DIAC Construction and Working in tamil

What is a DIAC?
A DIAC is a diode that conducts electrical current only after its breakover voltage (VBO) has been reached. DIAC stands for “Diode for Alternating Current”. A DIAC is a device which has two electrodes, and it is a member of the thyristor family. DIACs are used in the triggering of thyristors. The figure below shows a symbol of a DIAC, which resembles the connection of two diodes in series.

DIACs have no gate electrode, unlike some other thyristors that they are commonly used to trigger, such as a TRIAC.

The advantage of a DIAC is that it can be turned on or off simply by reducing the voltage level below its avalanche breakdown voltage. DIACs are also known as a transistor without a base. It should also be noted that a DIAC can be either turned on or off for both polarities of voltage (i.e. positive or negative voltage). They also still works when avalanche breakdown occurs.

Application of DIAC

The main application of a DIAC is its use in a TRIAC triggering circuit. The DIAC is connected to the gate terminal of the TRIAC. When the voltage across the gate decreases below a predetermined value, the gate voltage will be zero and hence the TRIAC will be turned off.
Some other applications of a DIAC include:

It can be used in the lamp dimmer circuit

It is used in a heat control circuit

It is used in the speed control of a universal motor

A DIAC can be used with a TRIAC in a series combination for triggering. The gate of TRIAC is connected with a terminal of the DIAC. When the applied voltage across the DIAC increases above the avalanche breakdown voltage, only then it can conduct.

However, when the voltage across DIAC decreases below its avalanche breakdown voltage it will be turned off, and hence the TRIAC will also remain in the off state.

Construction of DIAC
It is a device which consists of four layers and two terminals. The construction is almost the same as that of the transistor. But there are certain points which deviate from the construction from the transistor. The differentiating points are-
There is no base terminal in the DIAC
The three regions have almost the same level of doping
It gives symmetrical switching characteristics for either polarity of voltages

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From the figure above, we can see that a DIAC has two p-type material and three n-type materials. Also, it does not have any gate terminal in it.
The DIAC can be turned on for both the polarity of voltages. When A2 is more positive with respect to A1 then the current does not flows through the corresponding N-layer but flows from P2-N2-P1-N1. When A1 is more positive A2 then the currentflows through P1-N2-P2-N3.
The construction resembles the diodeconnected in series.