Do You know the Alternistor? (ART422E)

New components are always appearing in the world of electronics, giving the designer the possibility to create new designs, or to improve designs which already exist. However, in some cases only the component name is new and manufacturers take advantage to include their products in a new category. This is the case of alternistors or thyristors for alternating current that we discuss in this article.

The alternistors are nothing more than thyristors, that is, 4-layer diodes, designed for operation on alternate current circuits.

This name is especially adopted for the triacs, which is the most familiar element of the family, by companies like Teccor, Littelfuse and others.

The triac, as we have seen in many articles with applications and our course in power electronics, it is a four-layer diode or thyristor which can control current in both directions and therefore suitable for applications in control circuits in AC networks.

In Figure 1, we have its symbol in which we associate it with two SCRs connected in inverted way.

 

Figure 1 - The triac.
Figure 1 - The triac.

 

 

The characteristic curve of this component is shown in Figure 2.

 

 

Figure 2 - Characteristic curve
Figure 2 - Characteristic curve

 

 

Companies like Teccor have extensive lines of "alternistor triacs" with currents ranging from 6 to 40 A and voltages from 200 V to 1000 V, which are specifically designed for inductive load switching applications.

In these triacs, two inverted SCRs are integrated in the same chip, but electrically separated in order to improve the characteristics of dv/dt. (See more at: http://web.mit.edu/6.131/www/document/triac_alternistors. pdf)

However, if we consider the definition of "alternistor" as a thyristor for applications in AC circuits, we must go beyond the triacs.

In fact, thyristor is a four-layer diode (see our Electronic-Power Electronic Course), and in this family we can include others which are used to alternating current applications, as shown in Figure 3, thus generating a subfamily.

 

Figure 3 - The subfamily of the alternistors
Figure 3 - The subfamily of the alternistors

 

 

In addition to the triacs, we also have another type of thyristor family (four-layer diodes) specifically indicated for AC applications, most often at the triac shot which is known as diac (diode for Alternating Current) which we study in our course and we have specific articles.

The symbols themselves, shown in Figure 4, reminds us the triac.

 

 

Figure 4 - Symbols for the diac
Figure 4 - Symbols for the diac

 

 

And, another family component which also consists of a four-layer diode (thyristor) for AC circuit applications that we highlight is SIDAC.

Silicon (SI) diodes (D) for Alternating Current (AC) are special diodes of the thyristor family indicated for applications in AC circuits. They behave like a neon bulb firing when a voltage (in any direction) is applied to them. When triggering, intense currents can be driven. Sidacs can be used as trigger elements and relaxation oscillators in high voltage circuits connected to the power grid. In Figure 5, we have the characteristic curve of a SIDAC.

 

Figure 5 - The SIDAC
Figure 5 - The SIDAC

 

 

 

 


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