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 - E_sm with respect to ground while point B is at + E_sm with respect to ground, neglecting diode drop. Thus total peak voltage across D₂ is E_sm.

       where E_sm = 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 R_f of diode, E_sm ≈ I_m R_L.

       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   I_DC  = 2I_m/π

       Neglecting winding resistance, the regulation can be expressed as,
       where  R_f  = 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.