A Trisil is trade name for a thyristor surge protection device, an electronic component designed to protect electronic circuits against overvoltage. Unlike a transient voltage suppression diodes, such as Transil, it acts as a crowbar device, switching on when the voltage on it exceeds its breakover voltage. Overview A Trisil is bidirectional, behaving the same way in both directions. It is principally a voltage-controlled triac without gate. The behavior of a trisil is similar to a SIDAC, but… (More on Trisil)