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| P-N Junction as Rectifier |
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| Rectifier is a device which is used for converting alternating current/voltage into direct current /voltage. |
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| The A-C to be rectified is connected to the primary P1P2 of a step down transformer. S1S2 are the secondary coil of the transformer, which are connected to diode and load resistance R as shown. The output is taken across the resistance R. During the positive half cycle on account of induction, S1 is +ve and S2 is -ve. It forward biases the junction diode and hence a current flows in direction shown. We therefore get output across load resistance. During the negative half cycle S1 is negative and S2 is positive. The pn junction is reverse biased. It offers high resistance and hence there is no flow of current due to majority charge carriers and thus there is no output across load. In the output only one half of the wave is present and the other half is missing. |
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| The amount of DC voltage across the output of half wave rectifier is given by |
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| It is also called as average voltage, it is less than Vm always since out put of half wave is not a pure DC it is pulsating DC. Therefore the component of ripple is calculated by ripple factors it is denoted by gamma. |
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| i.e., 1.21 percent of ripple is present at the out put when compared at input that means unwanted signal is still increased by 21 percent. Therefore half wave rectifier is poor rectifier. |
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| For full wave rectification, we use two PN junctions. During the positive half of the input A-C (fig), the upper PN junction diode i.e., D1 is forward biased and D2 is reverse biased. The current flows in circuit due to majority charge carriers of D1 in the direction shown. During the negative half cycle, the diode D1 is reverse biased and D2 is forward biased. The current flows in the circuit due to majority charge carriers of D2 in the direction shown. The output signal voltage is unidirectional and current flows through the load resistance R during both the halves. |
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