A rectifier converts an AC signal into DC, and a bridge rectifier does this using a diode bridge. A diode bridge is a system of four or more diodes in a bridge circuit configuration, wherein two circuit branches are branched by a third. A bridge rectifier provides full-wave rectification.
Since current can only flow in one direction through a diode, current must travel different paths through the diode bridge depending on the polarity of the input. In either case, the polarity of the output remains the same. When there is an AC input, the current travels one path during the positive half cycle, and the other during the negative half cycle. This creates a pulsating DC output since the signal still varies in magnitude, but no longer in direction.
Current flow in a bridge rectifier during the positive half cycle.
Current flow in a bridge rectifier during the negative half cycle.
A bridge rectifier is a type of full wave rectifier. A full wave rectifier converts the input waveform to one of constant polarity, as opposed to a half-wave rectifier which only passes one half cycle while blocking the other. Another common method of full wave rectification uses two diodes and a center-tapped transformer. See App Note 6164: Build a Full-Wave Rectifier Circuit with a Single-Supply Op Amp for another method of full-wave rectification.
The bridge circuit configuration with four diodes allows for cost-effective full-wave rectification by utilizing two diodes during each half cycle. A half-wave rectifier can be constructed from a single diode, but is less efficient than a full-wave rectifier. A center-tapped rectifier provides full-wave rectification, but with the added cost and size of a center-tapped transformer.