Positive Bias When the input supply voltage Vi becomes greater than the battery voltage VB, the diode is forward biased and allows electric current. As a result, the signal appears at the output. During negative half cycle: During the negative half cycle, the diode is reverse biased by both input Series Clipper supply voltage Vi and battery voltage VB. So it doesn’t matter whether the Circuits input supply voltage is greater or less than the battery voltage VB, the diode always remains reverse biased. Therefore, during the negative half cycle, no signal appears at the output. 107 4. Series Negative Clipper Circuit with Bias Series Negative Clipper Circuit with Negative Bias Series Clipper Circuits 108 Series Negative Clipper Circuit with Positive Bias During positive half cycle: During the positive half cycle, the diode D is forward biased by both input supply voltage Vi and the battery voltage VB. So it doesn’t matter whether the input supply voltage is greater or less than battery voltage VB, the diode always remains forward biased. Therefore, during the positive half Series Clipper cycle, the signal appears at the output. Circuits During negative half cycle: During the negative half cycle, the diode D is reverse biased by the input supply voltage Vi and forward biased by the battery voltage VB. Initially, the input supply voltage Vi is less than the battery voltage VB. So the diode is forward biased by the battery voltage VB. As a result, the signal appears at the output. When the input supply voltage Vi becomes greater than the battery voltage VB, the diode will become reverse biased. As a result, no signal appears at the output. 109 1. Shunt Positive Clipper Circuit. Shunt Clipper Circuits 110 1. Shunt Positive Clipper Circuit. In shunt clipper, the diode is connected in parallel with the output load resistance. The operating principles of the shunt clipper are nearly opposite to the series clipper. The series clipper passes the input signal to the output load when the diode is forward biased and blocks the input signal when the diode is Shunt Clipper reverse biased. Circuits The shunt clipper on the other hand passes the input signal to the output load when the diode is reverse biased and blocks the input signal when the diode is forward biased. In shunt positive clipper, during the positive half cycle the diode is forward biased and hence no output is generated. On the other hand, during the negative half cycle the diode is reverse biased and hence the entire negative half cycle appears at the output. 111 2. Shunt Positive Clipper Circuit with Bias Shunt Positive Clipper Circuit with Positive Bias Shunt Clipper Circuits 112 Shunt Positive Clipper Circuit with Positive Bias During the positive half cycle, the diode is forward biased by the input supply voltage Vi and reverse biased by the battery voltage VB. However, initially, the input supply voltage Vi is less than the battery voltage VB. Hence, the battery voltage VB makes the diode to be reverse biased. Therefore, the signal appears at the output. However, when the input Shunt Clipper supply voltage Vi becomes greater than the battery voltage VB, the diode D is forward biased by the input supply voltage Vi. As a result, no signal Circuits appears at the output. During the negative half cycle, the diode is reverse biased by both input supply voltage and battery voltage. So it doesn’t matter whether the input supply voltage is greater or lesser than the battery voltage, the diode always remains reverse biased. As a result, a complete negative half cycle appears at the output. 113 2. Shunt Positive Clipper Circuit with Bias Shunt Positive Clipper Circuit with Negative Bias Shunt Clipper Circuits 114 Shunt Positive Clipper Circuit with Negative Bias During the positive half cycle, the diode is forward biased by both input supply voltage Vi and battery voltage VB. Therefore, no signal appears at the output during the positive half cycle. During the negative half cycle, the diode is reverse biased by the input supply voltage and forward biased by the battery voltage. However, Shunt Clipper initially, the input supply voltage Vi is less than the battery voltage VB. So Circuits the battery voltage makes the diode to be forward biased. As a result, no signal appears at the output. However, when the input supply voltage Vi becomes greater than the battery voltage VB, the diode is reverse biased by the input supply voltage Vi. As a result, the signal appears at the output 115 3. Shunt Negative Clipper Circuit. Shunt Clipper Circuits 116 3. Shunt Negative Clipper Circuit. For negative shunt clippers, during the positive half of input, the diode gets reverse biased. Thus no current flows through it, and the output current is observed at the load. Shunt Clipper Hence output signal is achieved for positive half of the input signal. Circuits During the negative half of the input signal, the diode gets forward biased and hence no load current is achieved. Ultimately no output is observed for negative half of the input signal 117 4. Shunt Negative Clipper Circuit with Bias Shunt Negative Clipper Circuit with Positive Bias Shunt Clipper Circuits 118 Shunt Negative Clipper Circuit with Positive Bias During the positive half cycle, the diode is reverse biased by the input supply voltage Vi and forward biased by the battery voltage VB. However, initially, the input supply voltage is less than the battery voltage. So the Shunt Clipper diode is forward biased by the battery voltage. As a result, no signal Circuits appears at the output. However, when the input supply voltage becomes greater than the battery voltage then the diode is reverse biased by the input supply voltage. As a result, the signal appears at the output. During the negative half cycle, the diode is forward biased by both input supply voltage Vi and battery voltage VB. So the complete negative half cycle is removed at the output. 119 4. Shunt Negative Clipper Circuit with Bias Shunt Negative Clipper Circuit with Negative Bias Shunt Clipper Circuits 120 Shunt Negative Clipper Circuit with Negative Bias During the positive half cycle, the diode is reverse biased by both input supply voltage Vi and battery voltage VB. As a result, the complete positive half cycle appears at the output. Shunt Clipper During the negative half cycle, the diode is forward biased by the input Circuits supply voltage Vi and reverse biased by the battery voltage VB. However, initially, the input supply voltage is less than the battery voltage. So the diode is reverse biased by the battery voltage. As a result, the signal appears at the output. However, when the input supply voltage becomes greater than the battery voltage, the diode is forward biased by the input supply voltage. As a result, the signal does not appear at the output. 121 Dual Clipper. Dual (Combination) Clipper Circuits 122 Sometimes it is desired to remove a small portion of both positive and negative half cycles. In such cases, the dual clippers are used. The dual clippers are made by combining the biased shunt positive clipper and biased shunt negative clipper. Dual Let us consider a dual clipper circuit in which a sinusoidal ac voltage is (Combination) applied to the input terminals of the circuit. Clipper Circuits 123 During Positive half cycle: - During the positive half cycle, the diode D1 is forward biased by the input supply voltage Vi and reverse biased by the battery voltage VB1. On the other hand, the diode D2 is reverse biased by both input supply voltage Dual Vi and battery voltage VB2. (Combination) Initially, the input supply voltage is less than the battery voltage. So the Clipper Circuits diode D1 is reverse biased by the battery voltage VB1. Similarly, the diode D2 is reverse biased by the battery voltage VB2. As a result, the signal appears at the output. However, when the input supply voltage Vi becomes greater than the battery voltage VB1, the diode D1 is forward biased by the input supply voltage. As a result, no signal appears at the output. 124 During Negative half cycle During the negative half cycle, the diode D1 is reverse biased by both input supply voltage Vi and battery voltage VB1. On the other hand, the diode D2 is forward biased by the input supply voltage Vi and reverse Dual biased by the battery voltage VB2. (Combination) Initially, the battery voltage is greater than the input supply voltage. Clipper Circuits Therefore, the diode D1 and diode D2 are reverse biased by the battery voltage. As a result, the signal appears at the output. When the input supply voltage becomes greater than the battery voltage VB2, the diode D2 is forward biased. As a result, no signal appears at the output. 125 Applications Clippers are commonly used in power supplies. Used in TV transmitters and Receivers They are employed for different wave generation such as square, Application rectangular, or trapezoidal waves. Clipper Circuits Series clippers are used as noise limiters in FM transmitters. 126 A Clamper Circuit is a circuit that adds a DC level to an AC signal. Actually, the positive and negative peaks of the signals can be placed at desired levels using the clamping circuits. As the DC level gets shifted, a clamper circuit is called as a Level Shifter. A typical clamper is made up of a capacitor, diode, and resistor. Some Clamper clampers contain an extra element called DC battery. The resistors and Circuits capacitors are used in the clamper circuit to maintain an altered DC level at the clamper output. The clamper is also referred to as a DC restorer, clamped capacitors, or AC signal level shifter. 127 A Clamper circuit can be defined as the circuit that consists of a diode, a resistor and a capacitor that shifts the waveform to a desired DC level without changing the actual appearance of the applied signal. The dc component is simply added to the input signal or subtracted from Clamper the input signal. A clamper circuit adds the positive dc component to the Circuits input signal to push it to the positive side. Similarly, a clamper circuit adds the negative dc component to the input signal to push it to the negative side. 128 If the circuit pushes the signal upwards then the circuit is said to be a positive clamper. When the signal is pushed upwards, the negative peak of the signal meets the zero level. On the other hand, if the circuit pushes the signal downwards then the circuit is said to be a negative clamper. When the signal is pushed Clamper downwards, the positive peak of the signal meets the zero level. Circuits The construction of the clamper circuit is almost similar to the clipper circuit. The only difference is the clamper circuit contains an extra element called capacitor. A capacitor is used to provide a dc offset (dc level) from the stored charge. 129 Types of Clamper Circuit Positive Clamper Negative Clamper Positive Clamper with Bias Clamper Negative Clamper with Bias Circuits 130 The positive clamper is made up of a voltage source Vi, capacitor C, diode D, and load resistor RL. In the below circuit diagram, the diode is connected in parallel with the output load. So the positive clamper passes the input signal to the output load when the diode is reverse biased and blocks the input signal when the diode is forward biased. Positive Clamper 131 During negative half cycle: During the negative half cycle of the input AC signal, the diode is forward biased and hence no signal appears at the output. In forward biased condition, the diode allows electric current through it. This current will flows to the capacitor and charges it to the peak value of input voltage Vm. Positive The capacitor charged in inverse polarity (positive) with the input voltage. Clamper As input current or voltage decreases after attaining its maximum value - Vm, the capacitor holds the charge until the diode remains forward biased. 132 During positive half cycle: During the positive half cycle of the input AC signal, the diode is reverse biased and hence the signal appears at the output. In reverse biased condition, the diode does not allow electric current through it. So the input current directly flows towards the output. When the positive half cycle begins, the diode is in the non-conducting state and the charge stored in the capacitor is discharged (released). Positive Therefore, the voltage appeared at the output is equal to the sum of the voltage stored in the capacitor (Vm) and the input voltage (Vm) { I.e. Vo = Clamper Vm+ Vm = 2Vm} which have the same polarity with each other. As a result, the signal shifted upwards. The peak to peak amplitude of the input signal is 2Vm, similarly the peak to peak amplitude of the output signal is also 2Vm. Therefore, the total swing of the output is same as the total swing of the input. The basic difference between the clipper and clamper is that the clipper removes the unwanted portion of the input signal whereas the clamper moves the input signal upwards or downwards. 133 During positive half cycle: During the positive half cycle of the input AC signal, the diode is forward biased and hence no signal appears at the output. In forward biased condition, the diode allows electric current through it. This current will flows to the capacitor and charges it to the peak value of input voltage in inverse polarity -Vm. As input current or voltage decreases after attaining its maximum value Vm, the capacitor holds the charge until the diode remains forward biased. Negative Clamper 134 During negative half cycle: During the negative half cycle of the input AC signal, the diode is reverse biased and hence the signal appears at the output. In reverse biased condition, the diode does not allow electric current through it. So the input current directly flows towards the output. Negative Clamper When the negative half cycle begins, the diode is in the non-conducting state and the charge stored in the capacitor is discharged (released). Therefore, the voltage appeared at the output is equal to the sum of the voltage stored in the capacitor (-Vm) and the input voltage (-Vm) {I.e. Vo = -Vm- Vm = -2Vm} which have the same polarity with each other. As a result, the signal shifted downwards. 135 Positive Clamper with positive biased If positive biasing is applied to the clamper then it is said to be a positive clamper with positive bias. The positive clamper with positive bias is made up of an AC voltage source, capacitor, diode, resistor, and dc battery. Positive Clamper with Bias 136 During positive half cycle: During the positive half cycle, the battery voltage forward biases the diode when the input supply voltage is less than the battery voltage. This current or voltage will flows to the capacitor and charges it. Positive When the input supply voltage becomes greater than the battery voltage Clamper with then the diode stops allowing electric current through it because the diode Bias becomes reverse biased. During negative half cycle: During the negative half cycle, the diode is forward biased by both input supply voltage and battery voltage. So the diode allows electric current. This current will flows to the capacitor and charges it. 137 Positive Clamper with negative biased During negative half cycle: During the negative half cycle, the battery voltage reverse biases the diode when the input supply voltage is less than the battery voltage. As a result, the signal appears at the output. Positive When the input supply voltage becomes greater than the battery voltage, the diode is forward biased by the input supply voltage and hence allows Clamper with electric current through it. This current will flows to the capacitor and charges it. Bias 138 During positive half cycle: During the positive half cycle, the diode is reverse biased by both input supply voltage and the battery voltage. As a result, the signal appears at the output. The signal appeared at the output is equal to the sum of the Positive input voltage and capacitor voltage. Clamper with Bias 139 Negative Clamper with Positive biased During Positive half cycle: During the positive half cycle, the battery voltage reverse biases the diode when the input supply voltage is less than the battery voltage. When the input supply voltage becomes greater than the battery voltage, the diode is Negative forward biased by the input supply voltage and hence allows electric current through it. This current will flows to the capacitor and charges it. Clamper with Bias 140 During Negative half cycle: During the negative half cycle, the diode is reverse biased by both input supply voltage and battery voltage. As a result, the signal appears at the output. Negative Clamper with Bias 141 Negative Clamper with Negative biased During Positive half cycle: During the positive half cycle, the diode is forward biased by both input supply voltage and battery voltage. As a result, current flows through the Negative capacitor and charges it. Clamper with Bias 142 During Negative half cycle: During the negative half cycle, the battery voltage forward biases the diode when the input supply voltage is less than the battery voltage. When the input supply voltage becomes greater than the battery voltage, the Negative diode is reverse biased by the input supply voltage and hence signal Clamper with appears at the output. Bias 143 Surface-mount (SM) diodes can be found anywhere there is a need for diode applications. SM diodes are small, efficient, and relatively easy to test, remove, and replace on the circuit board. Although there are a number of SM package styles, two basic styles dominate the industry: SM (surface mount) and SOT (small outline transistor). Surface Mount The SM package has two L-bend leads and a colored band on one end Diode (SMD) of the body to indicate the cathode lead. An SMD or Surface mounted device, is an electronic component that you would find on board. 144 An SMT, or surface mount technology, is the method of placing components (like an SMD) on the board. In electronic manufacturing services, the SMT process often works with SMDs Surface Mount Surface Mount Device/components are very small as compared to Diode (SMD) normal electronics components like resistor, capacitor etc. Surface Mount Device is specially designed for the integration of the circuit i.e to make the circuit as small as possible. Integrated Circuit (IC) is the example of the SMD components, if you open datasheet of any IC you can see the circuit diagram of that particular IC 145 The voltage multiplier is an electronic circuit that delivers the output voltage whose amplitude (peak value) is two, three, or more times greater than the amplitude (peak value) of the input voltage. The voltage multiplier is an electronic circuit that converts the low AC Voltage voltage into high DC voltage. Multiplier or The voltage multiplier is an AC-to-DC converter, made up of diodes and capacitors that produce a high voltage DC output from a low voltage AC input. 146 What is voltage multiplier? Voltage multiplier power supplies have been used for many years. Walton and Cockroft built an 800 kV supply for an ion accelerator in 1932. Since that time the voltage multiplier has been used primarily when high voltages and low currents are required. The use of voltage multiplier circuits reduces the size of the high voltage transformer and, in some cases, makes it possible to eliminate the transformer. Voltage The recent technological developments have made it possible to design a voltage multiplier that efficiently converts the low AC voltage into high Multiplier DC voltage comparable to that of the more conventional transformer- rectifier-filter-circuit. The voltage multiplier is made up of capacitors and diodes that are connected in different configurations. Voltage multiplier has different stages. Each stage is made up of one diode and one capacitor. These arrangements of diodes and capacitors make it possible to produce rectified and filtered output voltage whose amplitude (peak value) is larger than the input AC voltage. 147 Types of voltage multiplier. Voltage multipliers are classified into four types: 1. Half-wave voltage doubler Voltage 2. Full-wave voltage doubler Multiplier 3. Voltage tripler 4. Voltage quadrupler 148 1. Half-wave voltage doubler As its name suggests, a half-wave voltage doubler is a voltage multiplier circuit whose output voltage amplitude is twice that of the input voltage amplitude. A half-wave voltage doubler drives the voltage to the output during either positive or negative half cycle. The half-wave voltage doubler Half wave circuit consists of two diodes, two capacitors, and AC input voltage source. voltage doubler 149 During positive half cycle: The circuit diagram of the half-wave voltage doubler is shown in the below figure. During the positive half cycle, diode D1 is forward biased. So it allows electric current through it. This current will flows to the capacitor Half wave C1 and charges it to the peak value of input voltage I.e. Vm. voltage doubler However, current does not flow to the capacitor C2 because the diode D2 is reverse biased. So the diode D2 blocks the electric current flowing towards the capacitor C2. Therefore, during the positive half cycle, capacitor C1 is charged whereas capacitor C2 is uncharged. 150 During negative half cycle: During the negative half cycle, diode D1 is reverse biased. So the diode D1 will not allow electric current through it. Therefore, during the negative half cycle, the capacitor C1 will not be charged. However, the charge (Vm) stored in the capacitor C1 is discharged (released). Half wave On the other hand, the diode D2 is forward biased during the negative half voltage doubler cycle. So the diode D2 allows electric current through it. This current will flows to the capacitor C2 and charges it. The capacitor C2 charges to a value 2Vm because the input voltage Vm and capacitor C1 voltage Vm is added to the capacitor C2. Hence, during the negative half cycle, the capacitor C2 is charged by both input supply voltage Vm and capacitor C1 voltage Vm. Therefore, the capacitor C2 is charged to 2Vm. If a load is connected to the circuit at the output side, the charge (2Vm) stored in the capacitor C2 is discharged and flows to the output. 151 During negative half cycle: During the next positive half cycle, diode D1 is forward biased and diode D2 is reverse biased. So the capacitor C1 charges to Vm whereas capacitor C2 will not be charged. However, the charge (2Vm) stored in the capacitor C2 will be Half wave discharged and flows to the output load. Thus, the half-wave voltage doubler voltage doubler drives a voltage of 2Vm to the output load. The capacitor C2 gets charged again in the next half cycle. The voltage (2Vm) obtained at the output side is twice that of the input voltage (Vm). The capacitors C1 and C2 in half wave-voltage doubler charges in alternate half cycles. 152 The output waveform of the half-wave voltage doubler is almost similar to the half wave rectifier with filter. The only difference is the output voltage amplitude of the half-wave voltage doubler is twice that of the input voltage amplitude but in half wave rectifier with filter, the output voltage amplitude is Half wave same as the input voltage amplitude. voltage doubler The half-wave voltage doubler supplies the voltage to the output load in one cycle (either positive or negative half cycle). In our case, the half-wave voltage doubler supplies the voltage to the output load during positive half cycles. Therefore, the output signal regulation of the half-wave voltage doubler is poor. 153 Advantages of half-wave voltage doubler High voltages are produced from the low input voltage source without using the expensive high voltage transformers. Disadvantages of half-wave voltage doubler Half wave voltage doubler Large ripples (unwanted fluctuations) are present in the output signal. 154 2. Full-wave voltage doubler The full-wave voltage doubler consists of two diodes, two capacitors, and input AC voltage source. Full wave voltage doubler 155 During positive half cycle: During the positive half cycle of the input AC signal, diode D1 is forward biased. So the diode D1 allows electric current through it. This current will flows to the capacitor C1 and charges it to the peak value of input voltage Full wave I.e Vm. voltage doubler On the other hand, diode D2 is reverse biased during the positive half cycle. So the diode D2 does not allow electric current through it. Therefore, the capacitor C2 is uncharged. 156 During negative half cycle: During the negative half cycle of the input AC signal, the diode D2 is forward biased. So the diode D2 allows electric current through it. This current will flows to the capacitor C2 and charges it to the peak value of the input voltage I.e. Vm. On the other hand, diode D1 is reverse biased during the negative half cycle. So the diode D1 does not allow electric current through it. Full wave Thus, the capacitor C1 and capacitor C2 are charged during alternate half voltage doubler cycles. The output voltage is taken across the two series connected capacitors C1 and C2. If no load is connected, the output voltage is equal to the sum of capacitor C1 voltage and capacitor C2 voltage I.e. C1 + C2 = Vm + Vm = 2Vm. When a load is connected to the output terminals, the output voltage Vo will be somewhat less than 2Vm. The circuit is called full-wave voltage doubler because one of the output capacitors is being charged during each half cycle of the input voltage. 157 3. Voltage Tripler The voltage tripler can be obtained by adding one more diode-capacitor stage to the half-wave voltage doubler circuit. Voltage Tripler 158 During First positive half cycle: During the first positive half cycle of the input AC signal, the diode D1 is forward biased whereas diodes D2 and D3 are reverse biased. Hence, the diode D1 allows electric current through it. This current will flows to the capacitor C1 and charges it to the peak value of the input voltage I.e. Vm. During negative half cycle: Voltage Tripler During the negative half cycle, diode D2 is forward biased whereas diodes D1 and D3 are reverse biased. Hence, the diode D2 allows electric current through it. This current will flows to the capacitor C2 and charges it. The capacitor C2 is charged to twice the peak voltage of the input signal (2Vm). This is because the charge (Vm) stored in the capacitor C1 is discharged during the negative half cycle. Therefore, the capacitor C1 voltage (Vm) and the input voltage (Vm) is added to the capacitor C2 I.e Capacitor voltage + input voltage = Vm + Vm = 2Vm. As a result, the capacitor C2 charges to 2Vm. 159 During Second positive half cycle: During the second positive half cycle, the diode D3 is forward biased whereas diodes D1 and D2 are reverse biased. Diode D1 is reverse biased because the voltage at X is negative due to charged voltage Vm, across C1 and diode D2 is reverse biased because of its orientation. As a result, the voltage (2Vm) across capacitor C2 is discharged. This charge will flow to the capacitor C3 and charges it to the same voltage 2Vm. Voltage Tripler The capacitors C1 and C3 are in series and the output voltage is taken across the two series connected capacitors C1 and C3. The voltage across capacitor C1 is Vm and capacitor C3 is 2Vm. So the total output voltage is equal to the sum of capacitor C1 voltage and capacitor C3 voltage I.e. C1 + C3 = Vm + 2Vm = 3Vm. Therefore, the total output voltage obtained in voltage tripler is 3Vm which is three times more than the applied input voltage. 160 3. Voltage Quadrupler The voltage quadrupler can be obtained by adding one more diode- capacitor stage to the voltage tripler circuit. Voltage Quadrupler 161 During First positive half cycle: During the first positive half cycle of the input AC signal, the diode D1 is forward biased whereas diodes D2, D3 and D4 are reverse biased. Hence, the diode D1 allows electric current through it. This current will flows to the capacitor C1 and charges it to the peak value of the input voltage I.e. Vm. Voltage During First negative half cycle: Quadrupler During the first negative half cycle, diode D2 is forward biased and diodes D1, D3 and D4 are reverse biased. Hence, the diode D2 allows electric current through it. This current will flows to the capacitor C2 and charges it. The capacitor C2 is charged to twice the peak voltage of the input signal (2Vm). This is because the charge (Vm) stored in the capacitor C1 is discharged during the negative half cycle. Therefore, the capacitor C1 voltage (Vm) and the input voltage (Vm) is added to the capacitor C2 I.e Capacitor voltage + input voltage = Vm + Vm = 2Vm. As a result, the capacitor C2 charges to 2Vm. 162 During Second positive half cycle: During the second positive half cycle, the diode D3 is forward biased and diodes D1, D2 and D4 are reverse biased. Diode D1 is reverse biased because the voltage at X is negative due to charged voltage Vm, across C1 and, diode D2 and D4 are reverse biased because of their orientation. As
