Science Fair Project Encyclopedia
When just one diode is used to rectify AC (by omitting the negative portion of the waveform) the difference between the term diode and the term rectifier is merely one of usage, e.g. a rectifier depicts a diode that is being used to convert AC to DC.
However, almost all rectifiers comprise a plurality of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with just a single diode.
Full wave rectifiers reverse the negative portions of the alternating current waveform. The positive portions thus combine with the reversed negative portions to produce an entirely positive current.
For single phase AC, if the AC is center-tapped, then two diodes back-to-back (i.e. anodes-to-anode or cathode-to-cathode) form a full wave bridge rectifier. If there is no center tap, then four diodes, arranged in a bridge, are needed.
For three phase AC, six diodes are used. Typically there are three pairs of diodes, each pair, though, is not the same kind of double diode that would be used for a full wave single phase rectifier. Instead the pairs are in series (anode to cathode). Typically, commercially available double diodes have four terminals so the user can configure them as single phase split supply use, for half a bridge, or for three phase use.
Rectification efficiency measures how efficiently a rectifier converts a.c. to d.c. It is defined as the ratio of the d.c. output power to a.c. input power, where d.c. output power is a product of the average current and voltage.
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