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component of an electric circuit used to change alternating current to direct current. Rectifiers are made in various forms, all operating on the principle that current passes through them freely in one direction but only slightly or not at all in the opposite direction. One early type of rectifier was the diode electron tubeelectron tube,
device consisting of a sealed enclosure in which electrons flow between electrodes separated either by a vacuum (in a vacuum tube) or by an ionized gas at low pressure (in a gas tube).
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. Semiconductorsemiconductor,
solid material whose electrical conductivity at room temperature is between that of a conductor and that of an insulator (see conduction; insulation). At high temperatures its conductivity approaches that of a metal, and at low temperatures it acts as an insulator.
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 rectifiers are essentially diodesdiode
, two-terminal electronic device that permits current flow predominantly in only one direction. Most diodes are semiconductor devices; diode electron tubes are now used only for a few specialized applications.
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 made large enough to safely dissipate the heat caused by current flow. For heavy currents, they are often equipped with cooling fins or heat sinks. Rectifiers are commonly used in power supplies for electronics. There are two kinds of mechanical rectifiers. One, for polyphase alternating current, is a rotating switch that is synchronized with the fluctuations of the alternating current. The other uses a synchronized vibrating reed to change single-phase alternating current into pulsating direct current. Both have been largely superseded by solid-state devices.


A nonlinear circuit component that allows more current to flow in one direction than the other; ideally, it allows current to flow in one direction unimpeded but allows no current to flow in the other direction.


A nonlinear circuit component that allows more current to flow in one direction than in the other. An ideal rectifier is one that allows current to flow in one (forward) direction unimpeded but allows no current to flow in the other (reverse) direction. Thus, ideal rectification might be thought of as a switching action, with the switch closed for current in one direction and open for current in the other direction. Rectifiers are used primarily for the conversion of alternating current (ac) to direct current (dc). See Electronic power supply

A variety of rectifier elements are in use. The vacuum-tube rectifier can efficiently provide moderate power. Its resistance to current flow in the reverse direction is essentially infinite because the tube does not conduct when its plate is negative with respect to its cathode. In the forward direction, its resistance is small and almost constant. Gas tubes, used primarily for higher power requirements, also have a high resistance in the reverse direction. The semiconductor rectifier has the advantage of not requiring a filament or heater supply. This type of rectifier has approximately constant forward and reverse resistances, with the forward resistance being much smaller. Mechanical rectifiers can also be used. The most common is the vibrator, but other devices are also used. See Semiconductor rectifier

If the average current is subtracted from the current flowing in the rectifier, an alternating current results. This ripple current flowing through a load produces a ripple voltage which is often undesirable. Filter and regulator circuits are used to reduce it to as low a value as is required.

A half-wave rectifier circuit is shown in Fig. 1. The rectifier, a diode, is practically ideal. The ac input is applied to the primary of the transformer; secondary voltage e supplies the rectifier and load resistor RL. The rectifying action of the diode is shown in Fig. 2, in which the current i of the rectifier is plotted against the voltage ed across the diode. The applied sinusoidal voltage from the transformer secondary is shown under the voltage axis; the resulting current i flowing through the diode is shown at the right to be half-sine loops.

A full-wave rectifier circuit uses two separate diodes. The resulting current wave shape is shown in Fig. 3. A more continuous flow of direct current is produced because the first diode conducts for the positive half-cycle and the second diode conducts for the negative half-cycle.

When high dc power is required by an electronic circuit, a polyphase rectifier circuit may be used. It is also desirable when expensive filters must be used. This is particularly true of power supplies for the final radio-frequency and audiofrequency stages of large radio and television transmitters.


An electrical circuit used to convert AC into DC current. A rectifier is a diode that causes the current to flow in only one direction. The output of the rectifier is essentially half-AC current, which is then filtered into DC. Contrast with inverter. See diode.

The Switching Power Supply
This is a hypothetical example of a switching power supply that turns 120v AC into 9v DC. The rectifier creates the DC current that becomes square waves for the pulse transformer. For more details on this type of power supply, see transformer.