Full Wave Bridge

FULL WAVE BRIDGE:

It is built around a four - diode bridge configuration. This design is called as full wave bridge. It is most popular of full wave rectifier design.

A bridge rectifier makes use of four diode in a bridge arrangement to achieve full-wave rectification. It is a widely used configuration, both with individual diodes wired and with single component bridges where the diode bridge is wired internally.

It is most widely used rectifier. In the positive half cycle, D1 and D4 is forward biased and D2 and D3 are reverse biased. In the negative half cycle D2 and D3 are forward bias and D1 and D4 are reverse bias. The output voltage waveform is same but the advantage is that PIV rating of diodes are Vm and only single secondary transformer for Vm voltage is required. The main disadvantage is that it requires four diodes. When now d.c. voltage is required then secondary voltage is low and diode drop (1.4 V) becomes significant. The Xƒ1, required is of high rating (> 1.4 V).

For low d.c output we use center tap rectifier because only one diode drop is there.

Current directions for the full wave bridge rectifier for the positive and negative. half cycles of AC source waveform.

Regardless of the polarity of the input, the current flows in the same direction through the load (i.e) the negative half cycle of source is positive half cycle at the load. The current flow is through two diodes in series for both polarities. Thus two diode drops of the source voltage are lost (0.7 × 2 = 1.4 V for Si) in the diodes. This is a disadvantage compared with a full wave center, tap design. This disadvantage is only a problem in very low voltage power supplies.

Merits of Full Wave Rectifier:

• High efficiency.

• Low ripple factor.

• High TUF.

Demerits of Full Wave Rectifier:

• Complicated circuit

• High cost

SUMMARY

For half wave rectifier,

Idc = 1/π . Im = 0.318 Im

Irms = ½ .Irms = 0.5Im

Vdc = 1/π . Vm = 0.318 Vm

Vrms = ½ Vm = 0.5 Vm

For a full wave rectifier

Idc = 2/π . Im = 0.637 Im

Irms = 1/√2 .Im = 0.707Im

Vdc = 2/π . Vm = 0.637 Vm

Vrms = 1/√2 .Vm = 0.5 Vm