WHAT IS A THYRISTOR AND HOW DOES IT WORK?

What is a thyristor?

The thyristor is a power semiconductor that is used as a switch, either to conduct or interrupt the electric current, this component is known as power because they are used to handle large amounts of current and voltage, compared to the others semiconductors that handle relatively low quantities.

When speaking of thyristors, the thyristor is commonly classified as an SRC (silicon controlled rectifier), but this is not entirely correct since this type is the most popular and known but it is not the only one that exists.

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How does a thyristor work?

Thyristors are made up of 3 terminals an anode, a cathode, and a gate or better known «gate», their operation resembles that of a relay or a mechanical switch, since when you apply a current to the gate terminal it is activated and obtains the characteristic of letting electricity pass.

 

Thyristor types

There is a wide variety of thyristors each having different properties, characteristics, advantages, and disadvantages.

 

 

Phase Control or Rapid Communication (SCR)

This type is the most common and most used because they are able to switch quickly. One of the main characteristics of this thyristor is that it is only capable of conducting electricity in one direction only (like a diode when it is biased directly), once this component is activated it does not matter if you remove the current from the door as it will remain active until that one of two possible conditions is met. To deactivate it we have to cut the power supply or bring it to a very low point that the thyristor is unable to continue driving.

 

Bidirectional Face Controlled (BCT)

This type corresponds to two thyristors in the same package, even though they are together they do not interfere with each other and each has its gate terminals to be activated.

 

Photothyristor (LASCR)

This, as its name implies, is a thyristor which is activated by light.

 

It is used for alternating current since it contains two thyristors together in the same package, this time they only have one door terminal and this is capable of activating the two components at the same time.

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Reverse driving (RCT)

It could be said that it is an SCR with the integration of a diode placed in parallel but inversely, this is used to prevent eddy currents generated due to inductions from circulating against the current flow.

Gate Deactivation (GTO)

This type is an enhancement to the SCR thyristor as it can be deactivated through your door with the only condition of applying negative voltage.

 

Controlled by MOSFET (MCT)

It is only an improvement of the conventional thyristor using Mosfet, only that negative voltage is used to turn on and a positive voltage to turn off.

 

FET-CTH controlled

This type incorporates a thyristor and a parallel Mosfet transistor, which is responsible for generating the tripping current for the thyristor. This device is like the conventional ones it can be activated but not deactivated unless the current is removed from the circuit or the current is very low.

 

MTO

This is a combination of a GTO and a FET, and it overcomes the shutdown limitation of a GTO. This component has two gate terminals one for on and the other for off.

ETO

This is a combination between a GTO and a MOS, this thyristor also has two gates, one on and one off, but it works totally differently from an MTO, since to activate the thyristor it is necessary to apply a positive voltage to the two gates and to To turn it off a negative voltage must be applied at the shutdown door.

 

Integrated Gate Switched (IGCT)

This is the evolution of the GTO, its activation is through its door terminal, to deactivate it the same terminal is used, only this component incorporates a control stage to apply very high and very fast negative voltage.

Static induction (SITH)

This thyristor at first glance could seem like a normal diode, although it has a great difference which is that in order for it to activate, it has to pass the threshold voltage, usually 30v, once the required voltage passes, it allows the current to pass and when it is underneath it acts as an open switch.

Bidirectional Diode (DIAC)

Although it has two terminals and is more similar to a normal diode, it is also considered a thyristor since when a certain voltage passes it is activated, meanwhile it acts as an open switch

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