What this part is and where it fits
The ST T1235T-8FP is a Snubberless™ Alternistor triac rated for 800 V off-state voltage and 12 A RMS on-state current in a TO-220FPAB full-pack through-hole package. The Snubberless™ construction means it switches inductive loads (motors, solenoids, transformers) without the external RC snubber network that conventional triacs require — saves board space and BOM cost in AC switching applications like industrial motor drives, lighting ballasts, and HVAC valve actuators. The full-pack (isolated) TO-220 tab eliminates the need for an insulating washer when bolting to a grounded heatsink.
Key ratings and what they mean for the BOM
The 800 V off-state rating (Vdrm) and 12 A RMS continuous rating define the operating limits. Gate trigger current is 35 mA max (Igt). Holding current of 40 mA ensures the device latches on once triggered.