It only conducts when voltage increases above 30 volts.It offers smooth power control when used for triggering other thyristor and TRIAC.It can be easily switches by increasing or decreasing the applied voltage.The voltage drop increases with the voltage.Symmetrical switching helps in reducing the harmonics in a system.The DIAC offer symmetrical switching characteristics.The only difference between the 1 st and 3 rd quadrant is that the voltage and current are reverse. The device operates similarly in the 3 rd quadrant. The voltage across the device starts to reduce to steady ON-state voltage. Once the voltage increases, the DIAC triggers into ON-state and the current rises. As you can see, when the voltage is below the break over voltage V BO, the DIAC blocks the current except for the leakage current.

In 1 st quadrant, the voltage and current are positive. It is a symmetrical device therefore, the graph is symmetrical in both quadrants forming the shape of letter вЂњZвЂќ. As you can see, the DIAC only operate in 1 st and 3 rd quadrant. The following characteristic curve shows the relation between the main voltage and main current of a DIAC. As soon as it falls below the said limit, the device switches into off-state. The DIAC conducts current unless the current falls below the holding current limit. its forward break over voltage is equal to reverse break over voltage. It has symmetrical switching characteristics for both voltage polarities i.e. There is no difference in operation whatsoever if the polarities are swapped. Similarly, if the voltage polarities are swapped, the same process will repeat except the current will flow in reverse direction. The DIAC is triggered into conduction and the voltage across it reduces to ON-state voltage drop. When it happens, avalanche break down occurs at the reverse bias junction and the current starts to flow through it. In order to trigger the DIAC into conduction, the applied voltage V must exceed break over voltage V BO. At this moment, the applied Voltage V < V BO, so the middle junction remains reverse biased and does not allow current flow. Suppose the applied voltage at MT1 is positive with respect to MT2, the junctions at the ends become forwards biased and the middle junction becomes reverse biased. The DIAC can conduct current in both directions unless the applied voltage falls below the break over voltage. Related Post: What is the Difference Between DIAC and TRIAC?.The symmetrical structure provides symmetrical switching capabilities in both forward as well as reverse polarity. The doping and width of all layers are equal. The terminalвЂ™s regions are made of both P and N layer. It has a symmetrical structure made of 2 P-layer and 3 N-layers. The 5-layer DAIC construction resembles the combination of two SCR without the gate terminal. The break over voltage of such DIAC lies around 30 volts. The 3-layer structure is mostly used which is made by either sandwiching N or P between its alternating layers forming PNP or NPN structure. DIAC can be constructed in 3-layer and 5-layer symmetrical structure.

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