The 1.5SMCJ85CA: The 85 V standoff rating is the working voltage the diode presents to the line in normal operation; transients above that level trigger avalanche breakdown starting at 94.4 V minimum, clamping the peak to 137 V before the downstream circuit sees it.
Clamping ceiling and peak pulse capability
That gap matters: a part with a tighter standoff-to-clamping ratio leaves less headroom for the protected circuit during fast transients, and margin shrinks further as junction temperature climbs toward the 150 °C rated maximum. Power Line Protection is listed as No — this part is not intended for continuous power-line DC clamping roles; it is a transient suppressor sized for single-event surge absorption, not a clamp that sits across the rail continuously.
SMC footprint and thermal considerations
The DO-214AB SMC package mounts flush to the PCB; the cathode band on the body identifies the terminal that connects toward the line to be protected. Surface-mount termination is tin-lead finish on the SMC grade; adequate solder mask clearance around the landing pads ensures the thermal path from the diode body to the board copper carries the surge heat away without the solder joint becoming the bottleneck.