Just add a voltage between electrodes D1 and D2, regardless of their polarity, and as long as this voltage exceeds a certain voltage value (the collapse voltage), both electrodes will turn on. The bidirectional trigger diode with such a property can be used as a three-terminal bidirectional thyristor to obtain the trigger element, so it is also known as the trigger diode. The name DIAC comes from the fact that it acts as an alternating current (AC) switch with a DIODE.