Sunday, May 20, 2012

Full Wave Recftifier : Part3

1.11 Peak Inverse Voltage (PIV)

       We can observed from the circuit diagram that when the diode is reversed biased then full transformer secondary voltage gets impressed across it. The drop across conducting diode is assumed zero. Thus the peak value of the inverse voltage to which diode gets subjected is voltage across both the parts of the transformer secondary. This is shown in the Fig. 1.
Fig. 1

       When D2 is reverse biased, point A is at - Esm with respect to ground while point B is at + Esm with respect to ground, neglecting diode drop. Thus total peak voltage across D2 is Esm.
       where Esm = Maximum value of a.c. voltage across half the secondary of transformer.
       If the diode drop is considered to be 0.7 V then the PIV of reverse biased diode is,
       This is because only one diode conducts at a time.
1.12 Transformer Utilization Factor (T.U.F.)
       In full wave rectifier, the secondary current flows through each half separately in every half cycle. While the primary of transformer carries current continuously. Hence T.U.F. is calculated for primary and secondary windings separately and then the average T.U.F. is determined.

       Neglecting forward resistance Rf of diode, Esm Im RL.
       The primary of the transformer is feeding two half-wave rectifiers separately. These two half-wave rectifiers work independently of each other but feed a common load. We have already derived the T.U.F. for half wave circuit to be equal to 0.287. Hence
       T.U.F. for primary winding = 2 x T.U.F. of half wave circuit = 2 x 0.287 = 0.574.
       The average T.U.F. for fullwave circuit will be
       Average T.U.F. for full wave rectifier circuit = (T.U.F. of primary + T.U.F. of secondary)/2
                                                                          = (0.574 + 0.812)/2 = 0.693
...    Average T.U.F. for full-wave rectifier = 0.693
Note : Thus in full-wave circuit, transformer gets utilized more than the half wave rectifier circuit.
1.13 Voltage Regulation
       For a full wave circuit,
       The regulation can be expressed as,
       and   IDC  = 2Im
       Neglecting winding resistance, the regulation can be expressed as,
       where  R = Forward resistance of the diode.
       The regulation characteristics is drooping, as we see earlier in case of half wave rectifier as output voltage decreases as load increases from no load to full load.

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