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diode alternating current switch (DIAC)

The DIAC (DiodeAlternating CurrentSwitch) is a bidirectional semiconductor switch for switching low currents. It is a three-layer diode, usually PNP, with one PN junction and one NP junction. One of the two PN/NP junctions

is always operated in the forward direction, the other in the reverse direction. The diac has a high impedance

when not switched and alow impedance

when switched. It operates bidirectionally, equally in both directions, and switches when the breakdown voltage is exceeded. Switching

sign and characteristic of the diac

sign and characteristic of the diac

Switching is triggered by applying a voltage


If the applied voltage exceeds the breakdown voltage, the junction operated in the reverse direction switches to its low-impedance state, causing both junctions to conduct. If the applied voltage is reduced and falls below the holding voltage, then one of the two layers

flips to its reverse state and the diac is high impedance. The voltage and current values are over a hundred volts and a few amps.

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Englisch: diode alternating current switch - DIAC
Updated at: 17.11.2019
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