Half Wave Rectification

In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output.Half wave rectification can be achieved with a single diode in a one phase supply, or with three diodes in a three-phase supply.

During the first half cycle of the waveform the diode is forward biased and current flows around the circuit formed by the diode, the transformer winding and the load.
During the second half cyclethe diode is reverse biased and no current flows.
The diode only conducts on every other half cycle. Hence, HALF-WAVE RECTIFICATION.
The rectified voltage is DC (it is always positive in value). However, it is not a steady DC but PULSATING DC. It needs to be smoothed before it becomes useful.