Electricity in a home's power outlet is not in the form that's required by the circuitry inside electronic appliances. Power supplies are circuits made up of various components that convert the electricity that comes from the wall outlet into the various forms needed by the appliance. A bridge rectifier is a common part of those power supplies. It's a bridge-like setup involving four diodes that provides the same polarity of output voltage for either polarity of input voltage.
Converting AC To DC
Many electronic circuits require DC (direct current) rather than AC (alternating current), as well as different voltages than supplied through a home's electric outlet. The purpose of a power supply is to convert AC to DC, and to provide various voltages as needed by the appliance.
Diodes are semiconductor components that allow electrical current to pass through them only in one direction. If the polarity (the "plus" and "minus") is reversed, current is blocked.
Bridge Rectifier Configuration
When four diodes are placed in a certain configuration in an electric circuit and an alternating current is supplied to them, the resulting output is a direct current. This setup is known as a "bridge rectifier" because the alternating current is rectified or changed to direct current.
Bridge Rectifier Package
For applications where small amounts of power are required, complete bridge rectifiers are available in a single, compact package, similar to other integrated circuit chips. These components require much less space and reduce the number of components needed on a circuit board, because the four diodes are contained inside the package.
In the early days of electronics, before the advent of semiconductor technology, bridge rectifier circuits were created by using vacuum tubes. Some tubes were available that contained two diodes in one tube, enabling a bridge rectifier circuit to be constructed with just two vacuum tubes.