A Full Wave Rectifier

A FULL WAVE RECTIFIER Aim : To construct

a full wave rectifier and show that the Alternating

Components are rectified into a direct current. 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 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 like TV’s, Radios, Chargers, Lightings etc. There are several stages in a rectifier. Based on their rectification they are classified into two. The single staged & multi staged. In the multi 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 only 2 diodes, the 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%

Theory involved The input transformer steps down the A.C mains from 230V (nominal) to 6V between the center tap and either of 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 the waveform and peak value would be 6 × 2 = 8.4volts. 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 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 required in the construction : Connecting wires, a plug, single lead wire - 2m, 3 – nuts & Bolts of 2 to 3 cm length, Circuit board of mica, a small box to place the model, a transformer, A capacitor, A Resistor (1 K Ω ), P-N junction diodes, Insulation tape, Blades, soldering wax, soldering lead, soldering iron & sand paper.

Details of the materials used → i)

Connecting wires and a plug → A normal insulated copper wire able to withstand 230 – 250 v is required.

ii)

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.

iii)

A circuit board → A normal board of mica facilitated with clips to simplify the connection.

iv)

Nuts ad bolt → In order to fix the board & transformer firmly. Size 2 – 3 cm.

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)

A small box → To place the equipments safely.

vii)

A bulb → To test the output voltage whether Direct or not. Specification → 2.2 –6 v it will get burnt on application of A.C.

viii) A 6-0-6 transformer 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. It consists of a 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 that of the primary and the reverse in a step down transformer. Here we use a step

down transformer which steps down 230V to 6V between the secondary terminals and the center tap. ix)

A CAPACITOR →

The ability of a metal to store electric charges measures the capacitances of a conductor. It provides high impedance to Alternating Current and stores them while all the D.C components are let to pass. There are different types of capacitors – a) PARALLEL PLATE CAPACITOR b) SPHERICAL CAPACITOR c) CYLINDRICLAL CAPACITOR Here we deal with a Cylindrical Capacitor. It consists of two coaxial conducting cylindrical shells. Due to attraction between unlike charges, the charges spread out uniformly and thus it gets charged. Capacitance is measured in it µ Farads. The reactance a capacitors offers to A.C. Current is 1

= ωc, where ω is the frequency of the supply. It does not dissipate any power & the energy stored in it equal to ½ CV2 . In a capacitor Voltage does not change instantaneously. It leads current & voltage by an angle different of 900 .

The capacitor can be connected in 2 ways 1) In Series = 1 1 1 1  + + + .....  =  C C1 C 2 C 3 

& 2) In Parallel = (C = C1 + C2 + C3 ……) Here we use capacitor of 1000 µ F & 25 v. x)

A Resistor →

A resistor is an 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 – 1. Black - 0

6. Green - 5

2. Brown –1

7. Blue

3. Red

8. Violet - 7

-2

- 6

4. Orange – 3

9. Grey

5. Yellow – 4

10. White - 9

Tolerance → Gold

-

± 5%

-

± 10%

Colourless -

± 20%

Silver

- 8

Measurement

→

1st Colour

- 1st digit

2nd Colour

- 2nd digit

3rd Colour

- Power to 10

4th Colour

- Tolerance

For Eg: For a resistor of colour code – brown, black, green & gold. The resistance value is 10 × 105 ± 5% Here we use a single resistor of Brown, Red, Red & Gold colour rings. Its Value = 12 × 102 ± 5% Resistance can be connected in 2 ways – In series, R = (R1 + R2 + R3 …..) & In Parallel 1 1 1 1  + + + .....  =  R R1 R 2 R3  xi)

P-N junction Diodes →

When one side of a semiconductor crystal (Germanium or silicon) is doped with acceptor impurity atoms and the other side with donor impurity atoms a P-N junction is formed.

It is also called a

semiconductor or crystal diode. When diffusion of the two regions occur a resultant potential barrier is created between the two sides due to migration of electrons and holes.

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 the inner electrons occur and current flows. So theoretically no current flows through 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 grayish ring indicated the N side and the Black colouration the P side. xii)

Finally, small equipments such as 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.

Circuit diagram

Connection details Connections are done as in the circuit. The A.C. supply is given to both the input wires 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 one end of the capacitor and the other end to the center tap lead and to the resistor. Further, the other end of capacitor with the diode connection is 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 1st when the A.C. is supplied to the transformer, it steps down the 230V main supply to 6 volts. It has a capability of delivering a current of 500mA. The 6 volts A.C. appearing across the secondary is the RMS valur and the peak value is 6× 2 or 8.4 volts. During the 1st 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 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 S2D2ABEOS2 and 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, which filters 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 multi-meter. 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.

RECTIFIED D.C VOLTAGE

OBSERVATION: Capacitance (C) ( µ F) 1000 1000 1000 1000

Resistance (R) (K Ω ) 580 259.6 661.6 563.6

Output Voltage (DC) 15.03 13.51 14.69 14.68

Result: A full Wave rectifier is constructed & output voltage for different output resistance is measured and tabulated.

BIBILIOGRAPHY 1) 2) 3) 4) 5)

Electronic projects for beginners by A.K Manini Comprehensive physics (class_XIIth , NCERT based) Comprehensive practical physics NCERT based CBSE text for XIIth Website : www.yahoo.com