What is a Rectifier Diode

Author: Release time:2022-12-06 Source: Font: Big Middle Small View count:366

What is a Rectifier Diode


A rectifier diode is a diode that rectifies voltage and converts alternating current into direct current. They are often used in rectification circuits and are mostly made of silicon semiconductors, which are capable of carrying high current values. They can also be made of germanium semiconductors, which have a lower allowable reverse voltage and a lower allowable junction temperature. In digital electronics, the use of rectifier diodes through Schottky barriers is of great value. The diodes can control currents from mA to several KA and voltages from a few V to several KV.

 

Feature of rectifier diode


The forward characteristic of the rectifier diode varies with the current magnitude and temperature. In the low current region, V F is lower at high temperatures, while the opposite is true in the high current region. In general, the diode should be used with sufficient temperature margin below the Q point, which is the intersection of the two conditions mentioned above.


feature of rectifier diode.jpg


The blue region where carrier mobility dominates: V F decreases with increasing temperature. The VF is lower than at low temperatures because the carriers tend to move when they become hot. Red region where carrier collisions dominate: V F increases with increasing temperature.

 

When high current flows, a large number of carriers move. At high temperatures, the probability of collisions between carriers increases and V F becomes higher than at low temperatures.

 

Example: 1n4006 rectifier diode 


  • Model: 1N4006

  • Type: rectifier diode

  • Reverse repetitive peak voltage (VRRM): 800 V

  • Maximum average rectifier current (IO): 1 A

  • Non-repetitive peak forward current (IFSM): 30 A

  • Forward voltage drop (VF): 1.1 V

  • [Continuous forward current (IF) = 1 A]

  • Reverse leakage current (IR): 5 μA

  • Ambient temperature (Ta) = 25 °C]

  • Junction capacitance (Cj): 15 pF

  • Reverse root mean square voltage (VR(RMS)): 560 V

  • Package: DO-41

 

Purpose of a Diode in a Rectifier Circuit

 

1.  Prevent backflow of current role

 

Rectifier diode is the most prominent role is its ability to prevent backflow of current. When the rectifier diode plus positive voltage, the positive voltage of the starting part of the positive voltage is very small, can not effectively overcome the blocking effect of the electric field in the PN junction. When the positive current of the rectifier diode is almost zero, this part is called the dead zone, and the positive voltage that cannot guide the diode is called the dead zone voltage. 


When the positive voltage of the rectifier diode is greater than the deadband voltage, the electric field within the PN junction is effectively overcome, and the positive current of the rectifier diode rises rapidly with the increase in voltage. In the normal current range, the rectifier diode terminal voltage remains almost constant.


2. Play a role in protecting the circuit from being connected to the wrong positive and negative terminals


Rectifier diode can also play a protective role, when the rectifier diode applied reverse voltage does not exceed a certain range, the current through the rectifier diode minority carrier drift movement thus forming the reverse current, can prevent the wrong positive and negative terminals.


3. The Role of reverse breakdown


The role of rectifier diodes in the reverse breakdown, reverse breakdown according to the principle of mechanism is divided into Zener breakdown and avalanche breakdown two cases. Rectifier diode in the case of high doping concentration, rectifier diode because the width of the potential barrier area is very small, the reverse voltage is larger will destroy the covalent bond structure within the potential barrier, so that the electrons from the covalent bond binding, the generation of electron holes, the role of rectifier diode in another breakdown for the avalanche breakdown. 


When the rectifier diode reverse voltage increases to a larger value, the applied electric field will make the electron drift speed up, so that the rectifier diode covalent bond in the valence electron phase collision, the valence electrons out of the covalent bond, resulting in a new electron-hole pair.

 

How Many Diodes are Used in a Bridge Rectifier  

 

The answer is: Four.


The reason for using four diodes in a bridge rectifier circuit is determined by the operating principle of bridge rectification.

 

Rectification is the process of changing alternating current into direct current by means of a unidirectional conducting device. The simplest rectifier circuit is to connect a semiconductor diode in series with the AC supply. When the AC is in the positive half-cycle, can reach the load through the diode. When it is in the negative half-cycle, there is no way to pass through the diode because the current is in the opposite direction, so it has to be abandoned. Since only half of the AC waveform is used, it is also called half-wave rectification. As you can see from the diagram, the output after half-wave rectification is interrupted 50 times per second, and the energy loss is about 50% because the waveform is cut in half. However, the situation is much better after filtering. However, the half-wave rectifier circuit is simple and low cost, so it is still widely used in many circuits.

 

A full-wave rectifier is a circuit that uses both the positive and negative halves of the alternating current. Full-wave rectification is divided into two forms, one is the form of two diodes with the center tap of the transformer; the other is the bridge rectification in question.

 

half-wave rectifier circuit and full-wave rectifier circuit.jpg

 

Let's look at the common point of these two circuits, it is obvious that D1D2 can turn the positive and negative half of the alternating current into the positive output of the direct current respectively.

 

And any circuit with current passing through is a complete circuit, otherwise it is equivalent to turning off the power switch and no current will pass through. The role of the center tap of the transformer on the left is to provide a path for the current to pass. In the full-wave bridge rectifier on the right, the transformer does not have a tap, so the D3D4 is added to solve the current path, so it can be seen that in order to allow the current to form a circuit, the transformer tap or add two diodes, one of the two options must be chosen.

 

In the rectifier parts are very expensive years, especially in the vacuum diode era, the cost and power consumption of two more tubes are huge, so most use the transformer tap to reduce costs and energy consumption. But now the situation is different, the price of the diode has fallen to the price of cabbage leaves, compared to the price of seven wrapped wire in turn soared all the way up. So now the full-wave rectifier is almost always used in the bridge rectifier with four diodes.

 

But the bridge rectifier also has a fatal disadvantage is a slightly larger voltage drop, because its positive and negative half-cycle are to pass two diodes, respectively, due to the existence of silicon rectifier diodes 0.7V voltage drop, so the whole bridge rectifier will cause a voltage drop of 1.4V. This is for the conduction voltage "catty" circuit, is not a negligible factor. For example, the AC voltage file of the multimeter is rarely used bridge rectifier, mainly in view of the low voltage characteristics of the instrument. Of course, when used as a power supply, this area of 1.4 V is completely negligible.

 


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