What the clamping chain means for board-level protection
The 1.5SMCJ150C: At 150V reverse standoff, the device sits idle in normal operation and does not load the rail. The 5.6A peak pulse rating (10/1000 µs waveform) tells you the surge current the device survives without degradation — a value set by the 1500W peak pulse power rating. The two figures are linked: 268V × 5.6A ≈ 1500W, which is the power the package can dissipate as heat during the transient event. If the SMC pad is undersized or the adjacent components load the local thermal environment, the margin to 150°C shrinks faster than the ambient derating curve suggests.
Confirm BOM quantity, full lot traceability, and any required C-of-C documentation at quote time.