INTRODUCTION A full wave rectifier is a device which is used to rectify all the alternating current components in an alternating supply and make it purely a direct current. The two alternating halves of an alternation current are rectified in a full wave rectifier which is an advantage over a half wave rectifier. Most of electronic devices cannot withstand very high voltage or alternating current due to its intense high power. The use of batteries in all devices is not practical as their replacement and durability is a huge problem as the device has to be dismantled each time for such a replacement. So these rectifiers are used in most of the electronic devices devices like TV’s, Radios, Chargers and Lightings etc. The Th e re are ar e seve se vera rall s tage ta ges s in a r e cti ct i f ier. ie r. Bas Ba s e d on their rectification they are classified into two: The single staged & multi staged. I n the th e mul mu l ti staged rectifiers, more than two diodes are used and these are used in the above-mentioned devices. The singled staged rectifier has only 2 diodes, the one we are to discuss in this project. The multi diode rectifier has o n l y 2 d i o d e s , t h e one we are to discuss in this project. The multi diode rectifiers has an efficiency ~ 94.6% while that of the single is only 81.2%.
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THEORY INVOLVED : The input transformer steps down the A.C mains from 220V to 9V between the centre tap and either of the two ends of the secondary winding. The transformer has a capability of delivering a current Of 500mA. T h e 9 V A . C a p p e a r i n g a c r o s s t h e s e c o n d ary is the RMS value of the waveform and peak value would be .4826 volts=x The diodes rectify the A.C waveform appearing across the secondary with the help of alternate forward and reverse biasing. The capacitor further filters 99% of the resident components and this is left to pass through the resistance and emerges out as +ve and – v e. The bulb connected verifies the output as it works on Direct Current and if used on an Alternating Current, the fluctuation will burn out the bulb.
MATERIALS REQUIRED IN THE CONSTRUCTION :Connecting wires, a plug, single lead wire 2m, card board, a transformer, a f i l t e r , a r e s i s t o r ( 1 K ) Ω, P-N junction diodes, Insulation tape, Blades, soldering wax, soldering lead and soldering iron.
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Details of the materials used :i) Connecting Wires and a Plug. ii) A normal insulated copper withstand 220-250V is required.
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iii) Single Lead wire-Thin wire with one single strand of copper well insulated and able to conduct a current of 1 ampere or a D.C current efficiently. iv) A card Board. v) Soldering wax & lead.(The wires are to be soldered firmly to make the connection tight so for this a thin lead wire is required to affix the connections and wax to make the lead to hold on when soldered). vi) L.E.D – It is called light emitting diode(L.E.D). It is used to test the output voltage whether Direct or not. It glows on as we get a rectified direct current as an output. vii) Step Down TransformerA 9 - 0 - 9 t r a n s f o r m e r Transformer is a device used to change the voltage of an alternating current. The transformer which converts low voltage to high voltage is called a step up transformer whereas the one which converts high voltage to low voltage is called a step down transformer. Page | 3
I t c o n s i s t s o f laminated core consisting of two coils, a primary & a secondary coil. In a step up the number of turns in the secondary is greater that of the primary and the reverse in a step down transformer. Here we use a step down transformer which steps down 220V to 9V between the secondary terminals and the centre tap. viii) Filter - It is used to filter the the ripples, which is present in the output of the diode to an extent. Here we have used 1000MFD25V filter. ix) A Resistor- A resistor is electronic components whose resistance value tells us about the opposition it offers to the flow of electric current. Resistance is measured in ohms (Ω).We determine the value of a resistor using the colour coding on the rings of the resistor. x) P-N junction Diode :When one side of a semiconductor crystal (Germanium or silicon) is doped with acceptor impurity atoms and the other side with donor i m p u r i t y a t o m s a P N junction is formed. It is also called S e miconductor or crystal diode. When diffusion of the two regions occur a re sul ta nt po tent ia l barrier is created between the two sides due to migration of electrons and holes. Page | 4
When the diode is connected with P side to positive terminal of a battery & N side to – ve terminal it is said to be forward biased & reverse biased when reversed. In forward biasing the applied positive potential repels the holes and turns a current is made to flow overcoming the internal potential Barrier. While in reverse biasing the – ve electrons 1st attract the holes and widen the Barrier and then only the repulsion between inner elec trons occu r a nd c urre nt flows . So th eo re ti ca ll y no cu rr en t fl ow sthrough due to the widening of the Potential barrier but practically a very small current does flows through. Different types of diodes are present : 1.Zener diode, 2.P-N junction diode, 3.Led , 4.Lad, 5.Solar Cell, Here we use a P-N junction diode. The greyish ring indicated the N side and the Black colouration the P side. x i i ) F i n a l l y , s m a l l e q u i p m e n t s s u c h a s a soldering iron to solder the lead , Blades, holders, insulation tapes – to insulate the wire from shocking and sand paper – to rub the oxidized wire ends are used.
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CIRCUIT DIAGRAM :-
Connection details :Connections are done as in the circuit. The A.C. supply is given to b ot h t he i n pu t w i r e s of the transformer and the two ends of the secondary coil is given to the P side of the two diodes and the N side of the diodes are twined and then connected to the one end of the capacitor and the other end Page | 6
to the centre tap lead and to the resistor. Further, the other end of Filter with the d i o d e c on n e c t i o n i s connected to the other end of the resistor. Connect 2 leads on both the ends of the resistor to measure the output and this is connected to the +ve & -ve terminals of the bulb
WORKING :First when the A.C. is supplied to the transformer, it steps down the 220V main supply to 9 volts. It has a capability of delivering a Current Of 500mA. The 9 volts A.C. appearing across the secondary is the RMS value and the peak value is 26× or 8.4 volts. During the 1 st half cycle of the A.C. input Diode D1 is forward biased and a current flows in the circuit in the direction S1D1ABEOS1. During this time diode D2 is reverse biased. So it does not conduct any electric current. During the next half cycle the diode D2 is forward and D1 is reversed. Hence D2 conducts current in the direction S2D2ABEOS2and D1 does not conduct any current. In subsequent half cycles of the A.C current the above processes are repeated. In both the half cycles,it is clear that current flows through the resistor in only one direction ABE. Even though the voltage across RL is unidirectional it will still contain a few A.C components. This is filtered and made smooth using a capacitor filter, which filters Page | 7
99% of the A.C current. A resistor is then used to adjust the output voltage. We can then test the o/p Voltage using a multimeter. Efficiency of Rectification -η = D.C power output. Total A.C input power For a half wave rectifier,η ~ 0.406 = 40.6 %For a full wave rectifier, the one used here is η ~ 0.812 = 81.2 %By the use of more number of diodes the efficiency can be increase to a maximum of 94.6%. Here we only use 2 diodes. The use of multiple capacitors also nearly filters all A.C components from the supply and resistance is adjusted for the required output. As this is a simple circuit, only one capacitor and a resistance is being used. But there will be slight factor of A.C. current still left in the output but it is negligible.
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WAVEFORMS :-
RESULT :- A full Wave rectifier is constructed & a rectified d.c voltage is obtained as a output.
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BIBILIOGRAPHY :1)Electronic projects for beginners by A.K Manini 2) Scribd.com
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