Clamping and standoff — the two numbers that size the TVS
The 1.5SMCJ85AS_R1_00001: The 137 V maximum clamping voltage at 10.4 A peak pulse current is the clamping spec that drives downstream protection design — the downstream circuit must survive 137 V for the duration of the transient. The 85 V reverse standoff (typ) sets the rail voltage the TVS guards without turning on — a 24 VDC rail sits comfortably below this, so the device remains off during normal operation and activates only on a surge event.
Peak pulse power and temperature margin
The junction temperature limit is 150°C, which gives headroom in enclosed panels where ambient can run to 85°C — the derating curve in the datasheet tells you how much of the 1500 W is usable at your actual ambient. Unidirectional polarity means this is a DC-rail clamp — it protects the positive rail relative to ground. AC line protection requires a bidirectional TVS or a back-to-back pair.
Package and active sourcing
The SMC (DO-214AB) package is the standard JEDEC footprint for 1.5–3 kW TVS diodes — the cathode bar on the top face is the thermal and electrical contact; the recommended land pattern uses a copper pad sized to the datasheet thermal recommendation.