RECTIFICATION 



then, rectification is the process of producing from alternating suppHes an 

 output which is direct, proportional to the input and which may or may not 

 be constant with time. If it is steady with time it is called smooth. 



Half-wave rectifier — Suppose a diode, load resistance and generator are 

 connected in series as shown in Figure 6.4. Before describing what happens 



B 







Esin cot 



T 



Generator 

 voltage 



Load_ 

 current 



A A 



Figure 6-4 



Time 



Figure 6.5 



we introduce a convention, universal in electronics, which greatly facilitates 

 discussion, the earth connection at O. It does not greatly matter whether O 

 is actually earthed or not but it estabhshes a datum potential for O and we 

 can then speak simply of the potential at A being positive, or negative, or 

 rising, i.e. becoming more positive, or falling, instead of saying the difference 

 of potential between A and O does so and so. 



We have then, due to the generator, the potential at A swinging up and 

 down sinusoidally between +£" and —E. When A is positive the diode 

 exhibits very low resistance and a current 



E sin (Dt 



R 



flows through the load. When A is negative the diode resistance is high and 

 negligible current flows. This is illustrated in Figure 6.5 and is simple half- 

 wave rectification. The load current is uni-directional but intermittent. 



Full-wave rectifier — A steadier output current is had by a rectifier bridge 

 in which four diodes are arranged as in Figure 6.6a. When A is positive 



Generator 

 voltage 



Load /yTY^ 



current 



Time 



(a) 



(b) 



Figure 6.6 



diodes 1 and 2 conduct ; 3 and 4 are in a high resistance condition or 'cut off"' ; 

 power is delivered to the load. When A is negative, the situation reverses as 

 regards the diodes but power is still delivered to the load {Figure 6.6b). This 



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