What the 1.5SMCJ series ratings mean for secondary-side protection
The 1.5SMCJ150A_R1_00001: The 150V reverse standoff (typ) is the working voltage — the TVS stays off and invisible to the circuit up to that level, then clamps during a transient. The minimum breakdown of 167V gives enough guard band above standoff to avoid false triggering on normal line noise. When a surge fires, the 1500W peak pulse rating at 10/1000 µs defines the energy the device absorbs without degradation. At that event the clamping voltage ceiling is 243V — whatever the downstream load sees is held below that level.