Category: basic Electronics

Transformers based on Usage There are transformers which are classified depending upon the applications they have. Many of these transformers are large and bulky. Most of them are used by the Electricity department. Power Transformers The Power transformers are used in high power transfer applications for both step-up and step-down applications, where the operating voltages are more than 33KV generally rated above 200MVA. The flux density is much higher for them. All the transformers that are used for power control applications such as laminated core transformers, toroidal transformers, variable auto transformers, polyphaser transformers, stray leakage transformers come under this category. These are usually big in size depending upon the power handling capacity and its application. These transformers are available in three phase or single phase type. As these transformers are bulky, they are placed in large open area. These transformers tend to provide 100% efficiency in full load applications. Advantages They have high insulation level. Noise is low. They are highly efficient. High voltage rated ones to handle high power applications. Applications They are used in power generation systems. They are used in transmission sub stations. Measurement Transformers The Measurement transformers are used for measuring high voltage and high currents. These are mostly helpful in isolating the circuits from them. Usually, the Primary of a transformer is connected with high inputs of voltages and currents whereas Secondary of the transformer is connected to some relay or circuit which has to be provided some isolation. These are mainly of two types, Current transformers and Voltage transformers. Let us have a look at each of them. Current Transformer The Current transformers provide current in the secondary circuit proportional to the current in the primary circuit. These are used in protective relays and for measurement purposes. A single turn primary winding is passed through a well-insulated toroidal core transformer which is wounded with many turns, which makes a Current Transformer. This is always connected in series. The secondary winding can be designed to provide single output or it may have several tapping for different values. Care must be taken that the secondary winding is connected to its load having low impedance, while current flows in primary. This is to avoid sudden high voltages in open circuited secondary which might permanently damage the accuracy of the transformer. Voltage Transformers The Voltage Transformers provide voltage in the secondary circuit proportional to the voltage in the primary circuit. These transformers are also called as Potential Transformers. These are connected in parallel to the circuit. The primary of this transformer may have phase to phase connections but the secondary will have one terminal to ground. The figure below shows an image of a voltage transformer. There are three main types of a voltage transformers. They are Electromagnetic − uses a wire wound transformer having good flux linkages. Capacitor − uses a capacitor with potential divider network. Optical − makes use of electrical properties of optical materials. The voltage transformers are used in protective relays and for measurement purposes and also for phasor phase shift isolation. Protection Transformers These transformers are very accurate than measuring transformers, as these are used only to protect the circuits from high voltages and currents. The primary of these transformers are connected with high inputs whereas the secondary of the transformer keeps the circuit or relay, isolated from the sudden spikes or surges which might damage the circuit. Distribution Transformers The Distribution transformers are used for distribution of electrical energy at end-user level. The operating voltages are around 33KV for industrial purposes and 440v-220v for domestic purposes. These are generally rated below 200MVA. The large three phase auto transformers used in power distribution and the oil-cooled transformers also come under this category. The figure below shows an image of a distribution transformer. These transformers are usually smaller in size compared to power transformers. These transformers are placed in open but are not fully loaded like power transformers. Advantages They are small in size. They are easy to install. These transformers have low magnetic losses. Disadvantages These transformers have low efficiency. They are not fully-loaded. Applications They are used for distributing electricity in various areas like houses, farm yards, lands, railways, wind farms etc. Learning working make money

Basic Electronics – Special Purpose Diodes There are few diodes which are designed to serve some special purposes. There are many of such kinds like Transient voltage suppression diodes, Gold doped diodes, Super barrier diodes, Point contact diodes, Peltier diodes etc. But other than these, there are few prominent diodes, which have got many applications. Let us go through them. Varactor Diode A junction diode has two potentials on both sides where the depletion region can act as a dielectric. Hence there exists a capacitance. The Varactor diode is a special case diode that is operated in reverse bias, where the junction capacitance is varied. The Varactor diode is also called as Vari Cap or Volt Cap. The following figure shows a Varactor diode connected in reverse bias. If the reverse voltage applied is increased, the width of the dielectric region increases, which reduces the junction capacitance. When the reverse voltage decreases, the width of the dielectric decreases, which increases the capacitance. If this reverse voltage is completely null, then the capacitance will be at its maximum. The following figure shows various symbols used for Varactor diode which represents its function. Though all diodes have this junction capacitance, the Varactor diode is mainly manufactured to make use of this effect and increase the variations in this junction capacitance. Applications of Varactor diode This diode has many applications such as − It is used as a Voltage variable capacitor. It is used in variable LC tank circuit. Used as Automatic frequency control. Used as Frequency Modulator. Used as RF Phase shifter. Used as frequency multiplier in local oscillator circuits. Tunnel diode If the impurity concentration of a normal PN junction is highly increased, this Tunnel diode is formed. It is also known as Esaki diode, after its inventor. When the impurity concentration in a diode increases, the width of depletion region decreases, extending some extra force to the charge carriers to cross the junction. When this concentration is further increased, due to less width of the depletion region and the increased energy of the charge carriers, they penetrate through the potential barrier, instead of climbing over it. This penetration can be understood as Tunneling and hence the name, Tunnel diode. The Tunnel diodes are low power devices and should be handled with care as they easily get affected by heat and static electricity. The Tunnel diode has specific V-I characteristics which explain their working. Let us have a look at the graph below. Consider the diode is in forward-biased condition. As forward voltage increases, the current increases rapidly and it increases until a peak point, called as Peak Current, denoted by IP. The voltage at this point is called as Peak Voltage, denoted by VP. This point is indicated by A in the above graph. If the voltage is further increased beyond VP, then the current starts decreasing. It decreases until a point, called as Valley Current, denoted by IV. The voltage at this point is called as Valley Voltage, denoted by VV. This point is indicated by B in the above graph. If the voltage is increased further, the current increases as in a normal diode. For larger values of forward voltage, the current increases further beyond. If we consider the diode is in reverse-biased condition, then the diode acts as an excellent conductor as the reverse voltage increases. The diode here acts as in a negative resistance region. Applications of Tunnel diode There are many applications for tunnel diode such as − Used as a high-Speed Switching device Used as a memory storage device Used in Microwave oscillators Used in relaxation oscillators Schottky Diode This is a special type of diode in which a PN junction is replaced by a metal semiconductor junction. The P-type semiconductor in a normal PN junction diode is replaced by a metal and N-type material is joined to the metal. This combination has no depletion region between them. The following figure shows the Schottky diode and its symbol. The metal used in this Schottky diode may be gold, silver, platinum or tungsten etc. As well, for the semiconductor material other than silicon, gallium arsenide is mostly used. Operation When no voltage is applied or when the circuit is unbiased, the electrons in the N-type material has lower energy level than the ones in the metal. If the diode is then forward biased, these electrons in the N-type gain some energy and move with some higher energy. Hence these electrons are called as Hot Carriers. The following figure shows a Schottky diode connected in a circuit. Advantages There are many advantages of Schottky diode such as − It is a unipolar device and hence no reverse currents are formed. Its forward resistance is low. Voltage drops are very low. Rectification is fast and easy with the Schottky diode. There is no depletion region present and hence, no junction capacitance. So, the diode gets to OFF position quickly. Applications There are many applications of Schottky diode such as − Used as a detector diode Used as a Power rectifier Used in RF mixer circuits Used in power circuits Used as clamping diodes Learning working make money

Basic Electronics – Variable Capacitors There are many types of capacitors depending upon their function, the dielectric material used, their shape etc. The main classification is done according to fixed and variable capacitors. Types of Capacitors The classification is as shown in the following figure. The main classification is just like the above one. The fixed capacitors are the ones whose value is fixed at the time of manufacturing itself and the variable ones provide us with an option to vary the value of capacitance. Variable Capacitors Let us know something about the variable capacitors whose value alters when you vary, either electrically or mechanically. Variable capacitors in general consists of interwoven sets of metallic plates in which one is fixed and the other is variable. These capacitors provide the capacitance values so as to vary between 10 to 500pF. The ganged capacitor shown here is a combination of two capacitors connected together. A single shaft is used to rotate the variable ends of these capacitors which are combined as one. The dotted line indicates that they are connected internally. There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors. Tuning Capacitors Tuning capacitors are popular type of variable capacitors. They contain a stator, a rotor, a frame to support the stator and a mica capacitor. The constructional details of a tuning capacitor are shown in the following figure. The stator is a stationary part and rotor rotates by the movement of a movable shaft. The rotor plates when moved into the slots of stator, they come close to form plates of a capacitor. When the rotor plates sit completely in the slots of the stator then the capacitance value is maximum and when they don’t, the capacitance value is minimum. The above figure shows a ganged tuning capacitor having two tuning capacitors connected in a gang. This is how a tuning capacitor works. These capacitors generally have capacitance values from few Pico Farads to few tens of Pico Farads. These are mostly used in LC circuits in radio receivers. These are also called as Tuning Condensers. Trimmer Capacitors Trimmer capacitors are varied using a screwdriver. Trimmer capacitors are usually fixed in such a place where there is no need to change the value of capacitance, once fixed. There are three leads of a trimmer capacitor, one connected to stationary plate, one to rotary and the other one is common. The movable disc is a semi-circular shaped one. A trimmer capacitor would look like the ones in the following figure. There are two parallel conducting plates present with a dielectric in the middle. Depending upon this dielectric used, there are air trimmer capacitors and ceramic trimmer capacitors. The constructional details of a trimmer capacitor are as shown below. One of the two plates is movable, while the other is fixed. The dielectric material is fixed. When the movable plate is moved, opposite to the area between movable and fixed electrode, then the capacitance can be changed. The capacitance will be higher if the opposite area gets bigger, as both the electrodes act as two plates of a capacitor. The Trimmer Capacitors are easily fixed on a PCB (Printed Circuit Board) and they are mostly used for calibration of equipment. Learning working make money

Basic Electronics – Fixed Resistors Fixed resistors are one type of linear resistors. A resistor is said to be a fixed resistor, if its value is fixed. The value of fixed resistor can’t be varied like a variable resistor as its value is determined at the time of manufacturing itself. The following figures represent the symbol of a fixed resistor. The fixed resistors are classified into different types, depending upon their manufacturing processes and the materials used in their manufacturing. The classification is as follows. Carbon composition The Carbon composition resistors are a blend of carbon particles, graphite and ceramic dust mixed with a binder substance like clay. This mixture is treated with high pressure and temperature. After the whole thing is molded in a case, the leads are fixed. Thermal mass of the carbon composition resistor is higher so as to withstand high energy pulses. These resistors have low stability and high noise which is a disadvantage. The following figure shows an image of carbon composition resistor. Carbon composition resistors are used in Surge protection, Current limiting, and High voltage power supplies. Wire wound A Wire wound resistor is formed by wounding a wire made up of a resistive material around a core. The metallic core acts as a non-conductive material while the resistive wire conducts, but with some resistance. The image of a wire wound resistor is as shown below. Usually a nichrome wire or a manganin wire is used to wind the core because they offer high resistance. Whereas plastic, ceramic or glass is used for core. Wire wound resistors are very accurate. They work excellently for low resistance values and high power ratings. These are the oldest type of fixed resistors, but are being used even now. Thick Film The film resistors have a resistive layer on a ceramic base, whose thickness defines the type they belong to. The thickness of resistive layer on thick film resistors is much higher than thin film resistors. Thick film resistors are produced by firing a special paste, which is a mixture of glass and metal oxides, onto the substrate. There are three main types in thick film resistors like Fusible resistors, Cermet film resistors, and Metal oxide film resistors. Fusible Resistors The Fusible resistors are similar to wire wound resistors. But these resistors along with providing resistance, act as a fuse. The image of a fusible resistor is as shown below. In this resistor, the current flows through a spring loaded connection, which is placed closely to the body of the resistor. The blob that is attached to the spring wire of the resistor takes the heat generated by the resistor due to the current flow. If this heat is increased, the attachment to the blob gets melted up and opens the connection. Hence we can say that, these resistors limit the current, but if the circuit power rating exceeds a specified value, these resistors act as a fuse to open or break the circuit. The value of these resistors is usually of less than 10 Ohms. These resistors are generally used in TV sets, amplifiers and other expensive electronic circuits. Cermet Film Resistors The Cermet film resistors are the film resistors made up of a special material called Cermet. Cermet is a composite alloy made by combining Ceramic and Metal. This combination provides the advantages in both of these materials like high temperature resistance and wear resistance of ceramic along with flexibility and electrical conductivity of a metal. A metal film layer is wrapped around a resistive material and is fixed in a ceramic metal or cermet substrate. Leads are taken to make the connections easy while fixing on a PCB. They offer high stability as temperature cannot affect their performance. Metal Oxide film resistors A Metal oxide film resistor is formed by oxidizing a thick film of Tin chloride on a heated glass rod, which is a substrate. They have high temperature stability and can be used at high voltages. These resistors have low operating noise. Metal oxide film resistors differ with metal film ones only regarding the type of film coated. Metal oxide is a metallic compound like tin with oxygen to form tin oxide, which is coated as a film on the resistor. The resistivity of this resistor depends upon the amount of antimony oxide added to the tin oxide. Thin Film Thin film resistors have a resistive layer of width 0.1 micrometer or smaller on the ceramic base. Thin film resistors have a metallic film that is vacuum deposited on an insulating substrate. Thin film resistors are more accurate and have better temperature coefficient and is more stable. The thin film resistors are further divided into two types such as − Carbon film resistors Metal film resistors Carbon film resistor A Carbon film resistor is made by depositing a carbon film layer on a ceramic substrate. The carbon film acts as the resistive material to the current and the ceramic substance acts as an insulating substance. Metallic caps are fixed at both the ends and copper leads are drawn out. The following figure shows the construction of a carbon film resistor. The main advantages of these resistors are their high stability, wide operating range, low noise, and low cost. The carbon film resistors are the most preferred ones over carbon composition resistors due to their low noise. Metal Film Resistors The film coating makes the difference between metal oxide film resistors and metal film resistors. A thin film of metallic substance such as nickel chromium is used to coat the resistor in a metal film resistor whereas a film of metal oxide like tin oxide is used to coat the resistor in a metal oxide resistor. Metal film resistors have low temperature coefficient of resistance, which means the resistance is less affected by the temperature. Wattage While using a resistor, if the flow of current increases, the resistor dissipates some heat. If this value crosses a certain critical value, the resistor may get

Basic Electronics – Non linear Resistors There are many types of resistors according to the type of material used, the manufacturing procedure and their applications. The classification is as shown below. Linear resistors have linear VI characteristics and non-linear resistors has non-linear VI characteristics. Non-linear resistors are the resistors whose voltage and current characteristics vary non-linearly. The voltage and current values vary depending upon other factors like temperature and light, but they may not be linear. Thermistor Thermal means temperature. In this resistor, the resistance varies with temperature. If heat increases, the resistance decreases and vice versa. This is used for measurement and control purposes. The main types of thermistors are NTC and PTC. NTC is Negative Temperature Coefficient and in such devices, the resistance decreases as the temperature increases. These are used to protect the devices from over-voltage conditions. PTC is Positive Temperature Coefficient and in such devices, the resistance increases as the temperature increases. These are used to protect the devices from over current conditions. The following figure shows an NTC thermistor, along with its symbol. Photo Resistor Photo means light. In this resistor, the resistance varies with light. As light increases resistance decreases and vice versa. This is also used for measurement and control purposes. It is also called as LDR (Light Dependent Resistor) Varistors The resistance of a varistor, varies with the applied voltage. As the voltage increases, the resistance decreases and if the voltage decreases, the resistance increases. It is also called as VDR (Voltage Dependent Resistor). Surface Mount These are being highly used since the introduction of surface mount technology. These can be termed as chip resistors, which means a resistive layer integrated on a ceramic chip. These surface mount resistors are very small when compared to the normal resistors and hence occupy less space. They are effective and dissipate less heat. The invention of these resistors has changed the look of a PCB (Printed Circuit Board) and reduced its size greatly. The advantages of surface mount resistors are − These are compact in size. These are very stable. They have good tolerance. They are effective in reducing heat dissipation. The following figure shows the images of surface mount resistors. Learning working make money

Basic Electronics – Resistors Resist is the word which means “to oppose”. Resistance is the property of opposing the flow of electrons, in a conductor or a semiconductor. A Resistor is an electronic component which has the property of resistance. Symbol and Units The symbol for a Resistor is as shown below. The units of resistance is Ohms, which is indicated by Ω (omega). The formula for resistance is R = V/I Where V is Voltage and I is Current. It would really be difficult to manufacture the resistors with each and every value. Hence, few values are chosen and the resistors of such values are only manufactured. These are called as “Preferred Values”. In practice, the resistors with near values are chosen to match the required applications. This is how a practical resistor looks like − Color Coding A process called color coding is used to determine the value of resistance for a resistor, just as shown in the above figure. A resistor is coated with four color bands where each color determines a particular value. The below table shows a list of values which each color indicates. COLOUR DIGIT MULTIPLIER TOLERANCE Black 0 100 = 1 Brown 1 101 = 10 1 Red 2 102 = 100 2 Orange 3 103 = 1000 Yellow 4 104 = 10000 Green 5 105 = 100000 0.5 Blue 6 106 = 1000000 0.25 Violet 7 107 = 10000000 0.1 Gray 8 108 = 100000000 White 9 109 = 1000000000 Gold 10-1 = 0.1 5 Silver 10-2 = 0.01 10 (none) 20 The first two colored bands indicate the first and second digit of the value and the third color band represents the multiplier (number of zeroes added). The fourth color band indicates the tolerance value. Tolerance is the range of value up to which a resistor can withstand without getting destroyed. This is an important factor. The following figure shows how the value of a resistor is determined by color code. The five color band resistors are manufactured with tolerance of 2% and 1% and also for other high accuracy resistors. In these five band resistors, the first three bands represent digits, fourth one indicates multiplier and the fifth represents tolerance. Let us look at an example to understand the color coding process. Example 1 − Determine the value of a resistor with a color code yellow, blue, orange and silver. Solution − The value of yellow is 4, blue is 6, orange is 3 which represents multiplier. Silver is ±10 which is the tolerance value. Hence the value of the resistor is 46×103 = 46kΩ The maximum resistance value for this resistor is 46kΩ or 46000Ω + 10% = 46000 + 4600 = 50600Ω = 50.6kΩ The minimum resistance value for this resistor is 46kΩ or 46000Ω – 10% = 46000 – 4600 = 41400Ω = 41.4kΩ After having gone through different details regarding resistors, we have some terms to learn. Also we have to deal with different behaviors of a resistor for few types of connections. Important Terms There are a few terms which we need to discuss before going into the type of resistors we have. One needs to get introduced to these terms at this stage and can understand them as we progress further. Resistance Resistance is the property of a resistor that opposes the flow of current. When alternating current goes through a resistance, a voltage drop is produced that is in-phase with the current. Indication − R Units − Ohms Symbol − Ω Along with resistance, there are other important terms, called as reactance and impedance. Reactance The resistance offered to the alternating current because of the capacitances and inductances present in the circuit, can be understood as reactance. When alternating current goes through a pure reactance, a voltage drop is produced that is 90°out of phase with the current. Depending upon the phase i.e., +90° or -90° the reactance can be termed as inductive reactance or capacitive reactance. Indication − X Units − Ohms Symbol − Ω Impedance Impedance is the effective resistance to alternating current arising from the combined effects of ohmic resistance and reactance. When alternating current goes through an impedance, a voltage drop is produced which is somewhere between 0°to 90°out of phase with the current. Indication − I Units − Ohms Symbol − Ω Conductance This is the ability of a material to conduct electricity. It is the reciprocal of resistance. Indication − G Units − Mhos Symbol − ℧ Learning working make money

Basic Electronics – Capacitors ”; Previous Next A Capacitor is a passive component that has the ability to store the energy in the form of potential difference between its plates. It resists a sudden change in voltage. The charge is stored in the form of potential difference between two plates, which form to be positive and negative depending upon the direction of charge storage. A non-conducting region is present between these two plates which is called as dielectric. This dielectric can be vacuum, air, mica, paper, ceramic, aluminum etc. The name of the capacitor is given by the dielectric used. Symbol and Units The standard units for capacitance is Farads. Generally, the values of capacitors available will be in the order of micro-farads, pico-farads and nano-farads. The symbol of a capacitor is as shown below. The Capacitance of a capacitor is proportional to the distance between the plates and is inversely proportional to the area of the plates. Also, the higher the permittivity of a material, the higher will be the capacitance. The permittivity of a medium describes how much electric flux is being generated per unit charge in that medium. The following image shows some practical capacitors. When two plates having same area A, and equal width are placed parallel to each other with a separation of distance d, and if some energy is applied to the plates, then the capacitance of that parallel plate capacitor can be termed as − $$C::=::frac{varepsilon_{0}::varepsilon_{r}::d}{A}$$ Where C = Capacitance of a capacitor $varepsilon_{0}$ = permittivity of free space $varepsilon_{r}$ = permittivity of dielectric medium d = distance between the plates A = area of the two conducting plates With some voltage applied, the charge deposits on the two parallel plates of the capacitor. This charge deposition occurs slowly and when the voltage across the capacitor equals the voltage applied, the charging stops, as the voltage entering equals the voltage leaving. The rate of charging depends upon the value of capacitance. The greater the value of capacitance, the slower the rate of change of voltage in the plates. Working of a Capacitor A Capacitor can be understood as a two-terminal passive component which stores electrical energy. This electrical energy is stored in electrostatic field. Initially, the negative and positive charges on two plates of the capacitor are in equilibrium. There is no tendency for a capacitor to get charged or discharged. The negative charge is formed by the accumulation of electrons, while the positive charge is formed by the depletion of electrons. As this happens without any external charge given, this state is electrostatic condition. The figure below shows the capacitor with static charges. The accumulation and depletion of electrons according to the varying positive and negative cycles of the AC supply, can be understood as “current flow”. This is called as Displacement Current. The direction of this current flow keeps on changing as this is AC. Charging of a Capacitor When an external voltage is given, the electric charge gets converted into electrostatic charge. This happens while the capacitor is charging. The positive potential of the supply, attracts the electrons from the positive plate of the capacitor, making it more positive. While the negative potential of the supply, forces the electrons to the negative plate of the capacitor, making it more negative. The figure below explains this. During this process of charging, the electrons move through the DC supply but not through the dielectric which is an insulator. This displacement is large, when the capacitor starts to charge but reduces as it charges. The capacitor stops charging when the voltage across capacitor equals the supply voltage. Let us see what happens to the dielectric when the capacitor begins to charge. Dielectric behavior As the charges deposit on the plates of the capacitor, an electrostatic field is formed. The strength of this electrostatic field depends upon the magnitude of charge on the plate and the permittivity of the dielectric material. Permittivity is the measure of dielectric whether how far it allows the electrostatic lines to pass through it. The dielectric is actually an insulator. It has electrons in the outer most orbit of the atoms. Let us observe how they get affected. When there is no charge on the plates, the electrons in the dielectric move in circular orbit. This is as shown in the figure below. When charge deposition takes place, the electrons tend to move towards the positive charged plate, but still they keep on revolving as shown in the figure. If the charge increases further, the orbits expand more. But if it still increases, the dielectric breaks down shorting the capacitor. Now, the capacitor being fully charged, it’s ready to get discharged. It is enough if we provide a path for them to travel from negative to positive plate. The electrons flow without any external supply as there are too many number of electrons on one side and barely any electrons on the other. This imbalance is adjusted by the discharge of the capacitor. Also, when a discharge path is found, the atoms in the dielectric material tend to get to their normal circular orbit and hence forces the electrons to get discharged. This kind of discharge enables capacitors to deliver high currents in a short period of time, just as in a camera flash. Color Coding To know the value of a capacitor, it is usually labelled as below − n35 = 0.35nF or 3n5 = 3.5nF or 35n = 35nF and so on. Sometimes the markings will be like 100K which means, k = 1000pF. Then the value will be 100 × 1000pF = 100nF. Though these number markings are being used now-a-days, an International color coding scheme was developed long ago, to understand the values of capacitors. The color coding indications are just as given below. Band colour Digit A and B Multiplier Tolerance (t) > 10pf Tolerance (t) < 10pf Temperature coefficient Black 0 × 1 ±20% ±2.0pF Brown 1 × 10

Circuit Connections in Capacitors ”; Previous Next In a circuit, a Capacitor can be connected in series or in parallel fashion. If a set of capacitors were connected in a circuit, the type of capacitor connection deals with the voltage and current values in that network. Capacitors in Series Let us observe what happens, when few Capacitors are connected in Series. Let us consider three capacitors with different values, as shown in the figure below. Capacitance When the capacitance of a network whose capacitors are in series is considered, the reciprocal of the capacitances of all capacitors, is added to get the reciprocal of the total capacitance. To get this more clearly, $$frac{1}{C_{T}}::=::frac{1}{C_{1}}::+::frac{1}{C_{2}}::+::frac{1}{C_{3}}$$ Following the same formula, if simply two capacitors are connected in series, then $$C_{T}::=::frac{C_{1}::times::C_{2}}{C_{1}::+::C_{2}}$$ Where C1 is the capacitance across the 1st capacitor, C2 is the capacitance across the 2nd capacitor and C3 is the capacitance across the 3rd capacitor in the above network. Voltage The voltage across each capacitor depends upon the value of individual capacitances. Which means $$V_{C1}::=::frac{Q_{T}}{C_{1}}::V_{C2}::=::frac{Q_{T}}{C_{2}}::V_{C3}::=::frac{Q_{T}}{C_{3}}$$ The total voltage across the series capacitors circuit, $$V_{T}::=::V_{C1}::+::V_{C2}::+::V_{C3}$$ Where Vc1 is the voltage across the 1st capacitor, Vc2 is the voltage across the 2nd capacitor and Vc3 is the voltage across the 3rd capacitor in the above network. Current The total amount of Current that flows through a set of Capacitors connected in series is the same at all the points. Therefore the capacitors will store the same amount of charge regardless of their capacitance value. Current through the network, $$I::=::I_{1}::=::I_{2}::=::I_{3}$$ Where I1 is the current through the 1st capacitor, I2 is the current through the 2nd capacitor and I3 is the current through the 3rd capacitor in the above network. As the current is same, the storage of charge is same because any plate of a capacitor gets its charge from the adjacent capacitor and hence capacitors in series will have the same charge. $$Q_{T}::=::Q_{1}::=::Q_{2}::=::Q_{3}$$ Capacitors in Parallel Let us observe what happens, when few capacitors are connected in Parallel. Let us consider three capacitors with different values, as shown in the figure below. Capacitance The total Capacitance of the circuit is the equivalent to the sum of the individual capacitances of the capacitors in the network. $$C_{T}::=::C_{1}::+::C_{2}::+::C_{3}$$ Where C1 is the capacitance across the 1st capacitor, C2 is the capacitance across the 2nd capacitor and C3 is the capacitance across the 3rd capacitor in the above network. Voltage The voltage measured at the end of the circuit is same as the voltage across all the capacitors that are connected in a parallel circuit. $$V_{T}::=::V_{1}::=::V_{2}::=::V_{3}$$ Where Vc1 is the voltage across the 1st capacitor, Vc2 is the voltage across the 2nd capacitor and Vc3 is the voltage across the 3rd capacitor in the above network. Current The total current flowing is equal to the sum of the currents flowing through each capacitor connected in the parallel network. $$I_{T}::=::I_{1}::+::I_{2}::+::I_{3}$$ Where I1 is the current through the 1st capacitor, I2 is the current through the 2nd capacitor and I3 is the current through the 3rd capacitor in the above network. Print Page Previous Next Advertisements ”;

Basic Electronics – Optoelectronic Diodes ”; Previous Next These are the diodes which are operated on light. The word “Opto” means Light. There are types that conduction depending upon the light intensity and other types whose conduction delivers some light. Each type has got applications of their own. Let us discuss the prominent types among these ones. Some diodes conduct according to the intensity of light falls on them. There are two main types of diodes in this category. They are Photo diodes and Solar cells. Photo Diode Photo diode, as the name implies, is a PN junction which works on light. The intensity of light affects the level of conduction in this diode. The photo diode has a P type material and an N-type material with an intrinsic material or a depletion region in between. This diode is generally operated in reverse bias condition. The light when focused on the depletion region, electron-hole pairs are formed and flow of electron occurs. This conduction of electrons depends upon the intensity of light focused. The figure below shows a practical Photo diode. The figure below indicates the symbol for a photodiode. When the diode is connected in reverse bias, a small reverse saturation current flows due to thermally generated electron hole pairs. As the current in reverse bias flows due to minority carriers, the output voltage depends upon this reverse current. As the light intensity focused on the junction increases, the current flow due to minority carriers increase. The following figure shows the basic biasing arrangement of a photo diode. The Photo diode is encapsulated in a glass package to allow the light to fall onto it. In order to focus the light exactly on the depletion region of the diode, a lens is placed above the junction, just as illustrated above. Even when there is no light, a small amount of current flows which is termed as Dark Current. By changing the illumination level, reverse current can be changed. Advantages of Photo diode Photo diode has many advantages such as − Low noise High gain High speed operation High sensitivity to light Low cost Small size Long lifetime Applications of Photo diode There are many applications for photo diode such as − Character detection Objects can be detected (visible or invisible). Used in circuits that require high stability and speed. Used in Demodulation Used in switching circuits Used in Encoders Used in optical communication equipment Another diode of such a kind is Solar cell. It is termed as a cell though it is a diode. Let us get into the details. Solar Cell The light dependent diodes include Solar cell, which is a normal PN junction diode but has its conduction by the rush of photons which are converted into the flow of electrons. This is similar to a photo diode but it has another objective of converting maximum incident light into energy and storing it. The figure below represents the symbol of a solar cell. A solar cell has its name and symbol indicating storing of energy though it is a diode. The feature of extracting more energy and storing of it is concentrated in the solar cell. Construction of a Solar cell A PN junction diode with an intrinsic material in the deletion region is made to encapsulate in a glass. The light is made to incident on maximum area possible with thin glass on the top so as to collect maximum light with minimum resistance. The following figure shows the construction of a Solar cell. When the light is incident on the solar cell, the photons in the light collide with valence electrons. The electrons are energized to leave the parent atoms. Thus a flow of electrons is generated and this current is directly proportional to the light intensity focused onto the solar cell. This phenomenon is called as the Photo-Voltaic effect. The following figure shows how a solar cell looks like and how a number of solar cells together are made to form a solar panel. Difference between a Photo diode and Solar cell Photo Diode works faster and concentrates on switching rather than providing more power at the output. It has a low capacitance value because of this. Also the area of incidence of light energy is lesser in Photo diode, according to its applications. A Solar cell concentrates on delivering high output energy and storing the energy. This has high capacitance value. The operation is a bit slower than photo diode. According to the purpose of the solar cell, the area of incidence of light is larger than photo diode. Applications of Solar Cell There are many applications for Solar cell such as − Science and Technology Used in Solar panels for Satellites Used in telemetry Used in Remote lighting systems etc. Commercial Use Used in Solar panels for storage of electricity Used in Portable power supplies etc. Used in household uses such as cooking and heating using solar energy Electronic Watches Calculators Electronic Toys, etc. Some diodes emit light according to the voltage applied. There are two main types of diodes in this category. They are LEDs and Laser diodes. LED (Light Emitting Diodes) This one is the most popular diodes used in our daily life. This is also a normal PN junction diode except that instead of silicon and germanium, the materials like gallium arsenide, gallium arsenide phosphide are used in its construction. The figure below shows the symbol of a Light emitting diode. Like a normal PN junction diode, this is connected in forward bias condition so that the diode conducts. The conduction takes place in a LED when the free electrons in the conduction band combine with the holes in the valence band. This process of recombination emits light. This process is called as Electroluminescence. The color of the light emitted depends upon the gap between the energy bands. The materials used also effect the colors like, gallium arsenide phosphide emits either red or yellow, gallium

Discuss Basic Electronics ”; Previous Next This tutorial supplies basic information on how to use electronic components and explains the logic behind solid state circuit design. Starting with an introduction to semiconductor physics, the tutorial moves on to cover topics such as resistors, capacitors, inductors, transformers, diodes, and transistors. Some of the topics and the circuits built with the components discussed in this tutorial are elaborately discussed in the ELECTRONIC CIRCUITS tutorial. Print Page Previous Next Advertisements ”;