Clamping performance for board-level transient protection
The 1.5SMC91CA-E3/9AT: The standoff rating is 77.8V typ, which sets the continuous working voltage the line can carry without the device turning on. That 125V clamp ceiling is what the downstream circuits survive. A 1500W SMC-device in DO-214AB is a mid-range clamp in the 1.5SMC family; the clamping voltage and peak current are the two numbers that determine whether the protected load (MOSFET gate, bus regulator, communication port) sees a survivable spike or not. Junction temperature range is -65°C to 150°C — the upper limit is specified at the junction, not the ambient, so the board-level thermal design must keep the case temperature low enough that the junction stays within that window. The SMC (DO-214AB) package dissipates heat through the cathode tab into the PCB pad; adequate copper plane area under the device is required to hit the rated peak pulse without derating.
SMC package — surface-mount TVS in the field
Surface-mount in the DO-214AB (SMC) package means the cathode tab solders directly to the PCB pad — the lead form factor is non-retractable, so the placement profile is standard reflow. The Tape & Reel packaging suits high-volume SMT line feed; the unit count per reel follows the manufacturer's standard reel diameter for this package. Polarity is marked on the body — for the bidirectional 'CA' variant the band either side of the centre stripe indicates the two equivalent terminals. No power-line protection designation — this part is rated for general-purpose board-level protection, not for direct AC mains-line clamping without further qualification. If the design intent is 120/240 VAC line-side protection, the peak pulse and standoff ratings need evaluation against the applicable safety standard.