| Revision as of 21:08, 31 July 2005 edit212.74.96.201 (talk) added 'or positive'; tidied up 'smoothing' etc← Previous edit | Revision as of 21:23, 31 July 2005 edit undo212.74.96.201 (talk) removed unneccessary advertising( image of 3 ph rect and text)Next edit → | ||
| Line 1: | Line 1: | ||
| A rectifier is an ], comprising one or more ] arranged for converting ] (AC) to ] (DC). | A rectifier is an ], comprising one or more ] arranged for converting ] (AC) to ] (DC). | ||
| ] | ] | ||
| When just one diode is used to rectify AC (by blocking the negative or positive 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. | When just one diode is used to rectify AC (by blocking the negative or positive 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. | ||
| Line 7: | Line 7: | ||
| Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with just a single diode. | Almost all rectifiers comprise a number 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 voltage/current waveform. | Full wave rectifiers reverse the negative (or positive) portions of the alternating current waveform. The positive (negative) portions thus combine with the reversed negative (positive) portions to produce an entirely positive(negative) voltage/current waveform. | ||
| For single phase AC, if the AC is ]ped, 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 ], are needed. | For single phase AC, if the AC is ]ped, 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 ], 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 (] to ]). 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. | 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 (] to ]). 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. | ||
| ] | |||
| ==Smoothing== | ==Smoothing== | ||
| Line 19: | Line 17: | ||
| While half- and full-wave rectification suffices to deliver ''a form'' of DC output, neither produces steady DC. In order to produce 'steady' DC from a rectified AC supply, a '''smoothing''' circuit is required. In its simplest form this can be what is known as a ] or ] capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC ] voltage where the voltage is not completely smoothed. | While half- and full-wave rectification suffices to deliver ''a form'' of DC output, neither produces steady DC. In order to produce 'steady' DC from a rectified AC supply, a '''smoothing''' circuit is required. In its simplest form this can be what is known as a ] or ] capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC ] voltage where the voltage is not completely smoothed. | ||
| To further reduce this ripple, a ] can be used. This complements the reservoir capacitor with a ] and a second ], so that a steady DC output can be obtained across the terminals of the filter capacitor. The choke effectively presents a high impedance to the ripple current. | To further reduce this ripple, a ] can be used. This complements the reservoir capacitor with a ] and a second ], so that a steady DC output can be obtained across the terminals of the filter capacitor. The choke effectively presents a high ] to the ripple current. | ||
| ==Rectification efficiency== | ==Rectification efficiency== | ||
Revision as of 21:23, 31 July 2005
A rectifier is an electrical device, comprising one or more diodes arranged for converting alternating current (AC) to direct current (DC).
When just one diode is used to rectify AC (by blocking the negative or positive 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.
Almost all rectifiers comprise a number 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 (or positive) portions of the alternating current waveform. The positive (negative) portions thus combine with the reversed negative (positive) portions to produce an entirely positive(negative) voltage/current waveform.
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.
Smoothing
While half- and full-wave rectification suffices to deliver a form of DC output, neither produces steady DC. In order to produce 'steady' DC from a rectified AC supply, a smoothing circuit is required. In its simplest form this can be what is known as a reservoir capacitor or smoothing capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC ripple voltage where the voltage is not completely smoothed.
To further reduce this ripple, a capacitor-input filter can be used. This complements the reservoir capacitor with a choke and a second filter capacitor, so that a steady DC output can be obtained across the terminals of the filter capacitor. The choke effectively presents a high impedance to the ripple current.
Rectification efficiency
Rectification efficiency measures how efficiently a rectifier converts AC to DC. It is defined as the ratio of the DC output power to AC input power, where DC output power is a product of the average current and voltage.