A power supply rectifier is an electronic component used to convert the alternating current (AC) output of a power supply to direct current (DC). This is achieved by passing the current through a series of diodes connected in such a way that they cut out or smooth AC ripple. This is made possible by the diodes' ability to block the flow of current through them in one direction but allow current flow in the opposite direction. A power supply rectifier may consist of individual diodes or be presented as a single, integrated package. The power supply rectifier is used in power supplies of all sizes and can range from tiny surface mount components to very large industrial varieties.
Most power supplies serve two basic purposes: voltage reduction and voltage conversion. To this end, the supply will feature a step-down section, typically consisting of a transformer, which reduces a mains AC supply to the desired output voltage. The output of this stage of the power supply is still AC, however, and because a power supply generally feeds DC appliances, has to be converted accordingly. This is the job of the power supply rectifier which is placed between the step-down transformer and the power supply output, thereby producing a smoothed DC output.
The ripple or waves in an AC power supply are caused by a regular and constant changing of polarity in the supply. Polarity refers to the relationship between the positive and negative points of the output. In an AC supply, this reverses between 50 and 60 times per second, thereby giving an AC supply its characteristic waveform. A DC power supply features a constant relationship between the positive and negative output points.
The smoothing function of the power supply rectifier is made possible by passing the AC current through a series of interconnected diodes. Also known as a bridge rectifier or rectifier bridge, this arrangement harnesses the diodes' ability to block the flow of current in one direction and pass it in the other to remove almost all the AC ripple. The layout of the diodes and their unique qualities force the fluctuating polarity of the AC power to exit the rectifier at the same positive and negative point on each cycle, thereby producing a smooth DC output. Power supply rectifiers are used in all power supplies which produce DC outputs and may appear as very small surface mount components or large, robust industrial variants.