The process of conversion of AC in to DC is called rectification.
The p-n junction is used as a full wave rectifier are as shown in the figure.
An AC in put is applied to primary of the transformer in first half cycle of AC, end A of secondary centre taping transformer is +ve & end B is -ve diode D1 is in forward bias & hence current flows but diode D2 is reverse bias & hence current does not flow in next half cycle of AC end A of secondary centre taping transformer is -ve & end B is +ve diode D1 is reverse bias & hence current does not flow but diode D2 is in forward bias & hence current flows this process will continue & hence out put DC signal is obtained across the load resistance.