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CHITKARA INSTITUTE OF ENGG. AND TECHNOLOGY AE PROJECT BASED LEARNING ELECTRICAL ENGINEERING SUBMITED TO: SUBMITED BY:Er. TEJINDER SINGH Narinder kumar (e093034) SAGGU Manila Garg (e093031) Manoj Kmar (e093032) Mukul Gupta (e093032) Chandigarh-patiala National Highway, village jansla, Teshil Rajpura Disst. Patiala-140401. Phone : 01762-507085,507186 OBJECTIVE To Construct Variable DC Power Supply Using LM317 Regulator. ABSTRACTThis DC power supply circuit is adjustable using IC Voltage Regulator LM317. LM317 is a versatile and highly efficient 1.2-37V voltage regulator that can provide up to 1.5A of current with a large heat sink. It's ideal for just about any application. This was my first workbench power supply and I still use it. Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable!) package, indeed. Although voltage regulator LM317 is capable of delivering up to 37V, the DC power supply output circuit here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink. Make sure that the input voltage is at least a couple of Volts higher than the desired output. It's OK to use a trim-pot if you're building a fixed-voltage supply. TABLE OF CONTENTS INTRODUCTIONThis is a?variable DC power supply which in this circuit IC LM317 be a heart. LM317 is a voltage regulator IC that is well known among practitioners of the?power supply. It’s easy in assembling and calculating when wanting specific output voltage values. To construct this?variable DC power supply?using a transformer with a capacity of 2-3A with the output voltage of approximately 28V DC. The output of this?power supply?can be changed from 1.25V to 25 V DC by turning the potentiometer 5K.Capacitors are used on a?variable DC power supply?is intended to filter the?DC output voltage. Diode bridge rectifier is used to full wave to reduce noise in the discharge voltage. In the variable DC power supply schematic we will find a principle of calculation of an LM317 circuit. It can handle currents up to 1A. Use proper heat sink for LM317 if it has to dissipate more than 1W. COMPONENTS USEDThe Variable DC Power Supply project parts list is as shown below.? ? DESCRIPTION OF PROJECTVARIABLE DC POWER SUPPLYThis project is a positive variable power supply that is compact and easy to build. It is ideal for powering any application requiring a DC supply at current levels up to 1.5A. This power supply project should be among the first project that all electronic hobbyist should embark on. With this power supply, one can use it to power up many electronic kits and projects instead of using batteries. The features of this circuit are:· Output reverse polarity and back - voltage protection· LED power on indication· Variable output?voltage · AC or DC input voltage· Low noise? CIRCUIT DIAGRAM WORKINGDiodes D1 to D4 form a bridge rectifier which converts the AC input voltage into a DC level. Capacitor C1 smooth the DC output of the bridge whilst C2 provides high frequency decoupling. The LM317T is an adjustable regulator IC providing the desired output voltage. Diode D5 is reversed biased during normal operation and is used to protect the regulator if the output is connected to a voltage of the same polarity. Diode D6 protects the regulator if a reverse polarity voltage is connected to the output. The regulator develops a nominal 1.25V reference voltage between the output and adjust terminals. This constant voltage is applied across R1, causing a constant current to flow. This constant current flows through trim port VR1. By varying VR1, the voltage across it will vary and hence the output voltage can be set.The output voltage is calculated by: V(out) = 1.25(1 + VR1/R1) Capacitor C3 improves the ripple rejection of the regulator while capacitors C4 and C5 provide high and low frequency decoupling respectively. The LED indicates that power is present at the output. The current through the LED should be between 5 and 20mA and is set by resistor R2.The variable DC power supply using LM317T regulator is capable of supplying 1.5A over an input voltage range of 1.2V to 37V. It needs at least a 2.5V input-output voltage differential. In practice the limiting factor on the output voltage and current will be the power dissipated by the regulator. For example, if the input voltage is 30V & the output voltage is 10V and the output current is 1A then the power dissipated by the heat sink is (30-10)*1 or 20W. This would need a big heat sink. So it is desirable to keep the input voltage as low as possible to achieve the required output. This is done by using a right choice of step down transformer form the mains.A typical transformer value is 110/12 VAC or 110/18 VAC ratio is good enough depending on the variable output supply that is needed. SUMMARY AND CONCLUSIONSThis DC power supply circuit is adjustable using IC Voltage Regulator LM317. LM317 is a versatile and highly efficient 1.2-37V voltage regulator that can provide up to 1.5A of current with a large heat sink. Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable) package, indeed.Although voltage regulator LM317 is capable of delivering up to 37V, the DC power supply output circuit here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink. Make sure that the input voltage is at least a couple of Volts higher than the desired output. REFRENCESelectronic- ................
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