FULL WAVE RECTIFIER

                         A full wave rectifier is an electronic circuit which converts A.C voltage into pulsating D.C voltage using both half cycles of the applied A.C input voltage.

Construction:

                    Figure shows the basic circuit of a full wave rectifier. It consists of a transformer, two semiconductor diodes and a load resistor. The secondary winding of the transformer is center tapped. Hence two voltages V1 and V2 fed to the two diodes are equal magnitude but opposite in 180 phase difference. Terminal A of the transformer secondary is connected to the anode of the diode D1 and the other end terminal B is connected to the anode of  the diode D2. The load resistor RL is connected between the center tap C of the secondary winding and inter junction of two cathodes of diode D1 and D2.

Working:

                   When an A.C voltage is applied to the input circuit, the terminals A and B of the transformer secondary becomes positive and negative alternately. During positive half cycle of the A.C input voltage terminal A is at positive potential, C is at zero potential and terminal B is at negative potential. This makes the anode of the diode D1 positive with respect to cathode. Now the diode D1 is forward biased and D2 is reversed biased. Therefore D1 conducts and at the same time diode D2 remains non conducting. A current I1 flows through the load resistance RL in the direction as shown in figure.

                         During the negative half cycle of the A.C input voltage, terminal A is at negative potential , C is at zero potential and terminal B is at positive potential. This makes the anode of the diode D2 positive with respect to cathode.  Now the diode D2 is forward biased and D1 is reverse biased. Therefore the diode D2 conducts and diode D1 remains non conducting. A current I2 flows through the load resistor RL in the directions as shown in figure. 

                 Thus when an A.C voltage is applied to the full wave rectifier, during positive half cycle diode D1 conducts and during the negative half cycle diode D2 conducts. Further, current flows through the load resistor RL in the same direction in both half cycles of the A.C input. A pulsating D.C voltage is developed across the load resistor RL. The input and output waveforms are shown in figure.

Input and output waveforms:

Advantages:

Ø  High output voltage than half wave rectifier

Ø  Rectification efficiency is high

Ø  Ripple factor is low

Ø  D.C saturation of the core is avoided.

Disadvantages :

Ø  Cost is high when compared to half wave rectifiers

Ø  Requires tapped transformer which is more costly

Ø  Higher PIV rated diodes are necessary for the operation which increases the cost. 


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