What’s a bridge rectifier?

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A bridge rectifier is an electronic component that produces a direct current (DC) output from an alternating current (AC) input. The components are commonly found in AC converters used to power DC appliances or battery chargers and work by removing the constant polarity reversal that characterizes AC power supplies. This is accomplished by channeling the incoming AC power through an array of diodes forcing a constant set positive/negative relationship in the output power. The diodes in a bridge rectifier can be loose, single units soldered onto a printed circuit board (PCB), or be integrated into a single compact component. Bridge rectifiers can produce DC outputs from single-phase or three-phase AC supplies with configurations consisting of four and six diodes, respectively.

Unlike DC power sources such as batteries which have set negative and positive points, AC power reverses or alternates its polarity, i.e. positive/negative orientation, approximately 50 to 60 times per second. This regular change in polarity gives an AC power supply its characteristic sine wave shape. In contrast, DC power supplies exhibit a flat, uniform waveform with an unchanging positive-to-negative relationship. A bridge rectifier is a method of attenuating unwanted polarity ripple from an AC power supply for use in DC power supplies. These devices use the unidirectional current-carrying characteristics of semiconductor diodes to force the AC input to maintain a constant positive/negative output orientation.

This rectifier device operates through diodes placed in pairs, each having an AC input point and sharing common positive and negative DC output points. When AC power is applied to the bridge, each pair alternately blocks or allows the current to flow. This accounts for the polarity shifts of the AC supply, but ensures that the positive and negative peaks of each AC cycle exit at the same point on the bridge. This produces a DC power output with a set polarity and a smooth waveform and minimal residual AC ripple. Any ripple remaining in the DC product can then be further flattened by placing smoothing components such as capacitors across the output.

Bridge grinding can come in many forms depending on the specific application. Heavy-duty bridge rectifier applications typically use single diodes mounted on heat sinks or soldered to PCBs. For applications requiring lower current ratings, bridge rectifiers are usually supplied as individual compact components with built-in diodes. These small square enclosures have four wires, two for AC input and two for positive and negative DC outputs. The location of the positive lead on pack rectifiers is often identified by an angle cut obliquely on the rectifier body.

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