Let us discuss about, diac
Before going through the details about diac, let us examine, what will happen if two diodes
are connected in that nature
If, we apply positive voltage at A2, and, negative voltage at A1
Then diode A2, will behave as forward biased. And diode A1, will behave as reverse biased
If, one diode is forward biased, and another one is reverse biased, then no current will
flow through the system. If we gradually increase the voltage across the system, the reverse biased anode A1, is
broken down. At this time, the current through the system is suddenly raised
Now, if we apply positive voltage at terminal A1, and negative voltage at terminal A2, then
A1, will behave as forward biased and, A2, will behave as reverse biased
If, we increase the voltage across the system, then reverse biased diode A2, is broken down
System behave as a short circuit. So, the system is behaving as a bidirectional switch controlled by applied voltage
Now come to the actual point
This is the symbol of diac. Diac is an electronic component which does the same thing, when we connect a diac across
an alternating supply and if peak voltage of the supply waveform is more than avalanche
breakdown voltage of the diac, then it will conduct current. Diac is generally three layers, or five layers
Here, we have shown a three layer diac. There are two p-n junctions
If one is forward biased then another one will be reversed biased
Hope, you got basic idea about diac. Thank you