1500 W peak pulse — the clamping event that matters
The 1.5KE56: That power rating is the device's energy-handling ceiling for a single transient — it tells you how much surge the junction can absorb before failure, not the continuous dissipation.
Clamp voltage and the protection threshold
Reverse standoff voltage is 47.8 V — the DC or peak-AC voltage the line can carry without the diode conducting appreciable leakage. Breakdown occurs at 50.4 V minimum, and the clamping voltage at peak pulse current (19.7 A) is 80.85 V maximum. The gap between standoff and clamp defines the protection window: a 48 V rail sees the diode start to avalanche just above normal operation and hold the transient below 81 V. The DO-201AA axial-lead package (also known as DO-27) is a through-hole footprint that handles the thermal pulse of a 1500 W surge without requiring a heatsink — the lead frame and solder joint are the thermal path.
Obsolete — sourcing through independent channels
Littelfuse lists the 1.5KE56 as obsolete. Sourcing is through independent distribution — quantities are lot-specific, and availability is confirmed at the time of RFQ.