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Full wave rectifier

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28 Feb 2011 17:35:47 IST
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28 Feb 2011 17:35:47 IST
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Full wave rectifier
Engineering Entrance , JEE Main , JEE Main & Advanced , Physics , Modern Physics

Introduction to full wave rectifier output voltage:

A FWR is one which converts an A.C voltage into a pulsating voltage using positive and negative half - cycles of the applied A.C voltage .

It uses two diodes , one of which conducts and provides output during the positive half - cycle while the other diode conducts during the negative half - cycle .

Figure (1) shows the circuit diagram of a FWR . The step down transformer secondary windings are centre tapped , i.e., secondary voltage is equally divided with 180o out of phase as shown in figure (2) .

Therefore , diode D1 input gets positive half - cycle and at the same time D2 gets negative half - cycle .

Assume D1 and D2 are ideal diodes between 0 to 2  .

Let D1 gets positive half - cycle and D2 gets negative half - cycle .

Therefore , D1 is ON (forward biased ) and D2 is OFF (reverse biased)

Therefore , current I1 flows in RL due to D1 and I2 = 0 .

i.e.,   I1  =  Im sin  , 0 <  <

I2  =  0 .

Similarly , input between   to  D1  is negative and to D2 is positive .

Therefore , D1 is OFF (reverse biased) , D2 is ON (forward biased)

Therefore , I2 current flows in RL is in the same direction .

The total current ,

I  =  I1  +  I2

=   Im sin  + Im sin

=   2 Im sin

I  =  2 Im sin

Piv , Average Dc Voltage , Rms Current of Fwr:

Peak Inverse Voltage (PIV)

It is defined as the maximum reverse bias potential that can be applied before entering the zener region .

The peak Inverse Voltage (PIV) of the diode is of primary importance in the design of rectifiers .

For half - wave rectifier the PIV rating should be greater than or equal to maximum applied voltage . For a full - wave rectifier the PIV rating should greater than or equal to twice the maximum applied voltage .

Average D.C voltage

The average voltage available across the D.C voltage is given by ,

VDC  =    Vm sin

=

=

=     [ - (cos -  cos(0)) ]

VDC  =

RMS current

IDC  =

=

=

Irms  =

Ripple Factor of Fwr:

Ripple Factor

Ripple factor is a figure of merit of a rectifier circuit and is defined as the ratio of the A.C ripple quantity [ current or voltage ] to D.C quantity [ current or voltage ] .

The output of FWR can be represented mathematically as ,

Io  =        ------------- > (1)

Equation (1) indicates that the rectifier output contains D.C components plus A.C components .

Ripple factor ,    =           ---------------> (2)

Substitute the values of ,

IDC  =    and

Irms  =     in equation (2) , we get    =  0.48 .

The ripple factor of 0.48 implies a drastic improvement from 1.21 for HWR .

Therefore , FWR is good compared to HWR since  < 1 .

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