Diode as a Rectifier:
The main application of p-n junction diode is in rectification circuits. These circuits are used to describe the conversion of a.c signals to d.c in power supplies. Diode rectifier gives an alternating voltage which pulsates in accordance with time. The filter smoothes the pulsation in the voltage and to produce d.c voltage, a regulator is used which removes the ripples.
There are two primary methods of diode rectification:
- Half Wave Rectifier
- Full Wave Rectifier
Half Wave Rectifier:
In a half-wave rectifier, one half of each a.c input cycle is rectified. When the p-n junction diode is forward biased, it gives little resistance and when it is reversing biased it provides high resistance. During one-half cycles the diode is forward biased when the input voltage is applied and in the opposite half cycle, it is reverse biased. During alternate half cycles, the optimum result can be obtained.
The half wave rectifier has both positive and negative cycles. During positive half of the input, the current will flow from positive to negative which will generate only positive half cycle of the a.c supply. When a.c supply is applied to the transformer, the voltage will be decreasing at the secondary winding of the diode. All the variations in the a.c supply will reduce and we will get the pulsating d.c voltage to the load resistor.
In the second half cycle, current will flow from negative to positive and the diode will be reverse biased. Thus, at the output side, there will be no current generated and we cannot get power at the load resistance. A small amount of reverse current will flow during reverse bias due to minority carriers.
Full Wave Rectifier
Full wave rectifier utilizes both halves of each a.c input. When the p-n junction is forward biased, the diode offers low resistance and when it is reversing biased it gives high resistance. The circuit is designed in such a manner that in the first half cycle if the diode is forward biased then in the second half cycle it is reverse biased and so on.
Full wave rectifier is preferable than the half wave rectifier as the former increases efficiency in a shorter time and we get continuous output. However, a filter circuit is used to make it smoother.
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