Full Wave Rectifer

A center tapped rectifier is a type of full wave rectifier that uses two diodes connected to the secondary of a center tapped transformer, as shown in below diagram.  The input voltage is coupled through the transformer to the center tapped secondary .  Half of the total secondary voltage appears between the center tap and each end of the secondary winding as shown.

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Full wave Rectifier

For a positive half cycle of the input voltage, the polarities of the secondary voltages are shown in figure.  This condition forward biases diode D1 and reverse biases diode D2.  The current path is through D1 and the load resistor RL.

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During Positive half cycle, D1 is forward and D2 is Reverse Biased.

For a negative half cycle of the input voltage, the voltage polarities on te secondary are shown.  This condition reverse biases D1 and forward biases D2.  The current path is through D2 and RL.  Because the output current during both the positive and negative portions of the input cycle is in the same direction through the load the output voltage developed across the load resistor is a full wave rectified dc voltage.

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During negative half cycle, D2 is forward and D1 is reverse Biased.

Effect of the Turns Ratio o the Output Voltage:

If the transformer’s turns ratio is 1, the peak value of the rectified output voltage equals half the peak value of the primary input voltage less the barrier potential.  Half of the primary voltage appears across each half of the secondry winding.

In order to obtain an output voltage with a peak equal to the input peak ( less the diode drop), a step up transformer with a turns ratio of n = 2 must be used. In this case, the total secondry voltage is tice the primary voltage, so the voltage across each half of the secondry is equal to Vpri.

The output voltage of a center tapped full wave rectifier is always half of the total secondry voltage less the diode drop , no matter hat the truns ratio, so,

Vout = Vsec / 2  - 0.7 V 

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