Rectifier
Rectifier is a device which converts alternating current into unidirectional current. There are two types of rectifiers
Half Wave Rectifier
The secondary coil of transformer is connected across the p-n junction diode through a load resistance (RL). The input voltage is generated across secondary coil of the transformer where as output voltage is received across (RL) (V0 = IRL)
In the positive half cycle of input voltage, let P-type material is at higher potential than n-type i.e., the diode is in forward bias condition. In this case diode conducts current and generates output voltage, which is proportional to the current. So current, as will as the output Voltage, increases and then decreases along with the input voltage (Vi). In the negetive half cycle of (Vi), the diode is in reverse bias condition. So it doesn’t conduct current. So, in this part output voltage remains zero.
Thus the circuit remains operative only for half of cycle of input voltage, due to this it is called half wave rectifier.
Full Wave Rectifier :
In this circuit there is a centrally tapped transformer (A, B, C). C is the central terminal. In the positive half cycle of the input voltage let terminal A it at higher potential than terminal B.
The diode D1 is in forward bias where D2 is in reverse bias condition. D1 conduct current and the current increases and then decreases with increase & decreases of input voltage Vi. So the output voltage V0 also varies accordingly. In negetive half cycle of Vi let the terminal B is at higher potential than the terminal A. In this case D1 is in reverse bias & D2 is in forward bias. So D2 conducts current & this current flows through the load resistance RL in the same direction as it was flowing during the positive half cycle Vi . So for this current also the output voltage obtained, which is of same nature as it was earlier. So the circuit remains operative throughout the whole cycle of input voltage.
Half Wave & Full Wave Rectifiers
(In Hindi + English mix Language)
Note : The output of rectifier in unidirectional but it is not constant. This variation in current & output voltage is known as occurrence of ripple. It is due to the a.c. component that is remaining in the output of rectifier.
To eliminate the ripple factor from output of a rectifier, a circuit, called filter, is connected after the rectifier. The ripple factor can also be significantly eliminated if capacitor of high capacitance is connected in parallel to RL. The effect of capacitor is that when output voltage increases and attains the max. value, it gets charged. Now when the output voltage tends to decrease, the capacitor starts discharging through the resistance and thereby tries to maintain current and voltage constant.