Rectifiers

A rectifier is an electrical device which consists of one or more semiconductors, such as diodes, for converting alternating current to continuous current. When a single 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 basically just one of usage. In this case the term rectifier refers to a diode which is being used to convert AC to DC. The term rectification refers to a process in which alternating current (AC) is converted into direct current (DC).

Most rectifiers consist of numerous diodes that are specifically arranged for more efficiently converting AC to DC than can be done with just one diode. Rectification is generally done by semiconductor diodes. They have a PN junction where P is the anode or positive region and N is the negative region or cathode. When current is passed, it flows in one direction from the positive to the negative region. Before solid-state rectifiers were invented vacuum tube diodes were used. Rectifier diodes are made of selenium, silicon and germanium.

The basic types of rectifiers are half wave rectifiers and full wave rectifiers. Rectifiers are available in the following configurations: Schottky, fast recovery, bridge and center tap.

Full-wave rectifiers convert both polarities of the input waveform to DC. Although they are more efficient it can take up to four times as many full wave rectifiers as half-wave rectifiers, depending on the configuration of the transformer. This is because each output polarity requires two rectifiers each. A full wave rectifier converts all of the input waveform to either a constant positive or negative polarity at the output by reversing the negative or positive sections of the alternating current waveform. The opposite sections then combine with the reversed sections to produce an entirely positive or negative current.

A half-wave rectifier lets the positive or negative half of the AC wave is pass easily while it blocks the other half so only one half of the input waveform reaches the output. Half wave rectification can be performed by a one diode in a one phase supply.

While selecting a rectifier you need to consider various factors such as: the average rectified current, which is the maximum allowed current that flows continuously in the forward direction; the leakage current, which is the current flow with reverse bias; forward voltage and voltage that flows in the diode terminals.

Rectifiers are sold in IC packages like: diode outline, transistor outline, small outline diode, small outline transistor, surface mount or through hole mount, etc.


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