A half-wave rectifier converts an AC signal to DC by passing either the negative or positive half-cycle of the waveform and blocking the other. Half-wave rectifiers can be easily constructed using only one diode, but are less efficient than full-wave rectifiers.
Since diodes only carry current in one direction, they can serve as a simple half-wave rectifier. Only passing half of an AC current causes irregularities, so a capacitor is usually used to smooth out the rectified signal before it can be usable.
Half-wave rectifier circuit with capacitor filter and a single diode.
Alternating current (AC) periodically changes direction, and a rectifier converts this signal to a direct current (DC), which only flows in one direction. A half-wave rectifier does this by removing half of the signal. A full-wave rectifier converts the full input waveform to one of constant polarity by reversing the direction of current flow in one half-cycle. One example configuration for full-wave rectification is the full bridge rectifier, which uses four diodes to create a pulsating DC output.
A half-wave rectifier creates a purely positive signal by blocking the negative half-cycle, while a full-wave rectifier does this by changing the direction of the negative half-cycle.
Since only half of the input waveform is passed, the efficiency of a half-wave rectifier is lower than that of a full-wave rectifier. The maximum efficiency of a half-wave rectifier is about 40.5%, and the maximum efficiency of a full-wave rectifier is twice that.
Learn More: Half-Wave Rectifier Mini Tutorial