Glossary:SIDAC
A SIDAC or Silicon Diode for AC is a 2-terminal electronic component comprising 5 semiconductor layers which abruptly switches from a non-conducting to a conducting state when a certain voltage is applied, typically in the region of 150 - 300V depending on the type. It then remains conducting until the current falls below a small holding current. It is similar in operation to a DIAC except for the higher threshold voltage. It has a few niche applications in air ionisers and starting circuits for metal halide and other high pressure vapour lamps.