How to check the triac. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Triac - one of the radio elements of the "family" of thyristors. Two others: a dinistor is a two-electrode device, a trinistor is a three-electrode device. The triac, in fact, is also a three-electrode device, but if there are three p-n junctions in the trinistor, then there are four of them in the triac. A cross section of the trinistor crystal structure is shown in fig. 1 on the left, and the triac on the right.

Thanks to this structure of the triac, it is possible, unlike the trinistor, to control the conductivity in both directions using one control electrode. As a result, the triac is most often used as a key in AC circuits.

Structurally, the triac is made in the same package as the trinistor (Fig. 2). Similar to the trinistor, one extreme region with n-type conductivity is connected to the case and serves as pin 2. The other extreme region (n-type) is connected to pin 1. The middle region (p-type) is connected to the output of the control electrode.

When working in some device for opening a triac, a control pulse is applied to the control electrode relative to pin 1, and the polarity of the pulse depends on the polarity of the switched voltage applied between pins 1 and 2. If the voltage at pin 2 is positive, the triac opens with a voltage pulse of any polarity. With a negative voltage at this pin, the control pulse must be of negative polarity. Turning off (closing) the triac is carried out, as in the case of the trinistor, by removing the voltage from pin 2.

Having dealt with the device and the operation of the triac, it is now easy to learn how to check it using a simple prefix (Fig. 3).

Switches SA1 and SA2 change the polarity of the control and switching voltage, respectively. Button SB1 is used to supply control pulses, and SB2 - to turn off the triac. The indicator for turning on the triac is an HL1 incandescent lamp, designed for the voltage that is supplied to output 2 of the triac. It is necessary to feed the prefix from two separate sources.

Any suitable housing made of insulating material, for example, a plastic soap dish, can be used to mount the parts of the attachment (Fig. 4).

When the position of the movable contacts of the switches is indicated in the diagram and the SB1 button is pressed, the triac will open, the indicator lamp will light up. Then press the SB2 button, the triac closes, the lamp goes out. Next, the moving contacts of the SA1 switch are moved to the opposite position and the SB1 button is pressed again. If the triac is good, the lamp will flash.

Having moved the contacts of the switch SA2 to the opposite position, press the button SB1 in one and the other positions of the movable contacts of the switch SA1. The indicator lamp should only light up when a negative voltage is applied to the control electrode relative to terminal 1.

Author: I. Gorodetsky, Moscow

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