A rectifier is a device which converts AC voltage to pulsating DC voltage using one or more PN junction diodes.

The full wave rectifier conducts during both positive and negative half seconds of the input AC supply . In order to rectify both the half cycles of AC input, two diodes are used in the circuit. The Transformer used here is Center tap transformer the two diodes connected to a common load RL. The AC voltage is applied through a suitable power transformer with proper turns ratio

Operation

1 Consider the positive half cycle of the input voltage is applied, the diode D1 will be forward biased and hence it will conduct, while diode D2 will be reverse biased it will act as open circuit and it will not conduct. The load current iwill be the diode D1 current.

2 In the next half cycle of AC voltage, the process become reverse. Now the diode D2 conducts because it will be in forward bias while the diode D1 does not, being in Reverse bias. And the load current iwill be the diode current.

3 The load current flows in both half cycles of AC voltage and in the same direction through the load resistance hence we get rectifier output across the load

4 The load current is some of the individual diode currents, we should note that the two diodes do not conduct simultaneously

5 The output load current is still the pulsating DC and it’s not pure DC

centre-tap-full-wave-rectifier-waveform-e1497672372200.jpg
Full Wave Rectifier Waveform              Source

Full Wave Rectifier With Filter

1 During the positive half cycle, the diode (D1) current reaches the filter and charges the capacitor. However, the charging of the capacitor happens only when the applied AC voltage is greater than the capacitor voltage.

2 Initially, the capacitor is uncharged. That means no voltage exists between the plates of the capacitor. So when the voltage is turned on, the charging of the capacitor happens immediately.

3 During this conduction period, the capacitor charges to the maximum value of the input supply voltage. The capacitor stores a maximum charge exactly at the quarter positive half cycle in the waveform. At this point, the supply voltage is equal to the capacitor voltage.

4 During the negative half cycle, the diode (D2) current reaches the filter and charges the capacitor. However, the charging of the capacitor happens only when the applied AC voltage is greater than the capacitor voltage.

5 The capacitor is not completely uncharged, so the charging of the capacitor does not happens immediately. When the supply voltage becomes greater than the capacitor voltage, the capacitor again starts charging.

Advantages of Full Wave Rectifier 

1 The DC voltage and current or more than half wave rectifier
2 No DC current in transformer windings hence no possibility of saturation
3 Transformer utilisation factor is better so the losses in transformer are less
4 Higher efficiency
5 Ripple factor is less
6 Large DC auto power

Disadvantages

1 The peak inverse voltage rating of diode is higher
2 The diodes will be larger in size
3 The cost of center tapped transformer is higher

 

Advertisements