Electrical engineering and radio electronics are replete with many concepts, one of which is the Schottky diode, used in numerous electrical circuits. Many people ask questions about what a Schottky diode is, how it is indicated on the diagrams, and also what is the operating principle of a Schottky diode.

General information and operating principle

A Schottky diode is a diode semiconductor product that, when connected directly to a circuit, produces a small voltage reduction. This element consists of metal and semiconductor. The diode is named after the famous German test physicist W. Schottky, who invented it in 1938 of the 20th century.

In industry, such a diode with a limited reverse voltage is used - up to 250 V, but in practice, for domestic purposes, to prevent the flow of current in the opposite direction, mainly low-voltage options are used - 3-10V.

Schottky diodes can be divided into 3 classes according to power characteristics:

• high-power;
• medium-power;
• low-power.

A Schottky barrier diode (a more precise name for the product) consists of a conductor with metal used for contact, a ring of protection and glass passivation.

At the moment when current flows through the electrical circuit, negative and positive charges collect in different parts of the body throughout the area of ​​the semiconductor barrier and on the protective ring, which leads to the emergence of an electric field and the release of thermal energy - this is a big plus of the diode for many physical experiments.

Diode assemblies of this type can be produced in several variations:

• Schottky diodes with a common anode;
• diode products having an output from a common cathode;
• diodes assembled according to a doubling circuit.

Technical characteristics of popular modifications of Schottky diodes

Differences from other semiconductors

Schottky diodes differ from other diode products in that they have a barrier in the form of a transition - a semiconductor-metal, characterized by one-way electrical conductivity. The metal in them can be silicon, gallium arsenide, and less commonly, compounds of germanium, tungsten, gold, platinum and others can be used.

The performance of this electronic component will depend entirely on the metal chosen. Silicon is most often found in such designs, as it is more reliable and has excellent performance at high powers. Compounds of gallium and arsenic and germanium can also be used. Production technology This electronic product is simple, which makes it low in cost.

Schottky's product is characterized by more stable operation when electric current is applied than other types of semiconductor diodes. This is achieved due to the fact that special crystalline formations are introduced into its body.

Advantages and disadvantages

The diodes described above have some advantages, which are as follows:

• the electric current is perfectly contained in the circuit;
• the small capacity of the Schottky barrier increases the service life of the product;
• low voltage drop;
• speed in an electrical circuit.

The most significant drawback of the component is the huge reverse current, which even if this indicator jumps by several units leads to failure of the diode.

Note! When operating a Schottky electric element in circuits with a powerful electric current under unfavorable heat exchange conditions, a thermal breakdown occurs.

Schottky diode: designation and marking

A Schottky diode on electrical circuits is designated almost exactly the same as conventional semiconductors, but with some features.

It is worth noting that dual versions of the Schottky diode may also be found in the diagrams. This design consists of two connected diodes in a common housing, having soldered cathodes or anodes, which leads to the formation of three terminals.

The markings of such elements are affixed to the side in the form of letters and symbols. Each manufacturer labels its products in its own way, but in compliance with certain international standards.

Important! If the alphanumeric designation on the diode body is not clear, then it is recommended to look at the explanation in the radio engineering reference book.

Application area

The use of diode structures with a Schottky barrier can be found in many devices and electrical structures. They are most often used on electrical circuits in the following techniques:

• electrical appliances for the home and computers;
• Power supplies various types and voltage stabilizers;
• television, - and radio equipment;
• transistors and batteries powered by solar energy;
• other electronics.

Such a wide range of applications is due to the fact that such an electrical element greatly increases the efficiency and performance of the final product, restores the reverse resistance of the electric current, preserves it in the electrical network, reduces the number of losses in the dynamics of electrical voltage, and also absorbs quite a lot of different types of radiation.

Diagnostics of Schottky diodes

It is not difficult to check the serviceability of the Schottky electric element, but it will take some time. To diagnose faults, you must do the following:

1. It is necessary to initially remove the element of interest from the electrical circuit or diode bridge;
2. Conduct a visual inspection for possible mechanical damage, traces of chemical and other reactions;
3. Check the diode with a tester or multimeter;
4. If the test is carried out with a multimeter, then after turning it on, it is necessary to bring the probes to the ends of the cathode and anode, as a result, the device will display the real voltage of the diode assembly.

Important! When carrying out testing with a multimeter, you should take into account the electric current, which is usually indicated on the side of the product.

The result of these simple actions will be the establishment technical condition semiconductor. The diode can become faulty for the following reasons:

1. When holes occur, the Schottky element ceases to hold electric current, and accordingly turns from a semiconductor into a conductor;
2. When a break occurs in the diode bridge or the diode element itself, the flow of electric current stops altogether.

It is worth noting that in such incidents, neither smoke nor a burning smell will be visible, therefore, all diodes will need to be checked, and it is best to contact specialized workshops.

The Schottky diode is a simple and unpretentious, but at the same time an extremely necessary element in modern electronics, since it is thanks to it that it is possible to provide uninterrupted operation many devices and technical products.

Video

To the large family of semiconductor diodes named after the names of the scientists who discovered the unusual effect, we can add one more. This is a Schottky diode.

German physicist Walter Schottka discovered and studied the so-called barrier effect that occurs with a certain technology for creating a metal-semiconductor transition.

The main feature of the Schottky diode is that, unlike conventional diodes based on p-n junction, a metal-semiconductor junction is used here, which is also called the Schottky barrier. This barrier, just like semiconductor p-n transition has the property of one-way electrical conductivity and a number of distinctive properties.

The materials used to make Schottky barrier diodes are predominantly silicon (Si) and gallium arsenide (GaAs), as well as metals such as gold, silver, platinum, palladium and tungsten.

On circuit diagrams A Schottky diode is depicted like this.

As you can see, its image is somewhat different from the designation of a conventional semiconductor diode.

In addition to this designation, in the diagrams you can also find an image of a dual Schottky diode (assembly).

A dual diode is two diodes mounted in one common housing. The terminals of their cathodes or anodes are combined. Therefore, such an assembly, as a rule, has three outputs. IN pulse blocks Assemblies with a common cathode are usually used for power supplies.

Since two diodes are placed in the same housing and made in a single technological process, their parameters are very close. Since they are located in a single building, then temperature regime theirs is the same. This increases the reliability and service life of the element.

Schottky diodes have two positive qualities: a very low forward voltage drop (0.2-0.4 volts) across the junction and very high performance.

Unfortunately, such a small voltage drop occurs when the applied voltage is no more than 50-60 volts. As it increases further, the Schottky diode behaves like a regular silicon rectifier diode. The maximum reverse voltage for Schottky usually does not exceed 250 volts, although samples rated at 1.2 kilovolts (VS-10ETS12-M3) can be found on sale.

So, dual Schottky diode (Schottky rectifier) 60CPQ150 designed for a maximum reverse voltage of 150V, and each of the diodes of the assembly is capable of passing 30 amperes in direct connection!

You can also find samples whose half-cycle rectified current can reach a maximum of 400A! An example is the VS-400CNQ045 model.

Very often, in circuit diagrams, the complex graphical representation of the cathode is simply omitted and the Schottky diode is depicted as a regular diode. And the type of element used is indicated in the specification.

The disadvantages of diodes with a Schottky barrier include the fact that even if the reverse voltage is briefly exceeded, they instantly fail and, most importantly, irreversibly. While silicon power valves, after the excess voltage stops, are perfectly self-healing and continue to work. In addition, the reverse current of diodes very much depends on the junction temperature. At a large reverse current, thermal breakdown occurs.

In addition to high speed and, therefore, short recovery time, the positive qualities of Schottky diodes include a small junction (barrier) capacitance, which allows you to increase the operating frequency. This allows them to be used in pulse rectifiers at frequencies of hundreds of kilohertz. A lot of Schottky diodes find their application in integrated microelectronics. Schottky diodes made using nanotechnology are included in integrated circuits, where they bypass transistor junctions to improve performance.

Schottky diodes of the 1N581x series (1N5817, 1N5818, 1N5819) have taken root in amateur radio practice. All of them are designed for maximum forward current ( I F(AV)) – 1 ampere and reverse voltage ( V RRM) from 20 to 40 volts. Voltage drop ( V F) at the junction is from 0.45 to 0.55 volts. As already mentioned, the forward voltage drop ( Forward voltage drop) for diodes with a Schottky barrier is very small.

Another fairly well-known element is 1N5822. It is designed for a forward current of 3 amperes and is housed in a DO-201AD housing.

Also on printed circuit boards you can find diodes of the SK12 - SK16 series for surface mounting. They have quite small sizes. Despite this, SK12-SK16 can withstand forward current up to 1 ampere at a reverse voltage of 20 - 60 volts. The forward voltage drop is 0.55 volts (for SK12, SK13, SK14) and 0.7 volts (for SK15, SK16). Also in practice you can find diodes of the SK32 - SK310 series, for example, SK36, which is designed for a direct current of 3 amperes.

Application of Schottky diodes in power supplies.

Schottky diodes are actively used in computer power supplies and switching voltage stabilizers. Among the low-voltage supply voltages, the highest current (tens of amperes) are +3.3 volts and +5.0 volts. It is in these secondary power supplies that Schottky barrier diodes are used. Most often, three-terminal assemblies with a common cathode are used. It is the use of assemblies that can be considered a sign of a high-quality and technologically advanced power supply.

Failure of Schottky diodes is one of the most common faults in switching power supplies. It can have two “dead” states: pure electrical breakdown and leakage. If one of these conditions is present, the computer's power supply is blocked as the protection is triggered. But this can happen in different ways.

In the first case, all secondary stresses are absent. The protection has blocked the power supply. In the second case, the fan “twitches” and voltage ripples periodically appear and then disappear at the output of the power supplies.

That is, the protection circuit is periodically triggered, but the power source is not completely blocked. Schottky diodes are guaranteed to fail if the radiator on which they are installed is very hot until unpleasant odor. And the last diagnostic option is related to a leak: when the load on the central processor increases in multiprogram mode, the power supply turns off spontaneously.

It should be borne in mind that when professionally repairing a power supply, after replacing secondary diodes, especially with a suspected leak, you should check all power transistors that perform the function of keys and vice versa: after replacing key transistors, checking secondary diodes is a mandatory procedure. It is always necessary to be guided by the principle: trouble does not come alone.

Checking Schottky diodes with a multimeter.

You can check the Schottky diode using a commercial multimeter. The technique is the same as when testing a conventional semiconductor diode with a p-n junction. But there are pitfalls here too. A leaky diode is especially difficult to test. First of all, the element must be removed from the circuit for a more accurate check. It is quite easy to determine a completely broken diode. At all limits of resistance measurement, the faulty element will have infinitesimal resistance, both in forward and reverse connection. This is equivalent to a short circuit.

It is more difficult to check a diode with a suspected “leakage”. If we check with a DT-830 multimeter in the “diode” mode, we will see a completely serviceable element. You can try measuring its reverse resistance using an ohmmeter. At the “20 kOhm” limit, the reverse resistance is defined as infinitely large. If the device shows at least some resistance, say 3 kOhm, then this diode should be considered suspicious and replaced with a known good one. A complete replacement of Schottky diodes on the +3.3V and +5.0V power buses can provide a 100% guarantee.

Where else are Schottky diodes used in electronics? They can be found in rather exotic devices, such as alpha and beta radiation receivers, neutron radiation detectors, and recently, solar panels have been assembled on Schottky barrier junctions. So, they also supply electricity to spacecraft.

Many great scientists have studied p-n properties transition. As you may have guessed, this is a regular diode that can be seen in any electronic circuit. At the time of its invention, it was an element that produced a real revolution and changed all ideas about the future of electronics. Also, the technology of its production did not go unnoticed. The Zenner and Gunn diode appeared. The Schottky diode was also invented

has interesting properties. Its use in electronics was not as sensational as its famous “brothers”. The special properties of this element were previously used in highly specialized circuits and did not find wide application. It is all the more interesting that recently the Schottky diode has begun to be used as the main element in switching power supplies. It works in almost all electronic household appliances: TVs, tape recorders, personal computers, laptops, etc.

The special properties of the device are manifested in the low voltage drop across р-n junction. It does not exceed 0.4 Volts. That is, in terms of this parameter it is as close as possible to the ideal element used in the calculations. True, at a voltage of more than 50 volts, these properties disappear. But nevertheless, the Schottky diode began to be widely used in circuits with power supply for such circuits did not exceed 15 Volts of direct voltage, which made it possible to take full advantage of the properties of this device. It could stand in the feedback circuit as a limiting element or participate in the operation of regulators.

In addition to such an important property as at the p-n junction, the Schottky diode has a small capacitance. This allows it to work in high-frequency circuits. The almost “ideal” properties of this element do not distort the high-frequency signal. That is why they began to install it in switching power supplies, communication devices and regulators.

But in addition to the positive qualities, it is necessary to note the disadvantages. Schottky diodes are very sensitive even to short-term excess of the reverse voltage from the permissible value. This leads to failure of the element. Unlike its silicon “brothers”, it is not restored. Thermal breakdown leads either to the appearance of leakage currents or to the “transformation” of the device into a conductor.

The first malfunction will lead to unstable operation of everything electronic device. It is quite difficult to find and eliminate. As for thermal breakdown, for example, this will trigger protection from After replacing the faulty element, the power supply will work normally.

Modern industry produces fairly powerful Schottky diodes. The pulse current in such devices can reach 1.2 kA. The constant operating current in some types reaches 120 A. Such devices have a wide current range and good performance characteristics. They are successfully used in household appliances and industrial electronics.

Or in various electrical circuit diagrams there is such a thing as a Schottky diode. First of all, this is a special semiconductor diode, which has a small voltage drop when connected directly and consists of a semiconductor and metal. It got its name in honor of the German inventor Walter Schottky, who invented this electronic element.

In contact with

The permissible reverse voltage in an electronic component for industrial purposes is limited to 250 volts. On practice mainly used in low voltage circuits to prevent current flow in reverse side. Based on their power, they are divided into several groups: low-power, medium-power and high-power.

The device itself consists of a metal - semiconductor, glass passivation, a protective ring and metal. When an electric current begins to flow through the circuit, then on the protective ring and throughout the entire area of ​​the semiconductor barrier will accumulate positive and negative charges, but in different parts case, in which there will be electric field and heat is released, which is a big plus for some experiments in physics.

Difference from other semiconductors

This electronic element differs from others in that it uses metal as a barrier - a semiconductor, which has one-way electrical conductivity and has many other distinctive properties. Such semiconductor metals can be gallium arsenide, gold, silicon carbide, tungsten, germanium, palladium, platinum, and so on.

The entire operation of the Schottky electronic element will depend on the selected metal. Silicon is especially often used because it is more reliable than others and works well at high power. Also more often than other metals use a semiconductor based on gallium arsenide (GaAs) - chemical compound arsenic and gallium, less often - based on germanium (Ge). The manufacturing technology of these electronic elements is very simple, which is why it is the cheapest.

Also, the Schottky diode differs from others in its stable operation when current is supplied. For stability, special crystals are introduced into the body of this electronic element, which is a very delicate job, because negligence or inattention can lead to malfunction of the device. People rarely do this; most often this work is performed by a special robot - an automatic machine programmed for such an operation.

Schottky diode designation and marking

Like all electronic parts and elements have designations, on circuit diagrams this electronic element is depicted like this (see Fig. 1), which is somewhat different from the designation of a conventional semiconductor.

In the diagrams you can also see an image of a dual Schottky diode (see Fig. 2). These are two mounted electronic elements in one common building. Their anodes or cathodes are soldered, so they have three terminals.

This electronic element, like most, is marked on the side. And if the letters and numbers on the designation are not clear, then you can look at their decoding in the radio engineering reference book.

Advantages and disadvantages

This device has its own positive sides and your shortcomings.

1. Holds electric current well in the circuit;
2. Small barrier capacity made of semiconductor metals, which increases the long-term performance of the diode;
3. Unlike other semiconductors, a Schottky diode exhibits a low voltage drop;
4. IN electrical circuit This Schottky diode is fast acting.

Big minus The problem is that the reverse current can be very large. In some cases, for example, exceeding the required reverse current level even for a few amperes, the electronic element simply breaks down or fails at the most inopportune moment, regardless of whether it is new or old. Diode leaks can also often be observed, which can in some cases lead to dire consequences if semiconductor testing is neglected.

Schottky diode application

These electronic elements , presented above, can be found in our world almost everywhere: in computers, stabilizers, household appliances, radio broadcasting, television, power supplies, solar powered, transistors and in many other devices from all walks of life.

In all cases, increases efficiency and performance, reduces the number of losses voltage dynamics, restores the reverse resistance of the current, absorbs the radiation of alpha, beta and gamma charges, allows you to work for quite a long time without breakdowns, keeps the current in the voltage of the electrical circuit.

Diagnostics of Schottky diodes

You can diagnose the Schottky electronic element if the need arises, but this will take a little time. First of all, you need to unsolder one element from the diode bridge or electronic circuit. Inspect visually and check with a tester. As a result of these simple technical operations, you will find out whether the semiconductor is working or not. Although it is not necessary to desolder the entire assembly, because this is extra work, and most importantly - s waste of time.

You can also check this diode or diode bridge with a multimeter, but keep in mind that the manufacturer writes the current on the side of the device. We turn on the multimeter and bring its probes to the ends of the anode and cathode, and it will show us the voltage of the diode.

Sometimes it happens that a Schottky diode may become faulty due to some reasons. Let's look at them:

Moreover, in both cases you will not feel the smell of burning and you will not see smoke, since the housing has built-in special protection against such incidents. If suddenly in one transistor the above diode burned out, then make sure that this is the only device where you found a fault, because diodes definitely need to be checked.

Although sometimes there may not be such an opportunity to check the diodes for serviceability when necessary. Sometimes it happens like this that the computer starts to slow down, takes a very long time to turn on, and freezes. Perhaps the problem is related specifically to the diodes, and anyone can disassemble the processor and see what happened inside.

First of all, you need to turn off the power to the computer and open the power supply in the system unit. You can immediately notice the diodes. Check if there are holes or breaks in them. If there are, then you need to get them out and replace them with a new semiconductor, fixing the problems yourself, but it is better to seek help from professionals.

Schottky semiconductors in the modern world

Schottky diodes have gained wide popularity and distribution in all areas of modern life, especially in electronics. They can be found as dual rectifier diodes, where two semiconductors are installed in one package and the ends of the anodes or cathodes are connected to each other, and simple ones can also be very small (for example, very often found in small electrical parts).

This semiconductor is very often used in switching power supplies in household appliances, which significantly reduces losses and improves thermal operation. Also data electronic elements used in transistors as current rectifiers, and in such special diodes that are used to combine parallel power supplies.

An element such as Schottky diode although it was invented quite a long time ago, it appeared in the everyday life of radio amateurs relatively recently and this was due to the fact that the Schottky diode has two very important and useful properties: firstly, very high speed and secondly, low forward voltage drop across the junction.
Previously, these two factors were not of particular importance, but in modern equipment operating at higher frequencies than before, Schottky diode simply irreplaceable.

let's consider Schottky diode device(it is also called Schottky barrier diode).

The most interesting thing about a Schottky diode is that it does not have a p-n junction (!). Instead, a metal-semiconductor transition was made (see picture)

Designations in the figure: 1- semiconductor substrate, 2- epitaxial film; 3 - metal-semiconductor contact; 4 - metal film; 5 - external contact.

When passing electric current Through such a transition, excess electrons will be distributed over the near-contact region of the metal terminal, creating a kind of barrier (it was called the Schottky barrier) and due to this, rectifying properties are formed. Moreover, the height of the barrier can also be changed, thereby changing the properties of the diode.

Schottky diode designation in the diagram

In the diagrams, the Schottky diode is designated like this:

How to test a Schottky diode

As mentioned above, the Schottky diode has a low voltage drop across the junction: While ordinary silicon diodes have a forward voltage drop of about 0.6-0.7V, germanium diodes have about 0.4V, and the Schottky diode has even less - about 0.2V. And since the multimeter, when checking, shows nothing more than a voltage drop across the junction, the readings will be small: if when checking conventional diodes, the multimeter readings will be about 300...400 for germanium and 450...650 for silicon diodes, then when checking Schottky diode, the multimeter will show 100...150.

Disadvantages of a Schottky diode

It seems that the Schottky diode is good for everyone: it works at HF ​​currents and has no reverse capacitance and the voltage drop across it is minimal, but still, with all its charms, the Schottky diode also has disadvantages:

If the maximum reverse voltage is briefly exceeded, the Schottky diode irreversibly fails (short circuit - short circuit), unlike conventional silicon p-n diodes that switch to reversible mode breakdown, and, provided that the maximum power dissipated on the diode is not exceeded after a voltage drop, the diode completely restores its properties.

Schottky diodes are characterized by increased (relative to conventional silicon pn diodes) reverse currents that increase with increasing crystal temperature. For 30CPQ150, the reverse current at maximum reverse voltage varies from 0.12 mA at +25 °C to 6.0 mA at +125 °C. For low-voltage diodes in TO220 packages, the reverse current can exceed hundreds of milliamps (MBR4015 - up to 600 mA at +125 °C). Under unsatisfactory heat dissipation conditions, positive heat feedback in the Schottky diode leads to its catastrophic overheating.

What does a Schottky diode look like? Yes, just like the most ordinary diode and it can only be identified by markings and circuit designation