What is full-wave Bridge Rectifier?,Comparision b/w FW-Bridge Rectifier with FW-Center tapped transformer,Working principle of FW-bridge Rectifier ,Comparison of all types of rectifiers,FW-bridge rectifier applications.

Full-Wave Bridge Rectifier

                     A Full-Wave Bridge Rectifier is a circuit arrangement which makes use of both half cycles of input alternating current (AC) and converts them to direct current (DC) .In full-wave bridge rectifier we used four diode in the form of a bridge as shown in the diagram below. 

Comparison of FW-Bridge rectifier With Center Tapped Transformer

                     The FW-bridge rectifier uses four diodes instead of two but the it eliminated the need of a center-tapped transformer.The PIV-rating of the diode used in FW- Bridge rectifier should be better than Vmax rather than 2Vmax if we compared it with FW-rectifier with a center-tapped transformer.This means that the diodes used in FW-bridge rectifiers are cheap as diodes of high PIV-rating are always more expensive used in FW-Rectifier with center tapped transformer ,this is big advantages of FW-bridge rectifier. Similarly only one secondary winding of transformer will reduce the cost of transformer also.The current caring capacity of the FW-bridge rectifier is always half that of the FW-rectifier with a center tapped transformer.

                                                         

Full-Wave bridge rectifier

Full-Wave rectifier using a center-tapped transformer

Working Principle

Positive half-cycle of Vin

Fig. During +Vin D1 and D2 are ON & D3 and D4 are OFF

• During the positive half-cycles of the voltage across the secondary winding of the transformer Vin the upper point 1 will be positive with respect to the point 4 of the secondary winding of the transformer.Due to this the diodes D1 and D2 will be forward-bias and turned ON ,current will start conducting through the resistor Rl from top to bottom.Due to it the point 2 is more positive with respect to the point 3 which is infact the ground point of the circuit.
• During this positive half cycle the diodes D2 and D4 will be reverse biased and remains OFF.
• Above fig showed during positive half cycle .The out put voltage waveformVo across the load is shown in below fig. The waveform of input voltage Vin across the secondary winding of the transformer is given below.in fig. If we considered that diodes are ideal then the voltage across Rl will be equal to the max. amplitude of Vin then Vomax=Vom=Vmax.
• The reverse voltage across the non-conducting diodes D2 and D4 will be Vmax.we can calculate all voltages at points 1,2,3 and 4 are V1,V2,V3 and V4 respectively.

                   V1 = +Vmax

                    V2 = V1- Vd for ideal diode Vd=0V

                     V2 = Vmax

                 This shows that the N side of diode D2 is at Vmax which shows that the revers voltage across D2 is +Vmax.

                   Since Vd=0V for an ideal diode this means the reverse voltage across diode D4 will be    -Vmax .     If we consider silicon diode the value of reverse voltage across the non conducting diodes D2 and D4 will be less by 1.4 volts.

Negative Half Cycle

fig.During negative half cycle D2 and D4 are ON and D1 and D3 are OFF

• Now if we consider the negative half cycle of Vin as shown in the above fig. During this the point 4 will be positive with respect to the point 1.Due to this the diode D1 and D4 will be forward-biased and diodes D1 and D3 will be reverse biased.during negative half cycle the current will flow from the Rl from top to bottom .The direction of current is as as in the positive half cycle.So, the voltage across Rl will be positive at top (point-2) with respect to (point-3).
• In case of FW-bridge rectifiers two diodes which are opposite to each other always conduct at the same time while the other two remains in the OFF state.Due to this the voltage across the Rl is almost same which is our output voltage.In case of Silicon diode  we will subtract 2Vd = 1.4V from the Vmax  provided rd is small and can me neglected.
• The reverse voltage across the non-conducting diodes D1 and D3 will be nearly Vmax.It is the big advantages of Full-wave bridge rectifier over the Full-wave rectifier with center tapped transformer.Due to this we can use half PIV-rating diode in FW-bridge rectifier as compare to the FW-rectifier with center tapped transformer.
• it is very important point that although the FW-bridge rectifies use four diodes but still the cost of two diodes of the FW-rectifier with center-tapped transformer having high PIV-rating be more.

Important Note:- It is very important to keep in mind that for low Dc-voltage the full-wave rectifier with a center-tapped transformer is better bcs Vomax ( Vmax) across Rl is only less by 0.7 V for practical silicon diodes and PIV-rating of diodes is not very significant.The FW-bridge rectifier develops Vomax across Rl which is less by two diode voltage drops or 1.4V and in low dc-voltage applications it is considered a big disadvantage. In case of high Dc-voltage application the PIV rating of diodes become significant due to cost and the two diode voltage drop of 1.4V becomes insignificant.In this case FW-bridge rectifier are preferred over their counter part at high dc-voltages across the load.The two additional diodes required for FW-bridge rectifiers because of their half PIV-rating compared to FW-rectifiers with center-tapped transformer do not add much to the cost of the circuit.

                  The below fig. shows the Vin across secondary of the Transformer.

fig.

Comparison Of Rectifiers

                    

                    We can compare the different values like Dc voltage ,Dc current ,PIV rating of diodes Max. rectification efficiency Ripple factor Ripple frequency of all three types of rectifiers.

Full-Wave Bridge  rectifier Application

• FW-bridge rectifier is cheaper than FW-rectifiers with center tapped transformer so it is widely used in power supply circuits.
• The amplitude of the modulated radio signal can be detected by using the FW-bridge rectifier.
• A steady and polarized Dc-voltage can be supplied in welding through the FW-bridge rectifier.