The first diodes to be used were discovered back in the early s when the technology of wireless was in its infancy. The Cat's Whisker was one of the first types diode to be used. It consisted on a very thin piece of wire the cat's whisker itself that could be placed onto a piece of semiconductor type material typically a mineral crystal to make a point contact type of diode.
This was widely used up until the middle to late s when thermionic or valve technology became sufficiently cheap to be widely used for radios sets. Around the time of the Second World War, new diodes were needed for the radar sets being developed. Semiconductor diodes provided one option as their size meant they were able to operate better at the frequencies required for radar.
Like all electronic components, diodes have a circuit symbol that is used within electronic circuit diagrams. The basic circuit symbol for the diode consists of a triangle with its point touching a short line perpendicular to the wire on the circuit diagram.
Sometimes the triangle and even the line are just shown in outline, whilst at other times they are shown as filled black shapes. Sometimes the diode circuit symbol is shown only as an outline and without the filled in shapes.
The outline shape is equally acceptable,. There are many different types of diode and some use circuit symbols that are slightly modified from the basic diode symbol to indicate their function: Schottky diode, varactor diode and a number of others fall into this category. Traditionally many of these electronic components were contained in a small glass tube to encapsulate the actual semiconductor diode.
Now diodes are contained in a whole variety of different packages. There are still leaded packages and the glass encapsulated diodes still exist, but there are also many plastic packages as well.
These can vary in size according to the power dissipation required. With much PCB assembly these days using surface mount technology, there is a whole raft of diodes available as surface mount components, SMD diodes. There are many standard packages for SMD diodes including the SOT package which is used for many small discrete diodes. Only two of the three pins available are used and this enables the diode to be correctly orientated.
As these SMD diodes are small, there is not room for the full part number to be included on the diode and short-form number are used to enable them to be distinguished.
Whilst much PCB assembly uses surface mount technology, there are other areas of the electronics manufacturing industry that need diodes with much higher current capability.
These diodes can be contained within packages that bolt into heatsinks. There is a host of different types of diode that are manufactured and used in a variety of electronic circuit designs, RF designs and often digital designs as well.
Each type has different properties and this makes them suitable for the different circuits. Backward diode: This type of diode is sometimes also called the back diode. Although not widely used, it is a form of PN junction diode that is very similar to the tunnel diode in its operation.
It finds a few specialist applications where its particular properties can be used, typically at microwave frequencies. In reverse bias, it blocks until the reverse voltage reaches breakdown. After that, it allows the current flow with a constant voltage drop. Zener reverse breakdown is caused due to two reason i.
A Zener diode is mainly used in reverse bias configuration. It provides a stabilized voltage for protection of circuits from overvoltage. The backward diode or the back diode is a P-N junction diode, whose operation is similar to that of tunnel diode and Zener diode.
But the operating voltages are much lower. A backward diode is essentially a tunnel diode, whose one side of the junction has relatively less doping concentration compared to the other side. In the forward bias , it operates as a tunnel diode but its tunneling effect is much reduced as compared to tunnel diode. Otherwise, it operates as a normal P-N junction diode. In reverse bias , it operates as a Zener diode but the breakdown voltages are much lower.
It is not widely used but it can be used for rectification of a small voltage signal 0. Due to its fast switching speed, it can be used as a switch in RF mixer and multiplier. The Avalanche diode is a P-N junction diode that is specifically designed to operate in the avalanche breakdown region.
Avalanche breakdown is a phenomenon where sufficient reverse voltage is applied to the P-N junction. Avalanche diode works electrically similar to the Zener diode. However, the doping concentration of a Zener diode is relatively higher as compared to an avalanche diode. However, the avalanche diode has a wide junction because of light doping concentration. Thus, it requires a high voltage for its breakdown.
This wide junction makes it a better surge protector compare to a simple Zener diode. Transient voltage suppression diode or TVS diode is a type of avalanche diode that protects the circuit form high voltage surges. TVS diode has the capability of handling high voltages as compared to avalanche diode.
Unidirectional TVS diode operates similar to avalanche diode. Bidirectional TVS diode acts as two avalanche diodes opposing each other in series. It is manufactured as a single component. It operates both ways and provides surge protection when used in parallel with a circuit. In such type of diode, Gold or platinum is used as the dopant doping material.
It enables the diode to operate at fast switching speed but at the expense of increasing the forward voltage drop. Also, its reverse leakage current is higher than a normal P-N junction diode. It regulates the current flow through it up to a fixed level.
It limits the current just like Zener diode limits voltage. Step recovery diode or snap-off diode is a P-N junction diode which abruptly ceases the flow of current when its direction is reversed. Due to which, the charge carriers electron and holes near the junction also decrease in number. Hence, the charge storing capacity near the junction becomes negligible.
In a normal diode, when it is switched from forward conduction to reverse cutoff, the current flows briefly because of the stored charge. Due to which, the normal diode takes some time in switching. The SRD does not store charge, So it can cease the current flow instantaneously.
Peltier or thermal diode is a type of diode whose thermal resistance is different in one direction than the other direction. So the heat generated flows in one direction to one side terminal and leaving the other side cooler. This diode is used in the application of heat monitoring in microprocessor and in refrigerators for cooling effect. It is the simplest form of a diode made from a vacuum tube and two electrodes cathode and anode. The Anode and Cathode are enclosed inside the vacuum tube empty glass.
When the cathode heats up it emits electrons, the anode picks up the electrons and the flow continues. Schottky - Used for precision and when voltage needs to be conserved.
Look for pins. These will be chips in the form of a SMD surface mounted device. To identify these you will need to look at the number. Method 2. Go to alldatasheet. Determine the type from the results and even get the datasheet while doing it. Include your email address to get a message when this question is answered. If you cannot see number, it's best to throw it away and get a new one. Most diodes are cheap. Helpful 0 Not Helpful 0.
Helpful 1 Not Helpful 0. If your diode is not listed on all datasheets, recheck the number to make sure you put in the correct one. Use a search engine to find other datasheet sites.
Helpful 0 Not Helpful 1. In addition, it is even more crucial to be aware of the V-I characteristics of the PN junction diode. This signifies that the potential barrier restricts the current flow. Whereas when the diode operates in forwarding bias conditions, there will be a thinner potential barrier. In silicone type of diodes, when the voltage value is 0. In this, there will be a gradual increase in the current value and the resultant curve is non-linear where because the applied voltage level surmounts the potential barrier.
When the diode surmounts this potential barrier, the diode functions in normal condition, and the shape of the curve gradually gets sharp gets to linear shape with the rise of the voltage value. Where when the diode operates in reverse bias condition, there will be an increased potential barrier. As there will be the presence of minority charge carriers in the junction, this allows for the flow of reverse saturation current. When there is an increased level of applied voltage, the minority charge carriers possess risen kinetic energy that shows an impact on the majority charge carriers.
At this stage, the diode breakdown happens and this might lead to the diode getting damaged. The Schottky diode has a lower forward voltage drop than ordinary Si PN-junction diodes.
At low currents, the voltage drop may be between 0. To attain this performance they are designed in a different way to compare with normal diodes having a metal to semiconductor contact.
These diodes are extensively used in rectifier applications, clamping diodes, and also in RF applications. A step recovery diode is a type of microwave diode used to generate pulses at very HF high frequencies.
These diodes depend on the diode which has a very fast turn-off characteristic for their operation. The tunnel diode is used for microwave applications where its performance surpassed that of other devices of the day. In the electrical domain, tunneling signifies that it is the direct movement of electrons through the minimal width of the depletion region from the conduction band to the valency band. In the PN junction diode, the depletion region is developed because of both electrons and holes.
Because of these positive and negative charge carriers, the internal electrical field is developed in the depletion region. This creates a force in the opposite path of an external voltage. With the tunneling effect, when there is minimal forward voltage value, then the forward current value will be more. It can be functioned both in forward and reverse biased conditions. Because of the high level of doping , it can function in reverse biasing also. With the decrement of barrier potential, the breakdown voltage in reverse direction also gets decreased and reaches nearly to zero.
With this minimal reverse voltage, the diode may reach to breakdown condition. Because of this negative resistance region is formed. A varactor diode is one sort of semiconductor microwave solid-state device and it is used in where the variable capacitance is chosen which can be accomplished by controlling voltage.
These diodes are also called as variceal diodes. But, this diode is chosen for giving the preferred capacitance changes as they are different types of diodes.
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