Temperature Controlled Led free essay sample

TEMPERATURE CONTROLLED LED A Mini Project Report Submitted in partial fulfillment of the requirements For the award of degree of BACHELOR OT TECHNOLOGY IN ELECTRONICS AND ELECTRICAL ENGINEERING BY Name (Reg. no) N. V. R. Srikar 08P71A0216 M. Vivek Viswanath 08P71A0230 Under the Esteemed Guidance of Mrs N. Swarnalatha [pic] DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGG. SWAMI VIVEKANANDA INSTITUTE OF TECHNOLOGY(Approved by AICTE New Delhi, Affiliated to JNTU, Hyderabad) Mahboob College Campus, Rashtra Pathi Road, Secunderabad-500043 TEMPERATURE CONTROLLED LED A Mini Project Report Submitted in partial fulfillment of the requirements For the award of degree of BACHELOR OF TECHNOLOGY IN ELECTRICAL AND ELECTRONICS ENGINEERING BY Name (Reg. no) M. Vivek Viswanath 08P71A0230 Under the Esteemed Guidance of Mrs. N. Swarnalatha [pic] DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGG. SWAMI VIVEKANANDA INSTITUTE OF TECHNOLOGY (Approved by AICTE New Delhi, Affiliated to JNTU, Hyderabad) Mahboob College Campus, Rashtra Pathi Road, Secunderabad-50004 SWAMI VIVEKANANDA INSTITUTE OF TECHNOLOGY (COLLEGE OF ENGINEERING) (Approved by A. We will write a custom essay sample on Temperature Controlled Led or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page I. C. T. E. New Delhi,Affiliated to JNTU,Hyderabad) Mahboob College Campus,Rashtra Pathi Road,Secunderabad-500043 ____________________________________________________________ _ Department of Electrical Electronic Engineering CERTIFICATE This is to certify that the Mini Project report entitled â€Å"TEMPERATURE CONTROLLED LED† is being submitted by the following students in partial fulfillment of the requirements for the award of degree of Bachelor of Technology in Electrical and Electronic Engineering from Jawaharlal Nehru Technological University Hyderabad, Andhra Pradesh is record of bonafide work carried out during the academic year 2010-2011. N. V. R. Srikar 08P71A0216 M. Vivek Viswanath 08P71A0230 Under the supervision and guidance of Internal Guide Head of Department ACKNOWLEDGEMENT With great pleasure we want to take this opportunity to express our heartfelt gratitude to all the people who helped in making this mini project work a grand success. We express our deep sense of gratitude to Mr. Madhu for  his constant guidance throughout our mini project  work. We are grateful to Mrs N. Swarnalatha for  valuable suggestions and guidance given by  during the execution of this mini project work. We would like to thank  Mrs. N. Swarnalatha, Head of the  Department of Electrical and Electronics Engineering, for being   moral   support throughout the period of our study in  Swami Vivekananda Institute Of Technology. First of all we are highly indebted to Principal Dr. S. Kesavan, for giving us the permission to carry out this mini project. We would like to thank the Teaching and Non-Teaching staff of EEE department for sharing their knowledge with us. Last but not the least we express our sincere thanks to Chairman Dr. N. Prem Narayan and Secretary Dr. K Anil Kumar, Swami Vivekananda Institute of Technology, for their continuous care towards our achievements. Mr N. V. R. Srikar Mr M. Vivek Viswanath ACKNOWLEDGEMENT With great pleasure we want to take this opportunity to express our heartfelt gratitude to all the people who helped in making this mini project work a grand success. We express our deep sense of gratitude to Mr. Madhu for  his constant guidance throughout our mini project  work. We are grateful to Mrs N. Swarnalatha for  valuable suggestions and guidance given by  during the execution of this mini project work. We would like to thank  Mrs. N. Swarnalatha, Head of the  Department of Electrical and Electronics Engineering, for being moral   support throughout the period of our study in  Swami Vivekananda Institute Of Technology. First of all we are highly indebted to Principal Dr. S. Kesavan, for giving us the permission to carry out this mini project. We would like to thank the Teaching and Non-Teaching staff of EEE department for sharing their knowledge with us. Last but not the least we express our sincere thanks to Chairman Dr. N. Prem Narayan and Secretary Dr. K Anil Kumar, Swami Vivekananda Institute of Technology, for their continuous care towards our achievements. Mr M. Vivek Viswanath CONTENTS Title Pg. No Introduction 7 Circuit Diagram 8 Components Used 9 Working 10 Light Emitting Diode 11 Voltage Regulator 12 Transformer 15 Integrated Circuit(IC) 16 Basic structure of IC 18 Classification 19 Advantages 22 Limitations 23 LM35(Temperature Sensor) 23 Operational Amplifier 24 Ideal Op-Am 25 Applications 27 IC CA3130 29 Transistor 31 Advantages 33 Limitations 33 Conclusion 34 Bibliography 35 INTRODUCTION How many times you were victim to the hot water from your shower or washbasin? How many times components of your machine or gadgets were subjected to overheating? To compromise these problems we can use a light emitting diode (LED) to warn us if there is an increase in temperature, it can warn us if our machines temperature raises or the water coming from your shower or washbasin is hot or cold accordingly. Temperature controlled light emitting diodes (LEDs) are now-a-days used in many appliances. ADVANTAGES: ? Low power consumption ? Safety ? Automatic operation CIRCUIT DIAGRAM Temperature Controlled LED [pic] Circuit to convert the supply (220V AC 50Hz) to input(9V DC): [pic] Components used: †¢ Integrated Circuits IC1 7805 IC2 LM35 IC3 CA3130 †¢ Resistors R1 10K ohms R2 1K ohms R3 10K ohms R4 220 ohms R5 10K ohms R6 220 ohms †¢ Capacitors C1 100uF C2 10uF C3 1000uF †¢ Diodes D1 LED Red D2 LED Green D3 IN4007 D4 IN4007 D5 IN4007 D6 IN4007 †¢ Transformer 9V-0-9V †¢ Transistor Q1 BC107 Q2 BC557 WORKING An LED lamp (LED light bulb) is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. LED lamps are used for both general and special-purpose lighting. LEDs glow according to the temperature in â€Å"Temperature controlled LEDs†. The circuit has two LEDs (D1 and D2), whose status are controlled by the temperature of the surroundings. The famous IC LM35 is used as the temperature sensor here. Output of LM35 raises by 10mV per degree rise in temperature. Output of LM35 is connec ted to the non-inverting input of the op-amp CA3130. The inverting input of the same op-amp can be given with the required reference voltage using R2. If the reference voltage is 0. 8V, then the voltage at the non-inverting input (output of LM35) becomes 0. 8V when the temperature is 80 degree Celsius. At this point the output of IC3 goes to positive saturation. This makes the transistor Q1 On and LED D1 glows. Since the base of Q2 is connected to the collector of Q1, Q2 will be switched OFF and LED D2 remains OFF. When the temperature is below 45 degree Celsius the reverse happens. IC1 produces a stable 5V DC working voltage from the available 9V DC supply. Light Emitting Diode (LED) [pic] Light emitting diodes (LEDs) are semiconductor light sources. The light emitted from LEDs varies from visible to infrared and ultraviolet regions. They operate on low voltage and power. LEDs are one of the most common electronic components and are mostly used as indicators in circuits. They are also used for luminance and optoelectronic applications. Based on semiconductor diode, LEDs emit photons when electrons recombine with holes on forward biasing. The two terminals of LEDs are anode (+) and cathode (-) and can be identified by their size. The longer leg is the positive terminal or anode and shorter one is negative terminal. The forward voltage of LED (1. 7V-2. 2V) is lower than the voltage supplied (5V) to drive it in a circuit. Using an LED as such would burn it because a high current would destroy its p-n gate. Therefore a current limiting resistor is used in series with LED. Without this resistor, either low input voltage (equal to forward voltage) or PWM (pulse width modulation) is used to drive the LED. VOLTAGE REGULATOR: A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. It may use an electromechanical mechanism, or passive or active electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages. With the exception of shunt regulators, all modern electronic voltage regulators operate by comparing the actual output voltage to some internal fixed reference voltage. Any difference is amplified and used to control the regulation element. This forms a negative feedback servo control loop. If the output voltage is too low, the regulation element is commanded to produce a higher voltage. For some regulators if the output voltage is too high, the regulation element is commanded to produce a lower voltage; however, many just stop sourcing current and depend on the current draw of whatever it is driving to pull the voltage back down. In this way, the output voltage is held roughly constant. The control loop must be carefully designed to produce the desired tradeoff between stability and speed of response [pic] IC voltage regulators are three-terminal devices that provide a constant DC output voltage that is independent of the input voltage, output load current, and temperature. There are three types of IC voltage regulators: †¢ IC linear voltage regulators †¢ IC switching voltage regulators †¢ DC/DC converter chips IC linear voltage regulators use an active pass element to reduce the input voltage to a regulated output voltage. By contrast, IC switching voltage regulators store energy in an inductor, transformer, or capacitor and then use this storage device to transfer energy from the input to the output in discrete packets over a low-resistance switch. DC/DC converter chips, a third type of IC voltage regulators, also provide a regulated  DC voltage output from a different, unregulated input voltage. In addition, DC/DC converters are provide noise isolation regulate power buses. For each type of IC voltage regulator, the output voltage can be fixed or adjusted to a value within a specified range. Performance specifications for IC voltage regulators include regulated output voltage, output current, and dropout voltage, quiescent current and operating temperature. The regulated output voltage (Volt) represents minimum and maximum amounts in  continuous mode DC. The output current (IOUT)  is measured under specified conditions. Dropout voltage (VD) is the minimum voltage drop across the regulator that maintains output voltage regulation. IC voltage regulators that operate with small dropout voltages dissipate less internal power, but have relatively high efficiencies. Measured in amperes (A) during the idling state, the quiescent current never makes it to the load. Instead, it flows from the battery to power the regulator itself, the operating temperature is a full-required range IC voltage regulators are available with a variety of features. Some devices have more than one output or channel. Others have an internal circuit to control the amount of current produced, or an error flag for monitoring outputs that drop below a nominal value. Reverse voltage protection prevents damage in applications where users can accidentally reverse battery polarity. Thermal shutdown protection turns off IC voltage regulators when the temperature exceeds a predefined limit. Shutdown (inhibit) pins are used to disable regulator outputs. IC voltage regulators are available in a variety of IC package types. Dual in-line packages can be made of ceramic or plastic. Quad flat packages contain a large number of fine, flexible, gull wing shaped leads. SC-70, one of the smallest available IC packages, is well-suited for applications where space is extremely limited. Small outline (SO) packages are available with 8, 14, or 20 pins. Transistor outline (TO) packages are commonly available. TO-92 is a single in-line package used for low power devices. TO-220 is suitable for high power, medium-current, and fast-switching products. TO-263 is the surface-mount version of the TO-220 package. Other IC packages for IC voltage regulators include shrink small outline package (SSOP), small outline integrated circuit (SOIC), small outline package (SOP), small outline J-lead (SOJ), discrete package (DPAK), and power package (PPAK). TRANSFORMER: A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other. The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings:By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less. Transformers are some of the most efficient electrical machines, with some large units able to transfer 99. 75% of their input power to their output. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, though a variety of designs exist to perform specialized roles throughout home and industry. [pic] INTEGRATED CIRCUIT : In the early 1960 a new field of â€Å"mind electronics† was born primarily to meet the needs of the military, which wanted to reduce the size of the electronic circuits called integrated circuits (IC’S) ,which are so small that technicians using microscopes do their construction. Microelectronics is the branch of electronics engineering which details with microcircuits. Microcircuits are simply a miniature assembly of electronic components. One type of such circuit is the integrated circuit, generally abbreviated as â€Å"IC†. An IC has various omponents such as resistors, on a small semiconductor chip. Now circuits containing hundreds if components are fabricated on a small semiconductor chip to produce an IC is a fascinating feat of microelectronics. 1. Integrated circuits consist of a single crystal chip of silicon, typically 50 to 1 mm by 1mm in cross section, containing both active and passive elements and their interconnections. Electronics circuits have b een assembled from individual components for more than half a century. During this time, a circuit designer had a large number of different components available to him. 2. His job was confined to the proper selection and use of resistors capacitors, inductors, vacuum tubes or transistors, His choice of components was governed by such considerations availability, reliability, cost, size or weight. Integrated circuits design requires a different approach. The shapes, size and fabrication of the components in integrated circuits are vastly different. An IC is an electrical network formed upon a substrate made from semiconductor or insulating materials. [pic] BASIC STRUCTURE OF INTEGRATED CIRCUITS: This consists of the following four lower of different materials. 1. The first is P-type silicon layer and is 120? m thick this serves as a substrate upon which the IC is to be built. The second layer of IC of N-type material, this layer is only 20? m thick. All active and passive components are fabricated within this layer using a number of diffusion steps. In fabrication within this layer using a number of diffusion steps. 2. The entire above component it is necessary to diffuse impurities in certain precisely defined regions within this layer. The most complicated components fabricated are the transistor. 3. The third layer is of silicon dioxide material. This provides protection of the semiconductor material surface against contamination. 4. This is also called as a barrier in the selective diffusion of impurities in second layer, and protects portions of the water against impurity penetration. In these regions where diffusion id to take place, the Si2 layer is etched away, leaving the rest of the water protected against diffusion the Si2 layer must be subjected to photolithographic process to permit selective etching. 5. The fourth layer is a metallic layer made up of aluminum and is added to supply the necessary interconnections between different fabricated components. CLASSIFICATION The IC’s are classified as 1. Monolithic 2. Hybrid 1. In monolithic IC’s all components are formed simultaneously through diffusion process. 2. In hybrids IC’s the passive components (such as resistors, capacitors) and Inter connections between them are formed in an insulating substrate. IC’s are again classified based on the mode of operation. They are:- 1. Digital IC’s 2. Linear IC’s DIGITAL IC’S: They are the computer functioning logic networks that are equivalent of basic trainer logic circuit. They are used to form circuits such as gates, counters, and multiplexers, DE multiplexers etc. Since it is a complete designed package IC usually requires only one power supply with suitable components LINEAR IC’S: Linear IC is equivalent to discrete transistors network such as amplifier. They often require additional components for satisfactory operation. Ex; External resistors are required to control the voltage gain and the frequency response of an operational – Amplifier. In linear IC circuits the output electrical signal varies with respects to input. They are referred as analog circuits. [pic] ADVANTAGES: Some of the advantages offered by integrated circuit technology as compared with discrete components interconnected by conventional technique are as follows : Small size. Low cost due to the processing of large quantities of the components. Inter connections errors are non-existent. Temperature, differences between the parts if a circuit are small. Close matching of components and temperature coefficients is possible. Active device can be generously used, as they are cheaper than passive components. Economics are achieved in the cost of manufacture and inter connection of element of a system. High stability and reliability because all components are fabricated simultaneously and there are no soldered joints. Because of low cost, more complex circuitry may be used to obtain better functional characteristics. Hence there is improved performance. LIMITATIONS: †¢ If any component in an IC goes out of order whole IC has to be replaced. †¢ In an IC it’s neither convenient nor economical to fabricate capacitors exceeding 30pf therefore for high values of capacitance discrete, components exterior to IC chip are connected. It is not possible to fabricate inductors and transformers on the surface of the semiconductor on chip. Therefore these components are connected exterior to the chip. †¢ It is not possible to produce high power IC’s. LM35 (IC Temperature Sensor): LM35 is a precision IC temperature sensor with its output proportional to the temperature (in  oC). The sensor circuitry is sealed and therefore it is not subjected to oxidation and other processes. With LM35, temperature can be measured more accurately than with a thermistor. It also possess low self-heating and does not cause more than 0. 1  oC temperature rise in still air. The operating temperature range is from -55 °C to 150 °C. The output voltage varies by 10mV in response to every  oC rise/fall in ambient temperature,  i. e. ,  its scale factor is 0. 01V/  oC. [pic] OPERATIONAL AMPLIFIER: An operational amplifier, often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs [1] and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals and low output impedance are important typical characteristics. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume. Modern designs are electronically more rugged than earlier implementations and some can sustain direct short-circuits on their outputs without damage. CIRCUIT NOTIFICATION: Circuit diagram symbol for an op-amp The circuit symbol for an op-amp is shown in Figure 1 Where: V+: non-inverting input V? : inverting input[pic] Vout: output VS+: positive power supply VS? : negative power supply The power supply pins (VS+ and VS? ) can be labeled in different ways (See IC power supply pins). Despite different labeling, the function remains the same. Often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit. OPERATION OF IDEAL OP-AMPS: The amplifiers differential inputs consist of an inverting input and a non-inverting input, and ideally the op-amp amplifies only the difference in voltage between the two. This is called the differential input voltage. In its most common use, the op-amps output voltage is controlled by feeding a fraction of the output signal back to the inverting input. This is known as negative feedback. If that fraction is zero, i. e. , there is no negative feedback, the amplifier is said to be running open loop and its output is the differential input voltage multiplied by the total gain of the amplifier, as shown by the following equation: [pic] where V+ is the voltage at the non-inverting terminal, V? is the voltage at the inverting terminal and G is the total open-loop gain of the amplifier. Because the magnitude of the open-loop gain is typically very large and not well controlled by the manufacturing process, op-amps are not usually used without negative feedback. Unless the differential input voltage is extremely small, open-loop operation results in op-amp saturation (see below in nonlinear imperfections). An example of how the output voltage is calculated when negative feedback exists is shown below in Basic non-inverting amplifier circuit. Another typical configuration of op-amps is the positive feedback, which takes a fraction of the output signal back to the non-inverting input. An important application of it is the comparator with hysteresis (see Schmitt trigger). For any input voltages the ideal op-amp has †¢ infinite open-loop gain, †¢ infinite bandwidth, †¢ infinite input impedances (resulting in zero input currents), †¢ zero offset voltage, †¢ infinite slew rate, †¢ zero output impedance, and zero noise. The inputs of an ideal op-amp under negative feedback can be modeled using a nullator, the output with a norator and the combination (complete ideal op-amp) by a nullor. DISADVANTAGES OF OP-AMPS: Op-amps can only approach this ideal: in addition to the practical limitations on slew rate, bandwidth, offset and so forth mentioned above, real op-amp parameters are subject to drift over time and with changes in temperature, input conditions, etc. Modern integrated FET or MOSFET op-amps approximate more closely the ideal op-amp than bipolar ICs where large signals must be handled at room temperature over a limited bandwidth; input impedance, in particular, is much higher, although the bipolar op-amps usually exhibit superior (i. e. , lower) input offset drift and noise characteristics. Where the limitations of real devices can be ignored, an op-amp can be viewed as a black box with gain; circuit function and parameters are determined by feedback, usually negative. IC op-amps as implemented in practice are moderately complex integrated circuits; see the internal circuitry for the relatively simple 741 op-amp below, for example. APPLICATIONS : Use in electronics system design The use of op-amps as circuit blocks is much easier and clearer than specifying all their individual circuit elements (transistors, resistors, etc. , whether the amplifiers used are integrated or discrete. In the first approximation op-amps can be used as if they were ideal differential gain blocks; at a later stage limits can be placed on the acceptable range of parameters for each op-amp. Circuit design follows the same lines for all electronic circuits. A specification is drawn up governing what the circuit is required to do, with allowable limits. For example, the gain may be required to be 100 times, with a tolerance of 5% but drift of less than 1% in a specified temperature range; the input impedance not less than 1 megohm; etc. A basic circuit is designed, often with the help of circuit modeling (on a computer). Specific commercially available op-amps and other components are then chosen that meet the design criteria within the specified tolerances at acceptable cost. If not all criteria can be met, the specification may need to be modified. A prototype is then built and tested; changes to meet or improve the specification, alter functionality, or reduce the cost, may be made. Basic non-inverting amplifier circuit The general op-amp has two inputs and one output. The output voltage is a multiple of the difference between the two inputs (some are made with floating, differential outputs): Vout = G(V+ ? V? ) G is the open-loop gain of the op-amp. The inputs are assumed to have very high impedance; negligible current will flow into or out of the inputs. Op-amp outputs have very low source impedance. If the output is connected to the inverting input, after being scaled by a voltage divider K = R1 / (R1 + R2), then: V+ = Vin V? = K Vout Vout = G(Vin ? K Vout) Solving for Vout / Vin, we see that the result is a linear amplifier with gain: Vout/Vin = G /(1 + G K) If G is very large, Vout/Vin comes close to 1/K, which equals 1 + (R2/R1). This negative feedback connection is the most typical use of an op-amp, but many different configurations are possible, making it one of the most versatile of all electronic building blocks. When connected in a negative feedback configuration, the op-amp will try to make Vout whatever voltage is necessary to make the input voltages as nearly equal as possible. This, and the high input impedance, is sometimes called the two golden rules of op-amp design (for circuits that use egative feedback): †¢ No current will flow into the inputs. †¢ The input voltages will be nearly equal. The exception is if the voltage required is greater than the op-amps supply, in which case the output signal stops near the power supply rails, VS+ or VS?. Most single, dual and quad op-amps available have a standardized pin-out which permits one type to be substituted for another without wiring changes. A specific op-amp may b e chosen for its open loop gain, bandwidth, noise performance, input impedance, power consumption, or a compromise between any of these factors IC CA3130: CA3130 are integrated-circuit operational ampli? ers that combine the advantage of both CMOS and bipolar transistors on a monolithic chip. Gate-protected p-channel MOSFET (PMOS) transistors are used in the input circuit to provide very-high-input impedance, very-low-input current, and exceptional speed performance. The use of PMOS ? eld-effect transistors in the input stage results in common-mode input-voltage capability down to 0. 5 volt below the negative-supply terminal, an important attribute in single-supply applications. A complementary-symmetry MOS (CMOS) transistor-pair, capable of swinging the output voltage to within 10 millivolts of either supply-voltage terminal (at very high values of load impedance), is employed as the output circuit. The CA3130 Series circuits operate at supply voltages ranging from 5 to 16 volts, or  ±2. 5 to  ±8 volts when using split supplies. They can be phase compensated with a single external capacitor, and have terminals for adjustment of offset voltage for applications requiring offset-null capability. Terminal provisions can also made to permit strobing of the output stage. The CA3130A offers superior input characteristics over those of the CA3130. Applications: †¢ Fast Sample-Hold Ampli? ers †¢ Long-Duration Timers/Monostables †¢ High-Input-Impedance Comparators(Ideal Interface with Digital CMOS) †¢ High-Input-Impedance Wideband Ampli? ers †¢ Voltage Followers (e. g. Follower for Single-Supply D/A Converter) †¢ Voltage Regulators (Permits Control of Output Voltage Down to Zero Volts) †¢ Peak Detectors †¢ Single-Supply Full-Wave Precision Recti? ers [pic] TRANSISTORS: [pic] A  transistor  is a  semiconductor  device  used to  amplify  and switch  electronic  signals. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistors terminals changes the current flowing through another pair of terminals. Because the controlled (output)  power  can be much more than the controlling (input) power, a transistor can  amplify  a signal. Today, some transistors are packaged individually, but many more are found embedded in  integrated circuits. The transistor is the fundamental building block of modern  electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper  radios,  calculators, and  computers, among other things. The transistor is the key active component in practically all modern  electronics. Many consider it to be one of the greatest inventions of the 20th century. Its importance in todays society rests on its ability to be  mass produced  using a highly automated process (semiconductor device fabrication) that achieves astonishingly low per-transistor costs. The invention of the first transistor at  Bell Labs was named an  IEEE Milestone  in 2009. Although several companies each produce over a billion individually packaged (known as  discrete) transistors every year, the vast majority of transistors now are produced in  integrated circuits  (often shortened to  IC,  microchips  or simply  chips), along with  diodes,  resistors,  capacitors  and other  electronic components, to produce complete electronic circuits. A  logic gate  consists of up to about twenty transistors whereas an advanced microprocessor, as of 2011, can use as many as 3 billion transistors (MOSFETs). About 60 million transistors were built this year [2002] for [each] man, woman, and child on Earth. The transistors low cost, flexibility, and reliability have made it a ubiquitous device. Transistorized  mechatronic  circuits have replaced  electromechanical devices  in controlling appliances and machinery. It is often easier an d cheaper to use a standard  microcontroller  and write a  computer program  to carry out a control function than to design an equivalent mechanical control function. The  bipolar junction transistor  (BJT) was the most commonly used transistor in the 1960s and 70s. Even after MOSFETs became widely available, the BJT remained the transistor of choice for many analog circuits such as simple amplifiers because of their greater linearity and ease of manufacture. Desirable properties of MOSFETs, such as their utility in low-power devices, usually in the  CMOS configuration, allowed them to capture nearly all market share for digital circuits; more recently MOSFETs have captured most analog and power applications as well, including modern clocked analog circuits, voltage regulators, amplifiers, power transmitters and motor drivers. Advantages The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are †¢ Small size and minimal weight, allowing the development of miniaturized electronic devices. †¢ Highly automated manufacturing processes, resulting in low per-unit cost. †¢ Lower possible operating voltages, making transistors suitable for small, battery-powered applications. †¢ No warm-up period for cathode heaters required after power application. †¢ Lower power dissipation and generally greater energy efficiency. †¢ Higher reliability and greater physical ruggedness. Extremely long life. Some transistorized devices have been in service for more than 50 years. †¢ Complementary devices available, facilitating the design of  complementary-symmetry  circuits, something not possible with vacuum tubes. †¢ Insensitivity to mechanical shock and vibration, thus avoiding the problem of  micro phonics  in audio applications. Lim itations Silicon transistors typically do not operate at voltages higher than about 1000  volts  (SiC  devices can be operated as high as 3000 volts). In contrast, vacuum tubes have been developed that can be operated at tens of thousands of volts. High-power, high-frequency operation, such as that used in over-the-air  television broadcasting, is better achieved in vacuum tubes due to improved  electron mobility  in a vacuum. Silicon transistors are much more vulnerable than vacuum tubes to an  electromagnetic pulse  generated by a high-altitude  nuclear explosion. CONCLUSION: We can conclude that the LED glows when there is variation in room temperature. And the room temperature is sensed by a temperature sensor IC LM35. The circuit is named as â€Å"Automatic temperature controlled LED†. APPLICATIONS: This can be used in machines, home appliances to show change in temperature. ? We can even connect an alarm to raise an alarm if there is a temperature raise. ? It can be used in showers and wash basins to indicate that the water is hot. ? It can be used in PC’s where overheating may damage the system. BIBLIOGRAPHY; ? THEORY AND PERFORMANCE OF ELECTRICAL MECHINES. By: J. B. GUPTA ? ELECTRONICS DEVICES AND CIRCUITS By: JOCOB MILLIMEN ? ELECTRONICS FOR YOU. OCTOBER- 2008 MAGAZINE ? POWER ELECRONICS By: M D SINGH K B KHANCHANDANI P S BIMBRA ? ELECTRICAL MACHINES By: A. K. TEREJA B. L. TEREJA P. S. BIMHBRA