How to test a powerful thyristor. Self-healing of thyristors. Principle of operation and parameters of the thyristor

How often has it happened to us that an electrical circuit assembled with new parts did not work? The quality of components from a store, and even more so from the radio market, often leaves much to be desired, and there is no need to talk about electrical components that have already been used. In this case, it would definitely be a good idea to check them for serviceability before use. Today we will talk about how to check the serviceability of a thyristor.

What is a thyristor?

A thyristor is a semiconductor device made using classical single-crystal technology. On the built-in crystal there are several (most often three) p-n junctions that have completely opposite stable states. Basically, thyristors are used as an electronic switch and can successfully replace radio elements such as a mechanical relay. The main advantages of thyristors are:

• Smooth and adjustable activation.
• Control of the rate of rise of the operating current.
• Excellent integration into complex circuits.
• No sparking or interference.
• Compact detail.
• There is no need to constantly provide a control signal.

Checking a thyristor without a multimeter

If you don’t have a multimeter at hand, but you need to check the thyristor, there is a simple way to do this. You need to take a regular battery and a 1.5V light bulb and connect them in series through a thyristor. When control current is applied to the thyristor, the light should light up. Next, you should disconnect the battery, but keep the source of control current; if the light bulb continues to light, it means that its p-n junction is working. If light bulbs and batteries are not available, then the most the right way check the thyristor using a digital or analog multimeter.

Checking a thyristor with a multimeter

The first thing you need to do before checking is to make sure there is a fresh, undischarged battery in the device. You can check it with the device itself; it does not require power to measure voltage. Next, the sequence of actions for checking is as follows:

• Set the multimeter to dialing mode. Since the operating current is not enough for opening p-n transition, then the resistance will be high and no current will flow. In this case, the multimeter should show the number 1; if this is the case, then the transition is not broken and we can proceed to other tests.
• Without switching the multimeter mode, connect the control electrode to the anode. In this case, the current becomes sufficient to open the pn junction and the resistance decreases sharply. In this case, the device should show numbers less than one, which corresponds to the open state of the thyristor. In this way, the serviceability of the control element is checked.
• We open the contacts and the number 1 should light up on the multimeter display again. In this case, the thyristor cannot continue to be open, because the device does not generate enough current to trigger the thyristor by holding current. We cannot check this parameter using a multimeter.
• We change the polarity on the device and try to perform the same manipulations, the test will be unsuccessful. This way we can detect the absence of reverse breakdown in the thyristor.
• You can also check the thyristor for sensitivity. To do this, steps 1-3 should be performed with the ohmmeter mode on the multimeter turned on, and not the continuity mode. To begin with, the ohmmeter must be set to sensitivity x1, then to x10, and so on until the transition closes after turning off the control current. The lower the holding current, the more sensitive the thyristor is considered. When choosing parts and the possibility of testing them, you need to give preference to those thyristors whose sensitivity is higher.

If the thyristor is part of any wiring circuit, there is no need to remove it to check, just disconnect the control electrode.

As you can see, checking a thyristor at home is quite easy and does not require much time. Don't neglect checking radio components before assembling complex circuits. Spending a few seconds at the beginning will help save time spent later on identifying a part that is no longer working. assembled circuit. And finally, a visual video instruction on this process, good luck with the installation.

A dinistor is an important radio element in electrical circuits. It is intended for circuits with automatic switching of devices, pulse generators, high-frequency signal converters. Because of low cost and of simple design, such a radio component is considered ideal for use in power regulators.

But like any electronic element, it can fail. Therefore, it is extremely important to be able to correctly check a dinistor with a multimeter.

Purpose of the dinistor

Dinistor is semiconductor element, having two stable states: closed and open. It is made from a semiconductor single crystal with several p-n junctions. In general, it can be considered as an electronic key, when one of its states (closed) corresponds to low conductivity, and the other (open) to high conductivity.

The dinistor belongs to the “thyristor family” of radioelements and has no fundamental differences with the thyristor. The only thing is what distinguishes it is the conditions for changing the stable state. Unlike a thyristor, which has three terminals, a dinistor has only two of them, that is, it does not have a control input.

Hence its second name - diode thyristor. The terminals of the dinistor are called anode and cathode. The first is derived from the extreme p-region, and the second from the n-region.

The invention of thyristors is associated with the name of the English physicist William Bradford Shockley. After the invention of the point-point transistor, the scientist devoted his experiments to creating a monolithic element. Thus, in 1949, a prototype of a planar transistor was presented, and the very next year, Sparks and Teal, Shockley’s assistants, were able to produce a three-layer structure that made it possible to produce high-frequency radio elements based on p-n junctions. The scientist's research led to the creation of a semiconductor diode called the Shockley diode. Its design is a four-layer element with a pnpn type structure.

In modern electronics, dinistors are most often used in the startup circuit of energy-saving lamps and daylight control ballasts.

On diagrams and in literature, an element is designated using the Latin letters VD or VS, and its graphic designation is a triangle along with a straight line passing through its middle, symbolizing an electrical circuit. As a result, a kind of arrow is formed, indicating the direction of current flow. Two short lines are drawn perpendicular to the straight line in the middle and near the vertex of the triangle. The first denotes the base region and the second the cathode.

Operating principle

Considering a dinistor as a four-structure element, it can be represented in the form of two interconnected transistors of n and p conductivity type. For the transistor to operate, current must appear at the base-emitter junction. If voltage is not applied to it, then no current will pass through the radio element. This is due to the fact that the opening of the transistors is controlled by each other. In other words, to open one of these transistors, it is necessary to switch the other one to the open state.

There must be a certain voltage between the terminals of the dinistor, which allows one of the two transistors to switch to saturation mode. As a result, the second element will open and the dinistor will begin to pass current.

To switch the structure to the current cut-off mode, you will need to reduce the voltage, which will lead to the loss of the bias current and, accordingly, the base current on the second transistor. The dinistor will stop passing current.

The polarity of the voltage applied to the terminals of the radio component also plays a significant role. When a minus voltage is applied to the anode, practically no current passes through the element. This kind of inclusion is called inverse. If the polarity is changed, then a small current will begin to flow through the device - the closing current. The voltage corresponding to it determines highest value, in which the dinistor is in the closed state. To open the dinistor, you will need a voltage of the order of tens of volts.

Dinistors, like trinistors, pass current in only one direction. To allow current to flow in both directions, they are connected in an anti-parallel circuit. A five-layer pnpnp type structure can also be used for this.

Device characteristics

To correctly test a thyristor with a multimeter, you need to not only understand the principle of its operation, but also know its main characteristics. The most significant parameter of an element is its current-voltage characteristic (volt-ampere characteristic). It clearly shows the dependence of the current flow through the device on the voltage applied to its terminals. The current-voltage characteristic of the dinistor is S-shaped. This characteristic is divided into six zones:

1. Open area. At this gap, the element offers virtually no resistance to the current passing through it. Its conductivity is maximum. This zone ends at a point where current stops flowing.
2. Negative resistance area. Provokes the onset of an avalanche breakdown.
3. Breakdown of the collector junction. During this interval, the element operates in avalanche breakdown mode, which causes a sharp decrease in the voltage at its terminals.
4. Direct connection section. In this area, the dinistor is closed, since the potential difference applied to its terminals is less than that required for a breakdown to occur.
5. The fifth and sixth sections describe the operation of the device in the lower half of the current-voltage characteristic and correspond to the states of reverse switching on and breakdown of the element.

Analyzing the current-voltage characteristic, we can conclude that the operation of a dinistor is similar to a diode, but, unlike the latter, to open it it is necessary to apply a voltage several times higher than the diode value. At the same time, the dinistor is characterized by a number of parameters that determine its use in electrical circuits. Its main characteristics include the following values:

Device diagnostics

When checking a radio element for serviceability, a multimeter is most often used. The ease of use of this measuring device is explained by its versatility. With its help, you can ring an element for breakdown or measure threshold voltage levels. It does not matter whether the meter is analog or digital.

To obtain correct measurement results, you will need to prepare the multimeter for use. The whole essence of the preparatory operation comes down to checking the tester's battery. When using a digital device You need to pay attention to the flashing battery icon. If it is, then the battery needs to be replaced. For an analog device, the arrow is set to the zero position before operation. If this cannot be done, then the battery must be replaced.

For a reliable result, when measuring with a multimeter, it is also advisable to monitor the ambient temperature. This is due to the fact that as the temperature increases, the conductivity of semiconductors increases. The optimal temperature for measurement is considered to be around 22 °C.

Continuity without soldering

Due to the specifics of the device, checking the triac with a multimeter without desoldering is not so easy. For full check used electrical diagram, allowing for a number of necessary measurements. The only thing that can be done with a multimeter is to check it for obvious breakdown.

To do this, the tester switches to the diode vertebrae mode, after which the measuring probes touch the dinistor terminals. For any polarity, the tester should show a break, which will indicate the absence of a breakdown in the element. But this will not guarantee the serviceability of the device. If during measurement the multimeter shows a short circuit, then such a thyristor can no longer be checked, since it is faulty.

At the same time, you should know that ringing a radio element in the circuit will be incorrect, since other radio elements that affect the measurements can be connected in parallel with its output. Making a simple call, it is necessary to disconnect at least one of the dinistor inputs from printed circuit board. In order to check the dinistor without desoldering, you can use the capabilities of the circuit in which it is installed.

It is known that a radio element opens only when a certain voltage level is applied to its terminals, so you can try to reach this threshold value.

In this case, the multimeter switches to voltage measurement mode to check. Depending on the expected breakdown voltage, the measurement range is selected. The measuring probes are connected in parallel to the terminals of the element, after which the signal level is measured. If a voltage surge occurs when the input signal changes, this will indicate the breakdown voltage of the dinistor, that is, its performance.

Test circuit

To gain confidence in the functionality of the element, radio amateurs use test circuits. They come in varying degrees of complexity, which ultimately affects the accuracy of the result obtained. The most simple circuit consists of three elements:

• regulated power supply;
• resistor;
• indicator.

As the latter, you can use an LED. Having assembled such a diagram, we begin to check. A tester is connected parallel to the element in voltage measurement mode.

For example, to check the KU202N thyristor with a multimeter, first set the output voltage level to about twenty volts. In this case, the LED in the circuit should not light up. The level then slowly rises until the LED lights up. The glow of the indicator indicates that the dinistor has opened and has begun to pass through electric current. To close it, the voltage level is reduced.

The value of the potential difference at which the operating mode changes is the maximum opening voltage. In this case, the tester should show a value of about 50 volts, while the input signal level will be about 60 volts. Any type of resistor can be used. Its purpose is to limit the amount of current passing through the LED.

Knowing how to test the KU 202 thyristor, you can test any other type of thyristor, dinistor or triac. It should be noted that professionals use an oscilloscope instead of a multimeter. A test attachment is used together with it. The elements to be measured are connected to sockets X5 and X6. When using a thyristor, its control element is connected to socket X7. For elements with a control output, the voltage is changed using variable resistor R4. If the radio element is intact, then the oscillogram should be the same as in the figure.

25.06.2018

For switching AC electrical networks, they are used various elements. Most often, powerful triacs are used, which are necessary for the design of transformers and chargers.

Triacs are a type of thyristors that are analogues of silicon rectifiers in a housing. But, unlike thyristors, which are unidirectional devices, i.e., they transmit current only in one direction, triacs are two-way. With their help, you can transmit current in both directions. They have five thyristor layers that are equipped with electrodes. At first glance, domestic triacs resemble a pnp structure, but they have several regions with n-type conductivity. The last region, which is located after this layer, has a direct connection with the electrode, which ensures high signal conductivity. Sometimes they are also compared to rectifiers, but it is worth remembering that diodes transmit electrical signal only one way.

Photo - using a thyristor

A triac is considered an ideal device for use in switching networks because it can control the current flowing through both halves of an alternating cycle. The thyristor controls only a half-cycle, while the second half of the signal is not used. Thanks to this feature of operation, the triac perfectly transmits signals from any electrical devices; a triac is often used instead of a relay. But at the same time, a triac is rarely used in complex electrical devices such as transformers, computers, etc.

Photo - triac

Video: how a triac works

Operating principle

The principle of operation of a triac is very similar to a thyristor, but it is easier to understand based on the operation of the trinistor analogue of that component of electrical networks. Note that the fourth semiconductor component is separated, allowing the following functions:

1. Monitor the operation of the cathode and anode;
2. If necessary, swap them, which allows you to change the polarity of operation.

In this case, the operation of the device can be regarded as a combination of two counter-directed thyristors, but operating in a full cycle, i.e., not interrupting the signals. Marking on the diagram corresponding to two connected thyristors:

Photo - trinistor analogue of triac

According to the drawing, a signal is transmitted to the electrode, which is the control electrode, allowing the contact of the part to open. At the moment when there is a positive voltage at the anode, and a negative voltage at the cathode, the electric current will begin to flow through the thyristor, which is on the left side of the diagram. Based on this, if the polarity is completely changed, which reverses the charges of the cathode and anode, the current transmitted through the contacts will go through the right SCR.

Here the last layer on the triac is responsible for the voltage polarity. It controls the voltage at the contacts and, comparing it, transfers the current to a specific thyristor. Directly proportional to this, if the signal is not supplied, then all the thyristors are closed and the device does not work, i.e. it does not transmit any pulses.

If there is a signal, there is a connection to the network and the current must flow somewhere, then the triac in any case conducts it; the polarity of the direction in this case is dictated by the charge and polarity of the poles, cathode and anode.

Please note that the diagram above shows the current-voltage characteristic (volt-ampere characteristic) of the triac, in Figure 3. Each of the curves has a parallel direction, but in the other direction. They repeat each other at an angle of 180 degrees. This graph allows us to say that a triac is an analogue of a dinistor, but at the same time, the areas through which the dinistors do not transmit a signal are very easily overcome. The parameters of the device can be adjusted by applying current of different voltages, this will allow you to unlock the contacts in the desired direction simply by changing the polarity of the signal. In the drawing, places that may change are marked with dashed lines.

Photo - triacs

Thanks to this current-voltage characteristic, it becomes clear why the stabilized thyristor received such a name. Triac means “symmetrical” thyristor; in some textbooks and stores it may be called triac (foreign version).

Area of ​​use

Bidirectionality makes triacs very convenient switches for circuits AC, allowing them to control large flows of electrical energy passing through small contact poles. In addition, you can even control the percentage of inductive load current.

Photo - triac operation

The devices are used in radio engineering, electromechanics, mechanics and other industries where it may be necessary to control the flow of current. Optosimistors are often used in alarm systems and dimmers, where correct operation of the devices requires full cycle, not half-cycle. Although quite often the use of this radio component is not effective. For example, to operate a small microcontroller or transformer, it is sometimes better to connect low-power thyristors, which will ensure the operation of both periods equally.

Checking, pinout and use of triacs

In order to use the device in operation, you need to know how to test a triac with a multimeter or “ring” it. To check, you need to evaluate the characteristics of controlled silicon diodes. Such rectifiers allow you to set the desired readings and carry out tests. The negative terminal of the ohmmeter is connected to the cathode, and the positive terminal is installed on the anode. Then you need to set the ohmmeter to one, and connect the control electrode to the anode terminal. If the data is between 15 and 50 ohms, then the part works normally.

Photo - light control with triacs

But at the same time, when you disconnect the contacts from the anode, the ohmmeter readings should be saved on the device. Make sure that a simple measuring device does not show residual resistance, otherwise this will indicate that the part is not working.

In everyday life, triacs are often used to create devices that extend the service life of various devices. For example, for incandescent lamps or meters, you can make a power regulator (you will need a MAC97A8 or TC thyristor).

Photo - diagram of a power regulator on a triac

The diagram shows how to assemble a power regulator. Pay attention to elements DD1.1.DD1.3, where the generator is indicated; due to this part, about 5 pulses are produced, which represent half-cycles of one signal. The pulses are controlled using resistors, and a transistor with rectifying diodes controls the moment the triac is turned on.

Photo - triac measurement

This transistor is open, based on this, a signal approaches the input of the generator while the triacs and the remaining transistors are closed. But if at the moment of opening the contacts the state of the generator does not change, then the storage elements will generate a small pulse in order for the pinout to start. This dimmer circuit on a triac can be used to control the operation of lighting fixtures, a washing machine, the speed of a vacuum cleaner or incandescent lamps with a motion sensor. Use a tester to check the functionality of the circuit and you can use it.

Photo - triac operation

To improve the system, it is possible to control the triac through an optocoupler so that the element is switched on only after a signal. Please note that if, when scrolling the drum, movements occur very sharply, then it is faulty electronic module. Most often, a triac burns out; imported conductors often cannot withstand voltage surges. To replace it, simply select the same part.

Photo - thyristor charger

Similarly, according to the scheme, you can assemble a charger on a triac; depending on the requirements, you will just need to buy low-power or high-power parts KU208G, KR1182PM1, Z0607, BT136, BT139 (BTB - VTV, BTA - VTA are also suitable). In domestic imported conditions, foreign triacs are used, the prices of which are slightly higher.

To test radio elements for functionality, a multimeter is most often used. It is good because with its help you can quickly identify radical defects in most radio components. The downside here is that not every multimeter, and not every part, can be thoroughly tested.

Analog multimeter

Most often called a tester, less often - an avometer (Ampere-Volt-Ohm meter) and, almost never, directly a multimeter. Consists of a precision dial potentiometer head and complex switched measurement circuits. Moreover, the internal battery (4.5-9 V) is needed only for measuring resistance. Voltage and current can be measured without it.
You can check the thyristor with a multimeter of this type only if you have a fresh, not discharged battery.

Digital multimeter

That’s what they call it, less often – a tester, and almost never – an avometer. It consists of simplified switched measurement circuits serving a microcontroller with an ADC (analog-to-digital converter). His wide range measurements, sensitivity and accuracy, make it possible to do without them. The internal battery (1-9 V) is used not only to measure resistance, but also to power the microcontroller and its peripherals.

How to test a thyristor with a multimeter

Let's consider the sequence of actions to determine the performance of a thyristor.

1. Anode-cathode continuity, with any application of probes:
   • the analog one will show infinity, the arrow will not move;
   • digital will either not respond at all or will display a few megohms.
2. When checking the anode-control electrode:
   • analog will show from several to tens of kOhms;
   • digital will give the same numbers.
3. When checking the cathode-control electrode:
   • the same for both devices.

Now let's try to check the thyristor for opening, its main operation. To do this, we apply the negative probe to the cathode, the positive one to the anode, and with it, without lifting it from the anode, we briefly touch the control electrode. The thyristor must open (resistance drops to almost 0 Ohm) and remain in this state until the circuit breaks.
If this does not happen then:

• the positive and negative tester probes are mixed up;
• unsuitable tester or dead battery in it;
• The thyristor is faulty.

Before throwing away the thyristor, let’s check the multimeter and the correctness of our actions when working with it:

• The ground (case or COM) probe of an analog tester is positive, while for a digital multimeter, on the contrary, it is negative.
• the measurement range should be set to 100-2000 Ohms, depending on the gradation of the switching unit;
• The measuring device must be powered by a fresh, undischarged battery with a voltage of 4.5 to 9 volts;
• On the digital multimeter scale, in the resistance measurement sector, there should be a diode icon.

Digital toy testers, the size of a matchbox and powered by a watch battery, are not suitable for testing semiconductor elements. And you shouldn’t rely on their other measurements. But to say that it is impossible to test a thyristor with a digital multimeter (and such an opinion exists) is also incorrect. It is possible, and even many. Compliance with the above rules allows you to achieve positive results with different devices.

SCR- This special kind semiconductors, which belongs to the subclass of thyristors and to the class of diodes. It is a diode, but this "diode" also has a third terminal called Control Electrode(UE). It turns out that a trinistor is a diode with three terminals :-).Trinistors are also called by the type of subclass - thyristors - and there is no mistake in this, so in this article I will simply call them thyristors.

They look something like this:

And here is the circuit designation of the thyristor

The principle of operation of a thyristor is based on the principle of operation of a relay. A relay is an electromechanical product, while a thyristor is purely electrical. Let's look at the principle of operation of a thyristor, otherwise how can we check it then? I think everyone rode the elevator ;-). By pressing a button on any floor, the elevator’s electric motor begins its movement, pulls a cable with a cabin with you and your neighbor Aunt Valya, about two hundred kilograms, and you move from floor to floor. How did we use a tiny button to raise the cabin with Aunt Valya on board? This example is the basis of the operating principle of a thyristor. By controlling a small voltage on the button, we control a large voltage... isn't this a miracle? Moreover, there are no clicking contacts in the thyristor, like in a relay. This means that there is nothing to burn out and under normal operating conditions such a thyristor will serve you, one might say, indefinitely.

Currently, powerful thyristors are used for switching (switching) high voltages in electric drives, in installations for melting metal using an electric arc (in short, using Short circuit, as a result of which such powerful heating occurs that the metal even begins to melt)

The SCRs on the left are installed on aluminum radiators, and tablet SCRs are even installed on water-cooled radiators, because a crazy amount of current passes through them and they switch very high power.

Low-power SCRs are used in the radio industry and, of course, in amateur radio.

Let's understand some important parameters of thyristors. Without knowing these parameters, we will not catch up with the principle of testing a thyristor. So:

1) U y- - the lowest constant voltage on the control electrode, causing the thyristor to switch from a closed state to an open state. In short in simple language, the minimum voltage on the control electrode, which opens the thyristor and the electric current begins to flow quietly through the two remaining terminals - the anode and cathode of the thyristor. This is the minimum opening voltage of the thyristor.

2)U arr max - reverse voltage, which a thyristor can withstand when, roughly speaking, the plus is supplied to the cathode and the minus to the anode.

3) I OS Wed -average current value, which can flow through the thyristor in the forward direction without harm to its health.

The remaining parameters are not so critical for beginner radio amateurs. You can get acquainted with them in any reference book.

Well, finally we move on to the most important thing - checking the SCR. We will check the most popular and famous Soviet thyristor - KU202N.

And here is his pinout

To test the SCR we need a light bulb, three wires and a DC power supply. On the power supply we set the voltage for the light bulb to light up. We tie and solder wires to each terminal of the thyristor.

We supply “plus” from the power supply to the anode, and “minus” to the cathode through a light bulb.

Now we need to apply voltage relative to the anode to the Control Electrode (CE). For this type of thyristor U y- unlocking constant control voltage more than 0.2 Volt. We take a one and a half volt battery and supply voltage to the UE. Voila! The light bulb came on!

You can also use multimeter probes in continuity mode; the voltage on the probes is also more than 0.2 Volts

We remove the battery or probes, the light should continue to light.

We opened the thyristor by applying a voltage pulse to the UE. Everything is elementary and simple! In order for the thyristor to close again, we need to either break the circuit, that is, turn off the light bulb or remove the probes, or apply reverse voltage for a moment.

You can also test the thyristor using a Multimeter. To do this, we assemble it according to this diagram:

Since there is voltage on the cartoon probes in the dialing mode, we supply it to the UE. To do this, we close the anode and the UE between each other and the resistance through the Anode-Cathode of the thyristor drops sharply. In the cartoon we see a 112 millivolt voltage drop. This means that it has opened.

After release, the cartoon again shows an infinitely large resistance.

Why did the thyristor close? After all, the light bulb was on in the previous example? The thing is that the thyristor closes when the holding current becomes very small. In a multimeter, the current through the probes is very small, so the thyristor closed without voltage from the UE. There is also a diagram of an excellent device for testing a thyristor, you can look at it in this article.

I also advise you to watch the video from ChipDip about checking the thyristor and holding current:

Any electrical appliances and electrical circuit boards are based on a complex of various radioelements, which are the basis for the normal functioning of the entire variety of electrical equipment. One of the main elements of any electrical circuit is a triac, which is a type of thyristor.

When we say thyristor, we also mean triac. Its purpose is to switch loads in the AC network. Internal structure includes three electrodes for transmitting electric current: control and 2 power.

Purpose and use of triacs in radio electronics

The peculiarity of a thyristor is to pass current from one contact (anode) to another (cathode) and in the opposite direction. Any thyristor is controlled by both positive and negative current. For it to work, you need to apply a low-voltage pulse to the control contact. After such a signal is given, the triac opens and transitions from a closed state to an open state, passing current through itself. When the unlocking current passes through the control contact, it opens. Unlocking also occurs when the voltage between the electrodes exceeds a certain value.

When alternating current is applied, the thyristor state changes causes a polarity change voltage on the power electrodes. It closes when the polarity changes between the power terminals, and also when the operating current is lower than the holding current. To prevent false triggering of the triac caused by various radiomechanical interference, the devices used have additional protection. For this, a damper RC circuit (series connection of a resistor and a DC capacitor) is usually used between the power contacts of the triac. Sometimes inductance is used. It serves to limit the rate of change of current during switching.

Triacs in an electrical circuit

If we talk about triacs, it is necessary to take into account the fact that this is one of the types of thyristor, which also has three or more p-n junctions. Their difference is only in the control cathode, which determines the corresponding transient characteristics of the transmitted current and, in principle, operation in electrical circuits. Usually they begin their work immediately after starting the supply voltage to the desired contact.

Triac control circuit

The thyristor control circuit is simple and reliable. They are much simplify the circuit diagram with its presence, freeing it from unnecessary electrical parts and tracks. Thereby facilitating further repairs (checking and dialing) in case of need or failure of radio-electronic units with their participation.

Practical application of triacs

Necessary knowledge for checking, replacing and subsequent repair of various radio-electronic units involving triacs or thyristors will help any radio amateur in improving their professional and practical skills.

In electronic circuits of various devices, semiconductor devices - triacs - are often used. They are used, as a rule, when assembling regulator circuits. If an electrical appliance malfunctions, it may be necessary to check the triac. How to do this?

Why is verification needed?

During repair or assembly new scheme It is impossible to do without electrical parts. One of these parts is a triac. It is used in alarm circuits, light controllers, radio devices and many branches of technology. Sometimes it is reused after dismantling non-working circuits, and it is not uncommon to encounter an element whose markings have been lost due to long-term use or storage. It happens that new parts need to be checked.

How can you be sure that the triac installed in the circuit is really working, and in the future you will not need to spend a lot of time debugging the operation of the assembled system?

To do this, you need to know how to test a triac with a multimeter or tester. But first you need to understand what this part is and how it works in electrical circuits.

In fact, a triac is a type of thyristor. The name is made up of these two words - “symmetrical” and “thyristor”.

Types of thyristors

Thyristors are usually called a group of semiconductor devices (triodes) capable of passing or not passing electric current in a given mode and at certain periods of time. This creates conditions for the circuit to operate in accordance with its functions.

A thyristor is a semiconductor element made on the basis of a semiconductor single crystal, having three or more pn junctions and two stable states: a low conductivity state, which is called closed; and the high conductivity state is open.

A novice radio amateur may ask the question: “How is a thyristor checked?” In this article we will look at a technique for testing this semiconductor element. We will also look at what kind of device is needed to test thyristors.

There are several testing methods. Preliminary testing of the thyristor can be carried out using the following instruments: a tester or an ohmmeter. The multimeter must be turned on in diode testing mode, and the tester in resistance measurement mode. Using these devices, it is possible to check the transitions of the thyristor between the control electrode and the cathode, as well as between. The resistance value of the transition of the semiconductor element between the control electrode and the cathode should be 50-500 Ohms. The value of this resistance is approximately the same for both direct and reverse measurements. The higher the resistance value, the more sensitive the semiconductor thyristor. In other words, the device needs a small value of current at the control electrode to switch from a closed to an open state. A working thyristor has a resistance value between the anode-cathode electrodes during both direct and reverse measurements, tending to infinity.

A preliminary check of the thyristor gives the possibility that a used semiconductor element may contain a burnt-out cathode-anode junction. Measuring instruments such a malfunction cannot be determined.

The main test of the thyristor is carried out using additional ones. This operation completely eliminates the malfunction of the semiconductor device. The thyristor goes into the open state if a short-term pulse necessary to open the element is passed through the cathode - the control electrode. To do this, a circuit is assembled to test thyristors. There are many such schemes that can be assembled; let’s consider the most basic one. To do this, we will use a power source, two switches and a resistor. The circuit can be assembled on a test board or mounted. We assemble the circuit: we apply the minus of the power source (5-25 V) to the cathode of the thyristor. Plus the source through the normally closed button K1 and through the indicator lamp to the anode of the device.

We connect a resistor to the output of the control electrode, the second contact of which is normally open button K2 is connected between the lamp and button K1. The resistance value is selected so that the flowing current is sufficient to turn on the device. That's it, the circuit is ready, let's start testing. To do this, we close the K2 button, the control current will flow through the circuit: from the plus, through the K1 and K2 buttons, through the resistor, through the control electrode, to the cathode and to the minus of the source. The thyristor opens. Release button K2. The indicator lamp lights up. We press the normally closed button K1, the load current circuit through the thyristor breaks and it closes. The lamp goes out, the circuit returns to its original state.

First, take the trouble to learn how a thyristor works. Get an idea of ​​the varieties: triac, dinistor. It is required to correctly evaluate the test result. Below we will tell you how to test a thyristor with a multimeter, and we will even provide a small diagram that will help you accomplish your plans on a large scale.

Types of thyristors

Thyristor is different from bipolar transistor the presence of more p-n junctions:

1. A typical p-n junction thyristor contains three. Structures with hole, electronic conductivity alternate in the manner of a zebra. You can meet n-p-n-p concept thyristor. The control electrode is present or absent. In the latter case we get a dinistor. It works according to the voltage applied between the cathode and the anode: at a certain threshold value it opens, a decline begins, and the flow of electrons is cut off. As for thyristors with electrodes, control is carried out in either of the two middle p-n junctions - the collector side or the emitter side. The fundamental difference between the products and the transistor is that the mode remains unchanged after the control pulse disappears. The thyristor remains open until the current drops below a fixed level. Usually called holding current. Allows you to build cost-effective circuits. Explains the popularity of thyristors.
2. Triacs are different number of p-n transitions increase by at least one. Capable of passing current in both directions.

Start testing the thyristor with a multimeter

First, take the trouble to determine the location of the electrodes:

• cathode;
• anode;
• control electrode (base).

To open the thyristor switch, the cathode of the device is supplied with a minus (black multimeter probe), and a plus (red multimeter probe) is connected to the anode. The tester is set to ohmmeter mode. The resistance of an open thyristor is low. Stop setting the limit to 2000 Ohms. It's time to remind you: the thyristor is capable of being controlled (opened) by positive or negative pulses. In the first case, we close the anode to the base with a jumper made of a thin pin, in the second - the cathode. Here and there the thyristor should open, as a result the resistance will become less than infinity.

The testing process comes down to understanding what voltage the thyristor is controlled by. Negative or positive. Try this and that (if there is no marking). One attempt will definitely work if the thyristor is working properly.

The process then diverges from testing the transistor. If the control signal disappears, the thyristor will remain open if the current exceeds the holding threshold. The key may close. If the current does not reach the holding threshold.

1. Holding current is registered technical characteristics thyristor. Take the trouble to download complete documentation from the Internet and be aware of things.
2. A multimeter determines a lot. What voltage is supplied to the probes (traditionally 5 volts), how much power will it provide. You can check with the help of a large capacitor. You need to correctly connect the probes to the terminals of the device in resistance measurement mode, wait until the numbers on the display increase from zero to infinity. The capacitor has completed the charging process. Now let's go to measurement mode DC voltage look at the magnitude of the potential difference on the legs of the capacitor (the multimeter is in resistance measurement mode). Based on the current-voltage characteristics of the thyristor, it is easy to determine whether the value is sufficient to create a holding current.

Dinistors ring easier. Try to open the key. Depends on whether the power of the multimeter is enough to overcome the barrier. To guarantee a thyristor test, it is better to assemble a separate circuit. Like the one shown in the picture. The diagram is formed by the following elements:

Why did you choose +5 volt power? The voltage is easy to find on the phone adapter (charger). Take a closer look: there is an inscription like 5V– /420 mA. Output values ​​of voltage, current (immediately see if the thyristor is enough to hold). Every expert knows: +5 volts are available on the USB bus. The port is now supplied (in different formats) almost any gadget, computer. Avoid problems with nutrition. Just in case, let's take a closer look at this point.

Checking thyristors on the multimeter connector for transistors

Many people are interested in whether it is possible to test a thyristor with a multimeter using the standard socket for testing transistors on the front panel, designated pnp/npn. The answer is yes. You just need to apply the correct voltage. The gain shown on the display will most likely be incorrect. Therefore, avoid being guided by numbers. Let's see how it's done. If the thyristor opens with a positive potential, it must be connected to pin B (base) of the npn half-socket. The anode is plugged into pin C (collector), the cathode is plugged into pin E (emitter). It is unlikely that it will be possible to test a powerful thyristor with a multimeter; for microelectronics, the technique will work.

Where can a tester get food?

Position of the multimeter electrodes

The phone adapter provides a current of 100 - 500 mA. Often this is not enough (if you need to check the KU202N thyristor with a multimeter, the unlocking current is 100 mA). Where can I get more? Let's look at the USB bus: the third version will produce 5 A. Extremely high current for microelectronics, stop doubting the power characteristics of the interface. We'll look at the pinout online. Here is a picture showing the layout of typical USB ports. Two types of interfaces are shown:

1. First USB type And is typical for computers. The most common. You will find it on the adapters ( chargers) portable players, iPad. Thyristor testing circuits can be used as power supplies.
2. The second type B is more typical as a terminal one. Peripheral devices such as printers and other office equipment are connected. It is difficult to find as an initial power source, ignoring the fact of inaccessibility, the authors checked the layout.

If you cut the USB cable, we are sure that many will rush to destroy old equipment and tear off the tails of mice - the +5 volt power wire inside is traditionally red and orange. The information will help you dial the circuit correctly and get the required voltage. Present when the system unit is turned off (connected to the outlet). That's why the mouse's light continues to burn. For the duration of the test, it will be enough to put the computer into hibernation mode. By the way, it is not directly available in Windows 10 (if you go through the settings, you will find it in energy management).

USB Port Layout

Having enlisted the help of the circuit, let's check the thyristor without desoldering. The operating point is given relative to port ground, so external devices will play a small role. Traditionally grounding personal computer tied to the housing where the input harmonic filter wire goes out. Circuit +5 volts, ground is decoupled from the bus. It is enough to disconnect the circuit being tested from the power supply. To test the thyristor you will need to solder antennae to each terminal. To supply power, a control signal.

Many people squirm on their chairs, not understanding one thing: here we tell you how to test a thyristor with a multimeter, what does it have to do with the LED plus all the bells and whistles? Place the LED, you can - even better - turn on the tester probes and record the current. It is possible to use low supply voltage, always safer at the same time. As for a personal computer, it gives ample opportunities testing any elements, including thyristors. The system unit's power supply provides a set of voltages:

1. +5 V goes to coolers and many other systems. Actually standard supply voltage. Voltage wires are red.
2. +12 volts is used to power many consumers. The wire is yellow (not to be confused with orange).
3. — 12 volts are left to ensure compatibility with RS. The good old COM port through which adapters are programmed today industrial systems. Some sources uninterruptible power supply. The wire is usually blue.
4. The orange wire typically carries +3.3V.

You see, the spread is great, the main thing is the current. The power of computer power supplies fluctuates around 1 kW. Any thyristor will open! It's time to finish. We hope that now readers know how to test a thyristor with a multimeter. Sometimes you have to tinker. The KU202N thyristor mentioned above is equipped with a pnpn structure, non-lockable. After the control voltage is lost, the key does not close. You need to remove the power to turn off the LED. The unlocking voltage is positive. Fits the scheme. The only thing is that the holding current is 300 mA. The case when not everyone phone charger suitable for experimenting.