Diode vs Rectifier
A diode is a device used in electricity to allow a current to move in only one direction easily. There are several types of diodes available, with the most common type of diode being the semiconductor diode, which is present almost in any electrical circuit that you may look at. Whenever a current passes through a given diode, the diode is said to be forward biased, while a diode that does not allow the flow of electricity is said to be reverse biased. A rectifier, on the other hand, is also a diode whose main function is to rectify, as the name denotes, current.
Whenever a diode is functioning, several things are happening. Each and every time the diode is at work, there is a small amount of current that is lost. This current can be said to be negligible, but when a high current is passing through a diode, the value seems significantly larger. A rectifier diode is what is used when conversions from an AC to DC current is required. With regard to the mode of action, the rectifier diode is placed within one of the two AC lines before load is applied.
As earlier described, a diode will only allow current to flow in a single direction and not two as occurs with AC current, which effectively makes the AC current DC. It is the rectifier that is, in other words, referred to as the inverter, being able to convert AC current to DC. The DC current produced after the rectifier has been put in place comes in pulsations and is interrupted every half cycle by the rectifier diode that is in one of the lines of the AC load current.
Depending on how the diode is installed, it will determine on how easy the current flows. The diagrammatic representation of a diode can clearly state whether the diode is either forward biased or reverse biased. When the arrowhead points in the direction of the electron flow, the diode can be referred to as a forward biased diode. On the other hand, if the arrowhead points away from the flow of the electrons, the diode is a reverse biased diode and its main function is to impede the flow of electrons. A forward biased diode will ensure that most of the voltage passing through it goes to the preferred function with only minimal loss being seen.
The rectifier diode, on the other hand, when it converts AC to DC, can go a step further in ensuring that there is a good quality of DC current. The rectifier is therefore used in the purification of the current to ensure that the DC current produces is smooth and steady with no hiccups. Current flow is impeded in the reverse biased diode, as there is a very big depletion region as opposed to when the diode is forward biased, whereby the depletion region is very small.
Summary
A diode is a device that allows flow of current in one direction only.
A rectifier is a diode that is able to convert the current from AC to DC.
The rectifier is placed in one of the AC lines before the load.
The diode has a small leaked current whenever it is working.
The rectifier is used to purify the circuit.
A diode can be reverse biased or forward biased.
A forward biased diode is placed in the current’s direction and a reversed biased diode is placed against the flow of current.
The depletion region in a forward biased diode is small while the depletion region in a reverse biased diode is big.
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“Each and every time the diode is at work, there is a small amount of current that is lost.”
Actually when the diode if forward biased there is a small voltage drop across the diode (called a Forward voltage) not a current loss. The diode determines current flow direction but how much current flows. The lower voltage could mean less current flowing, however the current could actually increase because the load needs a steady amount of power (Voltage * Current) so the current must be increased to account for the lower voltage.
The average diode has from around 0.6 to 1.2 volts drop. This depend on the type of diode and the current levels. Low power diodes can have lower drops than 0.6 where high power diodes can exceed 1.2 volts. This voltage drop is important because the drop is dissipated as heat by the diode. (1.2 V * 10 A = 12 Watts of power). A reverse biased diode has a leakage that can be fairly high in high power diodes (10 mA or more is common). Smaller diode typically have very low leakage usually less than 1 mA.
Diode as classified into a few general types. Signal diodes operator with low current levels and typically have a low forward voltage, low leakage, and the switch very quickly. These diodes may be silicon or germanium. Power diodes typically handled high currents and higher voltages. They also generally will have higher leakage and forward voltage drops. Power diodes tend to also switch much slower but there are specialized power diode designed to work to high frequencies. Schottky diodes switch much faster, have lower forward voltages while handling high currents. They do have higher reverse leakage and the their reverse standoff voltages is limited to about 600V, for these reasons they are not used in a general purpose rectifier circuit. By they are heavily used in switch power supplies where higher frequencies are used.
A rectifier does not purify current. A rectifier is 1 or more diodes (or similar functioning devices) connected to produce a DC current from an AC current. With a single diode current is only flowing < 50% of the time. With two diode current is flowing twice as much as it flows from one diode or from the other, this does however require 2 phases of power. There is still two points per cycle when the AC voltage is at 0 that no current is flowing. Using three diodes and 3 phase power there is always a phase that is above 0 voltage thus producing the most continuous current.
These rectifier are often composed of separate diodes. But can be part of a common package. The most common type of rectifier is the bridge rectifier which used 4 diodes in a common package to produce the same power flow as using 2 diodes with 2 phase power but requires only a single power phase. If does have the disadvantage of doubling the forward voltage as current always has to flow through 2 diodes at a time.
Regardless of the diodes used, conversion of power from AC to DC typically needs one or more capacitors to smooth out the DC power for use by DC loads.
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