In half-rectifiers only one half cycles of the input are utilized but in full-wave rectifiers both half cycles of the input are utilized. Alternate half cycles are inverted to give unidirectional load current.There are two types of full-wave rectifier circuits namely
1. center-tap rectifier and 2. bridge rectifier.
center-Tap rectifier:
in such a rectifier, the ac input is applied through a transformer, the anodes of the two diodes D1 and D2 (having similar characteristics) are connected to the opposite ends of the center tapped secondary winding and two cathodes are connected to each other and are connected also though the load resistance RL and back to the center of the transformer as shown in figure.
when the top of the transformer secondary winding is positive,say during the first half cycle of the supply,the anode of Diode D1 is positive w.r.t. cathode, and anode of diode D2 is negative w.r.t cathode.Thus only diode D1 conducts,being forward biased and current flows from cathode to anode of ddiode D1, through load resistance RL and top half the transformer secondary making cathode end of load resistance RL positive.During the second half cycle of the input voltage the polarity is reversed,marking the bottom of the secondary winding positive w.r.t centre tap and thus diode D2 is forward biased and diode D1 is reverse biased. consequently during this half cycle of the input only the diode D2 conducts and current flows through the load resistance RL and bottom of the transformer secondary making the cathode end of the load resistance RL positive.Thus the direction of flow of current through the load resistance RL remains the same during both halves of the input supply voltage. Thus the circuit shown in figure acts as full-wave rectifier.
Bridge Rectifier: In the bridge circuit four diodes are connected in the form of a wheatstone bridge,two diametrically opposite junctuons of the bridge are connected to the secondary of a transformer and the other two are connected to the load, as shown in fig 2.
when the upper end of the transformer secondary winding is positive ,say during first half cycles of the input supply,diodes D1 and D3 are forward biased and current flows thorugh arm AB, enters the load at positive terminal, leaves the load at negative terminal, and returns back flowing through arm DC.
1. center-tap rectifier and 2. bridge rectifier.
center-Tap rectifier:
in such a rectifier, the ac input is applied through a transformer, the anodes of the two diodes D1 and D2 (having similar characteristics) are connected to the opposite ends of the center tapped secondary winding and two cathodes are connected to each other and are connected also though the load resistance RL and back to the center of the transformer as shown in figure.
when the top of the transformer secondary winding is positive,say during the first half cycle of the supply,the anode of Diode D1 is positive w.r.t. cathode, and anode of diode D2 is negative w.r.t cathode.Thus only diode D1 conducts,being forward biased and current flows from cathode to anode of ddiode D1, through load resistance RL and top half the transformer secondary making cathode end of load resistance RL positive.During the second half cycle of the input voltage the polarity is reversed,marking the bottom of the secondary winding positive w.r.t centre tap and thus diode D2 is forward biased and diode D1 is reverse biased. consequently during this half cycle of the input only the diode D2 conducts and current flows through the load resistance RL and bottom of the transformer secondary making the cathode end of the load resistance RL positive.Thus the direction of flow of current through the load resistance RL remains the same during both halves of the input supply voltage. Thus the circuit shown in figure acts as full-wave rectifier.
Bridge Rectifier: In the bridge circuit four diodes are connected in the form of a wheatstone bridge,two diametrically opposite junctuons of the bridge are connected to the secondary of a transformer and the other two are connected to the load, as shown in fig 2.
when the upper end of the transformer secondary winding is positive ,say during first half cycles of the input supply,diodes D1 and D3 are forward biased and current flows thorugh arm AB, enters the load at positive terminal, leaves the load at negative terminal, and returns back flowing through arm DC.
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