The acronym DIAC is short for “diode for alternating current”. A DIAC is a semiconductor switch that can be turned on in both forward and reverse polarities (full-wave or bi-directional). DIACS are also called "symmetrical trigger diodes".
A DIAC works by introducing a voltage, in either direction. A ’break over point’ is then reached when the device enters a negative resistance region. This will remain in a low resistant state until the current applied reduces below its holding value.
Most DIACs have a three-layer structure with break over voltage of approximately 30 V. Their behaviour is similar to that of a neon lamp, but it can be more precisely controlled and takes place at a lower voltage.
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