Schottky diode maximum forward voltage. Schottky diode - characteristics and principle of operation. Positive qualities of a Schottky diode

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

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 An electric field formed by these charges will arise in the contact area, and the energy zones will bend.

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 of type 25CTQ045 (for voltages up to 45 volts, for currents up to 30 amperes for each of a pair of diodes in the assembly) can be found in many switching 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 we 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.

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 of 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:

It is necessary to initially remove the element of interest from the electrical circuit or diode bridge;
Conduct a visual inspection for possible mechanical damage, traces of chemical and other reactions;
Check the diode with a tester or multimeter;
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:

When holes occur, the Schottky element ceases to hold electric current, and accordingly turns from a semiconductor into a conductor;
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 Schottky diode is another type of typical semiconductor diode; its distinctive feature is its low voltage drop when connected directly. It received its name in honor of the German physicist and inventor Walter Schottky. These diodes use a metal-semiconductor junction as a potential barrier, rather than a p-n junction. The permissible reverse voltage of Schottky diodes is usually about 1200 volts, for example CSD05120 and its analogues; in practice, they are used in low-voltage circuits with reverse voltages of up to several tens of volts.

On circuit diagrams they are designated almost like a diode, see the figure above, but with slight graphical differences; in addition, dual Schottky diodes are quite common.

A dual Schottky diode is two separate elements assembled in one common housing and the terminals of the cathodes or anodes of these components are combined. Therefore, a dual diode, usually three terminals. In switching and computer power supplies you can often see dual Schottky diodes with a common cathode.

Since both diodes are placed in a single housing and assembled using the same technological process, their technical parameters are almost identical. With such placement in one case, during operation they will be in the same temperature regime, and this is one of the main factors in increasing the reliability of the device as a whole.

Advantages

The voltage drop across the diode when connected directly is only 0.2-0.4 volts, while on typical silicon diodes this parameter is 0.6-0.7 volts. Such a low voltage drop across a semiconductor, when connected directly, is characteristic only of Schottky diodes with a reverse voltage of a maximum of tens of volts, but if the applied voltage level increases, the voltage drop across the Schottky diode is already comparable to a silicon diode, which quite severely limits the use of Schottky diodes in modern electronics.
Theoretically, any Schottky diode can have a low barrier capacitance. The absence of an explicit classical p-n junction allows one to significantly increase the operating frequency of the device. This parameter has found wide application in the production of integrated circuits, where Schottky diodes bypass the transitions of transistors used as logic elements. In power electronics, another parameter of Schottky diodes is important, namely, the low recovery time makes it possible to use power rectifiers at frequencies of hundreds of kHz and higher. For example, the MBR4015 radio component (15 V and 40 A) is used to rectify RF voltage, and its recovery time is only 10 kV/μs.
Due to the above-mentioned positive properties, rectifiers built on Schottky diodes differ from rectifiers on standard diodes by a lower level of interference, so they are used in analog secondary power supplies.

Minuses

In the event of a short-term excess of the permissible reverse voltage level, the Schottky diode fails, unlike typical silicon diodes, which will simply go into a reversible breakdown mode, provided that the power dissipation of the crystal is not higher than the permissible values, and after reducing the voltage the diode completely restores its characteristics .
Schottky diodes are characterized by higher values of reverse currents, which increase with increasing crystal temperature and, in the case of unsatisfactory operating conditions of the heat sink when working with high currents, lead to thermal breakdown of the radio component.

Schottky diodes, as I noted above, are actively used in computer power supplies and switching voltage regulators. They are used in the low-voltage and high-current parts of the computer UPS circuit at + 3.3 volts and + 5.0 volts. The most commonly used are dual diodes with a common cathode. It is the use of dual diodes that is considered a sign of high quality.

A burnt-out Schottky diode is one of the most common faults with. A diode can have two non-working states: electrical breakdown and leakage to the body. In any of these conditions, the UPS is blocked due to the built-in protection circuit.

In the event of an electrical breakdown, all secondary voltages in the power supply are absent. In the event of a leak, the computer power supply fan may “twitch” and output voltage pulsations may appear at the output and periodically disappear. That is, the protection module periodically fires, but complete blocking does not occur. Schottky diodes are 100% burned out if the radiator on which they are attached is very warm or has a strong burnt smell from them.

It should be said a few words that when repairing a UPS after replacing diodes, especially with suspected leakage to the case, you should ring all power transistors operating in switching mode. And also in the case of replacing key transistors, checking the diodes is mandatory and strictly necessary.

The technique for testing a Schottky diode is the same as for a standard standard diode. But there are small differences here too. It is very difficult to test a diode of this type already soldered into the circuit. Therefore, the assembly or individual element must first be removed from the circuit for inspection. It is quite easy to determine a completely pierced element. At all resistance measurement limits, the multimeter will display an infinitely low resistance or short circuit in both directions.

It is more difficult to check with a suspected leak. If we check with a typical multimeter, for example DT-830 in “diode” mode, we will see a serviceable component. However, if you take a measurement in ohmmeter mode, then the reverse resistance at the “20 kOhm” limit is determined to be infinitely huge (1). If the element shows some resistance, for example 5 kOhm, then it is better to consider this diode suspicious and replace it with one that is definitely operational. Sometimes it is better to immediately replace the Schottky diodes on the +3.3V and +5.0V buses in a computer UPS.

They are sometimes used in alpha and beta radiation receivers (dosimeters), neutron radiation clamps, and in addition, solar panels are assembled at Schottky barrier transitions that supply electricity to spacecraft plowing the expanses of our vast universe.

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

During the assembly of power supplies and voltage converters for car amplifiers, a problem often arises with rectifying the current from the transformer. Getting hold of powerful pulsed diodes is quite a serious problem, so I decided to publish an article that provides a complete list and parameters of powerful Schottky diodes. Some time ago, I personally had a problem with the converter rectifier for a car amplifier. The converter is quite powerful (500-600 watts), the output voltage frequency is 60 kHz, any common diode that can be found in old trash will immediately burn out like a match. The only available option at that time was the domestic KD213A. The diodes are quite good, they hold up to 10 Amps, the operating frequency is within 100 kHz, but they also overheated terribly under load.

In fact, powerful diodes can be found in almost everyone. A computer power supply is one that powers an entire computer. As a rule, they are made with a power from 200 watts to 1 kW or more, and since the computer is powered by, this means that the power supply must have a rectifier. Modern power supplies use powerful Schottky diode assemblies to rectify the voltage - they have a minimal voltage drop across the transition and the ability to work in pulsed circuits, where the operating frequency is much higher than the network 50 Hz. Recently they brought several power supplies for free, from where the diodes were removed for this short review. In computer power supplies you can find a variety of diode assemblies; there are almost no single diodes here - in one case there are two powerful diodes, often (almost always) with a common cathode. Here are some of them:

D83-004 (ESAD83-004)- Powerful assembly of Schottky diodes, reverse voltage 40 Volts, permissible current 30A, in pulse mode up to 250A - perhaps one of the most powerful diodes that can be found in computer power supplies.

STPS3045CW- Dual Schottky diode, rectified current 15A, forward voltage 570mV, reverse leakage current 200uA, reverse voltage constant 45 Volts.

Basic Schottky diodes found in power supplies

Schottky TO-220 SBL2040CT 10A x 2 =20A 40V Vf=0.6V at 10A
Schottky TO-247 S30D40 15A x 2 =30A 40V Vf=0.55V at 15A
Ultrafast TO-220 SF1004G 5A x 2 =10A 200V Vf=0.97V at 5A
Ultrafast TO-220 F16C20C 8A x 2 =16A 200V Vf=1.3V at 8A
Ultrafast SR504 5A 40V Vf=0.57
Schottky TO-247 40CPQ060 20A x 2 =40A 60V Vf=0.49V at 20A
Schottky TO-247 STPS40L45C 20A x 2 =40A 45V Vf=0.49V
Ultrafast TO-247 SBL4040PT 20A x 2 =40A 45V Vf=0.58V at 20A
Schottky TO-220 63CTQ100 30A x 2 =60A 100 Vf=0.69V at 30A
Schottky TO-220 MBR2545CT 15A x 2 =30A 45V Vf=0.65V at 15A
Schottky TO-247 S60D40 30A x 2 =60A 40-60V Vf=0.65V at 30A
Schottky TO-247 30CPQ150 15A x 2 =30A 150V Vf=1V at 15A
Schottky TO-220 MBRP3045N 15A x 2 =30A 45V Vf=0.65V at 15A
Schottky TO-220 S20C60 10A x 2 =20A 30-60V Vf=0.55V at 10A
Schottky TO-247 SBL3040PT 15A x 2 =30A 30-40V Vf=0.55V at 15A
Schottky TO-247 SBL4040PT 20A x 2 =40A 30-40V Vf=0.58V at 20A
Ultrafast TO-220 U20C20C 10A x 2 =20A 50-200V Vf=0.97V at 10A

There are also modern domestic diode assemblies for high current. Here are their markings and internal diagram:

Also produced , which can be used, for example, in power supplies for tube amplifiers and other equipment with increased power supply. The list is given below:

High voltage Schottky power diodes with voltages up to 1200 V

Although it is more preferable to use Schottky diodes in low-voltage powerful rectifiers with output voltages of a couple of tens of volts at high switching frequencies.

Schottky diode is another type of typical semiconductor diode, its distinctive feature is its low voltage drop when directly connected. It received its name in honor of the German physicist and inventor Walter Schottky. These diodes use a metal-semiconductor junction as a potential barrier, rather than a p-n junction. The permissible reverse voltage of Schottky diodes is usually about 1200 volts, for example CSD05120 and its analogues; in practice, they are used in low-voltage circuits with reverse voltages of up to several tens of volts.

On circuit diagrams they are designated almost like a diode, see the figure above, but with slight graphical differences; in addition, dual Schottky diodes are quite common.

Advantages

Minuses

A burnt-out Schottky diode is one of the most common faults. A diode can have two non-working states: electrical breakdown and leakage to the body. In any of these conditions, the UPS is blocked due to the built-in protection circuit.

The development of electronics requires increasingly higher standards from radio components. To operate at high frequencies, a Schottky diode is used, which is superior in its parameters to silicon analogues. Sometimes you can come across the name Schottky barrier diode, which basically means the same thing.

Design
Miniaturization
Use in practice

Design

The Schottky diode differs from ordinary diodes in its design, which uses a metal-semiconductor rather than a p-n junction. It is clear that the properties here are different, which means the characteristics should also be different.

Indeed, a semiconductor metal has the following parameters:

Leakage current is of great importance;
Low voltage drop across the junction when connected directly;
Restores charge very quickly, as it has a low value.

The Schottky diode is made of materials such as gallium arsenide, silicon; much less commonly, but can also be used, is germanium. The choice of material depends on the properties that need to be obtained, however, in any case, the maximum reverse voltage for which these semiconductors can be manufactured is not higher than 1200 volts - these are the highest voltage rectifiers. In practice, they are much more often used at lower voltages - 3, 5, 10 volts.

In the circuit diagram, the Schottky diode is designated as follows:

But sometimes you can see this designation:

This means a dual element: two diodes in one housing with a common anode or cathode, so the element has three terminals. Power supplies use such designs with a common cathode; they are convenient to use in rectifier circuits. Often the diagrams show the markings of a regular diode, but the description indicates that this is a Schottky diode, so you need to be careful.

Diode assemblies with a Schottky barrier are available in three types:

Type 1 – with a common cathode;

Type 2 – with a common anode;

Type 3 – according to the doubling scheme.

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This connection helps to increase the reliability of the element: after all, being in the same housing, they have the same temperature regime, which is important if powerful rectifiers are needed, for example, 10 amperes.

But there are also disadvantages. The thing is that the low voltage drop (0.2–0.4 V) of such diodes appears at low voltages, usually 50–60 volts. At higher values they behave like regular diodes. But in terms of current, this circuit shows very good results, because it is often necessary - especially in power circuits and power modules - for the operating current of semiconductors to be at least 10A.

Another major disadvantage: for these devices, the reverse current cannot be exceeded even for an instant. They immediately fail, while silicon diodes, if their temperature has not been exceeded, restore their properties.

But there are still more positive things. In addition to the low voltage drop, the Schottky diode has a low junction capacitance value. As you know: lower capacity - higher frequency. Such a diode has found application in switching power supplies, rectifiers and other circuits with frequencies of several hundred kilohertz.

The current-voltage characteristic of such a diode has an asymmetrical appearance. When a forward voltage is applied, it is clear that the current increases exponentially, and when reverse voltage is applied, the current does not depend on the voltage.

All this can be explained if you know that the operating principle of this semiconductor is based on the movement of the main carriers - electrons. For the same reason, these devices are so fast: they do not have recombination processes characteristic of devices with p-n junctions. All devices with a barrier structure are characterized by asymmetry of the current-voltage characteristics, because it is the number of electric charge carriers that determines the dependence of current on voltage.

Miniaturization

With the development of microelectronics, special microcircuits and single-chip microprocessors began to be widely used. All this does not exclude the use of hanging elements. However, if radioelements of conventional sizes are used for this purpose, this will negate the whole idea of miniaturization as a whole. Therefore, open-frame elements were developed - SMD components, which are 10 or more times smaller than conventional parts. The current-voltage characteristics of such components are no different from the current-voltage characteristics of conventional devices, and their reduced dimensions make it possible to use such spare parts in various microassemblies.

SMD components come in several sizes. SMD size 1206 is suitable for manual soldering. They have a size of 3.2 by 1.6 mm, which allows you to solder them yourself. Other SMD elements are more miniature, assembled at the factory with special equipment, and it is impossible to solder them yourself at home.

The operating principle of an smd component is also no different from its large counterpart, and if, for example, we consider the current-voltage characteristic of a diode, then it will be equally suitable for semiconductors of any size. The current range is from 1 to 10 amperes. The markings on the case often consist of a digital code, the decoding of which is given in special tables. They can be tested for suitability using a tester, just like their larger counterparts.

Use in practice

Schottky rectifiers are used in switching power supplies, voltage stabilizers, switching rectifiers. The most demanding current - 10A or more - are voltages of 3.3 and 5 volts. It is in such secondary power circuits that Schottky devices are most often used. To amplify the current values, they are connected together in a circuit with a common anode or cathode. If each of the dual diodes is rated at 10 amperes, you will get a significant safety margin.

One of the most common malfunctions of switching power modules is the failure of these same diodes. As a rule, they either completely break through or leak. In both cases, the faulty diode must be replaced, then the power transistors must be checked with a multimeter, and the supply voltage must also be measured.

Testing and interchangeability

Schottky rectifiers can be tested in the same way as conventional semiconductors, since they have similar characteristics. You need to ring it in both directions with a multimeter - it should show itself in the same way as a regular diode: anode-cathode, and there should be no leaks. If it shows even a slight resistance - 2-10 kilo-ohms, this is already a reason for suspicion.

A diode with a common anode or cathode can be tested like two ordinary semiconductors connected together. For example, if the anode is common, then it will be one leg out of three. We place one tester probe on the anode, the other legs are different diodes, and another probe is placed on them.

Can it be replaced with another type? In some cases, Schottky diodes are replaced with ordinary germanium diodes. For example, D305 at a current of 10 amperes gave a drop of only 0.3 volts, and at currents of 2–3 amperes they can generally be installed without radiators. But the main purpose of the Schottky installation is not a small drop, but a low capacity, so replacement will not always be possible.

As we see, electronics does not stand still, and further applications of high-speed devices will only increase, making it possible to develop new, more complex systems.

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 a Schottky diode is that, unlike conventional diodes based on a pn junction, it uses a metal-semiconductor junction, which is also called a 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.

In 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 the same housing and made in a single technological process, 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 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 checking 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 malfunctions in system power supplies arise from problems in the secondary circuits operating in conjunction with the power supplies. If previously power transistor switches very often failed, now the main problem is the breakdown of secondary rectifiers, the basis of which is a Schottky diode. It uses the principle of transition from metal to semiconductor. Typically, most of these diodes are used in low voltage circuits.

Positive qualities of a Schottky diode

If in conventional diodes the forward voltage drop is approximately 0.6 to 0.7 volts, then the use of Schottky diodes can reduce this figure from 0.2 to 0.4 volts. In this case, the maximum reverse voltage can be up to several tens of volts. This indicator limits the use of Schottky diodes and assumes their use only in low-voltage circuits.

With a small electrical capacitance of the junction, it becomes possible to significantly increase the operating frequency. Thanks to this property, the diode has found quite wide application in integrated circuits. In power electrical devices, junctions with low capacitance have a short recovery period, which allows rectifiers to operate at high frequencies.

Improved characteristics compared to conventional rectifiers allow them to be effectively used for switching power supplies and digital equipment.

Flaws

In the event that the maximum reverse voltage exceeds the permissible level for a short time, the Schottky diode completely fails. This is an irreversible process, after which it becomes impossible to restore the original properties.

In addition, increased reverse currents are observed, which increase with increasing temperature of the crystal itself. In case of poor quality heat removal, the action of positive thermal feedback can lead to emergency overheating of the diode.

In power supplies, Schottky diodes are effectively used to rectify currents in channels. Given the high output current, there is a need for fast action of rectifiers in order to reduce their energy losses. This factor leads to a significant increase in the efficiency of power supplies. In addition, reliable operation of the power units installed in the first part of the power supplies is ensured.

Thus, Schottky diodes are used in cases where it is necessary to reduce switching dynamic losses, as well as to eliminate short circuits during switching. This device is an effective rectifying element.