Half-wave Rectifi er

Chapter 6.9 Half-wave Rectifi er

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

  • Alternating Quantities 209It is the electronic equivalent of a mechanical valve, for example the valve in a car tyre. This device allows air to be pumped into the tyre, but prevents the air from escaping. The circuit symbol for a diode is shown in Fig. 6.8 . The ‘ arrow head ’part of the symbol is known as the anode. This indicates the direction in which conventional current can fl ow through it. The ‘ plate ’ part of the symbol is the cathode, and indicates that conventional current is prevented from entering at this terminal. Thus, provided that the anode is more positive than the cathode, the diode will conduct. This is known as the forward bias condition. If the cathode is more positive than the anode, the diode is in its blocking mode, and does not conduct. This is known as reverse bias. Note: The potentials at anode and cathode do not have to be positive and negative. Provided that the anode is more positive than the cathode, the diode will conduct. So if the anode potential is (say) 10 V, and the cathode potential is 8 V, then the diode will conduct. Similarly, if these potentials are reversed, the diode will not conduct. 6.9 Half-wave Rectifi er This is the simplest form of rectifi er circuit. It consists of a single diode, placed between an a.c. supply and the load, for which d.c. is required. The arrangement is shown in Fig. 6.9 , where the resistor Rrepresents the load. Fig. 6.8 Let us assume that, in the fi rst half cycle of the applied voltage, the instantaneous polarities at the input terminals are as shown in Fig. 6.10 . Under this condition, the diode is forward biased. A half sinewave of current will therefore fl ow through the load resistor, in the direction shown. In the next half cycle of the input waveform, the instantaneous polarities will be reversed. The diode is therefore reverse biased, and no current will fl ow. This is illustrated in Fig. 6.11 . Routputinput Fig. 6.9 Routputinputl Fig. 6.10