What Is a Bridge Rectifier Used For?
Bridge rectifiers, developed about 100 years ago, are an essential part of powering our electronic appliances. They take household current and change it to a more useful form. Having that fundamental ability has given us stereos, computers, television and radio, as well as powerful commercial and industrial equipment.
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Direct Current
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The reason we have bridge rectifiers is the need for D.C., or direct current. Direct current runs most of our home electronics. While it can be supplied by batteries, they have limited lifespan and power. It's better in many instances to have a strong, continuous source of D.C. We can get power from the household electrical outlet, but that's A.C., or alternating current. Fortunately, there's a way to change A.C. into D.C., and that's by using a power supply with a bridge rectifier.
Circuitry
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In a power supply, the rectifier's situated between a transformer and a set of capacitors. The transformer drops the 110-volt household current down to a safe and useful level, usually between 3 and 24 volts, depending on the appliance. This lower voltage, still A.C., is changed to D.C. by the bridge rectifier. The D.C. coming out of the rectifier is noisy and imprecise. For some uses, like a battery charger, this rough D.C. is adequate. For others, like running a stereo, the noise needs to be removed. The power is filtered by the capacitors and held to a fixed level by a regulator.
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Benefits
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The bridge rectifier, necessary for a strong, reliable supply of D.C. power, was an essential part of the electronics revolution, from radio and television to stereos, cell phones, and computers. Though batteries filled this need to some extent, they also added size and weight to electronic gear. Reducing or eliminating the need for batteries made equipment smaller, lighter, and more reliable.
Considerations
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Current and voltage are prime concerns for choosing the kind of bridge rectifier to use. The smallest can be used to power cell phones and mp3 players. These are a few millimeters on a side with modest cooling requirements. Larger items like stereos need a bigger rectifier, possibly with a heat sink. Commercial and industrial systems like telecommunications equipment need even more power, calling for larger or multiple rectifiers with forced-air cooling.
History
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The bridge rectifier has been around in many forms since the early 20th century, with the introduction of radio, telephone, radar, and other electronic equipment. The basic operating principles remain the same, though the materials used to make them have changed. Many early rectifiers used copper oxide plates. More efficient ones used selenium, though those were more difficult to make. With the development of semiconductors in the 1950s and 60s, germanium and silicon diodes gradually replaced metal oxide and selenium rectifiers. Their small size and high efficiency led to a whole new generation of high-fidelity stereo and portable televisions. Vacuum-tube diodes were used in some instances, though these were also largely displaced by semiconductors after the 1960s. Today, modern semiconductor bridge rectifiers, along with rechargeable batteries, have improved the power level of small appliances while improving their portability.
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