DIAC

From Free net encyclopedia

Image:DIAC.gif The DIAC, or DIode for Alternating Current, is a bidirectional trigger diode that conducts current only after its breakdown voltage has been exceeded momentarily. It stops conducting when the current through it drops below a value characteristic for the device, called the holding current. The behavior is typically the same for both directions of current flow. Most DIACs have a breakdown voltage around 30 V. In this way, their behavior is somewhat similar to (but much more precisely controlled and taking place at lower voltages than) a neon lamp.

DIACs are a form of thyristor. They are typically used for triggering TRIACs, another form of thyristor.

It is also called a symmetrical trigger diode due to the symmetry of its characteristic curve.

It is similar to two Shockley or Zener diodes connected in inverse parallel. Since the DIAC is a bidirectional trigger diode, its terminals are not labeled as anode or cathode but mostly labeled as A1 or MT1 and A2 or MT2.

The SIDAC is a less common electrically equivalent device, the difference in naming being determined by the manufacturer. In general, SIDACs have higher breakover voltages and current handling.

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