The simplest rectifier circuit is nothing more than a diode connected in series with the ac input. Since a diode passes current in only one direction, only half of the incoming ac wave will reach the rectifier output. Thus, this is a basic half-wave rectifier.
The orientation of the diode matters; as shown, it passes only the positive half-cycle of the ac input, so the output voltage contains a positive dc component. If the diode were to be reversed, the negative half-cycle would be passed instead, and the dc component of the output would have a negative polarity.
The output DC voltage of a half wave rectifier can be calculated with the following two ideal equations:
Vrms = Vpeak/2 Vdc = Vpeak/π
The output of above circuit has AC ripple that is not pure DC. To reduce the AC ripple we need to add some filter circuit, for example by adding a capcitor in output of this circuit.