Clamping and breakdown margins
The 1.5SMC250AS_R1_00001: Minimum breakdown voltage is 237V, giving a 23V guard band above the 214V standoff — the diode stays high-impedance under normal rail ripple and only conducts when a surge pushes the line past 237V. The 4.5A peak pulse current at the 344V clamp level means the TVS absorbs the surge energy without exceeding its 1500W rating, provided the source impedance limits the current to that value.
DO-214AB SMC footprint
The copper pad area under the cathode tab sets the thermal resistance — a 1 oz copper pour of at least 200 mm² on the PCB keeps the junction temperature rise within the rated limit during repetitive surges.