1500W peak pulse power in a DO-201AD axial package
That 1.5 kW rating means it can absorb a substantial transient — think inductive load dump or lightning surge on a 12V/24V rail — without failing short. The DO-201AD axial body handles the thermal pulse; the leaded package is a through-hole part, so it's a natural fit for point-of-entry protection on a PCB where the transient energy is highest.
Clamping voltage and standoff — the protection window
Reverse standoff is 17.1V typical; the device starts conducting at 19V breakdown minimum. Maximum clamping at rated Ipp is 27.7V. That 10.6V window between standoff and clamp is tight enough to protect a 24V nominal bus — the downstream DC-DC or load switch sees a peak well below its 30V absolute max. No power line protection feature is built in; this is a straight Zener clamp, no crowbar or foldback.
onsemi lists the 1N6278ARL4 as Obsolete. The Mosorb™ series has been widely replaced by newer TVS families (e.g., SMCJ, SMDJ) in surface-mount packages, but those are not pin-compatible with the DO-201AD axial footprint.
The DO-201AD axial package is rated for through-hole mounting — the leaded body dissipates heat into the PCB copper and surrounding air.