Electronic Devices - 3full Wave Rect

Full wave Rectification

BS P-III

Institute of Physics

Full wave rectification Objects of the experiment To understand the operation of full wave center tapped Rectifier. To understand the operation of full wave bridge rectifier.

Introduction RECTIFIER A rectifier is a circuit that converts pulsating ac into pulsating There are three basic types of rectifier circuits: the half wave, full wave (center tapped) and rectifiers. Of them, bridge rectifier is the most commonly used.

Full wave rectification Full wave rectification is the process through which an ac sinusoidal input voltage is converted into a pulsating dc voltage with two output pulses occurring for each RL. input cycle. The full wave rectifier consists of two diodes and a load

Load

D1

Transformer 5

RL =

1K

8

D2

Fig.1 A full wave rectifier

Operation: During the positive half cycle of a.c input voltage, point 5 is positive and point 8 is negative. This makes the diode D1 forward biased and reverse biased. Therefore D1 conducts the current and D2 does not conduct the current, so current will only flow across D1 through the load resistor R L in upper half cycle as D1 shown in fig.2.

Load

Transformer 5 RL 8 Vsec

1K D2

=

posetive half cycle.

Fig.2 Diode D1 conducts during posetive half cycle,while D2 acts as open switch.

During the negative half cycle, of a.c input voltage point 5 is negative and point 8 is positive. Under this condition the diode D2 is forward biased while diode D1 is reverse biased. There fore D2 conducts the current because D2 is in forward biased condition while D1 does not conduct the the D1 is in reverse biased condition. D1

Transformer

Load

5

1K

=

RL 8 Vsec

D2 1

Fig.3 Diode D2 conducts during posetive half cycle,while D1 acts as open switch.

Full wave Rectification

BS P-III

EQUIPMENT & COMPONENTS EQUIPMENT:

■ Oscilloscope COMPONENTS: ■ A bread board

■ 1K

resistor

■ Two diodes(IN 4007series)

■ Step down transformer (Center tapped) ■ A few connecting hard wires

PROCEDURE; 1. 2. 2. 3.

Make the Full wave circuit as shown in fig.1. Observe the rectified output on the Oscilloscope,by connecting its probe across R L . Observe the ripple on the Oscilloscope, using the feature of dc/ac coupling. Calculate the ripple factor .

OBSERVATION TABLE: Vout (peak)

S.No.

=

Vsec(peak) - 0.7 2

Vsec(peak)

Vout (peak) (meas) (Calc) %Error

Vavg= 2Vp/

= Vp 2

Ripple factor

REVIEW QUESTIONS: 1. What is Full wave Rectification process?

2. Why can't we implement the Center tapped full wave rectifier without center-tapped transformer ?

2

Full wave rectification

BS P-III

Full wave Bridge rectification

Introduction In full wave rectification the output current flows in the same direction during both half cycles of the alternating input voltage. There are two methods to achieve the full wave rectifier. • Bridge full wave rectification. • Center tapped full wave rectification. A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification as shown in figure 1. The bridge rectifier is the most commonly used full wave rectifier circuit for several reasons. 1. It does not require a center tapped transformer, and therefore can be coupled directly to the ac power line if desired. 2. Using a. transformer with the same secondary voltage produces a peak output voltage that is nearly double the voltage of the full wave center tapped rectifier. This results in a higher dc voltage from the supply. Function generator input

D3

5

D1 = RL

D4 8

1K

D2

Fig.1 A full wave bridge rectifier

Operation: When the input cycle is positive for bridge full wave rectification, diodes D1 and D2 are forward biased and conduct current as shown in fig 2 . At this time a voltage is developed across RL which look like the positive half of the input cycle. During this time diodes D3 and D4 are reverse biased. Function generator input

D3

D1

5

= D4 8

RL

1K

D2

Fig.2 Full wave bridge rectifier during positive half cycle

When input cycle is negative, the diodes D3 and D4 are forward biased as shown in figure 3 and conduct current in same direction through RL as during positive half cycle. During the negative half cycle, diodes D1 and D2 are reverse biased. D1

Function generator D3 5 input

= D4

RL

1K

8 D2

Fig.3 Full wave bridge rectifier during negetive half cycle 3

Full wave rectification

BS P-III

EQUIPMENT & COMPONENTS EQUIPMENT:

■ Oscilloscope ■ Function generator

COMPONENTS: ■ A bread board ■ Four diodes(IN 4007series) ■ 1 K resistor ■ A few connecting hard wires

PROCEDURE: 1. Setup the function generator to a suitable frequency and peak voltage. 2. Make the half wave circuit diagram as shown in fig 1. 3. Observe the rectified output at diffrent peak to peak voltge values. 4. Calculate the ripple factor in each case. 5. Observe the ripple on the Oscilloscope, using the feature of dc/ac coupling.

OBSERVATION TABLE:

Vout (peak)=Vin (peak) - 1.4 S.No. Vin (peak)

Vout (peak) (meas) (Calc)

%Error

Vavg= 2Vp/

= Vp

2

Ripple factor

10 7.5 5 4 3

1 2 3 4 5

REVIEW QUESTIONS: 1. What is full wave Bridge rectification? 2. Which type of rectifier has high ripple factor? 3. In bridge rectifier, how many diodes are forward biased during one cycle?

FINAL CHECK LIST: • •

Clean your equipment/materials and workbenches before you leave. Return all equipment and materials to their proper storage area.

4

Full wave rectification

BS P-III

Model measurements Full wave Bridge rectification S.No. 1 2 3 4 5

Vin (peak)

Vout (peak) (meas) (Calc) 8.5 6 3.6 2.6 1.6

10 7.5 5 4 3

%error

8.6 6.1 3.6 2.6 1.6

Vavg= 2Vp/ 5.41 3.82 2.29 1.66 1.02

1.16 1.64 0 0 0

= Vp 6.01 4.24 2.54 1.84 1.13

2

Ripple factor 0.484 0.482 0.480 0.478 0.477

Full wave center tapped rectifier S.No.

Vsec(peak)

1

17.5

Vout (peak) (meas) (Calc) %Error 8.00

8.05

0.6

Vavg= 2Vp/ 5.09

5

= Vp 2 5.66

Ripple factor 0.486