Unidirectional TVS clamping hierarchy
The 1.5SMCJ120A is a unidirectional Zener-type transient voltage suppressor in the DO-214AB (SMC) surface-mount package — one clamping direction, no bidirectional confusion in the layout. Reverse standoff is 120 V nominal, meaning the device sits idle below that rail; the minimum breakdown of 133 V defines where it first engages, and the maximum clamping voltage of 193 V at the peak 7.8 A surge current is what the downstream circuitry sees as its stress ceiling.
For sub-microsecond ESD events the clamping voltage will be higher than the datasheet figure due to the device's dynamic response.
Junction temperature and mounting
The board-level thermal pad under the SMC package must carry heat to the copper plane. Mounting type is surface mount, which aligns with automated board assembly. The SMC/DO-214AB footprint is one of the most widely placed packages in power-supply and protection circuits, so pad tooling is standard.
Listed as Active by Diotec Semiconductor.