Temperature Controlled Fan

AUTOMATIC TEMPERATURE CONTROLLED FANMINI PROJECT’11 INTRODUCTION All fans which are used now a day are controlled manually by voltage regulators which have different stages of speed. This process is done manually which can be done automatically by the use of this circuit. Here we are introducing an efficient fan speed regulation circuit, by which the speed of a fan can be controlled depending up on the room temperature. The circuit is highly efficient since energy loss can be minimized by power saving as the circuit automatically adjusts the fans speed. 1 DEPARTMENT OF EEE,VAST AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 PRINCIPLE OF OPERATION This circuit uses thermistor as the temperature sensor, i.e. one having a negative temperature coefficient. This circuit is designed in such a way that the speed of the fan increases/decreases with respect to the room temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain. 2 DEPARTMENT OF EEE,VAST AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 BLOCK DIAGRAM TEMPERATURE SENSOR & WHEATSTONE BRIDGE TRIGGERING CIRCUIT SWITCHING CIRCUIT LOAD Figure 1. Block Diagram 3 DEPARTMENT OF EEE,VAST D5.t.D4.R6 Resistors-R4.c TYN612 BZX79C18 1N4007 1000V BC327 BC337 10nF 63V 100K 1/4W 10K 1/4W 22K 1/4W 100R 1/4W 470R 1/4W 68K 2W - 1 1 1 4 2 1 1 1 2 2 1 1 2 1 1 1 1 As required Table No:1.D6 Transistors-Q1.R5 Resistor-R7 Resistor-R8 Resistors-R9.R10 Female Mains socket -SK1 Male Mains plug-PL1 PCB Breadboard Connecting Wires 15K @ 20°C n.Q2 Transistor-Q3 Polyester Capacitor-C1 Resistor-R2 Resistors-R3.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 COMPONENTS USED NAME OF COMPONENT SPECIFICATION 22K QUANTITY 1 Linear Potentiometer-P1 Thermistor-R1 SCR-D2 Zener Diode-D1 Diodes-D3. Component List 4 DEPARTMENT OF EEE.VAST . VAST .Automatic Temperature Controlled Fan Circuit 5 DEPARTMENT OF EEE.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 CIRCUIT DIAGRAM Figure 2. VAST . This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 Diode Bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. and Q1 is used as a bridge balance detector. generating a short pulse suitable to drive the SCR. so Q1 becomes forward biased. 6 DEPARTMENT OF EEE. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 WORKING R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage. pulse-charging C1. P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value. Q2 and Q3 form a trigger device. P1-R1 generate a temperature-sensitive "variable" voltage. thus producing minimal switching RFI from the SCR. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value. and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle. is a special type of diode with four layers of alternating N and P-type material. labelled anode and cathode. Symbol of SCR Figure 4. as long as the voltage across the device has not reversed). and continue to conduct for as long as they are forward biased (that is. arranged to cause the self-latching action. The thyristor is a four-layer.) The operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction transistors. is attached to p-type material near to the cathode. with each layer consisting of alternately N-type or P-type material. SCR Figure 3. three terminal semiconducting devices..VAST . also known as a SCR (silicon controlled rectifier). and the control terminal.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 COMPONENT DESCRIPTION . called the gate. (A variant called an SCS—Silicon Controlled Switch—brings all four layers out to terminals. conducting when their gate receives a current pulse. Pictorial Representation of SCR A thyristor. The main terminals. They act as bistable switches. for example P-N-P-N. are across the full four layers. 7 DEPARTMENT OF EEE. but the thyristor has not yet been triggered into conduction 3. Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode 2. Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current" 8 DEPARTMENT OF EEE. Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 Figure 5 Transistor Equivalent Circuit of an SCR Thyristors have three states: 1.VAST . J3 from the anode). J2. avalanche breakdown of . These gate pulses are characterized in terms of gate trigger voltage (VGT) and gate trigger current (IGT). Now if VAK is increased beyond the breakdown voltage VBO of the thyristor.VAST . junctions J1 and J3 are forward biased.6 Layer diagram of thyristor J2 takes place and the thyristor starts conducting (On state). the thyristor can be switched into the on state suddenly. such as the voltage output from a UJT relaxation oscillator. until both: (a) the potential VG is removed and (b) the current through the device (anode−cathode) is less than the holding current specified by the manufacturer. 9 DEPARTMENT OF EEE. As J2 is reverse biased. If a positive potential VG is applied at the gate terminal with respect to the cathode. the breakdown of the junction J2 occurs at a lower value of VAK.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 The thyristor has three p-n junctions (serially named J1. Gate trigger current varies inversely with gate pulse width in such a way that it is evident that there is a minimum gate charge required to trigger the thyristor. Fig . irrespective of the gate voltage. Hence VG can be a voltage pulse. It should be noted that once avalanche breakdown has occurred. no conduction takes place (Off state). By selecting an appropriate value of VG. while junction J2 is reverse biased.When the anode is at a positive potential VAK with respect to the cathode with no voltage applied at the gate. the thyristor continues to conduct. the device remains latched in the on-state (i.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 Figure 7 SCR Characteristic In a conventional thyristor. A thyristor can be switched off if the external circuit causes the anode to become negatively biased. This method is called forced commutation. 10 DEPARTMENT OF EEE. providing the anode current has exceeded the latching current (IL). In some applications this is done by switching a second thyristor to discharge a capacitor into the cathode of the first thyristor. it cannot be switched off until the anode current falls below the holding current (IH). As long as the anode remains positively biased. once it has been switched on by the gate terminal.e.VAST . does not need a continuous supply of gate current to conduct). the firing angle. or point during the half-cycle at which the SCR is triggered. determines the amount of current which flows through the device. 180 degrees in a half-cycle. and then closes to allow power flow after the trigger pulse is applied. and the number of degrees that the SCR remains conducting is known as the conduction angle. 11 DEPARTMENT OF EEE.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 SCR Phase Control In SCR Phase Control.8 Output Wave form of SCR Figure above shows an AC waveform being applied with a gating pulse at 45 degrees. Figure . The earlier in the cycle the SCR is gated ON. The number of degrees from the beginning of the cycle until the SCR is gated ON is referred to as the firing angle. the greater will be the voltage applied to the load. It acts as a highspeed switch which is open for the first part of the cycle. There are 360 electrical degrees in a cycle.VAST . 50 Hz or 60 Hz). For applications with frequencies higher than the domestic AC mains supply (e.9 Load voltage regulated by thyristor phase control.g. fast thyristors may be made by neutron irradiation of the silicon. Such fast thyristors are made by diffusing into the silicon heavy metals ions such as gold or platinum which act as charge combination centers. Alternatively. thyristors with lower values of tQ are required.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 Figure . 12 DEPARTMENT OF EEE.VAST . 10 Pictorial Representation of Thermistor Figure .11 Symbol of Thermistor A thermistor is a type of resistor whose resistance varies with temperature. The word is a portmanteau of thermal and resistor. temperature sensors.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 THERMISTOR Figure . The temperature responses of thermistor are typically achieve a higher precision within a limited temperature range [usually −90 °C to 130 °C]. The material used in a thermistor is generally a ceramic or polymer. and self-regulating heating elements. that the relationship between resistance and temperature is linear. self-resetting over current protectors. Thermistors are widely used as inrush current limiters. as a first-order approximation.VAST . then: Where ΔR = change in resistance ΔT = change in temperature k = first-order temperature coefficient of resistance 13 DEPARTMENT OF EEE.Assuming. The more charge carriers that are available.VAST . the more current a material can conduct. In this region the device has a small negative temperature coefficient. the resistance increases with increasing temperature. If k is positive. At the Curie point temperature. the dielectric constant drops sufficiently to allow the formation of potential barriers at the grain boundaries. Most PTC thermistors are of the "switching" type.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 Thermistors can be classified into two types. 14 DEPARTMENT OF EEE. and the resistance increases sharply. or posistor. the resistance decreases with increasing temperature. the material reverts to NTC behaviour. so that their resistance remains nearly constant over a wide temperature range.it promotes them into the conduction band. The dielectric constant of this ferroelectric material varies with temperature. depending on the sign of k. Here we are using a thermistor with negative temperature coefficient Resistors that are not thermistors are designed to have a k as close to zero as possible(smallest possible k). Many NTC thermistors are made from a pressed disc or cast chip of a semiconductor such as a sintered metal oxide. leading to a low resistance. and the device is called a negative temperature coefficient (NTC) thermistor. The devices are made of doped polycrystalline ceramic containing barium (BaTiO3) and other compounds. Below the Curie point temperature. At even higher temperatures. They work because raising the temperature of a semiconductor increases the number of electrons able to move about and carry charge . If k is negative. and the device is called a positive temperature coefficient (PTC) thermistor. the high dielectric constant prevents the formation of potential barriers between the crystal grains. which means that their resistance rises suddenly at a certain critical temperature. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 Another type of PTC thermistor is the polymer PTC. and then heat up and become much lower resistance to allow higher current flow during normal operation. not for proportional temperature measurement. which is sold under brand names such as "Polyswitch" "Semifuse". This type of thermistors is used for switching. and causing the resistance of the device to rise rapidly. They present a higher resistance initially which prevents large currents from flowing at turnon. This consists of a slice of plastic with carbon grains embedded in it. they monitor things like coolant temperature and/or oil temperature inside the engine and provide data to the ECU and.  NTC thermistors are regularly used in automotive applications. indirectly. When the plastic heats up. the carbon grains are all in contact with each other. Applications of Thermistor  PTC thermistors can be used as current-limiting devices for circuit protection. 15 DEPARTMENT OF EEE.  Thermistors are also commonly used in modern digital thermostats and to monitor the temperature of battery packs while charging.  NTC thermistors can be used as inrush-current limiting devices in power supply circuits. and "Multifuse". forming a conductive path through the device.  NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K. forcing the carbon grains apart. For example. as replacements for fuses. to the dashboard. When the plastic is cool.VAST . it expands. 2 V will exhibit a voltage drop of 3. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. a reverse-biased Zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the Zener diode at the Zener voltage. a diode with a Zener breakdown voltage of 3. a Zener diode conducts when the voltage reaches the diode's reverse 16 DEPARTMENT OF EEE. or as a voltage stabilizer for low-current applications.2 V if reverse bias voltage applied across it is more than its Zener voltage. the so-called Zener voltage.g. for an amplifier stage). By contrast with the conventional device. When connected in parallel with a variable voltage source so that it is reverse biased. but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". except the device is specially designed so as to have a greatly reduced breakdown voltage. For example.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 ZENER DIODE Figure.VAST .12 Zener Diode Symbol A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode. A Zener diode exhibits almost the same properties of the conventional solid-state diode. The Zener diode is therefore ideal for applications such as the generation of a reference voltage (e. the relatively low impedance of the diode keeps the voltage across the diode at that value.VAST . by analogy with locomotive switching points. A Zener diode used in this way is known as a shunt voltage regulator (shunt.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 breakdown voltage. and as long as the Zener stays in reverse breakdown. From that point on. In a sense. in this context. the diode will provide a stable voltage source to the load. Thus the voltage that the load sees is controlled by causing some fraction of the current from the power source to bypass it—hence the name.A load may be placed across the diode in the circuit. and the rest is through the load. a portion of the current through the resistor is shunted through the Zener diode. and voltage regulator being a class of circuit that produces a stable voltage across any load). meaning connected in parallel. 17 DEPARTMENT OF EEE. The boundary within the crystal between these two regions. called a PN junction. the most common type today. The crystal conducts conventional current in a direction from the p-type side (called the anode) to the n-type side (called the cathode). The term usually refers to a semiconductor diode. A modern semiconductor diode is made of a crystal of semiconductor like silicon that has impurities added to it to create a region on one side that contains negative charge carriers (electrons). called n-type semiconductor. This unidirectional behavior is called rectification. The diode's terminals are attached to each of these regions.VAST . is where the action of the diode takes place. the diode can be thought of as an electronic version of a check valve. but not in the opposite direction. called p-type semiconductor.13 Symbol of Diode A Diode is a two-terminal electronic component that conducts electric current in only one direction. and extract modulation from radio signals in radio receivers.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 DIODE Figure . and is used to convert alternating current to direct current. 18 DEPARTMENT OF EEE. and a region on the other side that contains positive charge carriers (holes). which is a crystal of semiconductor connected to two electrical terminals. The most common function of a diode is to allow an electric current to flow through it in one direction (called the diode's forward direction) while blocking current in the opposite direction (the reverse direction). Thus. 14 Pictorial Representation and Symbol of Transistors NPN PNP A transistor is a semiconductor device used to amplify and switch electronic signals.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 TRANSISTOR Figure . with at least three terminals for connection to an external circuit. A Bipolar transistor has terminals labelled base. It is made of a solid piece of semiconductor material.VAST . collector. A small current at the base terminal (that is. flowing from the base to 19 DEPARTMENT OF EEE. and emitter. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 the emitter) can control or switch a much larger current between the collector and emitter terminals. Most bipolar transistors used today are NPN. A small current entering the base in common-emitter mode is amplified in the collector output. 20 DEPARTMENT OF EEE. PNP The other type of BJT is the PNP with the letters "P" and "N" referring to the majority charge carriers inside the different regions of the transistor. The arrow in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. In other terms. The arrow in the PNP transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. NPN transistors consist of a layer of P-doped semiconductor (the "base") between two Ndoped layers. In other terms. an NPN transistor is "on" when its base is pulled high relative to the emitter. in which the letters "N" and "P" refer to the majority charge carriers inside the different regions of the transistor. Here we are using two types of transistors PNP and NPN. a PNP transistor is "on" when its base is pulled low relative to the emitter. because electron mobility is higher than hole mobility in semiconductors. A small current leaving the base in common-emitter mode is amplified in the collector output. NPN NPN is one of the two types of bipolar transistors. allowing greater currents and faster operation. PNP transistors consist of a layer of N-doped semiconductor between two layers of Pdoped material. Low installation cost. Power saving. Easily repairable.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 ADVANTAGES        Circuit is simpler in design. The use of voltage regulators in fans can be avoided. 21 DEPARTMENT OF EEE.VAST . Temperature variations can be easily tracked down. Since there is no complex circuitry setup involved. Less maintenance. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 APPLICATIONS This circuit can be employed in places such as railway stations and such public places where people use to gather and they don’t care about the working of these fans. Installing these circuits in such places leads to power saving as the circuit automatically adjusts the fans speed. Another application of these circuit is that this can be used in houses which uses air conditioners for power saving. 22 DEPARTMENT OF EEE.VAST . In such places these circuits can be employed so the voltage regulators need not be operated manually. VAST . 23 DEPARTMENT OF EEE. speed of the fan increased and vice versa. The circuit was found to be working as the temperature increased.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 RESULT Automatic temperature controlled fan circuit was setup and connected to 230V mains supply and obtained the required output according to different temperature conditions. VAST . 24 DEPARTMENT OF EEE. The passive infrared sensor can include a fresnel lens for sensing a 360° circumference beneath the fan so that the fan can be turned on and off based on motion of persons approaching and leaving a selected area .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 SCOPE FOR FUTURE WORK The circuit can be expanded by incorporating a passive infrared sensor along with the temperature sensor. VAST . Our project though simple is significant in the current status of our country facing energy crisis. Every small step is significant in the path of success.AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 CONCLUSION This circuit is found to be more reliable than a regulator circuit since this seems to be more efficient than conventional regulator circuits. Even though it is simple this has a significant role to play in the development of technology. 25 DEPARTMENT OF EEE. Since power consumption can be minimised to a greater extent. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 REFERENCES  http://www.pc-control.wikipedia.redcircuits.com/  http://en.howstuffworks.VAST .com/ 26 DEPARTMENT OF EEE.com/  http://www.co.allaboutcircuits.org/  http://www.uk/  http://www. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 APPENDIX 27 DEPARTMENT OF EEE.VAST . VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 DATA SHEET 28 DEPARTMENT OF EEE. VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 29 DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 30 DEPARTMENT OF EEE.VAST . AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 31 DEPARTMENT OF EEE.VAST . AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 32 DEPARTMENT OF EEE.VAST . VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 33 DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 34 DEPARTMENT OF EEE.VAST . AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 35 DEPARTMENT OF EEE.VAST . VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 36 DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 37 DEPARTMENT OF EEE.VAST . VAST .AUTOMATIC TEMPERATURE CONTROLLED FAN MINI PROJECT’11 38 DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE.VAST 39 . VAST 40 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE.VAST 41 . AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE.VAST 42 . VAST 43 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE. VAST 44 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE. VAST 45 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE. VAST 46 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE. AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE.VAST 47 . VAST 48 .AUTOMATIC TEMPERATURE CONTROLLED FAN PROJECT’11 MINI DEPARTMENT OF EEE.