Full-wave Bridge Rectifi er

Chapter 6.10 Full-wave Bridge Rectifi er

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 210Fundamental Electrical and Electronic PrinciplesRoutputinput Fig. 6.11 The graphs of the applied a.c. voltage, and the corresponding load current, are shown in Fig. 6.12 . The load p.d. will be of exactly the same waveshape as the load current. Both of these quantities are uni-directional, and so by defi nition, are d.c. quantities. The ‘ quality ’ of the d.c. so produced is very poor, since it exists only in pulses of current. The average value of this current is determined over the time period, 0 to t2 . The average value from 0 to time t1 will be 0.637 Im . From t1to t2 it will be zero. The average value of the d.c. will therefore be, Iav 0.318 Im .0input0ImIavt1t2t (s)t (s) Fig. 6.12 6.10 Full-wave Bridge Rectifi er Both the ‘ quality ’ and average value of the d.c. need to be improved. This may be achieved by utilising the other half cycle of the a.c. supply. The circuit consists of four diodes, connected in a ‘ bridge ’confi guration, as shown in Fig. 6.13 . We will again assume the instantaneous polarities for the fi rst half cycle as shown. In this case, diodes D 1 and D 4 will be forward biased. Diodes D 2 and D 3 will be reverse biased. Thus, D 1 and D 4 allow current to fl ow, as shown. In the next half cycle, the polarities are reversed. Hence, D 2 and D 3 will conduct, whilst D 1 and D 4 are reverse biased. Current will therefore fl ow as shown in Fig. 6.14 . Notice that