The process of converting alternating voltage/current into direct voltage/current is called rectification.
Diode is used as a rectifier for converting alternating current into direct current.
From I-V characteristics of the junction diode, we see that it allow current to pass only when it is forward biased. So if alternating voltage is applied across a diode, the current flows only in that part of the cycle, when the diode is in forward biased. This property is used to rectify the voltage/current.
There are two ways of using a diode as a rectifier.
1. Diode As A Half-Wave Rectifier
The half wave rectifier consists of a transformer, a junction diode D and a load R.
If the AC voltage to be rectified is connected to the primary coil of a step down transformer. Secondary coil is connected to the diode through register R across which output is obtained.
During positive half cycle of the input AC, the PN junction is in forward biased. Thus the resistance in PN junction is very low and current flows. Hence we get output in the load.
During negative half cycle of the input AC the PN junction in the reversed biased. Thus the resistance of PN junction is high and current does not flow. Hence, no output is in the load.
2. Diode As A Full-Wave Rectifier
In the full wave rectifier, two PN junction diode D₁ and D₂ are used.
During the positive half cycle of the input AC, the Diode D₁ is in forward biased and the diode D₂ is in reverse biased. The forward current flows through D₁.
During the negative half cycle of the input AC, the diode D₁ is in reverse biased and diode D₂ is in forward biased. Thus the current flows through D₂. So we find that during both of halves, current flows in the same direction.