PDF | Thyristor, Triac and Diac | ResearchGate, the professional network for scientists. The characteristics of a thyristor is shown below. The characteristics curve is shown in the below Diagram. In above figure a simple DIAC TRIAC Power circuit is shown, the working of this circuit is can be. the DIAC, Diode AC bi-directional switch is widely used with TRIACs to improve the fact that its switching characteristic is far more even than that of the TRIAC.

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The DIAC can be fabricated as either a two layer or a five layer structure. DIACs are often used in conjunction with TRIACs because these devices do not fire symmetrically as a result of slight differences between the two halves of the device.

It can be considered as two break-over diodes connected back to back. Also referred to as a SYDAC Silicon thYristor for Alternating Currentbi-directional thyristor breakover diodeor more simply a bi-directional thyristor diode, it is technically specified as a bilateral voltage triggered switch.

It conducts current only in one direction. Figure-2 depicts characteristics of SCR.

Its behaviour is bi-directional and therefore its operation occurs on both halves of an alternating cycle. Capacitor trjac Ceramic resonator Crystal oscillator Inductor Parametron Relay reed relay mercury switch. Charzcteristics Solid state switches.

Figure-5 depicts structure and symbol of DIAC. In some way this demonstrates the structure of the device which can be considered also as two junctions. The SIDAC remains nonconducting until the applied voltage meets or exceeds its rated breakover voltage.

DIACs are also called “symmetrical trigger diodes” due to the symmetry of their characteristic curve. It provides sufficient improvement in switching characteristics. A five layer DIAC structure is also available.


Potentiometer digital Variable capacitor Varicap.

What is a DIAC – Tutorial

Figure-8 depicts characteristics of UJT. Since the DIAC prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the TRIAC more even in both directions. For some applications the five layer device may be used. Figure depicts output characteristics of transistor in common base and common emitter configurations. Figure-7 depicts structure and symbol of UJT.

Below this value, the diode switches back to its high-resistance, non-conducting state. The term is an diqc of “diode for alternating current”.

Circuit symbol for the DIAC. Here I E is emitter current and V E is emitter power supply. Figure-6 depicts characteristics of DIAC. Hence resistance between two base terminals is quite high when emitter terminal is left open.

This characteristic in the 1st and 3rd quadrant is identical to SCR characteristic in the 1st quadrant. The three layer version of the device is the more common and can have a break-over voltage of around 30 V.

The diode remains in its conduction state until the current through it drops below what is termed the holding current, which is normally designated by the letters IH. This results from the fact that its switching characteristic is far more even than that of the TRIAC.

DIAC – Wikipedia

Accordingly there is a sharp increase in the level of current that is conducted by the device. This page was last edited on 1 Juneat The structure of a DIAC. When breakdown occurs, the diode enters a region of negative dynamic resistanceleading to a decrease in the voltage drop across the diode and, usually, a sharp increase in current through the diode.


This is due to the fact that it has only one PN junction. By using this characterstics, you agree to the Terms of Use and Privacy Policy. Somewhat anr in most electronicsthe SIDAC is relegated to the status of a special purpose device. This will give DIAC device symmetrical properties. This does not act in quite the same manner, although it produces an I-V curve that is very similar to the three layer version.

Junction Transistor Figure-9 depicts structure and symbol of Bipolar junction Transistor. Due to this feature, UJT is used in wide variety of applications such as sawtooth generator, pulse generator, switching etc.

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However, where part-counts are to be kept low, simple relaxation oscillators are needed, and when the voltages are too low for practical operation of a spark gap, the SIDAC is an indispensable component. In the three layer structure the switching occurs when the junction that is reverse biased experiences reverse breakdown.