1. INTRODUCTION-



TRANFORMAR LESS ATOMATIC NIGHT LIGHT (PROJECT) ABSTRACT Transformer less automatic night light is a simple yet powerful concept, which uses transistor as a switch. By using this system manual works are 100% removed. It automatically switches ON lights when the sunlight goes below the visible region of our eyes. This is done by a sensor calBULB Light Dependant Resistor (LDR) which senses the light actually like our eyes. It automatically switches OFF lights whenever the sunlight comes, visible to our eyes. By using this system energy consumption is also reduced because nowadays the manually operated street lights are not switched off even the sunlight comes and also switched on earlier before sunset. In this project, no need of manual operation like ON time and OFF time setting. This project clearly demonstrates the working of transistor in saturation region and cut-off region. The working of relay is also known. 1. INTRODUCTION- Transformer less light controllers are smarter versions of the mechanical or electronic timers previously used for street light ON-OFF operation. They come with energy conservation options like twilight saving, staggering or dimming. Also many street light controllers come with an astronomical clock for a particular location or a Global Positioning System (GPS) connection to give the best ON-OFF time and energy saving. Transformer less automatic night light is a simple and powerful concept, which uses transistor as a switch to switch ON and OFF the street light automatically. By using this system manual works are removed. It automatically switches ON lights when the sunlight goes below the visible region of our eyes. It automatically switches OFF lights under illumination by sunlight. This is done by a sensor cal BULB Light Dependant Resistor (LDR) which senses the light actually like our eyes By using this system energy consumption is also reduced because now-a-days the manually operated street lights are not switched off properly even the sunlight comes and also not switched on earlier before sunset. In sunny and rainy days, ON time and OFF time differ significantly which is one of the major disadvantage of using timer circuits or manual . This project exploits the working of a transistor in saturation region and cut-off region to switch ON and switch OFF the lights at appropriate time with the help of an electromagnetically operated switch. A street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate automatically in dark weather. In older lighting this function would have been performed with the aid of a solar dial. It is not uncommon for street lights to be on poles which have wires strung between them, or mounted on utility poles. This project exploits the working of a transistor in saturation region and cut-off region to switch ON and switch OFF the lights at appropriate time with the help of an electromagnetically operated switch Automatic Streetlight needs no manual operation of switching ON and OFF. The system itself detects whether there is need for light or not. When darkness rises to a certain value 2. BASIC PRINCIPLE- The automatic streetlight control system operates on 220v AC supply. The automatic streetlight controller has a photoconductive device whose resistance changes proportional to the extent of illumination, which switches ON or OFF the BULB with the use of transistor as a switch. Light dependent resistor, a photoconductive device has been used as the transducer to convert light energy into electrical energy. The central dogma of the circuit is that the change in voltage drop across the light dependent resistor on illumination or darkness switches the transistor between cut-off region or saturation region and switches OFF or ON the BULBAs we know property of LDR that during the time of day resistance is low therefore voltage at the inverting input ( IE pin 2) is higher than the voltage at the non-inverting input (pin3) hence the output at the pin6 is low so the transistor goes into the cut off state which means BULB or bulb will not glow. 3. CIRCUIT DIAGRAM – Figure – Circuit diagram of Transformer less Automatic Night light. 4. LIST OF COMPONENTS- S.NO. PARTS RANGE QUANTITY 1. LDR 1 2. TRANSISTOR BC -547 NPN 2 3. RESISTOR 33K,470K ohm24. CAPACITOR 470Mf,105k25. PCB 1 6. RELAY12V1 7DIODEIN400748.ZENOR DIODE11V13 5. SPECIFICATION OF COMPONENTS- 5.1. LDR (LIGHT DEPENDENT RESISTER) LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits. Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but when they are illuminated with light resistance drops dramatically. When the light level is low the resistance of the LDR is high. This prevents current from flowing to the base of the transistors. Consequently, the BULB does not light. A Light Dependent Resistor (LDR) or a photo resistor is a device whose resistivity is a function of the incident electromagnetic radiation. Hence, they are light sensitive devices. They are also called as photo conductors, photo conductive cells or simply photocells.They are made up of semiconductor materials having high resistance. There are many different symbols used to indicate a LDR, one of the most commonly used symbol is shown in the figure below. The arrow indicates light falling on it. Working Principle of LDRA light dependent resistor works on the principle of photo conductivity. Photo conductivity is an optical phenomenon in which the materials conductivity is increased when light is absorbed by the material. When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy strikes on the device, more and more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more current starts flowing through the device when the circuit is closed and hence it is said that the resistance of the device has been decreased. This is the most common working principle of LDR.5.2. TRANSISTORS BC547 is an NPN bi-pole junction transistor. A transistor, stands for transfer or resistance commonly used to amplify current. A small current at its base controls a larger current at collector & emitter terminals. BC547 is mainly used for amplification and switching purposes. It has a maximum current gain of 800. Its equivalent transits The transistor terminals require a fixed DC voltage to operate in the desired region of its characteristic curves. This is known as the biasing. For amplification applications, the transistor is biased such that it is partly on for all input conditions. The input signal at base is amplified and taken at the emitter. BC547 is used in common emitter configuration for amplifiers. The voltage divider is the commonly used biasing mode. For switching applications, transistor is biased so that it remains fully on if there is a signal at its base. In the absence of base signal, it gets completely off. Pin ConfigurationPin NumberPin NameDescription1CollectorCurrent flows in through collector2BaseControls the biasing of transistor3EmitterCurrent Drains out through emitter?BC547 Transistor FeaturesBi-Polar NPN TransistorDC Current Gain (hFE) is 800 maximumContinuous Collector current (IC) is 100mAEmitter Base Voltage (VBE) is 6VBase Current(IB) is 5mA maximumAvailable in To-92 Package?BC547 Equivalent TransistorsBC549, BC636, BC639,?2N2222?TO-92,?2N2222 TO-18, 2N2369, 2N3055, 2N3904,?2N3906, 2SC5200?Brief Description on BC547BC547 is a NPN transistor?hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. BC547 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 100mA, hence we cannot connect loads that consume more than 100mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.?When this transistor is fully biased then it can allow a maximum of 100mA to flow across the collector and emitter. This stage is called?Saturation Region?and the typical voltage allowed across the Collector-Emitter (VCE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When base current is removed the transistor becomes fully off, this stage is called as the?Cut-off Region?and the Base Emitter voltage could be around 660 mV.?BC547 as SwitchWhen a transistor is used as a switch it is operated in the?Saturation and Cut-Off Region?as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a Closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae.RB??= VBE?/ IBWhere, the value of VBE?should be 5V for BC547 and the Base current (IB?depends on the Collector current (IC). The value of IB?should not exceed mA.?BC547 as AmplifierA Transistors acts as an Amplifier when operating in?Active Region. It can amplify power, voltage and current at different configurations.Some of the configurations used in amplifier circuits areCommon emitter amplifierCommon collector amplifierCommon base amplifier?Of the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulaeDC Current Gain = Collector Current (IC) / Base Current (IB)?ApplicationsDriver Modules like Relay Driver, LED driver etc..Amplifier modules like Audio amplifiers, signal Amplifier etc..?Darlington pair?2D model of the componentIf you are designing a PCD or Perf board with this component, then the following picture from the Datasheet will be useful to know its package type and dimensions.5.3. RESISTORS- Resistor is an electrical component that reduces the electric current. The resistor's ability to reduce the current is Cal BULB resistance and is measured in units of ohms (symbol: Ω).If we make an analogy to water flow through pipes, the resistor is a thin pipe that reduces the water flow. The resistor is a passive electrical component to create resistance in the flow of electric current. In almost all electrical networks and electronic circuits they can be found. The resistance is measured in ohms. An ohm is the resistance that occurs when a current of one ampere passes through a resistor with a one volt drop across its terminals. The current is proportional to the voltage across the terminal ends. This ratio is ?represented by?Ohm’s law:Resistors are used for many purposes. A few examples include delimit electric current, voltage division, heat generation, matching and loading circuits, control gain, and fix time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude. They can be used to as electric brakes to dissipate kinetic energy from trains, or be smaller than a square millimetre for electronics.Resistor definition and symbolA resistor is a passive electrical component with the primary function to limit the flow of electric current.The international IEC symbol is a rectangular shape. In the USA the ANSI standard is very common, this is a zigzag line (shown on the right).Fixed resistor symbolANSI standardFixed resistor symbolOverview of types and materialsResistors can be divided in construction type as well as resistance material. The following breakdown for the type can be made:Fixed resistorsVariable resistors, such as the:PotentiometerRheostatTrimpotResistance dependent on a physical quantity:Thermistors?(NTC? and?PTC) as a result of temperature changePhoto resistor?(LDR)? as a result of a changing light levelVaristor (VDR)? as a result of a changing voltageMagneto resistor (MDR)?as a result of a changing magnetic fieldStrain Gauges as a result of mechanical loadFor each of these types a?standard symbol?exists. Another breakdown based on the material and manufacturing process can be made:Carbon compositionCarbon filmMetal filmMetal oxide filmWirewoundFoilThe choice of material technology is a specific to the purpose. Often it is a trade-off between costs, precision and other requirements. For example, carbon composition is a very old technique with a low precision, but is still used for specific applications where high energy pulses occur. Carbon composition resistors have a body of a mixture of fine carbon particles and a non-conductive ceramic. The carbon film technique has a better tolerance. These are made of a non-conductive rod with a thin carbon film layer around it. This layer is treated with a spiral cut to increase and control the resistance value. Metal and metal oxide film are widely used nowadays, and have better properties for stability and tolerance. Furthermore, they are less influenced by temperature variations. They are just as carbon film resistors constructed with a resistive film around a cylindrical body. Metal oxide film is generally more durable. Wirewound resistors are probably the oldest type and can be used for both high precision as well as high power applications. They are constructed by winding a special metal alloy wire, such as nickel chrome, around a non-conductive core. They are durable, accurate and can have very low resistance value. A disadvantage is that they suffer from parasitic reactance at high frequencies. For the highest requirements on precision and stability, metal foil resistors are used. They are constructed by cementing a special alloy cold rolled film onto a ceramic substrate.Resistor characteristicsDependent on the application, the electrical engineer specifies different?properties of the resistor. The primary purpose is to limit the flow of electrical current; therefore the key parameter is the resistance value. The manufacturing accuracy of this value is indicated with the resistor tolerance in percentage. Many other parameters that affect the resistance value can be specified, such as long term stability or the?temperature coefficient. The temperature coefficient, usually specified in high precision applications, is determined by the resistive material as well as the mechanical design.In high frequency circuits, such as in radio electronics, the capacitance and inductance can lead to undesired effects.?Foil resistors?generally have a low parasitic reactance, while? HYPERLINK "" \o "Wirewound resistor" wirewound resistors?are amongst the worst. For accurate applications such as audio amplifiers, the?electric noise?must be as low as possible. This is often specified as microvolts noise per volt of applied voltage, for a 1 MHz bandwidth. For high power applications the?power rating?is important. This specifies the maximum operating power the component can handle without altering the properties or damage. The power rating is usually specified in free air at room temperature. Higher power ratings require a larger size and may even require heat sinks. Many other characteristics can play a role in the design specification. Examples are the maximum voltage, or the pulse stability. In situations where high voltage surges could occur this is an important characteristic.Sometimes not only the electrical properties are important, but the designer also has to consider the mechanical robustness in harsh environments. Military standards sometimes offer guidance to define the mechanical strength or the failure rate.In the section?characteristics?a full overview is given of the main properties to specify a resistor.Resistor standardsMany?standards?exist for resistors. The standards describe ways to measure and quantify important properties. Other norms exist for the physical size and resistance values. Probably, the most well known standard is the color code marking for axial leaded resistors.Resistor color codeResistor with a resistance of 5600 ohm with 2 % tolerance, according to the marking code IEC 60062.The resistance value and tolerance are indicated with several colored bands around the component body. This marking technique of electronic components was already developed in the 1920’s. Printing technology was still not far developed, what made printed numerical codes too difficult on small components. Nowadays, the? HYPERLINK "" \o "Resistor color code" color code?is still used for most axial resistors up to one watt. In the figure an example is shown with four color bands. In this example the two first bands determine the significant digits of the resistance value, the third band is the multiplying factor and the fourth band gives the tolerance. Each color represents a different number and can be looked up in a resistor color code chart.Resistor color code calculatorThe color code can easily be decoded using this?calculator. It not only provides the resistance value, it also indicates when the value belongs to an E-series.SMD resistorsFor?SMD (Surface Mount Device) resistors?a numerical code is used, because the components are too small for color coding. SMD resistors are -just as leaded variants – mainly available in the preferred values. The size of the component (length and width) is standardized as well, and is referred to as resistor package. An example of an SMD resistor on a PCB is given in the picture below. The marking “331” means that the resistance has a value of 33Ω x 10^1 = 330Ω.Resistor Values (Preferred values)In the 1950s the increased production of resistors created the need for standardized resistance values. The range of resistance values is standardized with so called?preferred values. The preferred values are defined in E-series. In an E-series, every value is a certain percentage higher than the previous. Various E-series exist for different tolerances.Resistor applicationsThere is a huge variation in fields of applications for resistors; from precision components in digital electronics, till measurement devices for physical quantities. In this chapter several popular applications are listed.Resistors in series and parallelIn electronic circuits, resistors are very often connected in series or in parallel. A circuit designer might for example combine several resistors with standard values (E-series) to reach a specific resistance value. For series connection, the current through each resistor is the same and the equivalent resistance is equal to the sum of the individual resistors. For parallel connection, the voltage through each resistor is the same, and the inverse of the equivalent resistance is equal to the sum of the inverse values for all parallel resistors. In the articles?resistors in parallel?and?series?a detailed description of calculation examples is given. To solve even more complex networks,?Kirchhoff’s circuit laws?may be used.Measure electrical current (shunt resistor)Electrical current can be calculated by measuring the voltage drop over a precision resistor with a known resistance, which is connected in series with the circuit. The current is calculated by using Ohm’s law. This is a called an ammeter or?shunt resistor. Usually this is a high precision manganin resistor with a low resistance value.Resistors for LEDsLED lights need a specific current to operate. A too low current will not light up the LED, while a too high current might burn out the device. Therefore, they are often connected in series with resistors. These are called?ballast resistors?and passively regulate the current in the circuit.Blower motor resistorIn cars the air ventilation system is actuated by a fan that is driven by the blower motor. A special resistor is used to control the fan speed. This is called the blower motor resistor. Different designs are in use. One design is a series of different size wirewound resistors for each fan speed. Another design incorporates a fully integrated circuit on a printed circuit board.5.4. CAPACITOR-A board using two capacitor 105k 400v and 470mF. Capacitor is an electronic component that stores?electric charge. The capacitor is made of 2 close conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source. One plate accumulates positive charge and the other plate accumulates negative charge.The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.The capacitance is measured in units of?Farad?(F).The capacitor disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits.Capacitor pictures??Capacitor symbolsCapacitorPolarized capacitorVariable capacitor?CapacitanceThe capacitance (C) of the capacitor is equal to the electric charge (Q) divided by the voltage (V):C is the capacitance in farad (F)Q is the electric charge?in coulombs (C), that is stored on the capacitorV is the voltage between the capacitor's plates in volts (V)Capacitance of plates capacitorThe capacitance (C) of the plates capacitor is equal to the permittivity (ε) times the plate area (A) divided by the gap or distance between the plates (d):?C is the capacitance of the capacitor, in farad (F).ε?is the permittivity of the capacitor's dialectic material, in farad per meter (F/m).A is the area of the capacitor's plate in square meters (m2].d is the distance between the capacitor's plates, in meters (m).Capacitors in series?The total capacitance of capacitors in series, C1,C2,C3,.. :Capacitors in parallelThe total capacitance of capacitors in parallel, C1,C2,C3,.. :CTotal?=?C1+C2+C3+...Capacitor's currentThe capacitor's momentary current ic(t) is equal to the capacitance of the capacitor,times the derivative of the momentary capacitor's voltage vc(t):Capacitor's voltageThe capacitor's momentary voltage vc(t) is equal to the initial voltage of the capacitor,plus 1/C times the integral of the momentary capacitor's current ic(t) over time t:Energy of capacitorThe capacitor's stored energy?EC?in joules (J) is equal to the capacitance?C?in farad (F)times the square capacitor's voltage?VC?in volts (V) divided by 2:EC?=?C × VC?2?/ 2AC circuitsAngular frequencyω?= 2π fω - angular velocity measured in radians per second (rad/s)f? - frequency measured in hertz (Hz).Capacitor's reactanceCapacitor's impedanceCartesian form:Polar form:ZC?=?XC∟-90?Capacitor typesVariable capacitorVariable capacitor has changeable capacitanceElectrolytic capacitorElectrolytic capacitors are used when high capacitance is needed. Most of the electrolytic capacitors are polarizedSpherical capacitorSpherical capacitor has a sphere shapePower capacitorPower capacitors are used in high voltage power systems.Ceramic capacitorCeramic capacitor has ceramic dielectric material. Has high voltage functionality.Tantalum capacitorTantalum oxide dielectric material. Has high capacitanceMica capacitorHigh accuracy capacitorsPaper capacitorPaper dielectric material?5.5. PCB (PRINTED CIRCUIT BOARD)- A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. PCBs can be single sided (one copper layer), double sided (two copper layers) or multi-layer. Conductors on different layers are connected with plated-through holes calBULB bias. Advanced PCBs may contain components - capacitors, resistors or active devices - embedded in the substrate. 5.6. RELAY 12V- A relay is an?electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and most have?double throw(changeover) switch contacts as shown in the diagram.Circuit symbolRelays allow one circuit to switch a second circuit which can be completely separate from the first. For example, a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical.The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs cannot provide this current and a?transistor?is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA, enough to supply a relay coil directly.Relays are usuallly SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on?switches.The animated picture shows a working relay with its coil and switch contacts. You can see a lever on the left being attracted by magnetism when the coil is switched on. This lever moves the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT.Relay showing coil and switch contactsThe supplier's catalogue or website should show the relay's connections. The coil will usually be obvious and it may be connected either way round. Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a?protection diode?across the relay coil.Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.The relay's switch connections are usually labelled COM, NC and NO:COM?= Common, always connect to this, it is the moving part of the switch.NC?= Normally Closed, COM is connected to this when the relay coil is?off.NO?= Normally Open, COM is connected to this when the relay coil is?on.Connect to?COM and NO?if you want the switched circuit to be?on when the relay coil is on.Connect to?COM and NC?if you want the switched circuit to be?on when the relay coil is off.Choosing a relayYou need to consider several features when choosing a relay:Physical size and pin arrangement?If you are choosing a relay for an existing PCB you will need to ensure that its dimensions and pin arrangement are suitable. You should find this information in the supplier's catalogue or on their website.Coil voltage?The relay's coil voltage rating and resistance must suit the circuit powering the relay coil. Many relays have a coil rated for a 12V supply but 5V and 24V relays are also readily available. Some relays operate perfectly well with a supply voltage which is a little lower than their rated value.Coil resistance?The circuit must be able to supply the current required by the relay coil. You can use?Ohm's?law?to calculate the current:Relay coil current ? =???supply voltage?? coil resistanceFor example: A 12V supply relay with a coil resistance of 400?passes a current of 30mA. This is OK for a 555 timer IC (maximum output current 200mA), but it is too much for most ICs and they will require a?transistor?to amplify the current.Switch ratings (voltage and current)?The relay's switch contacts must be suitable for the circuit they are to control. You will need to check the voltage and current ratings. Note that the voltage rating is usually higher for AC, for example: "5A at 24V DC or 125V AC".Switch contact arrangement (SPDT, DPDT etc)?Most relays are SPDT or DPDT which are often described as "single pole changeover" (SPCO) or "double pole changeover" (DPCO). For further information please see the page on?switches.Rapid Electronics:?relaysProtection diodes for relaysTransistors and ICs must be protected from the brief high voltage produced when a relay coil is switched off. The diagram shows how a signal?diode?(eg 1N4148) is connected 'backwards' across the relay coil to provide this protection.Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.Protection diode for a relayRapid Electronics:?1N4148?diodeReed relaysReed relays consist of a coil surrounding a?reed?switch. Reed switches are normally operated with a magnet, but in a reed relay current flows through the coil to create a magnetic field and close the reed switch.Reed relays generally have higher coil resistances than standard relays (1000for example) and a wide range of supply voltages (9-20V for example). They are capable of switching much more rapidly than standard relays, up to several hundred times per second; but they can only switch low currents (500mA maximum for example).The reed relay shown will plug into a standard 14-pin?DIL?socket?('IC holder').5.7. DIODE1N4007 DiodePin Configuration:Pin No.Pin NameDescription1AnodeCurrent always Enters through Anode2CathodeCurrent always Exits through Cathode?Features:Average forward current is 1ANon-repetitive Peak?current is 30AReverse current is 5uA.Peak repetitive Reverse voltage is 1000VPower dissipation 3WAvailable in DO-41 Package?1N4007 Equivalent Diodes:1N4148, 1N4733A, 1N5408, 1N5822, Zennor Diodes?Description:A diode is a device which allows current flow through only one direction. That is the current should always flow from the Anode to cathode. The cathode terminal can be identified by using a grey bar as shown in the picture above.For?1N4007 Diode, the maximum current carrying capacity is 1A it withstands peaks up to 30A. Hence we can use this in circuits that are designed for less than 1A.? The reverse current is 5uA which is negligible. The power dissipation of this diode is 3W.?Applications of Diode:Can be used to prevent reverse polarity problemHalf Wave and Full Wave rectifiersUsed as a protection deviceCurrent flow regulators?2D representation (DO-41):5.8. ZENER DIODEIntroductionDiodes generally are known as a device that allows the flow of current in one direction (forward biased) and offers resistance to the flow of current when used in reverse bias.?Zener Diode(Named after the American scientist C. Zener who first explained its operational principles) on the other hand, not only allow the flow of current when used in forward bias, but they also allow the flow of current when used in the reversed bias so far the?applied voltage is above the breakdown voltage?known as the?Zener Breakdown Voltage. Or in other words?Breakdown voltage?is the voltage, on which Zener Diode starts conducting in reverse direction.?Operational Principle of Zener Diode: lIn normal?diodes, the breakdown voltage is very high and the diode gets damaged totally if a voltage above the breakdown diode is applied, but in Zener diodes, the breakdown voltage is not as high and does not lead to permanent damage of the zener diode if the voltage is applied.As the reverse voltage applied to the Zener diode increases towards the specified?Breakdown Voltage?(Vz), a current starts flowing through the diode and this current is known as the?Zener Current?and this process is known as?Avalanche Breakdown. The current increases to a maximum and get stabilized. This current remains constant over the wider range of applied voltage and allows the Zener diode to withstand with higher voltage without getting damaged. This current is determined by the series resistor.?Consider the Images below of a?normal diode in action.Lamp On (Forward Biased)?Lamp Off (Reversed bias)?To show the?operations of the zener diode, consider the two experiments (A and B) below.12v Zener diode operation6v Zener diode operation?In?Experiment A, a 12V zener diode is connected in reversed biased as shown in the image and it can be seen that the zener diode blocked the voltage effectively because it was less/equal to the breakdown voltage of the particular zener diode and the lamp thus stayed off.?In?Experiment B, a 6v Zener Diode used is conducting (the bulb comes on) in reverse biased because the applied voltage is greater than its breakdown voltage and thus shows that the?breakdown region is the region of operation of the zener diode.?The?current-voltage characteristic curve of the Zener diode?is shown below.Zener diode V-I characteristicsFrom the graph, it can be deduced that the zener diode operated in the reverse bias mode will have a fairly constant voltage irrespective of the amount of current supplied.?Applications of Zener Diode:Zener diodes are used in three main applications in electronic circuits;1. Voltage Regulation2. Waveform Clipper3. Voltage Shifter?1. Zener Diode as Voltage RegulatorThis is arguably the most common application of zener diodes.This application of the zener diodes relies heavily on the ability of the zener diodes to maintain a constant voltage irrespective of variations in supply or load current. The general function of a voltage regulation device is to?provide a constant output voltage?to a load connected in parallel to it irrespective of variations in the energy drawn by the load (Load current) or variations and instability in the supply voltage.The Zener diode will provide constant voltage provided current stays within the range of the maximum and minimum reverse current.The circuit diagram showing the?Zener diode being used as a Voltage regulator?is shown below.Zener Diode Voltage Regulator?A resistor,?R1?is connected in series with the zener diode to limit the amount of current flowing through the diode and the?input voltage?Vin (Which must be greater than the zener voltage)?is connected across as shown in the image and the output voltage Vout, is taken across the zener diode with?Vout = Vz (Zener Voltage).?Since the zener diode’s reverse bias characteristics are what is needed to regulate the voltage, it is connected in reversed bias mode, with the cathode being connected to the positive rail of the circuit.Care must be taken when selecting the value of?resistor R1, as a small value resistor will result in a large diode current when the load?is connected and this will increase the power dissipation requirement of the diode which could become higher than the maximum power rating of the zener and could damage it.The value of resistor to be used can be determined using the formula below.R1 = (Vin – VZ) / IZWhere;R1 is the value of the series resistance.Vin is the input voltage.Vz which is same as Vout is the Zener voltageAnd Iz is the zener current.By using this formula it becomes easy to ensure that the value of the resistor selected doesn’t lead to the flow of current higher than what the zener can handle.?One little problem experienced with zener diode based regulator circuits is that the?Zener sometimes generate electrical noise?on the supply rail while making attempts to regulate the input voltage. While this may not be a problem for most applications, this problem may be solve by the addition of a large value decoupling capacitor across the diode. This helps stabilize the output of the zener.Stabilizing the output of the Zener diode voltage regulator by adding Capacitor?2. Zener Diode as Waveform ClipperOne of the uses of normal diodes is in the application of?clipping and clamping circuits?which are circuits that are used?to shape or modify an input AC waveform or signal, producing a differently shaped output signal depending on the specifications of the clipper or clamper.Clippers circuits?generically are circuits that are used to prevent the output signal of a circuit from going beyond a predetermined voltage value without changing any other part of the input signal or waveform.These circuits along with clampers are widely used in Analog television and FM radio transmitters for the?removal of interference (clamping circuits)?and limiting noise peaks by clipping of high peaks.Since?Zener diodes generically behave like normal diodes?when the applied voltage is not equal to the breakdown voltage, they are also thus used in clipping circuits.Clipping circuits could be designed to clip the signal either in the positive, negative or bothregions. Although the diode will naturally clip off the other region at 0.7V irrespective of whether it was designed as a positive or negative clipper.For example, consider the circuit below.Zener Diode in as Clipper Circuit?The clipper circuit is designed to clip the output signal at 6.2v, so a 6.2v zener diode was used. The zener diode prevents the output signal from going beyond the zener voltage irrespective of the input waveform. For this particular example, a 20v input voltage was used and the output voltage on the positive swing was 6.2v consistent with the voltage of the zener diode.? During the negative swing of the AC voltage however, the zener diode behaves just like the normal diode and clips the output voltage at 0.7V, Consistent with normal silicone diodes.Generated Waveforms of Zener diode Clipper Circuit?To implement the clipping circuit for the negative swing of the AC circuit as well as the positive swing?in such a way that the voltage is clipped at different levels on the positive and negative swing, a double zener clipping circuit is used. The circuit diagram for the double zener clipping circuit is shown below.Generated Waveforms of Double Zener diode Clipper Circuit?In the clipping circuit above, the voltage Vz2 represents the voltage on the negative swing of the AC source at which the output signal is desired to be clipped, while voltage Vz1 represents the voltage on the positive swing of the AC source at which the output voltage is desired to be clipped.?3. Zener Diode as Voltage ShifterThe voltage shifter is one of the simplest but interesting applications of the zener diode. If you have had experience especially with connecting a 3.3v sensor to a 5V MCU, and have seen first-hand the errors in readings, etc, that this can lead to them you will appreciate the importance of voltage shifters.?Voltage shifters help convert signal from one voltage to another?and with the ability of the zener diode to maintain steady output voltage in the breakdown region, it makes them Ideal component for the operation.In a?zener diode based voltage shifter, the circuit, lowers the output voltage, by a value equal to the breakdown voltage of the particular zener diode that is used. The circuit diagram for the voltage shifter is illustrated below.Zener Diode as Voltage Shifter?Consider the experiment below,Getting 3.3v Zener diode based voltage shifter?The circuit describes a 3.3v zener diode based voltage shifter. The output voltage (3.72V) of the circuit is given by subtracting the breakdown voltage (3.3V) of the zener diode from the input voltage (7V).Vout = Vin –VzVout = 7 – 3.3 = 3.7vThe voltage shifter as describe earlier on has several applications in modern day electronic circuits design as the design engineer may have to work with up to three different voltage level at times during design process.?Types of Zener Diodes:Zener diodes are categorized into types based on several parameters which include;Nominal VoltagePower DissipationForward drive currentForward voltagePackaging typeMaximum Reverse Current?Nominal VoltageThe nominal Operation voltage of a zener diode is also known as the breakdown voltage of the zener diode, depending on the application for which the diode is to be used, this is often the most important criteria for Zener diode selection.?Power dissipationThis represents the maximum amount of power the zener current can dissipate. Exceeding this power rating leads to excessive increase in the temperature of the zener diode which could damage it and lead to the failure of the things connected to it in a circuit. ?Thus this factor should be considered when selecting the diode with the use in mind.?Maximum Zener CurrentThis is the maximum current that can be passed through the zener diode at the zener voltage without damaging the device.?Minimum Zener CurrentThis refers to the minimum current required for the zener diode to start operating in the breakdown region.?Other parameters that serve as the specification for the diode all need to be fully considered before a decision is made on the type on the kind of zener diode needed for that peculiar design.?Conclusion:Here are 5 points you should never forget about the zener diode.A zener diode is like an ordinary diode only that it has been doped to have a sharp a breakdown voltage.The Zener diode maintains a stable output voltage irrespective of the input voltage provided the maximum zener current is not exceeded.When connected in forward bias, the zener diode behaves exactly like the normal silicone diode. It conducts with the same 0.7v voltage drop that accompanies the use of the normal diode.The zener diode default operational state is in the breakdown region (reversed biased). It means it actually starts to work when the applied voltage is higher than Zener Voltage in reverse biased.The zener diode is mostly used in applications involving, voltage regulation, clipping circuits and Voltage shifters.5. WORKING Circuit of a compact and true solid-state automatic lawn light is described here. The circuit can be used to switch on incandescent garden light bulbs at desk and switch off them at dawn. A 10 mm encapsulated light dependent resistor (LDR) here works as the twilight detector. The whole circuit can be housed in a very small plastic cabinet. For powering the circuit AC household supply is needed. With a little skill and patience, you can easily modify this circuit to drive a number of white BULB strings, instead of the incandescent bulb load at the output. When ambient light is normal, transistor T1 is reverse biased by the low resistance of LDR. Multiturn plastic trimpotP1 sets the detection sensitivity. If ambient light dims, transistor T1 turns on to drive the triac T2. Now the lamp load at the output of T2 energises. When the ambient light level restores, circuit returns to its idle state and light(s) switched off by the circuit. Working voltage for the circuit is derived directly from the AC supply input through components R1, R2 and R3. This obviates the requirement of a bulky. If you wish to operate the, light bulb(s) on a little reduced power, just replace the triac T2 with a suitable silicon controlBULB rectifier (SCR). This may give a long life to the incandescent load. Finally, the LDR should not be mounted to receive direct sunlight. It may be mounted at the top of the enclosure, pointing to the sky say southwards. LDR offers Very high Resistance in darkness. In this case the voltage drop across the LDR is more than 0.7V.This voltage is more sufficient to drive the transistor into saturation region. In saturation region, IC (Collector current) is very high. Because of this IC. The relay gets energized, and switches on the lamp. LDR offers Very low Resistance in brightness. In this case the voltage drop across the LDR is less than 0.7V. This voltage is not sufficient to drive the transistor into saturation region. Hence, the transistor will be in cut-off region. In cut-off region, IC (Collector current) is zero. Because of this IC, The relay will not be energized, and the lamp will be in ON state only. Diode is connected across the relay to neutralize the reverse EMF generated. 6. PROCEDURE- Insert first transistor Q1-BC547 (NPN) on PCB board shown in the circuit diagram Connect another transistor Q2-BC547 (NPN) on PCB board shown in the circuit diagram. Connect wires across emitter pin of both transistor and negative terminal of battery on the PCB board. Connect a wire across collector pin of transistor Q1 and base pin of transistor Q2. Connect a resistor 1k across positive terminal of battery on the PCB board and collector pin transistor Q1. Connect LDR (Light Dependent Resistor) across positive terminal of the battery and base terminal of transistor Q1 Insert a transistor 330 ohm across base pin of transistor Q1 and negative terminal of battery. Connect a resistor 330 ohm across positive terminal of battery and anode terminal of BULB connect the cathode terminal of BULB to collector pin of transistor Q2. 7. ADVANTAGES & DISADVANTAGES- By using this automatic system for street light controlling ,we can reduce energy consumption because the manually operated street lights are not switch off properly even the sun light comes and Also not switched on earlier before sunset Low cost Automated operation Low power consumption Very flexible Easy to manufactured In sunny and rainy days, on and off time differ notice which is one of the major disadvantages of using timer circuit or manual operation for switching the street light system. 8. APPLICATION Used in street light applications. Used in Domestic applications. 9. CONCLUSION- The Streetlight controller using ldr based Light intensity & traffic density, in the todays up growing countries will be more effective in case of cost, manpower and security as compare with today's running complicated and complex light controlling systems. Automatic Street Light Controlling System puts up a very user friendly approach and could increase the power This paper elaborates the design and construction of automatic street control system circuit. Circuit works properly to turn street lamp ON/OFF. After designing the circuit which controls the light of the street as illustrated in the previous sections. LDR sensor and the photoelectric sensors are the two main conditions in working the circuit. If the two conditions have been satisfied the circuit will do the desired work according to specific program. Each sensor controls the turning ON or OFF the lighting column. The street lights has been successfully controlBULB by microcontroller. With commands from the controller the lights will be ON in the places of the movement when it's dark. furthermore the drawback of the street light system using timer controller has been overcome, where the system depends on photoelectric sensor. Finally this control circuit can be used in a long roadways between th 10. FUTURE SCOPE- We can save the energy for the future use and we can control the losses of the power . We can implemnted this project for the home lamp or night lamp of the room. This is also used for the signals. For further query- RAVISHANKAR THAKURM.SC PHYSICS SEM IVEMAIL- rsthakur5571@ ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download