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How Does a Rectifier Work?

2021-08-30 15:56   Үл хөдлөх зарна   Баян-Өлгий   5 views

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Rectifier, device that converts alternating electric current into direct current. It may be an electron tube (either a vacuum or a gaseous type), vibrator, solid-state device, or mechanical device. Direct current is necessary for the operation of many devices such as laptop computers, televisions, and certain power tools.


If only one polarity of an alternating current is used to produce a pulsating direct current, the process is called half-wave rectification. When both polarities are used, producing a continuous train of pulses, the process is called full-wave rectification.

You may wonder how power lines send electric currents across long distances for different purposes. And there are different "types" of electricity. The electricity that powers electric railway systems may not be appropriate for household appliances like phones and television sets. Rectifiers help by converting between these different types of electricity.


Bridge Rectifier and Rectifier Diode

AC DC rectifier lets you convert from alternating current (AC) to direct current (DC). AC is current that switches between flowing backwards and forwards at regular intervals while DC flows in a single direction. They generally rely on a bridge rectifier or a rectifier diode.

All rectifiers use P-N junctions, semiconductor devices that let electric current flow in only a single direction from the formation of p-type semiconductors with n-type semiconductors. The "p" side has an excess of holes (locations where there are no electrons) so it is positively charged. The "n" side is negatively charged with electrons in their outer shells.

Many circuits with this technology are built with a bridge rectifier. Bridge rectifiers convert AC to DC using its system of diodes made of a semiconductor material in either a half wave method that rectifiers one direction of the AC signal or a full wave method that rectifies both directions of the input AC.

Semiconductors are materials that let current flow because they're made of metals like gallium or metalloids like silicon that are contaminated with materials like phosphorous as a means of controlling current. You can use a bridge rectifier for different applications for a wide range of currents.

Bridge rectifiers also have the advantage of outputting more voltage and power than other rectifiers. Despite these benefits, bridge rectifiers suffer from having to use four diodes with the extra diodes compared to other rectifiers, causing a voltage drop that decreases the output voltage.


Silicon and Germanium Diodes

Scientists and engineers generally use silicon more frequently than germanium in creating diodes. Silicon p-n junctions work more effectively at higher temperatures than germanium ones. Silicon semiconductors let electric current flow more easily and can be created with lower costs.

These diodes take advantage of the p-n junction to convert AC to DC as a sort of electric "switch" that lets current flow in either the forward or reverse direction based on the p-n junction direction. Forward biased diodes let current continue to flow while reverse biased diodes block it. This is what causes silicon diodes to have a forward voltage of about 0.7 volts so that they only lets current flow if it's more than volts. For germanium diodes, the forward voltage is 0.3 volts.

The anode terminal of a battery, electrode or other voltage source where oxidization occurs in a circuit, supplies the the holes to the cathode of a diode in forming the p-n junction. In contrast, the cathode of a voltage source, where reduction occurs, provides the electrons that are sent to the anode of the diode.


Half Wave Rectifier Circuit

You can study how half wave rectifiers are connected in circuits to understand how they work. Half wave rectifiers switch between being forward biased and reverse biased based on the positive or negative half cycle of the input AC wave. It sends this signal to a load resistor such that the current flowing through the resistor is proportional to voltage.

You can measure the voltage across the load resistor as the supply voltage Vs, which is equal to the output DC voltage Vout. The resistance associated with this voltage also depends on the diode of the circuit itself. Then, the rectifier circuit switches to being reverse biased in which it takes the negative half cycle of the input AC signal. In this case, no current flows through the diode or the circuit and the output voltage drops to 0. The output current is, then, unidirectional.

Full wave rectifiers, in contrast, use the entire cycle (with positive and negative half cycles) of the input AC signal. The four diodes in a full wave rectifier circuit are arranged such that, when the AC signal input is positive, the current flows across the diode from D1 to the load resistance and back to the AC source through D2. When the AC signal is negative, the current takes the D3-load-D4 path instead. The load resistance also outputs the DC voltage from the full wave rectifier.

The average voltage value of a full wave rectifier is twice that of a half wave rectifier, and the root mean squared voltage, a method of measuring AC voltage, of a full wave rectifier is √2 times that of a half wave rectifier.

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