The 1N6155AUS is a bidirectional Zener TVS diode rated for 1500W peak pulse power at 10/1000µs — that 1.5 kW pulse rating tells you the die area is substantial, and the scorch mark on a failed board won't be subtle. The 27.4V reverse standoff voltage means it sits across a 24V rail and stays dark until a transient pushes past 34.2V breakdown minimum. It clamps at 49.9V maximum at the 30.1A peak pulse current, which is the number you use to size the upstream fuse or PTC so the TVS takes the hit and the rest of the board survives.
The junction temperature range spans -55°C to 175°C — that's the full military-grade window, so this part is comfortable in an engine bay, a satellite power bus, or a downhole tool where the ambient hits 125°C and the die runs hotter. The SQ-MELF, C package is a hermetic surface-mount ceramic barrel — no plastic to outgas or crack under thermal shock. The gold-plated end caps solder to the board with a standard reflow profile; the thermal mass is low enough that a hot-air rework station can swap it without cooking adjacent parts.
Active production — no end-of-life scramble
The base product number is 1N6155, so the AUS suffix identifies the bidirectional, SQ-MELF variant. If your BOM calls for the unidirectional version, check the 1N6155 family table — the suffix changes, but the package and footprint stay the same.