The 1.5SMCJ40: The 1.5 kW peak pulse rating at 10/1000 µs defines this as a mid-range TVS class — above the 500 W consumer-grade devices, below the 3 kW industrial types that push the SMC package thermally. Rated for unidirectional protection on a single channel: the cathode connects to the line to be protected, the anode grounds. Maximum clamping voltage is 71.4 V at the 21 A peak pulse current — the protected load sees no more than that during a surge event.
Voltage window and junction temperature
The 40 V standoff / 44.4 V breakdown / 71.4 V clamping sequence defines the protection window. A 24 V rail with typical transients sits comfortably below standoff — the TVS adds no load. A genuine surge that exceeds 44.4 V on the line activates the clamp and diverts current to ground. Operating junction temperature runs from -50°C to +150°C, so the part survives the thermal excursion of a large clamp event without derating issues in most enclosed panels. DO-214AB (SMC) is a surface-mount package — the cathode tab provides the thermal pad to the board. Follow the manufacturer's solder profile for the strip packaging orientation during reflow.