Schottky diodes or more precisely - Schottky barrier diodes are semiconductor devices made on the basis of a metal-semiconductor contact, while conventional diodes use semiconductor p-n-transition.

The Schottky diode owes its name and appearance in electronics to the German physicist and inventor Walter Schottky, who in 1938, while studying the newly discovered barrier effect, confirmed the previously put forward theory, according to which although the emission of electrons from a metal is prevented by a potential barrier, but as the applied external electric field, this barrier will decrease. Walter Schottky discovered this effect, which was then called the Schottky effect, in honor of the scientist.

Examining the contact between a metal and a semiconductor, one can see that if near the surface of the semiconductor there is a region depleted of major charge carriers, then in the region of contact of this semiconductor with the metal on the side of the semiconductor, a region of space charge of ionized acceptors and donors is formed, and a blocking contact is realized - the same Schottky barrier . Under what conditions does this barrier arise? Thermionic emission current from the surface of a solid body is determined by the Richardson equation:

Let us create conditions when, when a semiconductor, for example n-type, comes into contact with a metal, the thermodynamic work function of electrons from the metal would be greater than the thermodynamic work function of electrons from the semiconductor. Under such conditions, in accordance with the Richardson equation, the thermionic emission current from the surface of the semiconductor will be greater than the thermionic emission current from the metal surface:

At the initial moment of time, upon contact of the named materials, the current from the semiconductor to the metal will exceed the reverse current (from the metal to the semiconductor), as a result of which space charges will begin to accumulate in the near-surface regions of both the semiconductor and the metal - positive in the semiconductor and negative in the semiconductor. metal In the contact area there will be electric field, formed by these charges, and the bending of energy bands will take place.

Under the influence of the field, the thermodynamic work function for the semiconductor will increase, and the increase will occur until the thermodynamic work functions and the corresponding thermionic emission currents in relation to the surface are equalized in the contact region.

The picture of the transition to an equilibrium state with the formation of a potential barrier for a p-type semiconductor and a metal is similar to the considered example with an n-type semiconductor and a metal. The role of external voltage is to regulate the height of the potential barrier and the electric field strength in the space charge region of the semiconductor.

The figure above shows band diagrams of various stages of the formation of the Schottky barrier. Under equilibrium conditions in the contact area, thermionic emission currents have leveled off, and as a result of the field effect, a potential barrier has arisen, the height of which is equal to the difference in the thermodynamic work functions: φк = ФМе - Фп/п.

Obviously, the current-voltage characteristic for the Schottky barrier turns out to be asymmetrical. In the forward direction, the current increases exponentially with increasing applied voltage. In the opposite direction, the current does not depend on the voltage. In both cases, the current is due to electrons as the majority charge carriers.

Schottky diodes are therefore fast-acting, because they eliminate diffuse and recombination processes that require additional time. The dependence of current on voltage is associated with a change in the number of carriers, since these carriers participate in the process of charge transfer. External voltage changes the number of electrons that can move from one side of the Schottky barrier to the other side.

Due to the manufacturing technology and based on the described principle of operation, Schottky diodes have a low voltage drop in the forward direction, significantly less than traditional p-n diodes.

Here, even a small initial current through the contact area leads to the release of heat, which then contributes to the appearance of additional current carriers. In this case, there is no injection of minority charge carriers.

Schottky diodes therefore have no diffuse capacitance, since there are no minority carriers, and as a result, the performance is quite high compared to semiconductor diodes. The result is something like a sharp asymmetrical p-n junction.

Thus, first of all, Schottky diodes are microwave diodes for various purposes: detector, mixing, avalanche-transit, parametric, pulsed, multiplying. Schottky diodes can be used as radiation receivers, strain gauges, nuclear radiation detectors, light modulators, and finally, high-frequency current rectifiers.

Schottky diode designation on diagrams

Schottky diodes today

Today, Schottky diodes are very widespread in electronic devices. In the diagrams they are depicted differently than conventional diodes. You can often find dual Schottky rectifier diodes, made in a three-terminal package typical of power switches. Such dual designs contain two Schottky diodes inside, connected by cathodes or anodes, more often by cathodes.

The diodes in the assembly have very similar parameters, since each such assembly is manufactured in a single technological cycle, and as a result, their operating temperature conditions are the same, and their reliability is correspondingly higher. A forward voltage drop of 0.2 - 0.4 volts along with high speed (several nanoseconds) are the undoubted advantages of Schottky diodes over their p-n counterparts.

The low voltage drop feature of the Schottky barrier in diodes manifests itself at applied voltages of up to 60 volts, although the performance remains unshakable. Today, Schottky diodes type 25CTQ045 (for voltage up to 45 volts, current up to 30 amperes for each of a pair of diodes in the assembly) can be found in many pulsed sources power supplies, where they serve as power rectifiers for currents with frequencies up to several hundred kilohertz.

It is impossible not to touch upon the topic of the shortcomings of Schottky diodes, of course they exist, and there are two of them. Firstly, a short-term excess of the critical voltage will instantly damage the diode. Secondly, temperature greatly affects the maximum reverse current. At a very high junction temperature, the diode will simply break even when operating at rated voltage.

Not a single radio amateur can do without Schottky diodes in his practice. Here you can note the most popular diodes: 1N5817, 1N5818, 1N5819, 1N5822, SK12, SK13, SK14. These diodes are available in both lead-out and SMD versions. The main thing for which radio amateurs value them so much is their high performance and low voltage drop across the junction - a maximum of 0.55 volts - at the low price of these components.

It is a rare printed circuit board that does not have Schottky diodes for one purpose or another. Somewhere the Schottky diode serves as a low-power rectifier for the feedback circuit, somewhere it serves as a voltage stabilizer at the level of 0.3 - 0.4 volts, and somewhere it is a detector.

In the table below you can see the parameters of the most common low-power Schottky diodes today.

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As current statistics on failures of modern system power supplies show, the largest number of faults occur in the secondary circuits of power supplies. Failures of power transistor switches (the most typical malfunction of power supplies of previous generations) are extremely rare today, which is an indicator of the successes that have been achieved over the past five years by manufacturers of power semiconductor electronics. One of the most problematic components of modern power supplies are secondary rectifiers based on Schottky diodes, which is due to the large output currents of the power supply. It was the high failure rate of Schottky diodes that became the basis for the appearance of this publication on the pages of our magazine.

The Schottky diode (named after the German physicist Walter Schottky) is a semiconductor diode with a low voltage drop when connected directly. Schottky diodes use a metal-semiconductor junction as a Schottky barrier (instead of a pn junction like conventional diodes). The permissible reverse voltage of industrially produced Schottky diodes is limited to 250 V (MBR40250 and analogues); in practice, most Schottky diodes are used in low-voltage circuits with a reverse voltage of the order of a few and several tens of volts.

Advantages of Schottky diodes

While conventional silicon diodes have a forward voltage drop of about 0.6 - 0.7 V, the use of Schottky diodes makes it possible to reduce this value to 0.2 - 0.4 V. Such a low forward voltage drop is characteristic only of Schottky diodes with a maximum reverse voltage of the order of tens of volts. At high reverse voltages, the forward drop becomes comparable to that of silicon diodes, which limits the use of Schottky diodes to low-voltage circuits. For example, for a 30Q150 Schottky power diode with the maximum possible reverse voltage (150 V) at a forward current of 15 A, the voltage drop is normalized at a level from 0.75 V (T = 125°C) to 1.07 V (T = −55°C).

The Schottky barrier also has a lower electrical capacitance of the junction, which makes it possible to significantly increase the operating frequency of the diode. This property is used in integrated circuits, where Schottky diodes shunt the transitions of logic element transistors. In power electronics, low junction capacitance (i.e., short recovery time) allows rectifiers to be built that operate at frequencies of hundreds of kHz and higher. For example, the MBR4015 diode (15 V, 40 A), optimized for high-frequency rectification, is rated to operate at dV/dt up to 1000 V/ms.

Due to better timing characteristics and small junction capacitances, rectifiers based on Schottky diodes differ from traditional diode rectifiers in their reduced noise level, which makes them most preferable for use in switching power supplies for analog and digital equipment.

Disadvantages of Schottky diodes

Firstly, if the maximum reverse voltage is briefly exceeded, the Schottky diode irreversibly fails, unlike silicon diodes, which go into reverse breakdown mode, and provided that the maximum power dissipated on the diode is not exceeded, after a voltage drop the diode completely restores its properties.

Secondly, Schottky diodes are characterized by increased (relative to conventional silicon diodes) reverse currents, which increase with increasing crystal temperature. For the above 30Q150, 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 TO-220 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.

The current-voltage characteristic of the Schottky barrier (Fig. 1) has a pronounced asymmetric appearance. In the forward bias region, the current increases exponentially with increasing applied voltage. In the reverse bias region, the current does not depend on the voltage. In both cases, with forward and reverse bias, the current in the Schottky barrier is due to the majority charge carriers - electrons.

For this reason, diodes based on the Schottky barrier are fast-acting devices, since they lack recombination and diffusion processes. Asymmetry current-voltage characteristics The Schottky barrier is typical of barrier structures. The dependence of current on voltage in such structures is due to a change in the number of carriers taking part in charge transfer processes. The role of external voltage is to change the number of electrons passing from one part of the barrier structure to another.

Schottky diodes in power supplies

In system power supplies, Schottky diodes are used to rectify the current of the +3.3V and +5V channels, and, as is known, the output currents of these channels amount to tens of amperes, which leads to the need to take very seriously the issues of rectifier performance and reducing their energy losses. Solving these issues can significantly increase the efficiency of power supplies and increase the reliability of the power transistors in the primary part of the power supply.

So, to reduce dynamic switching losses and eliminate short-circuit mode during switching, in the highest current channels (+3.3V and +5V), where these losses are most significant, Schottky diodes are used as rectifier elements. The use of Schottky diodes in these channels is due to the following considerations:

1) The Schottky diode is an almost inertia-free device with a very short recovery time of reverse resistance, which leads to a decrease in the reverse secondary current and to a decrease in the surge current through the collectors of the power transistors of the primary part at the moment the diode switches. This greatly reduces the load on power transistors, and, as a result, increases the reliability of the power supply.

2) The forward voltage drop across the Shockey diode is also very small, which at a current value of 15–30 A provides a significant gain in efficiency.

Since in modern power supplies the +12V voltage channel also becomes very powerful, the use of Schottky diodes in this channel would also give a significant energy effect, but their use in the +12V channel is impractical. This is due to the fact that when the reverse voltage exceeds 50V (and in the +12V channel the reverse voltage can reach 60V), Schottky diodes begin to switch poorly (too long and at the same time significant reverse leakage currents arise), which leads to the loss of all the advantages of their applications. Therefore, high-speed silicon pulse diodes are used in the +12V channel. Although the industry now produces Schottky diodes with high reverse voltage, their use in power supplies is considered inappropriate for various reasons, including economic ones. But there are exceptions to any rule, so in individual power supplies you can find Schottky diode assemblies in +12V channels.

In modern system power supplies for computers, Schottky diodes are, as a rule, diode assemblies of two diodes (diode half-bridges), which clearly increases the manufacturability and compactness of power supplies, and also improves the cooling conditions of the diodes. The use of individual diodes (Fig. 2), rather than diode assemblies, is now an indicator of a low-quality power supply.

Diode assemblies are produced mainly in three types of packages (Fig. 3):

TO-220 (less powerful assemblies with operating currents up to 20 A, sometimes up to 25-30 A);

TO-247 (more powerful assemblies with operating currents of 30 - 40 A);

TO-3P (powerful assemblies).

The electrical circuit and pinout of the Schottky diode assembly are shown in (Fig. 4).

The electrical characteristics of diode assemblies most commonly used in modern system power supplies are presented in table. 1.

The interchangeability of diode assemblies is determined based on their characteristics. Naturally, if it is impossible to use diode assembly with exactly the same characteristics, it is better to replace it with a device with higher current and voltage values. Otherwise, it will be impossible to guarantee stable operation of the power supply. There are cases when manufacturers use diode assemblies in their power supplies with a significant power reserve (although more often we observe the opposite situation), and during repairs it is possible to install a device with lower current or voltage values. However, with such a replacement, it is necessary to carefully analyze the characteristics of the power supply and its load, and all responsibility for the consequences of such modification, naturally, falls on the shoulders of the specialist performing the repair.

Manifestation of faults in Schottky diodes

As already noted, the failure of Schottky diodes is one of the main problems of modern power supplies. So what preliminary signs can be used to presumably determine their malfunction? There are several such signs.

Firstly, in the event of breakdowns and leaks of the secondary rectifier diodes, as a rule, the protection is triggered and the power supply does not start. This can manifest itself in different ways:

1) When the power supply is turned on, the fan “twitches”, that is, it makes several revolutions and stops; After this, the output voltages are completely absent, i.e. the power supply is blocked.

2) After turning on the power supply, the fan “twitches” constantly, voltage ripples can be observed at the outputs of the power supply, i.e. the protection is triggered periodically, but the power supply is not completely blocked.

3) A sign of a malfunction of Schottky diodes is extremely strong heating of the secondary radiator on which they are installed.

4) A sign of leakage of Schottky diodes may be the spontaneous shutdown of the power supply, and therefore the computer, when the load increases (for example, when running programs that ensure 100% processor load), as well as the inability to start the computer after an “upgrade”, although the power of the power supply is sufficient.

In addition, it is necessary to realize that in power supplies with poor and ill-conceived circuit design, leakage of rectifier diodes leads to overloads of the primary circuit and to current surges through the power transistors, which can cause their failure. Thus, a professional approach to repairing power supplies dictates a mandatory check of the secondary rectifier diodes each time the power transistors-switches of the primary part of the power supply are replaced.

Diagnostics of Schottky diodes

Checking and accurately diagnosing Schottky diodes, in practice, is quite a difficult task, since much here is determined by the type of used measuring instrument and experience of similar measurements, although determining the usual breakdown of one or two diodes of a Schottky diode assembly is not particularly difficult. To do this, you need to unsolder the diode assembly and check both diodes with a tester according to the diagram in Fig. 5. For such diagnostics, the tester must be set to diode testing mode. A faulty diode will show the same resistance in both directions (usually very small, i.e. it will show a short circuit), which indicates its unsuitability for further use. However, obvious breakdowns of diode assemblies are very, very rare in practice.

Rice. 5

Basically, you have to deal with leaks (and often thermal leaks) of Schottky diodes. But leaks cannot be detected this way. When tested with a tester in the “diode” mode, a “leaking” diode is in the vast majority of cases fully operational. Guaranteed diagnostic accuracy, in our opinion, can only be achieved by replacing the diode with a known-good similar device.

But still, you can try to identify a “suspicious” diode using a technique that involves measuring the resistance of its reverse junction. To do this, we will not use the diode testing mode, but a regular ohmmeter.

Attention! When using this technique, it should be remembered that different testers may give different readings, which is explained by differences in the testers themselves.

So, we set the measurement limit to a value and measure the reverse resistance of the diode (Fig. 6). As practice shows, serviceable diodes at this measurement limit should show infinitely high resistance.

If the measurement reveals some, usually small, resistance (2–10 kOhm), then such a diode can be considered “very suspicious” and it is better to replace it, or at least check it using the replacement method. If you check at the measurement limit, then even serviceable diodes can show very little resistance in the opposite direction (units and tens of kOhms), which is why it is recommended to use the limit. Naturally, at large measurement ranges (2 MΩ, 20 MΩ, etc.), even an absolutely serviceable diode turns out to be completely open, since its p-n junction is applied too high (for Schottky diodes) reverse voltage. At the limit, you can check using the comparative method, i.e., take a guaranteed-functional diode, measure its reverse resistance and compare it with the resistance of the diode being tested. Significant differences in these measurements will indicate the need to replace the diode assembly.

Sometimes there are situations when only one of the diodes in the assembly fails. In this case, the fault is also easily identified by comparing the reverse resistance of two diodes of the same assembly. Diodes of the same assembly must have the same resistance.

The proposed method can also be supplemented by testing for thermal stability. The essence of this check is as follows. At the moment in time when the resistance of the reverse junction is checked at the measurement limit (see the previous paragraph), it is necessary to touch the contacts of the diode assembly with a heated soldering iron, thereby warming up its crystal. A faulty diode assembly almost instantly begins to “float”, i.e. its reverse resistance begins to decrease very quickly, while a serviceable diode assembly maintains the reverse resistance at an infinitely large value for a long time. This check is very important, because during operation the diode assembly gets very hot (it’s not for nothing that it is placed on a radiator) and, due to heating, changes its characteristics. The considered technique provides a test of the stability of the characteristics of Schottky diodes to temperature fluctuations, because increasing the housing temperature to 100 or 125°C increases the value of the reverse leakage current by a hundred times (see data in Table 1).

This is how you can try to check a Schottky diode, but the proposed methods should not be abused, i.e. you should not carry out tests at too high a resistance measurement limit and heat the diode too much, because theoretically, all this can lead to damage to the diode.

In addition, due to the possibility of failure of Schottky diodes under the influence of temperature, it is necessary to strictly adhere to all recommended soldering conditions (temperature conditions and soldering time). Although we must pay tribute to diode manufacturers, since many of them have achieved that the installation of assemblies can be carried out at a high temperature of 250 ° C for 10 seconds.

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, p-n basis transition, a metal-semiconductor junction is used here, which is also called the Schottky barrier. This barrier, just like the semiconductor pn junction, 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. Switching power supplies usually use common cathode assemblies.

Since two diodes are placed in one housing and made in a single technological process, then their parameters are very close. Since they are placed in a single housing, their temperature conditions are 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 the 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 are quite small in size. 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 an unpleasant odor appears. 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 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 panels have been assembled on Schottky barrier junctions solar panels. So, they also supply electricity to spacecraft.

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

Name	Reverse Peak Voltage Limit	Limit rectifier current		Peak forward electric current	Limit reverse current	Limit forward voltage
Unit measurements	IN	A	OS	A	µA	IN
1N5817	20	1	90	25	1	0,45
1N5818	30	1	90	25	1	0,55
1N5819	40	1	90	25	1	0,6
1N5821	30	3	95	80	2	0,5
1N5822	40	3	95	80	2	0.525

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. The production technology of this electronic product is simple, which results in its low 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 malfunctions, 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 steps will be to establish the technical condition of the 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 ensure the uninterrupted operation of many devices and technical products.

Video

The semiconductor diode, which uses the barrier effect as the principle of its operation, bears the name of the German scientist who described it, Walter Schottky.

Important! The barrier effect is a serious influence of the total space charge on the development of a discharge in a gap with a sharply uneven field.

Additional Information. What is a diode - an electronic element with unequal ability to conduct electricity, depending on its direction.

Schottky diode: operating principle

The Schottky valve differs from the classic type in that the basis of its operation is a semiconductor-metal pair. This pair is often referred to as the Schottky barrier. This barrier, in addition to its ability to conduct electricity in one direction, similar to a pn junction, has several useful features.

Gallium arsenide and silicon are the main suppliers of material for the production of electronic elements in industrial settings. In more rare cases, precious chemical elements are used: platinum, palladium and the like.

Its graphical expression is electrical diagrams ah does not coincide with classical diodes. The markings of electronic components are similar. There are also double diodes in the form of an assembly.

Important! A double diode is a pair of diodes combined in a common volume.

Dual Schottky barrier diode

In double valves, the outputs of the cathodes or anodes are combined. It follows that such a product has three ends. Common cathode assemblies, for example, work where impulse blocks nutrition. Schottky diodes with a common anode are used much less frequently.

The diodes are located in a single housing and use the same production technology for their manufacture, so in terms of their set of parameters they are like twin brothers. Their operating temperature is also the same, because... are in a common space. This property significantly reduces the need to replace them due to loss of performance.

The most important distinguishing properties of the valves under consideration are a slight forward voltage drop (up to 0.4 V) at the moment of transition and a high response time.

However, the mentioned voltage drop has a narrow range of applied voltage - no more than 60 V. And this value itself is small, which sets a rather narrow range of applications for these diodes. If the voltage exceeds the specified value, the barrier effect disappears and the diode begins to operate in normal mode. rectifier diode. The reverse voltage for most of them does not go beyond 250 V, however, there are samples with a reverse voltage of 1.2 kV.

When designing electrical circuits, designers often do not highlight the Schottky diode graphically on circuit diagrams, but in the specifications for the order they indicate its use, specifying it in the type. Therefore, when ordering equipment, you need to pay close attention to this.

Among the inconveniences in working with valves with a Schottky barrier, it is necessary to note their extreme “tenderness” and intolerance to the slightest, even very short-term, excess of the reverse voltage rating. In this case, they simply fail and are no longer restored, which, in comparison with silicon diodes, is not to their benefit, because the latter have the property of self-healing, after which they can continue to work as usual without requiring replacement. We also must not forget that the reverse current in them critically depends on the degree of transition. If a significant reverse current appears, breakdown cannot be avoided.

An increased operating frequency due to low transient capacitance and a short recovery period due to high performance are positive properties that allow these diodes to be used, for example, by radio amateurs. They are also used at frequencies reaching several hundred kHz, for example, in pulsed rectifiers. A large number of produced diodes are used in microelectronics. The current level of development of science and industry allows the use of nanotechnology in the manufacturing process of valves with a Schottky barrier. The valves created in this way are used to shunt transistors. This solution significantly increases the response of the latter.

Schottky diodes in power supplies

IN computer units Schottky valves are often located in the power supply. Five-volt voltage provides a serious current of tens of amperes, which is a record for low-voltage power systems. Schottky valves are used for these power supplies. Basically, dual diodes with a single cathode are used. Not a single high-quality modern computer power supply unit can do without such an assembly.

Diagnosis.“Burnt” power supply electronic device most often means the need to replace a burnt-out Schottky assembly. There are only two reasons for the malfunction: increased leakage current and electrical breakdown. When the described conditions occur power supply stops feeding to the computer. The defense mechanisms worked. Let's look at how this happens.

There is no voltage at the computer input on a constant basis. The power supply is completely blocked by the protection built into the computer.

There is an “incomprehensible” situation: the cooling fan starts working, then again the characteristic noise disappears. This means that the voltage at the computer input (output of the power supply) appears and disappears. Those. The protection handles periodic errors, but is in no hurry to completely block the source. Do you have an unpleasant odor coming from a hot block? The diode block definitely needs replacing. Another method of home diagnostics: when the CPU load was heavy, the power supply turned off by itself. This is a sign of a leak.

After repairing the power supply associated with replacing dual Schottky diodes, it is necessary to “ring” the transistors. In the reverse procedure, diodes also require checking. This rule is especially relevant if the cause of the repair is a leak.

Checking Schottky diodes

A household multimeter does a good job of testing any type of Schottky barrier diode. The testing method is very similar to checking a regular diode. However, there are some secrets. An electronic component with a leak is especially difficult to check correctly. First, the diode assembly must be removed from the circuit. For this you will need a soldering iron. If the diode is broken, then a resistance close to zero in all possible operating modes will indicate its inoperability. In terms of physical processes, this resembles a closure.

A “leak” is more difficult to diagnose. The most common multimeter for the public is the dt-830; in most cases, measurements in the “diode” position will not detect a problem. When the regulator is moved to the “ohmmeter” position, the ohmic resistance will go to infinity. Also, the device should not indicate the presence of ohmic resistance. Otherwise, replacement is required.

Schottky diodes are common in electrical and radio electronics. The scope of their use is wide, including alpha radiation receivers and various spacecraft.

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