What the three-voltage spec set means for protection design
The 1.5SMCJ12A_R1_00001: 19.9V at 75.3A is the clamping ceiling under the 10/1000µs surge waveform — the diode survives that event and returns to blocking without degradation, which is what makes a TVS different from a plain Zener regulator.
Peak pulse rating and thermal margin
1500W peak pulse at 10/1000µs is the IEC 61000-4-5 Class 2 surge class rating — a board protecting a 12V rail to that standard needs a clamping voltage under 30V and enough joule budget to absorb the surge energy without the junction temperature exceeding 150°C.
Package and sourcing posture
The SMC (DO-214AB) package is the standard unidirectional TVS footprint — pin 1 is the cathode, tied to the protected rail, with the anode grounded; the cathode bar marking on the package top follows the industry convention so it mounts correctly on the first attempt.