Thyristor is a semiconductor device designed to work as a key. It has three electrodes and the structure of P-N-P-N from the four semiconductor layers. Electrodes are referred to as an anode, cathode and control electrode. The structure of P-N-P-N is functionally similar to a nonlinear resistor, which is capable of taking two states:

• with very large resistance, turned off;
• with very low resistance included.

Views

On a thyristor turned on, a voltage of about one or more volts is preserved, which slightly increases with an increase in the current strength flowing through it. Depending on the type of current and voltage applied to the electrical circuit with a thyristor, it uses one of the three modern species of these semiconductor devices. On the constant toke. Work:

• included trinics;
• three varieties of locked thyristors, referred to as

Symistors work on alternating and constant current. All of these thyristors contain a control electrode and two other electrodes through which the load current is a tester. For trinistors and locked thyristors, it is an anode and a cathode, for simistors, the name of these electrodes is due to the correct determination of the properties of the control signal supplied to the control electrode.

The presence in a thyristor structure P-N-P-n allows it to divide it conditionally into two areas, each of which is bipolar transistor appropriate conductivity. Thus, these interrelated transistors are an equivalent of a thyristor, which has the form of a scheme on the image on the left. The first in the market appeared trinistors.

Properties and characteristics

In fact, it is an analogue of a self-locking relay with one normally open contact, the role of which is performed by a semiconductor structure located between the anode and the cathode. The difference from the relay is that for this semiconductor device, several ways to turn on and off can be applied. All these methods are explained by the transistor equivalent of trinistore.

Two equivalent transistors are covered by positive feedback. It repeatedly enhances any current changes in their semiconductor transitions. Therefore, there are several types of exposure to trinistore electrodes to turn it on and off. The first two ways allow you to turn on the anode.

• If the voltage on the anode increases, the effects of the starting breakdown of the semiconductor structures of the transistors will begin to affect its definite significance. The initial current appeared is avalanche-like intensify with positive feedback and both transistors will be included.
• With a fairly rapid increase in voltage on the anode, the charge of interelectrode containers, which are present in any electronic components. In this case, the electrodes appear the charging currents of these capacities, which picks up positive feedback And everything ends with the inclusion of trinistra.

If the voltage changes listed above are missing, the inclusion usually occurs the current base is equivalent n-P-N transistor. You can turn off the trinistor by one of two ways that also become clear due to the interaction of equivalent transistors. Positive feedback in them acts, starting with some values \u200b\u200bof currents flowing in the P-N-P-N structure. If the current value is less than these quantities, the positive feedback will work on the rapid disappearance of currents.

Another shutdown method uses an interrupt of the positive feedback by a voltage pulse, which changes the polarity on the anode and the cathode. With this effect of the direction of currents between the electrodes, it changes to the opposite and the trinistor turns off. Since the semiconductor materials are characterized by the photo effect, there are photo and optology, in which the inclusion may be due to the lighting or a receiving window, or the LED in the case of this semiconductor device.

There are also so-called dyninists (unmanaged thyristors). In these semiconductor devices, there is no control electrode constructively. In essence, it is a trinistor with one absent conclusion. Therefore, their state depends only on the tension of the anode and the cathode and they cannot engage in the control signal. In the rest of the processes in them are similar to ordinary trinistrators. The same applies to the simistors that are essentially two trinists connected in parallel. Therefore, they are applied to control alternating current Without additional diodes.

Locked thyristors

If it is possible to make a complete controllability of a thyristor by a thyristor by a thyristor from the control electrode area in a certain way to make the fields of the P-N-P-N structure near the databases of equivalent transistors. This design of the P-N-P-N structure is shown in the image on the left. You can turn on and off such a thyristor with appropriate signals at any time feeding them to the control electrode. The remaining methods of inclusion applied to trinistrators are also suitable for locked by thyristors.

However, these methods do not apply to such semiconductor devices. They, on the contrary, are excluded by those or other circuitry solutions. The goal is to obtain reliable turning on and off only on the control electrode. This is necessary to use such thyristors in powerful inverters of increased frequency. GTO operates at frequencies up to 300 hertz, and IGCT are capable of significantly higher frequencies reaching 2 kHz. Nominal values \u200b\u200bof currents can be several thousand amps, and the voltage is a few kilovolt.

A comparison of various thyristors is shown in the table below.

A variety of thyristor	Benefits	disadvantages	Where used
Trinistor.	Minimum voltage in the on state with maximum current and overloads. Most reliable from all. Good scalability of schemes by collaboration of several trinistores connected either in parallel or sequentially	There is no possibility of an arbitrary managed shutdown only by the control electrode. The lowest operating frequencies.	Electric drives, power supply power supply high power; welding inverters; control of powerful heaters; static compensators; Switches in alternating circuits
GTO.	The ability to arbitrary managed shutdown. Relatively high ability to overload overloads. Ability to work reliably with sequential connection. Operating frequency up to 300 Hz, voltage up to 4000 V.	Significantly voltage in the on state with maximum currents and overloads and the loss corresponding to them, including in control systems. Complex circuitry of the construction of the system as a whole. Large dynamic lies.
Igct.	The ability to arbitrary managed shutdown. Relatively high ability to overload overloads. Relatively low voltage in the on state with maximum current and overloads. Operating frequency - up to 2000 Hz. Simple control. The ability to reliably work with a sequential connection.	The most expensive of all thyristors	Electric drives; Static compensators reactive power; Sources of power supply of high power, induction heaters

Thyristors are manufactured for wide range Current and voltages. The design is determined by the sizes of the P-N-P-N structure and the need to obtain a reliable heat removal from it. Modern thyristors, as well as their designations on electrical circuits Showing images below.

January 8, 2013 at 19:23

Thyristors for teapots

• Electronics for beginners

Good evening hubr. Let's talk about such a device like a thyristor. Thyristor is a semiconductor device with two stable states having three or more interacting straightening transitions. By functionality, they can be correlated to electronic keys. But there is one feature in a thyristor, he cannot go into a closed state unlike the normal key. Therefore, it is usually possible to find it called - not a fully managed key.

The figure shows the usual view of a thyristor. It consists of four alternating types of electro-conductivity of the semiconductor regions and has three outputs: anode, cathode and control electrode.
Anode is a contact with an external p-layer, a cathode with an external N-layer.
Refresh the memory of the P-N transition can be.

Classification

Depending on the number of conclusions, you can withdraw the classification of thyristors. In fact, everything is very simple: a thyristor with two conclusions is called dynistora (only anode and cathode has only). Thyristor with three and four conclusions are called triode or thickets. There are also thyristors and with large quantity alternating semiconductor regions. One of the most interesting is a symmetric thyristor (SIMISTOR), which is included with any voltage polarity.

Principle of operation

Usually, a thyristor is represented in the form of two transistors related to each other, each of which works in active mode.

In connection with such a pattern, you can call the extreme areas - emitter, and the central transition is collector.
To figure out how the thyristor works, it is worth a look at the volt-ampere characteristic.


A thyristor anode filed a small positive tension. Emitter transitions are included in the forward direction, and the collector in the opposite. (In essence, all the voltage will be on it). A section from zero to a unit on a volt-ampere characteristic will be roughly similar to the feed branch of the diode characteristics. This mode can be called - the closed state of the thyristor.
With an increase in the anode voltage, the injection of the main carriers in the base area occurs, thereby accumulating electrons and holes, which is equivalent to the potential difference on the collector transition. With increasing current through a thyristor, the voltage at the collector transition will begin to decrease. And when it decreases to specified valueOur thyristor will go into a state of negative differential resistance (in the figure section 1-2).
After that, all three transitions will be shifted in the forward direction. Thereby turning the thyristor to the open state (in the figure section 2-3).
In the open state, the thyristor will be as long as the collector transition is shifted in the forward direction. If a thyristor current is reduced, then as a result of recombination, the number of nonequilibrium carriers in the base regions and the collector transition will be shifted in the opposite direction and the thyristor goes into the closed state.
When converting a thyristor, a volt-ampere characteristic will be similar as in two successively included diodes. The reverse voltage will be limited in this case by the breakdown voltage.

General parameters of thyristors

1. Inclusion voltage - It is the minimum anode voltage at which the thyristor goes into the included state.
2. Direct voltage - This is a direct voltage drop at maximum anode current.
3. Reverse voltage - This is the maximum allowable voltage on a thyristor in a closed state.
4. Maximum allowable direct current - This is the maximum current in the open state.
5. Reverse current - Current at maximum reverse voltage.
6. Maximum electrode control current
7. Turning / off delay time
8. Maximum allowable power dissipation

Conclusion

Thus, in a thyristor there is a positive feedback on the current - an increase in current through one emitter transition leads to an increase in current through another emitter transition.
Thyristor is not a fully control key. That is, by going to the open state, it remains in it even if it is stopped feeding the signal to the control transition if the current is supplied above a certain amount, that is, the deduction current.

The principle of the action of a thyristor

Thyristor It is a power electronic not fully controlled key. Therefore, sometimes in the technical literature it is called a single control thyristor, which can only be translated into a conductive state, that is, to be turned on. To turn off (when working on a constant current), it is necessary to take special measures to comply with the direct current to zero.

The thyristor key can only carry out the current in one direction, and in the closed state is able to withstand both direct and reverse voltage.

Thyristor has a four-layer P-N-P-N-structure with three conclusions: anode (a), cathode (C) and control electrode (G), reflected in Fig. one

Fig. 1. Ordinary thyristor: a) - conditionally graphic designation; b) - Voltamper characteristic.

In fig. 1, B is a family of output static WAs at different values \u200b\u200bof IG control current. The limit direct voltage that is withstanding a thyristor without its inclusion, has the maximum values \u200b\u200bat Ig \u003d 0. With an increase in the current Ig, the direct voltage, which is reduced by a thyristor, is reduced. The insertion of the thyristor corresponds to the branch II, turned off - branch I, the inclusion process - branch III. Holding current or deduction current is minimally the permissible value of the direct current Ia, in which the thyristor remains in a conductive state. This value also corresponds to the minimum possible value of direct voltage drop on the thyristor turned on.

The branch IV is the dependence of the current leakage of the reverse voltage. If the reverse voltage is exceeded, the UBO value begins a sharp increase in the reverse current associated with the thyristor breakdown. The nature of the breakdown may correspond to an irreversible process or the process of avalanche breakdown characteristic of semiconductor stabitron.

Thyristors are the most powerful electronic keys capable of switching chains with a voltage of up to 5 kV and currents up to 5 kA at a frequency of not more than 1 kHz.

The constructive design of thyristors is shown in Fig. 2.

Fig. 2. Construction of thyristor housings: a) - tablet; b) - pinch

Thyristor in DC circuit

The inclusion of a conventional thyristor is carried out by supplying a current pulse into a chain of a positive control circuit, relative to the cathode, polarity.On the duration of the transition process, when the nature of the load (active, inductive, etc.), the amplitude and the rate of increase of the Ig control pulse pulse, the temperature of the semiconductor structure of the thyristor, the applied voltage and the load current, and the load current are applied. In the chain containing a thyristor, there should be no unacceptable values \u200b\u200bof the rapid voltage rate of the DUAC / DT, in which spontaneous inclusion of a thyristor may occur in the absence of an IG control signal and the rate of increasing the DIA / DT current. At the same time, the steepness of the control signal must be high.

Among the methods of turning off, thyristors, it is customary to distinguish between natural shutdown (or natural switching) and forced (or artificial commutation). Natural switching occurs when thyristors are working in alternating current circuits at the time of decaying the current to zero.

Methods forced switching are very diverse. The most characteristic of them are the following: connecting a pre-charged condenser with the key S (Fig. 3, a); Connecting a LC circuit with a pre-charged CK condenser (Figure 3 b); Use the oscillatory nature of the transition process in the load circuit (Figure 3, B).

Fig. 3. Methods of artificial switching of thyristors: a) - by means of a charged condenser with; b) - by the oscillatory discharge of the LC-contour; c) - due to the oscillatory nature of the load

When switching according to the scheme in Fig. 3, and connecting a switching condenser with reverse polarity, such as another auxiliary thyristor, will cause its discharge on the conductive thyristor. Since the discharge current of the capacitor is directed to the direct current of the thyristor, the latter decreases to zero and the thyristor will turn off.

In the diagram in fig. 3, B connection LC contour causes a oscillatory discharge of a switched capacitor SC. At the same time, at the beginning, the discharge current flows through a thyristor ongoing its direct current when they become equal, the thyristor turns off. Further, the LC-contour current moves from a vs thyristor into a VD diode. While the circuit current flows through the VD diode, the VS thyristor will be applied the reverse voltage equal to the voltage drop on the outdoor diode.

In the diagram in fig. 3, in the inclusion of a thyristor VS to a complex RLC load will cause a transition process. For defined parameters Loads This process may have a oscillatory character with a change in the polarity of the load current IH. In this case, after turning off the thyristor VS, the VD diode is turned on, which begins to carry out the current of the opposite polarity. Sometimes this switching method is called quasistless, as it is associated with a change in the polarity of the load current.

Thyristor in alternating current circuit

When the thyristor is turned on to the variable current circuit, it is possible to perform the following operations:

Enabling and shutdown electrical chain with active and active reactive load;

changing the average and current current values \u200b\u200bthrough the load due to the way it is possible to adjust the moment of feeding the control signal.

Since the thyristor key is capable of conducting electricity Only in one direction, then for the use of thyristors on alternating current, their counter-parallel inclusion is used (Fig. 4, a).

Fig. 4. Meet-parallel inclusion of thyristors (a) and current form at the active load (b)

Average and vary due to changes in the moment of supplying Tristors VS1 and VS2 opening signals, i.e. Due to the corner and (Fig. 4, b). The values \u200b\u200bof this angle for thyristors VS1 and VS2 changes simultaneously using the control system. The angle is called an angle of control or an angle of unlocking a thyristor.

The widest use in the power electronic devices received phase (Fig. 4, A, B) and pulsed thyristor (Fig. 4, c).

Fig. 5. Type of stress at the load at: a) - phase control of thyristor; b) - phase control of thyristor with compulsory switching; c) - a pulse pulse control of thyristor

With a phase method of controlling a thyristor with compulsory switching load current control is possible as due to the change of the angle? and corner? . Artificial switching is carried out with the help of special nodes or when using fully managed (locked) thyristors.

With pulse control (pulse modulation latitude and pulse modulation)during the time of Tactor, the thyristor is served by the control signal, they are open and the voltage UAN is applied to the load. During the Tzacrol Time, the control signal is missing and thyristors are in a non-conductive state. The current current value in the load

where is it - Load current with Tzacr \u003d 0.

The current curve in the load with phase control of thyristors is unnsuited, which causes a distortion of the voltage form of the supply network and violations in the work of consumers sensitive to high-frequency interference - there is a so-called electromagnetic incompatibility.

Locked thyristors

Thyristors are the most powerful electronic keys used to switch high-voltage and high-current (strong-flow) chains. However, they have a significant drawback - incomplete controllability, which manifests itself in that it is necessary to create a reducing current reduction conditions to zero. This in many cases limits and complicates the use of thyristors.

To eliminate this disadvantage, thyristors are developed, locked by a signal according to the control electrode G. Such thyristors are called lockable (GTO - Gate Turn-off thyristor) or two-operative.

Locked thyristors (ZT) have four-layer r-P-R-P structureBut at the same time have a number of essential design features that give them a fundamentally different from traditional thyristors are a complete controllability property. Static whaled thyristors in the forward direction is identical to the usual thyristors. However, block large return voltages, the thyristor lockable is usually not capable and is often connected to a counter-parallel to the diode turned on. In addition, significant rapid voltage drops are characterized for locked thyristors. To turn off the thyristor locked, you must be submitted to the control electrode circuit, a powerful negative current pulse (approximately 1: 5 relative to the value of the direct current), but a short duration (10-100 μs).

Locked thyristors also have lower values \u200b\u200bof limit voltages and currents (by about 20-30%) compared to conventional thyristors.

Main types of thyristors

In addition to locked thyristors developed a wide range of thyristors different types, characterized by speed, control processes, the direction of currents in a conductive state etc. Among them should be noted the following types:

a thyristor diode, which is equivalent to a thyristor with a counter-parallel diode (Fig. 6.12, a);

diode thyristor (Distoror)flowing into a conductive condition when a certain voltage level is exceeded between A and C (Fig. 6, b);

locked thyristor(Fig. 6.12, c);

symmetrical thyristor or simistorwhich is equivalent to two contemplated thyristors in parallel (Fig. 6.12, d);

fast inverter thyristor (shutdown time 5-50 μs);

thyristor with field control over control electrode, for example, based on a combination of a MOS transistor with a thyristor;

optotristor controlled by light flux.

Fig. 6. Conditional graphic designation of thyristors: a) - a thyristor diode; b) - diode thyristor (Distoror); c) - locked thyristor; d) - Symistor

Protection of thyristors

Thyristors are appliances critical to direct current rates of DIA / DT and direct voltage DUAC / DT. Thyristors, as well as diodes, inherent in the phenomenon of the reverse recovery current, whose sharp decoration to zero aggravates the possibility of overvoltages with a high DUAC / DT value. Such overvoltages are a consequence of a sharp cessation of current in the inductive elements of the scheme, including installation. Therefore, for the protection of thyristors, various CTTP schemes are usually used, which in dynamic modes are protected from invalid values \u200b\u200bof DIA / DT and DUAC / DT.

In most cases, the internal inductive resistance of the sources of voltage included in the circuit of the inclusive thyristor turns out to be sufficient not to introduce the additional inductance of Ls. Therefore, in practice, it becomes more often the need for CTTP, which reduces the level and speed of overvoltages when turned off (Fig. 7).

Fig. 7. Typical thyristor protection scheme

For this purpose, RC circuits are usually used parallel to the thyristor. There are various schematic modifications of RC chains and methods for calculating their parameters for different conditions of use of thyristors.

For delayed thyristors, the chains of formation of the switching trajectory are used similar to the transistor CTTP circuitry.

Thyristor is a semiconductor key, the design of which is four layers. They have the ability to move from one state to another - from closed to open and vice versa.

The information presented in this article will help to give an exhaustive answer to the question of this device.

The principle of functioning of thyristor

In specialized literature, this device is also called a single source thyristor. This name is due to the fact that the device is not fully manageable. In other words, when receiving a signal from the control object, it can only go to the mode of the on. In order to turn off the device, the person will have to perform additional actions that will lead to a drop in the voltage level to zero.

The operation of this device is based on the use of the power electric field. To switch it from one state to another, the control technology transmitting certain signals is used. At the same time, the thyristor current can only move in one direction. In the off state, this device has the ability to withstand both direct and reverse voltage.

Ways to turn on and off a thyristor

The transition to the working state of the standard type of unit is carried out by teaching the pulse current voltage In a certain polarity. On the speed of inclusion and on how it will later work, the following factors affect:

Turning off a thyristora can be carried out in some ways:

1. Natural shutdown. In technical literature, such a concept is also found as natural switching - it is similar to the natural shutdown.
2. Forced shutdown (forced switching).

The natural shutdown of this unit is carried out in the process of its operation in alternating circuits when the current level decreases to the zero mark.

Forced shutdown includes a large number of Most varied ways. The most common one is the following method.

The condenser, denoted by the Latin letter C, connects to the key. It must be marker in S. In this case, the capacitor must be charged before the closure.

Main types of thyristors

Currently, there is a considerable amount of thyristors who differ in each other technical characteristics - speed of functioning, methods and processes of management, current directions when in conducting condition, etc.

The most common types

1. Thyristor diode. Such a device is similar to a device that has a counter-parallel diode in the on mode.
2. Diode thyristor. Another name is Distoror. The distinctive characteristic of this device is that the transition to the conductive mode is carried out at the moment when the current level is exceeded.
3. Lockable thyristor.
4. Symmetric. It also is called the Simistor. The design of this device is similar to two devices with counter-parallel diodes when in operation mode.
5. High-speed or inverter. This type of device has the ability to move into non-working status for a record short time - from 5 to 50 microseconds.
6. Optotristor. Its work is carried out using a light flux.
7. Thyristor under the field control over the leading electrode.

Providing protection

Thyristors are included in the list of devices that are critical affect the change of speed Increase direct current. As for diodes and thyristors, the process of recovery reverse current is characteristic. A sharp change in its speed and drop to zero mark leads to an increased risk of overvoltage.

In addition, the overvoltage in the design of this device may occur due to the complete disappearance of the voltage in a variety component parts Systems, for example, in small installation inductors.

Upon the above reasons in the overwhelming majority of cases, various CFTP schemes are used to ensure reliable protection of these devices. Scheme data when in dynamic mode helps protect the device from invalid voltage values.

A reliable means of protection is also application of varistor. This device is connected to inductive load places.

In very general The use of such an instrument as a thyristor can divided into the following groups:

Thyristora restrictions

When working with any type of this device, certain safety regulations should be followed, as well as to remember some of the necessary restrictions.

For example, in the case of inductive load in the functioning of such a variety of instrument as a simistor. In this situation, restrictions relate to the rate of change in the voltage level between the two main elements - its anodes and the working current. To limit the effect of current and overload rC chain applies.

Absolutely any thyristor can be in two stable states - closed or open

In the closed state, it is in a state of low conductivity and the current almost does not go, in the open, on the contrary, the semiconductor will be in a state of high conductivity, the current passes through it actually without resistance

It can be said that a thyristor is an electric power managed key. But in fact, the control signal can only open the semiconductor. To locate it back, you need to perform the conditions aimed at reducing the direct current almost to zero.

Structural thyristor represents the sequence of four, layers p. and n. Type forming structure P-N-P-N and connected sequentially.

One of the extreme areas on which the positive pole power is called anode, p - type
The other to which the negative voltage pole is connected, called cathode, - N type
Managing electrode Connected to the inner layers.

In order to deal with the work of a thyristor, consider several cases, the first: voltage to the control electrode is not servedThe thyristor is connected according to the Distor's scheme - the positive voltage enters the anode, and the negative to the cathode, see the drawing.

In this case, the collector P-N-n-transition of the thyristor is in a closed state, and the emitter - open. Open transitions have a very low resistance, so almost all the voltage that follows from the power source is applied to the collector transition, due to the high resistance of which the current flowing through the semiconductor device is very low.

On the graph of the Wah, this state is relevant for the area of \u200b\u200bthe marked digit 1 .

With an increase in the voltage level, until a certain point, the thyristor current is almost not growing. But reaching a conditional critical level - inclusion voltage U inclIn Disterore, the factors appear in which the collector transition begins a sharp increase in free charge carriers, which almost immediately avalanche. As a result, a reversible electric sample occurs (on the presented figure - point 2). IN p.The original collector transition appears excessive accumulated zone positive charges, in n.- Registration, on the contrary, electron accumulation takes place. The increase in the concentration of free charge carriers leads to a drop in a potential barrier on all three transitions, the injection of charge carriers begins through emitter transitions. Avalanche-like character increases even more, and leads to switching collector transition to open state. At the same time, the current in all areas of the semiconductor increases, as a result, it occurs with a drop in the voltage between the cathode and the anode, shown in the graph above the segment of the marked number three. At this point in time, the Distoror has a negative differential resistance. On resistance R N. There is a voltage and semiconductor switches.

After opening the collector transition, Distor's batteries becomes the same as on a direct branch - Cut No. 4. After switching the semiconductor device, the voltage decreases to one volt level. In the future, an increase in the voltage level or resistance will lead to an increase in the output current, one to one, like the operation of the diode when it direct inclusion. If the level of supply voltage is reduced, then the high resistance of the collector transition is almost instantly restored, dististor closes, current drops sharply.

Inclusion voltage U incl, It is possible to configure, bringing in any of the intermediate layers, next to the collector transition, minor, charge carriers for it.

For this purpose, a special managing electrode, powered from an additional source from which the control voltage follows - U URR. As it can be seen from the graph - with the growth of U UPR, the inclusion voltage is reduced.

The main characteristics of thyristors

U incl Inclusion voltage - with it is carried out by the transition of a thyristor in an open state
U O6P.max - Pulsed repeated reverse voltage when it takes an electric breakdown p-N Transition. For many thyristors will be true expression U O6P.max. \u003d U incl
I Max - Maximum allowable current
I cf. - average current for the period U NP. - Direct voltage drop with an open thyristor
I O6P.MAX - Reverse maximum current starting leak when app U O6P.max, due to the movement of non-core charge carriers
I carry The deduction current is the value of an anode current at which a thyristor locking is carried out
P Max - Maximum power dissipation
t disc from - Time shutdown required to lock a thyristor

Locked thyristors - has a classic four-layer p-N-P-N structure, but at the same time possesses a number of constructive features that give such functional opportunityas complete handling. Thanks to this impact from the control electrode, the thyristors lockable can move not only in the open state from the closed, but also from the open in the closed. To do this, the control electrode comes the voltage opposite to the one that previously opens a thyristor. To lock the thyristor on the control electrode, it follows a powerful, but short-duration pulse of a negative current. When applying locked thyristors, it should be remembered that their limit values \u200b\u200bare 30% lower than that of the usual. In circuitry, locked thyristors are actively applied as electronic keys in converting and impulse techniques.

Unlike its four-layer relatives - thyristors, they have a five-layer structure.

Thanks to such a semiconductor structure, they have the ability to pass the current in both directions - both from the cathode to the anode and from the anode to the cathode, and the voltage of both polarities comes to the control electrode. Due to this property, the helmet-ampere characteristic of the simistor has a symmetric view in both axes of coordinates. You can learn about the work of the Simistor from the video tutorial on the link below.

Principle of operation of Simistor

If the standard thyristor has an anode and cathode, then the electrodes of the simistor are so described. It is not possible to describe each hugo electrode is both an anode and cathode at the same time. Therefore, the simistor is able to skip the current in both directions. That is why it works great in alternating current circuits.

A very simple scheme explaining the symbistor principle is a regulator of a simistra power regulator.

After the voltage is supplied to one of the conclusions of the simistra, an alternating voltage is received. On an electrode that is managers with diode Bridge The negative control voltage is received. If you exceed the power threshold, the simistor unlocks and the current enters the connected load. At the time when the polarity of the voltage changes at the inlet of the simistor, it is locked. Then the algorithm is repeated.

The higher the level of control voltage, the faster, the simistor is triggered and the pulse duration on the load increases. When the level of control voltage is reduced, the pulse duration on the load is also reduced. At the exit of the simistor regulator, the voltage will be a sawdowed form with an adjustable pulse duration. Thus, adjusting control voltage We can change the brightness of the incandescent bulb or the temperature of the soldering iron connected as a load.

So the Symistor is controlled by both negative and positive voltage. Let's lay out its minuses and pros.

Pros: low cost, long service life, lack of contacts and, as a result, lack of sparking and barbell.
Cons: It is quite sensitive to overheating and it is usually mounted on the radiator. It does not work at high frequencies, since it does not have time to move out of the open state in the closed. Reacts to external readings that cause false response.

It should also be mentioned on the features of the installation of simistors in modern electronic technology.

For small loads or if short pulse currents proceed in it, the installation of the simistors can be carried out without a heat sink radiator. In all other cases - its presence is strictly necessary.
Thyristor can be recorded with a fastening clip or screw
To reduce the likelihood of false response due to noise, the length of the wires must be minimal. To connect it is recommended to use shielded cable or twisted pair.

Or optotristor specialized semiconductors, constructive feature which is the presence of a photocell, which is the control electrode.

Modern and promising variety of simistra is an optosyristor. Instead of the control electrode in the case there is a LED and control occurs by changing the supply voltage on the LED. When the luminous stream is hit, the photocell switches the thyristor in the open position. The most basic function in the optoamistor is that there is a complete electroplating omission between the control circuit and the power. This creates just a great level and reliability of the design.

Power keys. One of the main points affecting the demand for such schemes is low power that a thyristor is capable of disperse in switching schemes. In the locked state, the power is practically not spent, because current is close to zero values. And in the open state, the dissipated power is small due to low voltage values

Thresholding devices - They implement the main property of thyristors - to open when the required level is achieved. It is used in phase power regulators and relaxation generators.

For interrupt and turn on-off Use locking thyristors. True, in this case schemes require a certain refinement.

Experimental devices - They use the property of a thyristor to have a negative resistance, being in transition

Principle of operation and properties of Distoror, diagrams on dynistora

Distoror is a variety semiconductor diodes Class of thyristors. The dynisterist consists of four areas of different conductivity and has three P-n transitions. In electronics, he found quite limited use, walking it can be found in structures energy Saving Lamps Under the E14 and E27 base, where it is used in the launch schemes. In addition, it comes across in the broad-regulating devices of daily lamps.