What this triac is and where it fits
The STMicroelectronics BTA08-400CRG is a standard triac rated for 400 V off-state and 8 A RMS on-state current, housed in a TO-220-3 through-hole package. It is a general-purpose AC switch for loads like resistive heaters, small motors, lighting dimmers, and solid-state relays in industrial and commercial equipment. The 25 mA gate trigger current and 25 mA holding current are typical for standard triacs, making it compatible with common optocoupler and logic-level drive circuits.
Temperature range and environment
Rated for -40°C to 125°C junction temperature. The heatsink must keep the junction below 125°C.
Lifecycle and sourcing
The BTA08-400CRG is listed as Active and ROHS3 compliant. It is a current-production part from STMicroelectronics, so no last-time-buy risk. For dual-sourcing or a higher voltage variant, the BTA08-600CRG (600 V off-state) is a direct pin-compatible alternative with the same 8 A rating and package. The BTB08-600CRG is another 600 V option, also standard gate. If you need a sensitive-gate version for low-current logic drive, the BTA08-600TWRG is the one to look at — same package, but the gate trigger drops to a few milliamps.