What the 500W peak pulse power buys you
The SMAJ78E3/TR13 is a Zener-type TVS diode rated for 500W peak pulse power under the 10/1000µs waveform. That 500W rating is the energy-absorption ceiling for a single pulse — it tells you how much transient energy the diode can clamp before the junction gives up. For a 78V rail, the 139V clamp means the protected line sees a hard ceiling at that voltage during the event, which keeps downstream silicon inside its breakdown margin. The reverse standoff voltage of 78V is the DC bias the diode ignores — your rail must stay below that in normal operation, or the diode conducts continuously and overheats. Unidirectional, single-channel, so it clamps only one polarity; the other polarity forward-biases the Zener junction like a standard diode.
Package and temperature reach
Housed in DO-214AC (SMA), a standard surface-mount footprint that reflows on a standard profile — no exotic pad geometry. The operating junction temperature range is -65°C to 150°C, which covers industrial outdoor enclosures, engine-bay electronics, and cold-start down to -65°C. That's wider than the typical commercial 0°C–70°C grade, so it fits in telecom cabinets and automotive modules that see thermal cycling. No power line protection, meaning it's designed for signal or low-power DC rails, not AC mains.
The base product number is SMAJ78, so any variant with that base shares the same die and package family.