The Triac BTA420Y-800CT,127 is a 3-quadrant hi-com 800V 20A TO220AB manufactured by WeEn Semiconductor. It has an Igt of 35mA and an Ifsm of 200A. It is an electronic part designed to switch power supplies in AC circuits to control the power output. It has the capability to control both positive and negative cycles of an AC waveform.