Curves typical of the Tiristor

To understand better the explanation given up to this moment on the functioning of the tiristor, it will be suitable that we see the curve typical of this component, as we did in the section of the diode with the above mentioned semiconductor, since this curve is going to clarify to us possible doubts about the way of the tiristor behaving.
We can see this curve in the graph as an imaginary tiristor, which we can compare, for the best comprehension, with the curve typical of the diode. Now, we see represented first of all the characteristics that the tiristor presents in the state of step of direct current. There is initially, a blockade characteristic at the moment of the step of the current in direct sense, which is represented by the whole line A. Here the direct tension grows without the tiristor allowing the step of the current. But cuado this one reaches a certain point known with the tension name of operation, the tiristor allows the step of the current in direct sense, what is represented by the ascending line B. Now the current of direct step is high.
When the direct current descends from value it is supported up to the called current of retention or current of mantenimieto (C), below which the step of the current is interrupted in direct sense.
In the inverse sense, the tiristor endures like a normal diode, that is to say, impidieno the step of the current, although opsee, as the diode Zener, an acodamiento in the typical curve to which, not obsante and in normal service, it does not usually go over.
In accordance with the above mentioned, we see that the tiristor of or a way similar to a normal diode if it was not for the 'flaw' for which it produces in his typical curve the points O-C-D to itself, as one sees in the second graph where the current must suffer like a shot to obtain the step in the direct sense. In fact, when the tension between plate and cathode grows from zero (now we refer to a void tension between electrode of government and cathode) the representative point displaces porla curve O-C up to obtaining the value V2 of the tension with a value of very weak intensity. At the moment of coming to V2 the conduction in direct sense appears brucamente, in an instantaneous way, between CD so that here the same intensity is supported, but for a very low tension. If the tension increases the step of the corrente it increases also but very quickly across the curve D-B, with strong intensities for very small tensions.
For a better final knowledge of the tiristor we are going to do a summary of his maner of acting. for it we are going to consider three possibilities that appear before him and that are:

a) without tension in the government electrode.
b) with alternate tension between plate and cathode.
c) with positive tension applied to the electrode of government.

a) The functioning is the explained one previously and it corresponds to the line gruezo of the curve of the last graph. In short we can say:
· If the value of the tension is supported to the left of the point V1 an avalanche exists type Zener in inverse sense; but if the tension is supported between V1 and O only a light current of escape can exist in inverse sense of despicable value.
· Between Or and V2 there is no current of direct step (except a despicable current of escape).
· In the point V2 the fattening takes place and the tiristor allows the step of big currents along D-B. So that the aso of the current should be interrupted it is required that the intensity should go down below the values of the current of maintenance (I1) that corresponds to the points D-C. In this moment the tiristor has a mental block instantaneously.

b) The tiristor is first of all it is a diode rectificaador so that it is used also being part of bridges of diodosrectificadores in the altenadores. Considering the characteristics exhibited till now it is necessary to wonder: How does this element act opposite to an alternating current that applies, consequently an alternate tension between plate and cathode where the tensions are comprised between V1 and V2? The answer is simple. A normal diode behaves omo because, on having come, the tension to V2 closes the circuit and becomes an assistant.

c) If the positive tension is applied to the electrode electrode the circuit O-C-D remains replaced for O-C1-D1, so that it is modified suscaracerísticas of isparo to the direct current. But according to the value of the tensions on the shot electrode values would be had as O-C2-D2 or O-C3-D3, etc. Of it it is deduced that the fattening produced for the step of the direct current is allowed or facilitated by the existence of a tension and the electrode of government. This new facet of the tiristor will be also of big interest altar many of his applications.

 

He keeps on reading on Tiristores:

Functioning of the Tiristor.
Variety of Tiristores.
Code of designation of diodes controlled semiconductors (Tiristores).

To return to the principal Tiristores page->