Diacs

Diac electronic element

Diacs

Diac (Diac - diode for alternating current) is a type of diode for alternating current that conducts current only when reaching the voltage that was before a given event. It is an electronic element with a three-, four- and five-layer structure. In the event of a breakdown or some event of improper operation, the diode enters a negative dynamic resistance, which leads to a sharp increase in the current through the diode and a decrease in the voltage drop across it. The diode remains conductive until the current passing through it drops to the previous values ​​characteristic of the device. When the threshold is reached the diode reverts back to its high resistance, non-conducting state.

Bidirectional diode

Unlike ordinary diodes, diacs are bidirectional and work for both directions of current. Most diacs have a three-layer structure with a cut-off voltage of approximately 30V and an on-voltage of less than 3V. Their behavior is analogous to the turn-on and turn-off voltages of a neon lamp, but can be more repeatable and occurs at lower voltages. Diodes are also called "symmetric trigger diodes" because of the symmetry of their characteristic curve. Since diacs are bidirectional devices, their terminals are not labeled as anode and cathode, but as A1 and A2 or main terminals MT1 and MT2.