What Are Rectifier Diodes and Their Types?
Generators and alternators are both common systems used to generate electrical current, but while a generator is able to produce direct current (DC) voltage, an alternator supplies alternating current (AC) voltage. Although AC voltage can be useful for a number of applications, it cannot be used for devices such as batteries that are commonly found in automobiles and aircraft alike. Despite this, alternators are a very common feature in such vehicles, providing the power necessary to charge batteries and power electrical systems. Since AC voltage cannot be used in these instances, devices known as rectifier diodes must be in place for the means of transforming AC voltage into DC voltage.
During standard operations, the rectifier will receive alternating current that is at an average of zero volts, and with this, the diode will have an output of direct current with a net value over zero volts. The diode is the most important element of the rectifier that allows for the process of rectification to be carried out. Diodes are a basic building block of countless electrical assemblies, and they are components capable of permitting the flow of current in a single direction with the use of an anode and cathode. As alternating current passes through the rectifier diode, it will allow for half of the signal to pass through while mitigating any reverse polarity that falls under the breakdown voltage value. Depending on the circuit and its components, either half- or full-wave rectification may be used.
Despite their differences, half- and full-wave rectifier diodes both perform the same task of receiving an AC input signal that has an average voltage of zero while having an output of a DC signal with non-zero average voltage values. With a half-wave rectifier diode, a single polarity of the input signal will be allowed to pass, and the reverse polarity is blocked. With this simple operation, the transmitted signal exhibits a single polarity with a value greater than zero volts. On the other hand, full-wave rectifier diodes generate a unidirectional DC current, and this is done by rectifying the positive and negative half-cycles of the AC input signal at the same time.
For the diode itself, either a PN junction or Schottky diode will be present. PN junction diodes are best for general-purpose use, and they feature two semiconductors that come in the form of an anode and cathode. With an applied forward bias voltage, current will flow in a single direction as electrons from the anode fill the holes in the cathode region. Meanwhile, Schottky diode components feature a junction that is present between a metal layer and semiconductor. The metal layer is the cathode, and it contains conduction-band electrons. The anode semiconductor element, meanwhile, is light doped so that when forward-biased, the higher-energy electrons in the semiconductor region flow into the metallic region. This method allows for high switching speeds as the Schottky diode flips between ON and OFF states.
For the rectifier itself, a bridge, center-tap, or single diode rectifier will be present. Bridge rectifiers are a type of full wave variation that features four diodes placed in a bridge configuration. With a center-tap rectifier, a center-tap transformer will be wired through two diodes. These rectifiers also utilize the full-wave of the AC input. The last type is the single diode, that of which can rectify AC input signals through the standard diode method. While this device performs the same role as other options, the single diode is not the most efficient as half of the input signal will be lost when rectification occurs.
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