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Explain the use of the junction diode as a half wave rectifier by drawing a circuit and draw input and output waves. |
Answer» Solution :The HALF wave rectifier is made of a transformer, a junction diode and a load resistance `R_(L)`.  The primary coil of transformer is connected to a.c. mains voltage. The secondary coil of transformer is connected in series with junction diode and load resistance `R_(L)`. This circuit is called half wave rectifier. The required AC voltage is obtained between ends A and B of the secondary of transformer. During the first positive half of a.c. voltage the end A is positive with respect to B as a result p-n junctiondiode will be in forward bias and current flows through load resistance`R_(L)` from direction X to Y. Now, during the second half cycle, A becomesnegative with respect to B as a result p-n junction diode will be in reverse bias and no current will flow in load resistance `R_(L)`. During the half cycle of incoming cycles, the current flow in `R_(L)` in the X to Y direction. The reverse saturated current for diode is zero so it is ignored. The reverse breakdown voltage of the diode must be sufficiently higher than the peak ac voltage at the secondary of the transformer to protect the diode from reverse breakdown. The a.c. voltage to the ends of `R_(L)` and the waveform of rectified voltage are shown in the figure below.  Figure shows the waveform of voltage parallel to `R_(L)` for input a.c. and output a.c. This type of input receivesvoltages in ONE direction only during half cycle of each full cycle of a.c. but no voltage is received during the second half cycle , hence it is called half wave rectifier. D.C. current flowing through `R_(L)` and as a result the voltage developed ACROSS `R_(L)` is ALSO a DC voltage and only one junction diode is used. |
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