What is a Bridge Rectifier?

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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 13 May 2020
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A bridge rectifier is a 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 function by removing the constant polarity reversal which characterizes AC power supplies. This is achieved by channeling the incoming AC power through a series of diodes that forces a constant, set positive/negative relationship in the output power. The diodes in a bridge rectifier may be loose, individual units soldered onto a printed circuit board (PCB) or be integrated into a single, compact component. Bridge rectifiers may produce DC outputs from single or three-phase AC supplies with the 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 shift in polarity lends an AC power supply its characteristic sinusoidal wave form. In contrast, DC power supplies feature a flat, even waveform with an unchanging positive to negative relationship. A bridge rectifier is one method of smoothing the unwanted polarity ripple from an AC supply for use in DC power supplies. These devices make use of the one-way current conducting characteristics of semiconductor diodes to force the AC input to maintain a constant positive/negative output orientation.

This rectifier device functions by way of 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 current to pass through it. This accommodates the polarity shifts of the AC power but ensures that each AC cycle's positive and negative peaks exit at the same point on the bridge. This produces a DC power output with a set polarity and smooth waveform and minimal residual AC ripple. Any ripple remaining in the DC product may then be further flattened by inserting smoothing components such as capacitors across the output.

Bridge rectification may be presented in a number of guises depending on the specific application. Heavy duty bridge rectifier applications typically use individual diodes mounted on heat sinks or soldered onto PCBs. For applications requiring lower current values, bridge rectifiers are usually supplied as compact single components which feature inbuilt diodes. These small square packages have four leads, two for the AC input and two for the positive and negative DC outputs. The positive lead position on package rectifiers is often identified by a obliquely cut corner on the rectifier body.

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Post 2

I am trying to drive a couple of 12 V LED lights on 230 AC. Could I build or buy a rectifier and then drive 19 LEDs in series to get between 13 and 16 Volts on each? They are rated 10-30 Volts, so some spikes from the AC could be tolerated, but I have read elsewhere that there can be transients up to 1800 Volts on the grid, is that correct?

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