LEDs are gaining more and more popularity these days. Connecting different types of these light elements has its own characteristics, but the first thing to start with in any case is the need to correctly determine where the “+” and “-” are in the device.

How can you visually determine the plus and minus

There are several types of diodes used by electricians, both amateurs and professionals, but the methods for visually determining the polar poles are about the same:

Battery detection

To check the polarity on a diode bulb, you can use a source that produces a constant voltage. This source can be a car battery or power supply (battery).

The diode must be connected to the power supply and gradually increase the voltage. If the lamp is connected correctly, it lights up. If this light is not there, then you need to change the polarity and connect with the other ends. Remember that over 3-4 V you do not need to increase the voltage, because the element may burn out.

You can also check the compliance of the anode-cathode using a battery, a battery from a car or a mobile phone with a voltage of 4.5 to 12 V. You can also make this design - connect 1.5 V batteries in series together.

You can not connect a diode directly to the battery, because it will burn out. To connect, you must use a resistor that limits the current. The resistance of this device for low-power diode bulbs is from 680 Ohm to 1-2 kOhm. For high-power LED lamps, it is necessary to use a resistor of tens of kOhm.

Checking with a multimeter

Using this device, you can determine not only the polarity, but also the performance of the LED element. Measurements are carried out in the ohmmeter mode. Modern models of multimeters have a built-in function - “diode testing”.

To determine the plus or minus, connect the probes of the device to the element under test and observe the readings of the measuring apparatus. If the screen shows “infinite” resistance, then the probes need to be swapped with each other.

If the device displays the final resistance test result on the screen, this indicates that the polarity is determined correctly and the anode-cathode position at the LED element can be determined using the multimeter probes.

It is necessary to take into account such a nuance - for some models of pointer devices, the polarity of the probes does not match when determining the voltage and when operating in the ohmmeter mode. Such discrepancy is observed in testers of old models (TL-4M).

Therefore, before testing the LED element, you need to check the cathode-anode correspondence on the probes when operating in different modes.

Multimeter testing can be done with a voltmeter.

The principle of hardware testing is no different from testing with a battery - if the element is working and connected correctly, it starts to glow. But at the same time, not all diodes glow, because an open LED has a voltage drop of up to 1.5-3.2 V, and this is much more than that of a semiconductor device.

The voltage drop rate directly depends on the power of the LED and its color. Measuring devices with low voltage voltage do not have enough current on the probes to light the light in LED light bulb. It is impossible to determine the performance of the LED element with low-voltage testers.

If the tester has a compartment for testing PNP and NPN transistors, then it can also be used to determine the polarity of the LED lamp. If the cathode is inserted into the hole “C” into the PNP compartment, and the opposite end is inserted into “E”, then the LED device will start to glow. In the NPN compartment, the legs must be swapped - and then the LED element will also give light.

This is the fastest method of instrumental testing.

Each polarity testing method has disadvantages and advantages. You have to choose it based on the conditions in which you need to be tested, and the availability of improvised tools.

Designation different types diodes in the diagram. Diode in the diagram where is the anode and where is the cathode

Diode purpose, diode anode, diode cathode,

How to test a diode with a multimeter

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The purpose of a diode is to conduct electricity in one direction only. Once upon a time, lamp diodes were used. But now mainly semiconductor diodes are used. Unlike lamps, they are much smaller in size, do not require filament circuits, and are very easy to connect in various ways.

Symbol of the diode on the diagram

The picture shows symbol diode in the diagram. The letters A and K, respectively, denote the anode of the diode and the cathode of the diode. The anode of a diode is the terminal that connects to the positive terminal of the power supply, either directly or through circuit elements. The cathode of the diode is the output from which the current of the positive potential exits and then through the circuit elements it enters the negative electrode of the current source. Those. Current flows through the diode from the anode to the cathode. And in the opposite direction, the diode does not pass current. If some of its terminals the diode is connected to the source AC voltage, then on its other output a constant voltage is obtained with a polarity depending on how the diode is connected. If it is connected by the anode to an alternating voltage, then we will get a positive voltage from the cathode. If it is connected to the cathode, then a negative voltage will be received from the anode, respectively.

How to test a diode with a multimeter

How to check a diode with a multimeter or tester - such a question arises when there is a suspicion that the diode is faulty. But, the answer to this question gives another answer, where is the anode of the diode, and where is the cathode. Those. if we do not initially know the pinout of the diode, then we simply put a multimeter or tester on the continuity of the diodes (or on the measurement of resistance) and in turn ring the diode in both directions. If the diode is good, our device will show the passage of current in only one of the options. If the diode passes current in both cases, the diode is broken. If it does not pass in any variant, the diode has burned out and is also faulty. In the case of a working diode, when it conducts current, we look at the terminals of the device, the diode terminal that is connected to the positive terminal of the tester is the anode of the diode, and the one to the negative terminal is the diode cathode. Testing diodes is very similar to testing transistors.

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Determine the polarity of the LED. Where is the plus and minus of the LED

Any hobbyist of DIY and electronics use diodes as indicators, or as lighting effects and lighting. In order for the LED device to glow, you need to connect it correctly. You already know that a diode only conducts current in one direction. Therefore, before soldering, you need to determine where the anode and cathode of the LED are.

You may see two LED designations on a circuit diagram.

The triangular half of the designation is the anode, and vertical line- cathode. The two arrows indicate that the diode emits light. So, the anode and cathode of the diode are indicated on the diagram, how to find it on a real element?

Pinout 5mm diodes

To connect the diodes as in the diagram, you need to decide where the LED has plus and minus. To begin with, let's look at the example of common low-power 5 mm diodes.

The figure above shows: A - anode, K - cathode and schematic designation.

Pay attention to the flask. Two parts are visible in it - this is a small metal anode, and a wide part that looks like a bowl is the cathode. Plus is connected to the anode, and minus to the cathode.

If you are using new LED elements, it is even easier for you to determine their pinout. The length of the legs will help determine the polarity of the LED. Manufacturers make short and long legs. Plus is always longer than minus!

If you are not soldering a new diode, then the plus and minus are the same length. In this case, a tester or a simple multimeter will help determine the plus and minus.

How to determine the anode and cathode for diodes 1W or more

In flashlights and spotlights, 5mm samples are used less and less, they have been replaced by powerful elements with a power of 1 watt or SMD. To understand where the plus and minus are on a powerful LED, you need to carefully look at the element from all sides.

The most common models in this case have a power of 0.5 watts. In the figure, the polarity mark is circled in red. In this case, the plus sign marks the anode at the 1W LED.

How to know the polarity of SMD?

SMD is actively used in almost any technology:

• light bulbs;
• LED strips;
• flashlights;
• an indication of something.

You won't be able to see their insides, so you'll either need to use test tools or rely on the LED case.

For example, on the SMD 5050 case there is a mark on the corner in the form of a cut. All pins located on the label side are cathodes. There are three crystals in its body, this is necessary to achieve a high brightness of the glow.

A similar designation for SMD 3528 also indicates the cathode, take a look at this photo of the LED strip.

The marking of the SMD 5630 pins is similar - the cut indicates the cathode. It can also be recognized by the fact that the heat sink on the bottom of the case is shifted towards the anode.

How to determine the plus on a small SMD?

AT individual cases(SMD 1206) you can find another way to indicate the polarity of the LEDs: using a triangle, U-shaped or T-shaped pictogram on the surface of the diode.

The protrusion or side that the triangle points to is the direction of current flow, and the terminal located there is the cathode.

Determine the polarity with a multimeter

When replacing diodes with new ones, you can determine the plus and minus of the power supply of your device from the board.

LEDs in spotlights and lamps are usually soldered on an aluminum plate, on top of which a dielectric and current-carrying tracks are applied. From above, it usually has a white coating, it often contains information about the characteristics of the power source, and sometimes pinouts.

But how to find out the polarity of the LED in a light bulb or matrix if there is no information on the board?

For example, this board shows the poles of each of the LEDs and their name is 5630.

To check for serviceability and determine the plus and minus of the LED, we will use a multimeter. We connect the black probe to minus, com or a socket with a ground sign. The designation may differ depending on the model of the multimeter.

Next, select the Ohmmeter mode or the diode test mode. Then we connect in turn the probes of the multimeter to the terminals of the diode, first in the same order, and then vice versa. When at least some values ​​appear on the screen, or the diode lights up, then the polarity is correct. In the diode test mode, the values ​​\u200b\u200bare equal to 500-1200mV.

In measurement mode, the values ​​will be similar to those in the figure. A unit in the leftmost digit indicates an excess of the limit, or infinity.

Other ways to determine polarity

The easiest option for determining where the LED has a plus is the batteries from the motherboard, size CR2032.

Its voltage is about 3 volts, which is quite enough to light the diode. Connect the LED, depending on its glow, you will determine the location of its outputs. In this way, any diode can be tested. However, this is not very convenient.

You can assemble a simple probe for LEDs, and not only determine their polarity, but also the operating voltage.

Diagram of a homemade probe

With a properly connected LED, a current of the order of 5-6 milliamps will flow through it, which is safe for any LED. The voltmeter will show the voltage drop across the LED at that current. If the polarity of the LED and the probe match, it will light up and you will determine the pinout.

You need to know the operating voltage, as it differs depending on the type of LED and its color (red takes on less than 2 volts).

And last way shown in the photo below.

Turn on the Hfe mode on the tester, insert the LED into the transistor test connector, into the area marked as PNP, into holes E and C, with a long leg in E. This way you can check the operation of the LED and its pinout.

If the LED is made in a different form, for example, smd 5050, you can use this method simply - insert ordinary sewing needles into E and C, and touch them with the LED contacts.

Any lover of electronics, and homemade products in general, needs to know how to determine the polarity of an LED and how to check them.

Be careful when choosing the elements of your circuit. At best, they will simply fail faster, and at worst, they will instantly flare up with a blue flame.

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Designation of LEDs and other diodes on the diagram

The name diode translates as "two-electrode". Historically, electronics originates from electrovacuum devices. The fact is that the lamps that many people remember from old TVs and receivers were named like 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 conductance characteristics, which depend on the polarity of the voltage applied to the terminals. The designation of the diode tells us the conductive direction. The current flow coincides with the arrow on the UGO of the diode.

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

Diodes, what are they?

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

Diode bridge designation

For example, this is how a diode bridge is depicted for rectifying a single-phase voltage alternating current. And below is the appearance of diode bridges and assemblies.

Another type of rectifier device is the Schottky diode - designed to work in high-frequency circuits. Available both in discrete form and in assemblies. They are often found in impulse blocks power supply, such as a power supply for personal computer AT or ATX.

Usually, on Schottky assemblies, its pinout and internal wiring diagram are indicated on the case.

Specific Diodes

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

Zener diode designation (Zener diode)

Outwardly, it looks like an ordinary diode - a black cylinder with a label 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 in parallel with the load in the opposite direction, i.e. the cathode is connected to the plus power, and the anode to the minus.

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

Varicap - designation on the diagram and appearance

Dinistor - the designation of which looks like a diode crossed out across. In fact, it is - it is a 3-transition, 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 run an oscillator, and other power supplies built according to this scheme.

Dinistor designation

LEDs and optoelectronics

Since the diode emits light, then the designation of the LED should indicate 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 article about this in more detail. Below, for example, the pinout of the green LED.

Typically, the LED pin marking is performed either with a label or with legs of different lengths. The short leg is a minus.

Photodiode, a device inverse in its action from the LED. It changes the state of its conductivity depending on the amount of light that hits its surface. Its designation:

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

It is often used in light sensors, on devices for automatically turning on and off lighting circuits, for example:

Optoelectronics is a field that has become widespread in data transmission and communication and control devices. Due to its speed and ability to carry out galvanic isolation, it provides safety for 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 luminous flux, begins to pass current through the LED1 LED, marked in green.

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

There are a great many 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 conclusions.

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

If you didn’t understand something, leave comments and ask questions, in the following articles we will definitely reveal all incomprehensible questions and interesting points!

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How to check a diode with a multimeter - Practical electronics

In radio electronics, two types of diodes are mainly used - these are just diodes, and there are also LEDs. There are also zener diodes, diode assemblies, stabistors, and so on. But I do not attribute them to any particular class.

In the photo below we have a simple diode and an LED.

The diode consists of a P-N junction, so the whole trick in checking the diode is that it passes current only in one direction, and does not pass in the other. If this condition is met, then the diode can be diagnosed as absolutely healthy. We take our famous cartoon and put the twist on the diode test icon. I talked about this and other icons in more detail in the article How to measure current and voltage with a multimeter?.

I would like to add a few words about the diode. A diode, like a resistor, has two ends. And they are called in a special way - the cathode and the anode. If a plus is applied to the anode and a minus to the cathode, then the current will flow calmly through it, and if a plus is applied to the cathode and minus to the anode, the current will NOT flow.

We check the first diode. We put one probe of the multimeter on one end of the diode, the other probe on the other end of the diode.

As we can see, the multimeter showed a voltage of 436 millivolts. This means that the end of the diode that touches the red probe is the anode, and the other end is the cathode. 436 millivolts is the voltage drop across the forward junction of the diode. According to my observations, this voltage can be from 400 to 700 millivolts for silicon diodes, and for germanium diodes from 200 to 400 millivolts. Next, swap the leads of the diode.

A one on the multimeter means that no current is flowing through the diode. Therefore, our diode is quite working.

But how to check the LED? Yes exactly the same! An LED is exactly the same simple diode, but its trick is that it glows when a plus is applied to its anode and a minus to the cathode.

Look, it glows a little! This means the output of the LED, on which the red probe is the anode, and the output on which the black probe is the cathode. The multimeter showed a voltage drop of 1130 millivolts. This is fine. It can also vary, depending on the "model" of the LED.

We change the probes in places. The LED didn't light up.

We pass the verdict - a fully functional LED!

But how to check diode assemblies, diode bridges and zener diodes? Diode assemblies are a connection of several diodes, mainly 4 or 6. We find a circuit diagram of the diode assembly, and poke the cartoon probes on the conclusions of this same diode assembly and look at the cartoon readings. Zener diodes are tested in the same way as diodes.

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Diode marking: designation table

Content:

1. Marking of imported diodes
2. Diode marking anode cathode

The standard design of a semiconductor diode is in the form of a semiconductor device. It has two terminals and one rectifying electrical junction. In the operation of the device used various properties associated with electrical transitions. The entire system is connected in a single housing made of plastic, glass, metal or ceramic. The part of the crystal with a higher concentration of impurities is called the emitter, and the region with a low concentration is called the base. Diode marking and designation scheme are used in accordance with their individual properties, design features and technical characteristics.

Characteristics and parameters of diodes

Depending on the material used, diodes can be made of silicon or germanium. In addition, indium phosphide and gallium arsenide are used for their manufacture. Diodes made of germanium have a higher transfer coefficient compared to silicon products. They have high conductivity at a relatively low voltage. Therefore, they are widely used in the production of transistor receivers.

In accordance with technological features and designs, diodes are distinguished as planar or point, pulsed, universal or rectifier. Among them, a separate group should be noted, which includes LEDs, photodiodes and thyristors. All of these features make it possible to determine the diode in appearance.

The characteristics of diodes are determined by parameters such as forward and reverse currents and voltages, temperature ranges, maximum reverse voltage, and other values. Depending on this, the corresponding designations are applied.

Designations and color marking of diodes

Modern designations of diodes correspond to new standards. They are divided into groups, depending on the limiting frequency at which the amplification of current transfer occurs. Therefore, diodes are of low, medium, high and ultra-high frequency. In addition, they have different power dissipation: small, medium and large.

Diode marking is a short symbol for an element in a graphic design, taking into account the parameters and technical features conductor. The material from which the semiconductor is made is marked on the case with the corresponding letter symbols. These designations are affixed together with the purpose, type, electrical properties of the device and its symbol. This helps, in the future, to correctly connect the diode to the electronic circuit of the device.

The anode and cathode terminals are indicated by an arrow or plus or minus signs. Color codes and marks in the form of dots or stripes are applied near the anode. All designations and color markings allow you to quickly determine the type of device and correctly use it in various schemes. A detailed interpretation of this symbolism is given in the reference tables, which are widely used by specialists in the field of electronics.

Marking of imported diodes

At present, foreign-made SMD diodes are widely used. The design of the elements is made in the form of a board, on the surface of which a chip is fixed. Too small dimensions of the product do not allow marking on it. On larger elements, the designations are present in full or abbreviated form.

In electronics, SMD diodes make up about 80% of all used products of this type. Such a variety of details makes you pay more attention to the designations. Sometimes they may not match the declared technical characteristics, so it is advisable to conduct an additional check of questionable elements if they are planned to be used in complex and accurate circuits. It should be borne in mind that the marking of diodes of this type can be different on exactly the same cases. Sometimes there is only alphabetic symbols, without any numbers. In this regard, it is recommended to use tables with standard sizes of diodes from different manufacturers.

For SMD diodes, the package type SOD123 is most often used. A colored stripe or embossing can be applied to one of the ends, which means a cathode with negative polarity to open the pn junction. The only inscription corresponds to the body designation.

Package type does not play a decisive role when using a diode. One of the main characteristics is the dissipation of a certain amount of heat from the surface of the element. In addition, the values ​​of the operating and reverse voltages, the maximum allowable current through the pn junction, the power dissipation and other parameters are taken into account. All this data is indicated in the directories, and the marking only speeds up the search for the desired element.

It is not always possible to determine the manufacturer by the appearance of the case. To search for the desired product, there are special search engines in which you need to enter numbers and letters in a certain sequence. In some cases, diode assemblies do not carry any information at all, so only a reference book can help in such cases. Such simplifications, which make the diode designation very short, are explained by the extremely limited space for marking. When using screen printing or laser printing manages to accommodate 8 characters per 4 mm2.

It is worth considering the fact that completely different elements can be denoted by the same alphanumeric code. In such cases, the entire circuit diagram.

Sometimes the marking indicates the date of issue and the batch number. Such marks are applied to be able to track more modern product modifications. Appropriate corrective documentation is issued with a number and date. This allows you to more accurately set specifications elements when assembling the most critical circuits. Using old parts for new drawings, you can not get the expected result, the finished product in most cases simply refuses to work.

Diode marking anode cathode

Each diode, like a resistor, is equipped with two terminals - an anode and a cathode. These names should not be confused with plus and minus, which mean completely different parameters.

However, very often it is required to determine the exact correspondence of each diode terminal. There are two ways to determine the anode and cathode:

• The cathode is marked with a strip, which is noticeably different from the general color of the case.
• The second option involves checking the diode with a multimeter. As a result, not only the location of the anode and cathode is established, but the performance of the entire element is also checked.

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DIODES

A diode is a two electrode semiconductor device. These are respectively the Anode (+) or positive electrode and the Cathode (-) or negative electrode. It is customary to say that a diode has (p) and (n) regions, they are connected to the terminals of the diode. Together they form a p-n junction. Let's take a closer look at what this p-n junction is. A semiconductor diode is a purified silicon or germanium crystal, in which an acceptor impurity is introduced into the (p) region, and a donor impurity is introduced into the (n) region. Arsenic ions can act as a donor impurity, and India ions can act as an acceptor impurity. The main property of a diode is the ability to pass current in only one direction. Consider the figure below: This figure shows that if the diode is turned on with the Anode to the plus of the power supply and the Cathode to the minus of the power supply, then the diode is in the open state and conducts current, since its resistance is negligible. If the diode is turned on by the Anode to the minus, and the Cathode to the plus, then the resistance of the diode will be very large, and there will be practically no current in the circuit, or rather it will be, but so small that it can be neglected. More details can be found by looking at the following chart, Volt-ampere characteristic diode: AT direct connection, as we can see from this graph, the diode has a small resistance, and accordingly passes the current well, and in the reverse connection up to a certain voltage value, the diode is closed, has a high resistance and practically does not conduct current. It is easy to verify this, if you have a diode and a multimeter at hand, you need to put the device in the sound continuity position, or by setting the multimeter switch opposite the diode icon, in extreme cases, you can try to ring the diode by setting the switch to position 2 KΩ resistance measurement. The diode is depicted on the schematic diagrams as in the figure below, remember where which conclusion is easy: the current, as you know, always flows from plus to minus, and so the triangle in the image of the diode, as it were, shows the direction of the current with its apex, that is, from plus to minus. By connecting the red probe of the multimeter to the Anode, we can make sure that the diode passes current in the forward direction, on the device screen there will be numbers equal to ~ 800-900 or close to it. By connecting the probes the other way around, the black probe to the anode, the red probe to the cathode, we will see a unit on the screen, which confirms that the diode does not pass current in the reverse connection. The diodes discussed above are planar and point. Planar diodes are designed for medium and high power and are used mainly in rectifiers. Point diodes are designed for low power and are used in radio detectors, they can operate at high frequencies. Planar and point diode What are the types of diodes? A) The photo shows the diode we discussed above. B) This figure shows a zener diode, (a foreign name is a Zener diode), it is used when the diode is turned back on. The main goal is to keep the voltage stable. Dual-anode zener diode - image on the diagram C) Double-sided (or double-anode) zener diode. The advantage of this zener diode is that it can be turned on regardless of polarity. D) Tunnel diode, can be used as an amplifying element. E) Inverted diode, used in high-frequency circuits for detection. E) Varicap, used as a variable capacitor. G) Photodiode, when the device is illuminated in the circuit connected to it, a current arises due to the appearance of pairs of electrons and holes. H) Light-emitting diodes, known to all, and probably the most widely used devices, after conventional rectifier diodes. Used in many electronic devices for display and more. Rectifier diodes are also produced in the form of diode bridges, let's analyze what it is - these are four diodes connected to obtain a constant (rectified) current in one housing. They are connected according to the Bridge scheme, standard for rectifiers: They have four marked outputs: two for connecting alternating current, and plus and minus. The photo shows the KTs405 diode bridge: Now let's take a closer look at the scope of LEDs. LEDs (or rather LED lamp) are produced by industry and for lighting rooms, as an economical and durable light source, with a base that allows them to be screwed into a conventional incandescent lamp holder. LED lamp photo LEDs exist in different packages, including SMD. The so-called RGB LEDs are also produced, inside them there are three crystals of LEDs with a different glow of Red-Green-Blue, respectively Red - Green - Blue, these LEDs have four outputs and allow any color to be visible by mixing colors. These SMD LEDs are often available as strips with pre-installed resistors and allow you to connect them directly to a 12 volt power supply. You can use a special controller to create lighting effects: rgb controller When used, LEDs do not like when they are supplied with a supply voltage higher than that for which they are designed and can burn out immediately or after some time, so the power supply voltage must be calculated using formulas. For Soviet LEDs of the AL-307 type, the supply voltage should be approximately 2 volts, for imported 2-2.5 volts, naturally with current limitation. To power LED strips, if a special controller is not used, a stabilized power supply is required. Material prepared - AKV. Forum on radio components Caution sign high voltage gost How to measure the angle between current and voltage in three-phase video What is the name of the connection if all the elements have the same voltage

LEDs have recently been considered one of the most common light sources. However, not so long ago, its use was limited only to indication properties. With the development of technology and optics, this semiconductor device with an electron-hole junction has taken a leading place in the creation and organization of safe, economical, and environmentally friendly lighting. Its luminous flux lies in a narrow range of the spectrum and appears only when current passes in a certain direction. The LED works only on constant voltage, and if connected incorrectly, it can easily fail. Here one of the absolutely logical questions arises - how to determine the polarity of the LED?

Determining the polarity of LEDs can be done in several ways:

• Visually;
• Using a measuring device (tester, multimeter, ohmmeter);
• By supplying voltage from a power source;
• Finding this device in the handbook or in the attached technical documentation;

All these methods are simple, effective and even a person without electrical education can use them.

Visual Definition

How to determine the polarity of the LED visually, because this is the easiest way that does not require special devices. In electronics, there are several types of packages in which this semiconductor device is produced. One of the common types of LEDs is a small electronic device with a cylindrical body, the diameter of which is 3.5 mm or more.

In order to determine its polarity, that is, to which terminal to connect the plus, and to which minus, from a constant voltage source, you need to carefully consider the LED itself. In this case, it can be seen through the transparent surface that the area of ​​the cathode (negative terminal) is much larger than that of the anode (positive). Even if it is impossible to see a larger electrode inside the case of a cylindrical LED, the conclusions from it will also differ in size, and the negative one will be more massive.

Also in the latest models of LED lamps you can find SMD LEDs, which are used for surface mounting. They are widely used both in LED lamps, spotlights, and in special tapes. Such light sources have a special bevel or as it is called a key that points to the negative connection electrode - the cathode.

However, on some SMD LEDs, you can see it with a careful external study of it. special character, which will indicate its polarity. It should also be noted that the more powerful the LED, the larger and more massive it is, which means that determining where it has a cathode and where the anode will be easier during visual inspection.

Determination with a multimeter

Most radio amateurs, at least somehow connected with electricity, have multimeters in their arsenal, which can be either pointer or digital. It is with them that you can easily and accurately determine the polarity of the LED, as well as check its performance. This type of test is performed with a multimeter (tester) in ohmmeter mode.

To do this, you need to find out which of the probes of the tester contains a negative and which positive potential. If you connect the probes of the measuring device in the forward direction (that is, the anode of the LED will be connected respectively to the positive probe, and the cathode to the negative one), the readings of the device will show some resistance value in Ohms. If you swap the probes, a working LED will show a rather large resistance, which can be several hundred kOhm or, in general, infinity. When using and testing some low power LEDs and when properly (directly) connected, you can even see a slight glow between the anode and cathode. This is also a very good sign that the LED is not only serviceable and ready for use, but also that its polarity matches the polarity of the ohmmeter probes.

Determination by applying voltage

Excellent results are also shown by the method of determining the polarity of the LED by applying a small voltage. This method, like the previous one, allows you to determine not only the polarity, but also the health of the element. To check, you need a DC source, it can be a battery, accumulator or power supply. The best and safest for the LED is a power supply with continuously variable output DC voltage.

If the connection is correct, then when the voltage is raised to 3-5 volts, the LED will emit a luminous flux, the saturation and strength of which will depend on the power of the LED. If, when connected, the polarity of the power source and the polarity of this semiconductor device do not match, then the LED will not even light up a little, so you should not raise the voltage more than 5 volts so as not to disable it. It is also recommended to connect a current-limiting resistor with a resistance of 600 Ohm to several kOhm in series with the LED, this will additionally protect the LED from high current, and hence from breakdown.

Determination of polarity using technical documentation

A fairly large amount of information about this semiconductor device can also be found in the technical documentation provided by the manufacturer. It indicates not only the limits of the operating voltage and current, but also data such as weight, dimensions and many more electronic parameters that may not be entirely clear. Of course, when buying one LED, no one will give such information, this will require large quantities of goods. Sellers in specialized stores will not always give necessary information, for this, at least you need to find out the brand of this LED, and then find its parameters and characteristics either on the Internet or in special reference books.

In any case, you need to understand that only observing the correct polarity of the LED and other electrical parameters, this semiconductor device will serve for a long time, because it is not afraid of either frequent switching on and off, or the effects of external factors such as temperature or dust.

Video about determining the polarity of LEDs

How to find out where the LED is plus and where is minus? The polarity of the diode in the diagram

How to determine the polarity of the diodes: plus or minus

Diodes are categorized electronic appliances, working on the principle of a semiconductor, which reacts in a special way to the voltage applied to it. FROM appearance and the circuit designation of this semiconductor product can be found in the figure below.

General view of the product

A feature of the inclusion of this element in the electronic circuit is the need to observe the polarity of the diode.

Additional explanation. By polarity is meant a strictly established switching order, which takes into account where is the plus and where is the minus of this product.

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

Features of functioning

It is known that any semiconductor diode, when a constant or alternating voltage is applied to it, passes current in only one direction. In the event of its reverse D.C. does not leak, since the n-p junction will be biased in the non-conductive direction. It can be seen from the figure that the minus of the semiconductor is located on the side of its cathode, and the plus is on the opposite end.

Location and designation of conclusions

Especially clearly the effect of one-way conduction can be confirmed by the example of semiconductor products, called light-emitting diodes, which work only if they are turned on correctly.

In practice, situations are not uncommon when there are no obvious signs on the body of the product 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 methods, each of which is suitable for certain situations and will be considered separately. These methods are conditionally divided into the following groups:

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

Let's consider each of these approaches separately.

visual inspection

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

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

On this basis, it is usually determined where such a diode has a plus, and where is the opposite contact.

Application of the measuring device

The simplest and reliable way determination of polarity - the use of a measuring device of the "multimeter" type, included in the "Continuity" mode. When measuring, you should always remember that a plus is supplied to the cord in red insulation from the built-in battery, and minus to the cord in black insulation.

After arbitrarily connecting these "ends" to the terminals of a diode with unknown polarity, you need to follow the readings on the display of the device. If the indicator shows a voltage of the order of 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 based on this it will be possible to judge its polarity.

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

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

Inclusion in the scheme

In an extreme case, when it is not possible to visually determine the location of the pins, and there is no measuring device at hand, you can use the method of including a diode in a simple circuit shown in the figure below.

Checking with a light bulb

When it is included in 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 battery plus will be connected to the positive output of the product (anode), and in the second case, on the contrary, to its cathode.

In conclusion, we note that there are quite a few ways to determine the polarity of a diode. At the same time, the choice of a specific method for its detection depends on the conditions of the experiment and the capabilities of the user.

Video

elquanta.ru

How to Determine the Polarity of an LED - 2 Easy Ways

LED is a semiconductor optical device that transmits electric current in the forward direction. When connected, there will be no inversion current in the circuit, and, of course, there will be no glow. To prevent this from happening, you need to observe the polarity of the LED.

The LED in the diagram is indicated by a triangle in a circle with a cross line - this is the cathode, which has a “-” (minus) sign. On the opposite side is the anode, which has a "+" (plus) sign.

The wiring diagrams must contain a pinout (or pinout) of the leads to identify all the contacts of the connection.

How to determine the polarity of the diode, holding a tiny light bulb in your hands? After all, for correct connection you need to know where he has a minus, and where a plus. If the pinout is mixed up, the circuit will not work.

Visual method for determining polarity

The first way to determine is visual. The diode has two terminals. The short leg will be the cathode, the anode of the LED is always longer. It is easy to remember, since there is an initial letter "k" in both words.

When both leads are bent or the instrument is removed from another board, it can be difficult to determine their length. Then you can try to see a small crystal in the case, which is made of a transparent material. It sits on a small stand. This pin corresponds to the cathode.

Also, the cathode of the LED can be determined by a small notch. New models of LED strips and lamps use semiconductors for surface mounting. The available key in the form of a bevel indicates that this is a negative electrode (cathode).

Sometimes the LEDs are marked "+" and "-". Some manufacturers mark the cathode with a dot, sometimes with a green line. If there is no mark or it is difficult to see because the LED was removed from another circuit, a test should be made.

Testing with a multimeter or battery

It's good to have a multimeter handy. Then the determination of the polarity of the LED will occur in one minute. Having selected the ohmmeter mode (resistance measurement), it is easy to perform the following action. By attaching the probes to the legs of the LED, the resistance is measured. The red wire should be connected to positive and the black wire to negative.

When properly turned on, the device will give a value approximately equal to 1.7 kOhm, and a glow will be observed. When you turn it back on, the display of the multimeter will display an infinitely large value. If the check shows that the diode shows low resistance in both directions, then it is broken and should be disposed of.

Some devices have a special mode. It is designed to check the polarity of the diode. Direct switching will signal the diode illumination. This method is suitable for red and green semiconductors.

The blue and white LEDs only give an indication of voltages above 3 volts, so the desired result cannot be achieved. To test them, you can use multimeters such as DT830 or 831, which provide a mode for determining the characteristics of transistors.

Using the PNP part, one lead of the LED is inserted into the collector socket, the second into the emitter hole. In the case of a direct connection, an indication will appear, the inversion connection will not give a similar effect.

How to determine the polarity of the LED if there is no multimeter at hand? You can resort to a conventional battery or accumulator. To do this, you need another resistor. This is necessary to protect the LED from breakdown and failure. A series connected resistor, the resistance value of which should be approximately 600 ohms, will limit the current in the circuit.

And a few more tips:

• if the polarity of the LED is known, it can no longer be reversed. Otherwise, there is a possibility of breakdown and failure. With proper operation, the LED will serve properly, as it is durable, and its body is well protected from moisture and dust;
• some types of LEDs are sensitive to static electricity (blue, purple, white, emerald). Therefore, they must be protected from the influence of "static";
• when testing the LED with a multimeter, it is desirable to perform this action quickly, touching the terminals should be short-term in order to avoid breakdown of the diode and its failure.

lampagid.ru

how to determine polarity in six ways

These semiconductor radio components are used in various electronic circuits as display elements. As a rule, there are no problems with their installation on the board. To solder 2 legs inserted into the corresponding holes on the "tracks", you do not need to be a major specialist in this field. But with the polarity, which must be taken into account when working with all p / n devices, and not just LEDs, people without experience have difficulties. How to correctly determine the polarity?

By lead length

The easiest way is if the LED is new, never used. His conclusions are not the same - one is a bit longer. It is easy to remember this analogy here. The words "cathode" and "short" begin with the same letter - "K".

Therefore, the other leg, the longer one, is the anode of the LED. Knowing this, it is difficult to confuse. Although some manufacturers are different - they may be the same. Worth considering.

By internal filling

If the flask is clearly visible, then finding the "cup" (and this is the cathode) is not at all difficult.

Knowing the polarity of the LED is not all. It must be installed correctly on the board. A schematic representation of this semiconductor is shown in the figure. The top of the device symbol (triangle) points to the cathode (negative terminal).

By body

So you can not check the polarity of all LEDs, as it depends on the manufacturer. But some have a small risk (notch) on the "rim" opposite the cathode. If you look closely, it's easy to spot. As an option - a small point, a cut.

With battery

Also a simple technique, but here it is necessary to take into account that different types of LEDs differ in breakdown voltage. In order not to disable the semiconductor (partially or completely), a limiting resistance must be connected in series in the circuit. A nominal value of 0.1 - 0.5 kOhm is enough.

multimeter

By the way, it is quite possible to use a household multimeter, which is already equipped with everything you need - a power source and probes. It's even better.

Polarity detection method 1 - based on the property of the LED to “light up” when current passes through it. Therefore, its anode will be where the “plus” of the multimeter batteries is (the “+” probe socket), and the cathode, respectively, where is the minus. To check for "glow", the switch of the device is set to the "diode measurement" position.

Polarity detection method 2 - measured here p-n resistance transition. Multimeter switch - to the "resistance measurement" position, the limit, depending on the modification of the tester, to a position of more than 2 kOhm. For example, at 10.

Touching the leads of the LED with the probes is only short-term, so as not to disable the radio component. If the polarities of the p / n and the power source are the same, then the resistance will be small (from hundreds of ohms to several kOhms). In this case, the red probe (it is customary to insert it into the “+” socket of the device) points to the anode leg, and the black (“-”), respectively, to the cathode.

If the multimeter shows high resistance, then the polarity was reversed when the probes touched the leads. You should repeat the measurement, changing it to make sure that there is no internal break. Only in this case it is possible to speak not only about the polarity of the LED, but also about its serviceability and readiness for its intended use.

At various thematic forums, there are judgments that nothing terrible will happen; you can connect the power supply in any polarity, and the LED will not be affected. But it is not so.

• Firstly, it all depends on the magnitude of the breakdown voltage, that is, the characteristics of a particular semiconductor.
• Secondly, it may continue to work, but partially lose its properties. Simply put, shine, but not as much as it should.
• Thirdly, such experiments have a negative impact on the service life of the LED. If its manufacturer-guaranteed MTBF is about 45,000 hours (on average), then after such polarity checks it will last much less. Proven in practice!

electroadvice.ru

Rectifier diodes, principle of operation, characteristics, connection diagrams

The principle of operation, the main characteristics of semiconductor rectifier diodes can be considered using their current-voltage characteristic (CVC), which is schematically shown in Figure 1.

It has two branches, corresponding to the direct and reverse switching on of the diode.

When the rectifier diode is directly turned on, a noticeable current begins to flow through it when a certain voltage Uopen is reached on the diode. This current is called direct Ipr. Its changes have little effect on the voltage Uopen, so for most calculations you can take its value:

• 0.7 volts for silicon diodes,
• 0.3 Volt - for germanium.

Naturally, the direct current of the diode cannot be increased to infinity; at its certain value Ipr.max, this semiconductor device will fail. By the way, there are two main malfunctions of semiconductor diodes:

• breakdown - the diode begins to conduct current in any direction, that is, it will become an ordinary conductor. Moreover, first a thermal breakdown occurs (this state is reversible), then an electric one (after that, the diode can be safely thrown away),
• cliff - here, I think, explanations are superfluous.

If the diode is connected in the reverse direction, a small reverse current Irev will flow through it, which, as a rule, can be neglected. When a certain value of the reverse voltage Uobr is reached, the reverse current increases sharply, the device, again, fails.

The numerical values ​​of the considered parameters for each type of diode are individual and are its main electrical characteristics. I should note that there are a number of other parameters (self-capacitance, various temperature coefficients, etc.), but for a start, the listed ones will suffice.

Here I propose to finish with pure theory and consider some practical schemes.

DIODES CONNECTION DIAGRAM

To begin with, let's look at how a diode works in a DC (Fig. 2) and AC (Fig. 3) current circuit, which should be taken into account when switching on diodes in one way or another.

When a forward constant voltage is applied to the diode, a current begins to flow through it, determined by the load resistance Rн. Since it should not exceed the limit allowable value you should determine its value, and then select the type of diode:

Ipr \u003d Un / Rn - everything is simple - this is Ohm's law.

Un=U-Uopen - see the beginning of the article. Sometimes the Uopen value can be neglected, there are times when it must be taken into account, for example, when calculating the LED connection diagram.

When a diode is connected to an alternating current circuit, among other things, a reverse voltage Uobr periodically appears on it. Keep in mind that its amplitude value should be taken into account (For Upr, by the way, too). For example, for a household electrical network, the usual voltage of 220V is effective, and its amplitude value is 380V. You can see more about this on this page.

This is the most important thing to remember.

Now - several diode connection schemes that are often encountered in practice.

Without a doubt, the diode bridge circuit used in all kinds of rectifiers is the leader here (Figure 4). It can look different, the principle of operation is the same, I think everything is clear from the picture. By the way, last option- symbol of the diode bridge as a whole. It is used to simplify the designation of the two previous schemes.

1. Diodes can act as "decoupling" elements. The control signals Upr1 and Upr2 are combined at point A, and there is no mutual influence of their sources on each other. By the way, this the simplest option implementation of the logical scheme "or".
2. Protection against polarity reversal (slang - "protection against fools"). If there is a possibility wrong connection polarity of the supply voltage, this circuit protects the device from failure.
3. Automatic transition to power from an external source. Since the diode "opens" when the voltage across it reaches Uopen, then at Uext

© 2012-2018 All rights reserved.

All materials presented on this site are for informational purposes only and cannot be used as guidelines and normative documents.

eltechbook.com

semiconductor diode

A semiconductor diode is the simplest semiconductor device, consisting of a single PN junction. Its main function is to conduct electric current in one direction, and not to pass it in the opposite direction. The diode consists of two layers of semiconductor types N and P.

At the junction of the P and N connection, a PN junction (PN junction) is formed. The electrode connected to P is called the anode. The electrode connected to N is called the cathode. The diode conducts current in the direction from the anode to the cathode, and does not conduct back.

Diode at rest

Let's see what happens inside the PN junction when the semiconductor diode is at rest. That is, when no voltage is connected to either the anode or the cathode.

So, in part N there are free electrons - negatively charged particles. In the P part there are positively charged ions - holes. As a result, in the place where there are particles with charges of different signs, an electric field arises that attracts them to each other.

Under the action of this field, free electrons from the N part drift through the PN junction to the P part and fill some holes. The result is a very weak electric current, measured in nanoamps. As a result, the density of the substance in the P part increases and diffusion occurs (the desire of the substance to uniform concentration), pushing the particles back to the N side.

Diode Reverse

Now let's see how a semiconductor diode can perform its main function - to conduct current in only one direction. Connect the power supply - plus to the cathode, minus to the anode.

In accordance with the force of attraction that has arisen between charges of different polarity, the electrons from N will begin to move towards the plus and move away from the PN junction. Likewise, holes from P will be attracted to minus, and will also move away from the PN junction. As a result, the density of the substance at the electrodes increases. Diffusion comes into play and starts to push the particles back, striving for a uniform density of the substance.

As we can see, in this state the diode does not conduct current. As the voltage increases, there will be less and less charged particles in the PN junction.

Diode direct connection

We change the polarity of the power source - plus to the anode, minus to the cathode. In this position, a repulsive force arises between charges of the same polarity. Negatively charged electrons move away from the minus and move towards the pn junction. In turn, the positively charged holes are repelled by the plus and directed towards the electrons. The PN junction is enriched with charged particles with different polarity, between which an electric field arises - the internal electric field of the PN junction. Under its action, electrons begin to drift to the P side. Some of them recombine with holes (fill in the place in atoms where there is not enough electron). The remaining electrons rush to the plus of the battery. A current ID went through the diode.

To avoid confusion, let me remind you that the direction of current in electrical circuits is opposite to the direction of electron flow.

Disadvantages of Real Semiconductor Diode

In practice, in a real diode, when the voltage is reversed, a very small current occurs, measured in micro or nanoamps (depending on the model of the device). Due to too high voltage, the crystal structure of the semiconductor in the diode can be destroyed. In this case, the device will begin to conduct current well also with reverse bias. This voltage is called breakdown voltage. The process of destruction of the semiconductor structure is unrecoverable, and the device becomes unusable.

When connected directly, the voltage between the anode and cathode must reach a certain value Vϒ in order for the diode to begin to conduct current well. For silicon devices, Vϒ is about 0.7V, and for germanium - about 0.3V. More details about this, and other characteristics of a semiconductor rectifier diode, will be discussed in the article CVC of a semiconductor diode.

hightolow.ru

What is a diode and how to test it

Greetings friends!

We are so used to computers that we cannot imagine our lives without them. These buzzing boxes on our desks are made up of many different pieces of hardware. It is interesting to note that none of these building blocks by itself can boast of the properties that a computer has.

And put together, they are something completely unique!

Whatever brick you take is just a piece of baked clay; it is not immediately and clear to what business it - in itself - can be adapted.

It's like a house built with bricks.

But several thousand such pieces of clay, collected in a certain way, are a dwelling that protects from bad weather and provides a roof over your head.

Of course, you can use a computer (and live in a house) and not imagine how these things work.

But if you want to learn how to "heal" your computers, you will have to figure out how their components are arranged.

Therefore, today we will talk about one of the computer "building blocks" in a little more detail. We will try to briefly get acquainted with what semiconductor diodes are and why they are needed.

What is a diode?

Diodes are used in computer power supplies to rectify alternating current.

A rectifier diode is a part that has two types of semiconductors connected together - p-type (positive - positive) and n-type (negative - negative).

When they are connected (fusion), a so-called p-n junction is formed. This transition has a different resistance at different polarity of the applied voltage.

If the voltage is applied in the forward direction (the positive terminal of the voltage source is connected to the p-semiconductor - the anode, and the negative terminal - to the n-semiconductor - the cathode), then the resistance of the diode is small.

In this case, the diode is said to be open. If the polarity of the connection is reversed, then the resistance of the diode will be very large. In this case, the diode is said to be closed (locked).

When the diode is open, some voltage drops across it.

This voltage drop is created by the so-called forward current flowing through the diode and depends on the magnitude of this current.

Moreover, this dependence is non-linear.

The specific value of the voltage drop depending on the flowing current can be determined from the current-voltage characteristic.

This characteristic is necessarily given in the full technical description (data sheets, reference sheets).

For example, on a common 1N5408 diode used in a computer power supply, when the current changes from 0.2 to 3 A, the voltage drop changes from 0.6 to 0.9 V. The more current flowing through the diode, the greater the voltage drop across it and , respectively, the power dissipated on it (P = U * I). The more power dissipated on the diode, the more it heats up.

In a computer power supply, when rectifying the mains voltage, a bridge rectification circuit is usually used - 4 diodes connected in a certain way.

If terminal 1 has a positive potential relative to terminal 2, then the current will flow through the diode VD1, the load and the diode VD3.

If terminal 1 has a negative terminal 2 potential, then the current will flow through the VD2 diode, the load and the VD4 diode. Thus, the current through the load, although it varies in magnitude (with an alternating voltage), always flows in one direction - from terminal 3 to terminal 4.

This is the straightening effect. If there were no diode bridge, the load current would flow in different directions. With the bridge, it flows in one. Such a current is called pulsating.

In the course of higher mathematics, it is proved that the pulsating voltage contains a constant component and the sum of harmonics (frequencies that are multiples of the fundamental frequency of the alternating voltage of 50 Hertz). The DC component is separated by a filter (large capacitance), which does not allow harmonics to pass through.

Rectifier diodes are also present in the low-voltage part of the power supply. Only the switching circuit consists there not of 4 diodes, but of two.

An attentive reader may ask: “Why are different switching schemes used? Is it possible to use a diode bridge in the low-voltage part as well?”

It is possible, but it will not be the best solution. In the case of a diode bridge, the current flows through the load and two diodes connected in series.

In the case of using 1N5408 diodes, the total voltage drop across them can be 1.8 V. This is very small compared to the mains voltage of 220 V.

But if such a circuit is applied in the low-voltage part, then this drop will be very noticeable compared to voltages of +3.3, +5 and +12 V. The use of a two-diode circuit reduces losses by half, since one diode is connected in series with the load , not two.

In addition, the current in the secondary circuits of the power supply is much greater (at times) than in the primary.

It should be noted that for this circuit, the transformer must have two identical windings, not one. A two-diode rectifier circuit uses both half-cycles of the AC voltage, just like a bridge circuit.

If the potential of the upper end of the secondary winding of the transformer (see diagram) is positive with respect to the lower one, then the current flows through terminal 1, diode VD1, terminal 3, load, terminal 4 and the middle point of the winding. Diode VD2 is locked at this time.

If the potential of the lower end of the secondary winding is positive with respect to the upper one, then the current flows through terminal 2, diode VD2, terminal 3, load, terminal 4 and the middle point of the winding. Diode VD1 is locked at this time. It turns out the same pulsating current as in the bridge circuit.

Now let's put an end to boring theory and move on to the most interesting thing - to practice.

To begin with, let's say that before starting to test diodes, it would be good to familiarize yourself with how to work with a digital tester.

This is covered in related articles here, here and here.

The diode on electrical circuits is depicted symbolically in the form of a triangle (arrow) and a stick.

The stick is the cathode, the arrow (it indicates the direction of the current, i.e. the movement of positive charges) is the anode.

You can check the diode bridge with a digital tester by setting the operation switch in the diode test position (the pointer of the tester range switch should be opposite the symbolic image of the diode).

If you connect the red probe of the tester to the anode, and the black probe to the cathode of a separate diode, then the diode will be opened by the voltage from the tester.

The display will show a value of 0.5 - 0.6 V.

If you change the polarity of the probes, the diode will be locked.

The display will then show the unit in the leftmost digit.

The diode bridge often has a symbolic designation of the type of voltage on the case (~ alternating voltage, +, - direct voltage).

The diode bridge can be checked by installing one probe on one of the "~" terminals, and the second - alternately on the "+" and "-" terminals.

In this case, one diode will be open, and the other closed.

If you change the polarity of the probes, then the diode that was closed will now open, and the other will close.

It should be noted that the cathode is the positive terminal of the bridge.

If any of the diodes is shorted, the tester will show zero (or very little voltage).

Such a bridge, of course, is unsuitable for work.

You can verify that the diode is shorted by testing the diodes in the resistance measurement mode.

With the diode shorted, the tester will show little resistance in both directions.

As already mentioned, a two-diode rectification circuit is used in the secondary circuits.

But even on one diode, a sufficiently large voltage drops compared to the output voltages of +12 V, +5 V, +3.3 V.

Consumption currents can reach 20 A or more, and more power will be dissipated on the diodes.

As a result, they will get very hot.

The power dissipation will decrease if the forward voltage across the diode is lower.

Therefore, in such cases, so-called Schottky diodes are used, in which the direct voltage drop is less.

Schottky diodes

The Schottky diode does not consist of two different semiconductors, but of a metal and a semiconductor.

The resulting so-called potential barrier will be smaller.

In computer power supplies, dual Schottky diodes are used in a three-terminal package.

A typical representative of such an assembly is the SBL2040. The voltage drop across each of its diodes at maximum current will not exceed (according to the datasheet) 0.55 V. If you check it with a tester (in diode test mode), it will show a value of about 0.17 V.

The lower voltage value is due to the fact that a very small current flows through the diode, far from the maximum.

In conclusion, let's say that the diode has such a parameter as the maximum allowable reverse voltage. If the diode is closed, a reverse voltage is applied to it. When replacing diodes, this value must be taken into account.

If in a real circuit the reverse voltage exceeds the maximum permissible value, the diode will fail!

The diode is an important "piece of iron" in electronics. How else would we rectify the voltage?

That's all for today. I hope you were interested.

Victor Geronda was with you.

See you on the blog!

vsbot.ru

Polarity - Diode - The Big Encyclopedia of Oil and Gas, article, page 1

Polarity - diode

Page 1

The polarity of the diodes is determined by the tester.

The polarity of the diodes KIPD 02A - 1K, KIPD02B - 1K is indicated on the drawing; the rest of the diodes have reverse polarity.

By changing the polarity of the diode and the voltage reference, you can get a limit from below.

Only there is a different polarity of the diodes and they are included directly in the arms of the rectifier bridge, but here they are replaced by the image of the diode inside the square, symbolizing the rectifier bridge. If you want to trace the entire path of the current rectified by the diodes V1 - V4, write them in the sides of the square.

To measure the negative peak value, the polarity of the diodes must be reversed.

Another type of amplifying circuit is based on the minority carrier accumulation effect that occurs when the polarity of a diode is reversed. G, which feeds it with a signal voltage in the form of pulses.

Knowing the polarity of the ohmmeter, it is easy to determine the polarity of the diode, since in the case when the ohmmeter shows the minimum resistance, the polarities of the diode and ohmmeter are the same.

The polarity of the diode is chosen such that it passes current in half cycles of reverse polarity.

Are issued in the glass case with flexible conclusions. The polarity of the diode is indicated by a yellow dot on the case near the positive (anode) terminal. The type of diode is given on the additional container.

Marked with color dots on the body: AL336A - one red, AL336B - two red, AL336V - one green, AL336G - two green, AL336D - one yellow, AL336E - two yellow, AL336Zh - three yellow, AL336I - one white, AL336K - one black . The polarity of the diodes AL336A, AL336B and AL336K is indicated on the drawing. Diodes AL336V - AL336I have reverse polarity.

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LED is a semiconductor optical device that transmits electric current in the forward direction. When connected, there will be no inversion current in the circuit, and, of course, there will be no glow. To prevent this from happening, you need to observe the polarity of the LED.

The LED in the diagram is indicated by a triangle in a circle with a cross line - this is the cathode, which has a “-” (minus) sign. On the opposite side is the anode, which has a "+" (plus) sign.

The wiring diagrams must contain a pinout (or pinout) of the leads to identify all the contacts of the connection.

How to determine the polarity of the diode, holding a tiny light bulb in your hands? After all, for a correct connection, you need to know where it has a minus, and where it has a plus. If the pinout is mixed up, the circuit will not work.

Visual method for determining polarity

The first way to determine is visual. The diode has two terminals. The short leg will be the cathode, the anode of the LED is always longer. It is easy to remember, since there is an initial letter "k" in both words.

When both leads are bent or the instrument is removed from another board, it can be difficult to determine their length. Then you can try to see a small crystal in the case, which is made of a transparent material. It sits on a small stand. This pin corresponds to the cathode.

Also, the cathode of the LED can be determined by a small notch. New models of LED strips and lamps use semiconductors for surface mounting. The available key in the form of a bevel indicates that this is a negative electrode (cathode).

Sometimes the LEDs are marked "+" and "-". Some manufacturers mark the cathode with a dot, sometimes with a green line. If there is no mark or it is difficult to see because the LED was removed from another circuit, a test should be made.

Testing with a multimeter or battery

It's good to have a multimeter handy. Then the determination of the polarity of the LED will occur in one minute. Having selected the ohmmeter mode (resistance measurement), it is easy to perform the following action. By attaching the probes to the legs of the LED, the resistance is measured. The red wire should be connected to positive and the black wire to negative.

When properly turned on, the device will give a value approximately equal to 1.7 kOhm, and a glow will be observed. When you turn it back on, the display of the multimeter will display an infinitely large value. If the check shows that the diode shows low resistance in both directions, then it is broken and should be disposed of.

Some devices have a special mode. It is designed to check the polarity of the diode. Direct switching will signal the diode illumination. This method is suitable for red and green semiconductors.

The blue and white LEDs only give an indication of voltages above 3 volts, so the desired result cannot be achieved. To test them, you can use multimeters such as DT830 or 831, which provide a mode for determining the characteristics of transistors.

Using the PNP part, one lead of the LED is inserted into the collector socket, the second into the emitter hole. In the case of a direct connection, an indication will appear, the inversion connection will not give a similar effect.

How to determine the polarity of the LED if there is no multimeter at hand? You can resort to a conventional battery or accumulator. To do this, you need another resistor. This is necessary to protect the LED from breakdown and failure. A series connected resistor, the resistance value of which should be approximately 600 ohms, will limit the current in the circuit.

And a few more tips:

• if the polarity of the LED is known, it can no longer be reversed. Otherwise, there is a possibility of breakdown and failure. With proper operation, the LED will serve properly, as it is durable, and its body is well protected from moisture and dust;
• some types of LEDs are sensitive to static electricity (blue, purple, white, emerald). Therefore, they must be protected from the influence of "static";
• when testing the LED with a multimeter, it is desirable to perform this action quickly, touching the terminals should be short-term in order to avoid breakdown of the diode and its failure.