TVS for a 75V rail — what the ratings tell you
Its 500W peak pulse power rating (10/1000µs waveform) means it can absorb a 3.7A surge for that duration without failing — the 134V clamp voltage is the ceiling the downstream circuitry sees. The 83.3V minimum breakdown voltage gives a guard band above the 75V standoff, so the part stays off during normal operation and only conducts when a transient pushes the rail past that threshold.
Voltage window and surge current
Three numbers define the protection envelope: 75V reverse standoff (the rail voltage it protects), 83.3V minimum breakdown (where avalanche conduction starts), and 134V maximum clamp at the rated 3.7A peak pulse current. The 8.3V gap between standoff and breakdown means the TVS does not leak significantly at the nominal rail, while the 50.7V clamp-to-standoff ratio is typical for a Zener-type TVS in this voltage class. If the load can tolerate a 134V transient for 1 ms, this part covers the rail.
Microchip lists the SMAJ75E3/TR13 as Active.
Surface-mount assembly on DO-214AC (SMA) — the cathode tab is the thermal path; the copper pad area under it sets the junction-to-ambient thermal resistance.