What is a diode? In order to answer this question, we need to dig deep, to the very beginning, namely, where the semiconductor begins.

Introduction from theory

Conductor

Let's try to imagine a piece of conductor material, for example, copper. How it is characterized: it contains free charge carriers - electrons. Moreover, there are a lot of such negative particles in it.

If a plus is applied to this area, then all these negative elements will rush towards it, that is, current will flow through the copper. This is a well-known fact, which is why copper is used as conductive materials. Conductors also include elements of the periodic table such as aluminum, iron, gold and many others.

Dielectric

A dielectric is a material that does not have free charge carriers and, therefore, does not conduct current.

Semiconductor

A semiconductor is both a metal and a non-metal. A material that both conducts current and does not. There are few free charge carriers in it. Typical semiconductors are silicon and germanium.

What is a diode

Silicon is a tetravalent element. To turn it into a conductor, pentavalent arsenic is added to it. As a result of this connection, extra electrons appear, that is, free charge carriers. And if you add trivalent indium to silicon, positrons, particles lacking an electron, will appear in the material. The diode consists of such areas.

The resulting structure is called a PN element or PN junction. P is the positive part, N is the negative part. One part of the material is enriched with positive positrons, the other - with negative electrons.

How does a diode work?

You may not physically see the diodes themselves, but the result of their action surrounds us everywhere. These devices allow you to control the flow of current in a specified direction. There are many different versions of diodes. In what cases is this necessary? Below we will discuss examples and, to some extent, the operating principle of semiconductor diodes.

If you add two metal plates to the P and N working areas of the material, you get anode and cathode electrodes. The connection diagram of the electrodes to the source can work as follows:

• supplying voltage from the battery to the N electrode ensures the attraction of positrons, respectively, to the P electrode – electrons;
• the absence of tension returns everything to its original state;
• changing the polarity of the applied voltage ensures the attraction of electrons in the opposite direction to the positive plate, and positrons to the negative one.

In the latter case, excess charges accumulate on the metal plates, while a dead insulating zone is formed in the center of the material itself. Thus, the central section of the material becomes a dielectric. The device does not pass current in this direction.

For information. The word comes from di (double) + -ode. The definition of the terms cathode and anode of a diode related to contacts is known to every person. The cathode is the negative electrode, the anode is the positive electrode. If you apply plus to the anode and minus to the cathode, the diode will open and electric current will flow through it.

Thus, a diode is a device that has two electrodes: a cathode and an anode. A simple nonlinear electronic device consisting of two different semiconductors. How the diode works is clearly visible in the image.

Diodes are semiconductors consisting of P and N regions. Due to the properties of a PN junction, a diode conducts current in only one direction. This is the principle of operation of these devices. What are they for?

Purpose of diodes

Diodes come in various designs: from bulky Soviet ones to miniature modern ones. The device may have the same power, but due to the release time, differ in size. High current diodes require cooling, so they are manufactured with mounting under a radiator. Accordingly, devices without a radiator are designed for low current.

Application of diodes

Diode devices can be designed to limit or stop the flow of current. An extremely common application is its use as a straightener.

Rectifiers

Since a diode only allows current to flow in one direction, alternating current only passes the positive or negative portion of the sine wave voltage through the diode. This means that it is possible to efficiently convert alternating current to direct current using diodes arranged in a full-wave rectifier.

For example, there is an alternating current source. At the output of it, a diode is placed in the circuit through which the load is connected. What will happen? If the source produces a sinusoid, then only a positive half-wave will pass through the diode output. And so on until the next half-wave. But if you turn the diode on the other side, the output will be a negative half-wave, that is, the device passes current only in one direction.

If you replace the diode with a bridge consisting of four diodes, then the output will be a signal in the form of half-waves, reminiscent of a camel's hump. The half-waves will all be deployed in the same direction. When installing an additional capacitor after the diodes, you will get the same half-waves, only smoothed.

Varicaps

The graphical icon of a varicap is very reminiscent of a conventional image of a semiconductor diode. A varicap is an ordinary diode. The operation of the device is based on the dependence of the barrier capacitance of the p-n junction on the reverse voltage. If a small voltage is applied, the capacitance becomes large; if a high voltage is applied, the capacitance becomes small. In reality, varicaps change their capacity several times (up to 7 times).

Zener diodes

A zener diode is a semiconductor diode that operates under reverse bias in breakdown mode. Choose a zener diode with a large supply of power dissipation, because it constantly operates in breakdown mode. The main purpose of zener diodes is voltage stabilization.

The main purpose of a voltage regulator is to maintain a constant voltage across the load, regardless of changes in input voltage and load current. Under varying load current conditions, a zener diode can be used to obtain a stabilized output voltage. This is the main reason for using a zener diode as a voltage stabilizer.

Schottky diodes

A Schottky diode is a low-voltage device that uses a metal and an electron-rich semiconductor as electrodes. The voltage of such a diode is approximately 0.2-0.4 V, compared to a conventional diode, this value is half as much.

The application area of ​​the Schottky diode is limited, since it cannot operate without a zener diode. Schottky diodes are mainly used in devices operating in low-voltage circuits with a reverse voltage of the order of a few and several tens of volts.

LEDs

Light-emitting diodes are currently widely used as diode blocks for light energy-saving light bulbs. They become indispensable for people's lives, as they help reduce rising electricity prices.

For information. Flashing LEDs are often used in various signal circuits to decorate home interiors. There are circuits that can be used to make LEDs blink. Making blinking LEDs is a completely doable task.

We often hear that this or that device operates on diodes. What is a diode?

A diode is an electronic element that passes current well in one direction but exhibits strong resistance when trying to pass current through it in the opposite direction.

How modern diodes work

Currently, semiconductor type diodes made of germanium or silicon are used. Such a diode is a plate divided into two parts. In one part, a lack of electrons is artificially created. This is a region with p-type conductivity (from the word positive). The positive terminal of the diode is called the anode.

The other part has an excess of electrons. This is a region with n-type conductivity (from the word negaive). The negative terminal of the diode is called the cathode.

The boundary between these areas is called a p-n junction.

How does a diode work?

If you connect the positive pole of the power source to the anode of the diode, and the negative pole to the cathode, then an electric current will flow through such a circuit. If the circuit also includes a light bulb, it will light up. What will the diode do if the positive and negative terminals of the power supply are reversed? It will provide strong resistance to the current. The current will become so weak that the light bulb will not light.

What are diodes for?

The main application of diodes is the conversion of alternating current to direct current. The diode is the main structural element of all power supplies, including the one currently on your computer.

Diodes are also widely used in logic circuits in which it is necessary to ensure the passage of current in the desired direction. Such circuits are used in analog-type devices.

The name diode translates as “two-electrode”. Historically, electronics originates from electric vacuum devices. The fact is that the lamps, which many remember from old televisions and receivers, bore names such as diode, triode, pentode, etc.

The name included the number of electrodes or legs of the device. Semiconductor diodes were invented at the beginning of the last century. They were used to detect radio signals.

The main property of a diode is its conductivity characteristics, which depend on the polarity of the voltage applied to the terminals. The diode designation tells us the conducting direction. The movement of the current coincides with the arrow on the UGO diode.

UGO – conventional graphic designation. In other words, this is an icon that denotes an element on the diagram. Let's look at how to distinguish the LED designation on the diagram from other similar elements.

Diodes, what are they?

In addition to individual rectifier diodes, they are grouped according to application into one housing.

Designation of the diode bridge

For example, this is how it is depicted diode bridge for rectification of single-phase AC voltage. And below is the appearance of diode bridges and assemblies.

Another type of rectifier is Schottky diode– designed for operation in high-frequency circuits. Available both in discrete form and in assemblies. They can often be found in switching power supplies, for example power supplies for an AT or ATX personal computer.

Typically, on Schottky assemblies, its pinout and internal connection circuit are indicated on the case.

Specific diodes

We have already looked at the rectifier diode, let's take a look at Zener diode, which in Russian literature is called - zener diode.

Zener diode designation (Zener diode)

Outwardly, it looks like a regular diode - a black cylinder with a mark on one side. Often found in a low-power version - a small red glass cylinder with a black mark on the cathode.

It has an important property - voltage stabilization, therefore it is switched on parallel to the load in the opposite direction, i.e. The plus of the power supply is connected to the cathode, and the anode to the minus.

The next device is varicap, the principle of its operation is based on changing the value of the barrier capacitance, depending on the magnitude of the applied voltage. Used in receivers and in circuits where it is necessary to perform operations on the signal frequency. Designated as a diode combined with a capacitor.

Varicap - designation on the diagram and appearance

– the designation of which looks like a diode crossed across. In fact, this is what it is - it is a 3-junction, 4-layer semiconductor device. Due to its structure, it has the property of passing current when overcoming a certain voltage barrier.

For example, dinistors of 30V or so are often used in “energy-saving” lamps, to start an autogenerator, and other power supplies built according to such a circuit.

Dinistor designation

LEDs and optoelectronics

Since the diode emits light, the designation means LED there should be an indication of this feature, so two outgoing arrows were added to the usual diode.

In reality, there are many different ways to determine polarity; there is a whole section on this below, for example, the pinout of a green LED.

Typically, an LED's pins are marked either with a mark or with legs of different lengths. The short leg is a minus.

Photodiode, the device is the opposite in action to the LED. It changes its conductivity state depending on the amount of light falling on its surface. Its designation:

Such devices are used in televisions, tape recorders and other equipment that is controlled by a remote control in the infrared spectrum. Such a device can be made by cutting off the body of a regular transistor.

Often used in light sensors, on devices for automatically turning on and off lighting circuits, for example the following:

Optoelectronics is a field that has become widespread in data transmission and communication and control devices. Thanks to its fast response and galvanic isolation capability, it ensures safety for the powered devices in the event of a high-voltage surge on the primary side. However, not in the form as indicated, but in the form of an optocoupler.

At the bottom of the diagram you see an optocoupler. The LED is turned on here by closing the power circuit using an optotransistor in the LED circuit. When you close the switch, current flows through the LED in the optocoupler, in the bottom square on the left. It lights up and the transistor, under the influence of the light flux, begins to pass current through LED1, marked green.

The same application is used in the current or voltage feedback circuits (to stabilize them) of many power supplies. The scope of application starts from mobile phone chargers and power supplies for LED strips, to powerful power supply systems.

There are a great variety of diodes, some of them are similar in their characteristics, some have completely unusual properties and applications, they are united by the presence of only two functional terminals.

You can find these elements in any electrical circuit; their importance and characteristics cannot be underestimated. The correct selection of a diode in the snubber circuit, for example, can significantly affect the efficiency and heat dissipation of power switches, and, accordingly, the durability of the power supply.

If there was anything unclear to you, leave comments and ask questions; in the following articles we will definitely reveal all the unclear questions and interesting points!

This is a diode- a semiconductor device that allows electrical current to flow in only one direction.This is a very brief description of the properties of the diode and its operation and the most accurate. Now let's take a closer look, especially since you begin your acquaintance with the huge family of semiconductors with the diode.What is a semiconductor?From the name itself, a semiconductor, it is clear, is half conductive. In a specific case, a diode allows electric current to pass in only one direction and does not allow it to pass in the opposite direction. It works like a nipple or spool system in the chamber of a car or bicycle. The air forced by the pump through the spool or nipple enters the car's chamber and does not come back out due to its being locked by the spool. The figure shows a diode as it is designated on electrical diagrams.

In accordance with the figure, the triangle (anode) shows in which direction the electric current flows from plus to minus, the diode will be “open” respectively on the side of the vertical strip (cathode) the diode will be “locked”.

This property of the diode is used to convert alternating current to direct current; for this, diodes are assembled diode bridge.

Diode bridge

How does a diode bridge work? The following figure shows a schematic diagram of a diode bridge. Please note that the input of the diode bridge is supplied alternating current, at the output we already get D.C. Now let's figure out how AC is converted to DC.

If you read my article “What is alternating current” you must remember that alternating current changes its direction with a certain frequency. Simply put, at the input terminals of the diode bridge, plus and minus will change places with the network frequency (in Russia this frequency is 50 Hertz), which means (+) and (-) change places 50 times per second. Let’s say in the first cycle there will be a positive potential (+) at terminal “A” and negative potential (-) at terminal “B”. The plus from terminal “A” can only pass in one direction along the red arrow, through the diode “D1” to the output terminal with the (+) sign and then through resistor (R1) through diode “D3” to the minus terminal “B”. In the next cycle, when the plus and minus switch places, everything will happen exactly the opposite. The plus from terminal “B” will pass through the diode “D2” to the output terminal with the sign (+) and then through resistor (R1) through diode “D4” to the minus terminal “A”. Thus, at the input of the rectifier we obtain a constant electric current that moves only in one direction from plus to minus (as in a regular battery). This method of converting alternating current into direct current is used in all electronic devices that are powered by a 220-volt electrical network. In addition to diode bridges assembled from individual diodes, electronic components are used in which, for ease of installation, rectifier diodes are enclosed in one compact housing. Such a device is called “diode assembly”.

There are not only rectifier diodes. There are diodes whose conductivity depends on the illumination, they are called “photodiodes” they are designated as follows:

They might look like this:

LEDs are well known to you; they are found in Christmas tree garlands and in powerful spotlights and car headlights. In the diagram they are designated as follows -

LEDs look like this:

How to test a diode

Check diode You can use a regular multimeter - how to use a multimeter In this article, to check, switch the tester to dialing mode. We connect the probes of the device to the electrodes of the diode, the black probe to the cathode

(on modern diode cases the cathode is marked with a ring mark),connect the red probe to the anode (as you already know, diodes only pass voltage in one direction)The diode resistance will be small i.e. The numbers on the meter will make a big difference.

We switch the probes of the device the other way around -

The resistance will be very large, almost infinite. If everything works out as I wrote, the diode is working, if in both cases the resistance is very high, then the “open diode” is faulty and does not pass voltage at all, if the resistance is very small, then the diode is broken and passes voltage in both directions.

How to check a diode bridge

If the diode bridge is assembled from individual diodes, each diode is checked separately, as described above. It is not necessary to desolder each diode from the circuit, but it is better to disconnect the positive or negative terminal of the rectifier from the circuit.

If you need to check a diode assembly, where the diodes are in one housing and it is impossible to reach them, proceed as follows:

We connect one probe multimerta to the plus of the diode assembly, and with the second we touch in turn the terminals of the assembly where alternating current is supplied. In one direction, the device should show low resistance when changing probes in the opposite direction, very high resistance. Then we also check the rectifier against the negative output. If during measurement the readings in both directions are small or large, the diode assembly is faulty. This testing method is used when electronics are repaired.

High-frequency diodes, pulse diodes, tunnel diodes, varicaps - all these diodes are widely used in household and special equipment. In order to understand and figure out how to properly use and where to use which diodes, you need to improve your knowledge, study specialized literature and, of course, do not hesitate to ask questions.

Diodes belong to the category of electronic devices that operate on the principle of a semiconductor, which reacts in a special way to the voltage applied to it. The appearance and circuit designation of this semiconductor product can be found in the figure below.

A feature of including this element in an electronic circuit is the need to maintain the polarity of the diode.

Additional explanation. Polarity means a strictly established order of switching on, which takes into account where the plus and where the minus is for a given product.

These two symbols are tied to its terminals, called anode and cathode, respectively.

Features of operation

It is known that any semiconductor diode, when DC or AC voltage is applied to it, passes current only in one direction. If it is turned back on, no direct current will flow, since the n-p junction will be biased in a non-conducting direction. The figure shows that the minus of the semiconductor is located on the side of its cathode, and the plus is located on the opposite end.

The effect of one-way conduction can be especially clearly confirmed by the example of semiconductor products called LEDs, which only work if they are turned on correctly.

In practice, there are often situations when there are no obvious signs on the product body that allow you to immediately tell where it has which pole. That is why it is important to know the special signs by which you can learn to distinguish between them.

Methods for determining polarity

To determine the polarity of a diode product, you can use various techniques, each of which is suitable for certain situations and will be considered separately. These methods are divided into the following groups:

• A visual inspection method that allows you to determine the polarity based on existing markings or characteristic features;
• Checking with a multimeter turned on in dialing mode;
• Finding out where is the plus and where is the minus by assembling a simple circuit with a miniature light bulb.

Let's consider each of the listed approaches separately.

Visual inspection

This method allows you to decipher the polarity using special marks on the semiconductor product. For some diodes this may be a point or an annular strip shifted towards the anode. Some samples of the old brand (KD226, for example) have a characteristic shape, pointed on one side, which corresponds to a plus. On the other, completely flat end, there is a minus, respectively.

Note! When visually examining LEDs, for example, it is discovered that one of their legs has a characteristic protrusion.

Based on this feature, it is usually determined where such a diode has a plus and where the opposite contact is.

Application of the measuring instrument

The simplest and most reliable way to determine polarity is to use a multimeter-type measuring device turned on in the “Dialing” mode. When measuring, you should always remember that the red-insulated cord from the built-in battery is supplied with a plus, and the black-insulated cord is supplied with a minus.

After arbitrarily connecting these “ends” to the terminals of a diode with unknown polarity, you need to monitor the readings on the device display. If the indicator shows a voltage of about 0.5-0.7 Volts, this means that it is turned on in the forward direction, and the leg to which the probe in red insulation is connected is positive.

If the indicator shows “one” (infinity), we can say that the diode is turned on in the opposite direction, and on the basis of this it will be possible to judge its polarity.

Additional Information. Some radio amateurs use a socket designed for measuring transistor parameters to test LEDs.

In this case, the diode is turned on as one of the transitions of the transistor device, and its polarity is determined by whether it lights up or not.

Inclusion in the scheme

As a last resort, when it is not possible to visually determine the location of the terminals, and there is no measuring instrument at hand, you can use the method of connecting a diode to the simple circuit shown in the figure below.

When it is connected to such a circuit, the light bulb will either light up (this means that the semiconductor passes current through itself) or not. In the first case, the plus of the battery will be connected to the positive terminal of the product (anode), and in the second, on the contrary, to its cathode.

In conclusion, we note that there are quite a few ways to determine the polarity of a diode. In this case, the choice of a specific method for identifying it depends on the conditions of the experiment and the capabilities of the user.

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