PROJECT ON
FULL WAVE RECTIFIER
BY-VARUN CLASS-XII B
AIM
To construct a full wave rectifier and show that the Alte rnatingComponents are rectified into a direct current.
INTRODUCTION A full wave rectifier is a device which is used to rectify al l the alternatingcurrent components in an alternating supply and make it purely a directcurrent. The two alternating halves of an alternation current are rectified in afull wave rectifier which is an advantage over a half wave rectifier. Mostelectronic devices cannot withstand very high voltage or alternating currentdue to it s inten se high power. The use of bat teries in al l d evices is no t practical as their replacement and durability is a huge problem as the devicehas to be dismantled each time for such a replacement. So these rectifiers areused in most of the electronic devices like TV’s, Radios, Chargers, Lightingsetc. There are several stages in a rectifier. Based o n thei r rectification th eyare classified into two. The single staged & multi staged.In the multi staged rectifiers, more than two diodes are used and these aroused in the above-mentioned devices. The singled staged rectifier has only 2diodes, the one we are to discuss in this project. The multi diode rectifier has only 2 dio des, the one we are to discu ss in thi s project.
1 The Full Wave Rectifier
The first building block i the dc power supply is the full wave rectifier. The purpose of the full wave ectifier (FWR) is to create a rectified a output from a sinusoidal ac inp t signal. It does this by using the nonlin ar conductivity characteristics of diodes to direct the path of the c rrent.
Figure 1. Common our-diode bridge configuration for the WR
Consider the curren path in the diode bridge rectifier. In he positive half cycle of Vin, diodes
4 and D3 will conduct. During the n gative half
cycle, diodes D2 and D1 will conduct. As a result, the load will pas current in the same direction in each half cycle of the input.
Forward Bias o
If we consider a simple, piece-wise linear model for the diode IV curve, the diode forward current is zero until Vbias >= Vthreshold, where Vthreshold is 0.6 V to 0.8 V. The current increases abruptly as Vbias increases further. Due to this turn-on or threshold voltage associated with the diode in forward bias
o
around is Vthreshold is more gradual than the piece-wise model, the actual diode performance will differ from the simple model.
Reverse Bias o
In reverse bias (and neglecting reverse voltage breakdown), the current through the diode is approximately the reverse saturation current, Io. The voltage across the load during reverse bias will be Vout = Io Rload.
o
In specifying a diode for use in a circuit, you must take care that the limits for forward and reverse voltage and current are not exceeded.
o
we should expect a 0.6 to 0.8 V voltage drop across each forward biased diode in the rectifier bridge. In the case of the full wave rectifier diode bridge, there are two forward biased diodes in series with the load in each half cycle of the input signal.
o
The maximum output voltage (across load) will be Vin - 2 Vthreshold, or ~ Vin - 1.4 V.
o
Since some current does flow for voltage bias below Vthreshold and the current rise
THEORY
The input transformer steps down the A.C mains from 230V (nominal) to6V between the center tap and either o f the two ends of the secondary winding. The transformer has a capability of delivering a current of 500 mA.The 6V A.C appearing across the secondary is the RMS value of thewaveform and peak value would be .4.826 volts
=× The diodes rectify theA.C waveform appearing across the secondary with the help of alternateforward and reverse biasing. The capacitor further filters 99% of the resident components and this is let to pass through the resistance and emerges out as+ve and –ve. 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 REQUIREDlead, soldering iron & sand paper,tape, Blades, soldering wax, soldering Connecting wires, a plug, single lead wire - 2m, 3 – nuts & Bolts of 2 to 3c m l e n g t h , C i r c u i t b o a r d o f m i c a , a s m a l l b o x t o p l a c e t h e m o d e l , atransformer, A capacitor, A Resistor (1 K Ω
), P-N junction diodes,Insulation
CIRCUIT DIAGRAM
CONNECTION DETAILS—
Connections are done as in the circuit. The A.C. supply is given to bo th the inpu t wires o f the tran sformer and the two end s of thesecondary coil is given to the P side of the two diodes and the N sideo f th e di od es are twine d an d the n con nec ted to on e end of th ecapacitor and the other end to the center tap lead and to the resistor.Fur the r, the oth er end of capacitor with the diode connection isconnected to the other end of the resistor . Connect 2 leads on boththe ends of the resistor to measure the output and this is connected tothe +ve & -ve terminals of the bulb.
IAGRAM
WORKING 1 st when the A.C. is supplied to the transformer, it steps down the230V main supply to 6 volts. It has a capability of delivering a currentof 500mA. The 6 volts A.C. appearing across the secondary is the RMS valur 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‘I’ flows in the circuit in the direction S1D1ABEOS1. During thistime diode D2 is reverse biased. So it does not conduct any electriccurrent. During the next half cycle the diode D2 is forward and D1 isreversed. Hence D2 conducts current in the direction S2D2ABEOS2and D1 does not conduct any current. In subsequent half cycles of theA.C current the above processes are repeated. In both the half cyclesit is clear that current flows through the resistor in only one directionABE. Even though the voltage across RL is unidirectional it will stillcontain a few A.C compone nts. This is filter ed and made smoothusing a capacitor, which filters 99% of the A.C current. A resistor isthen used to adju st the output voltage . We can then te st the o/ pVoltage using a multi-meter.Efficiency of Rectification η
= D.C power outputTotal 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 toa 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 andresistance is adjusted for the required output. As this is a simplecircuit, only one capacitor and a resistance is being used. But therewill be slight factor of A.C. current still left in the output but it isnegligible.
RECTIFIED VOLTAGE
BIBLIOGRAPHY
Following books and websites were a source of my project -
N.C.E.R.T PHYSICS – PART – II
www.google.com
www.wikipidea.com
www.scrbd.com
