What the 1500W rating means for your rail
The 1.5KE43-B is a 1500W (1.5kW) peak pulse power TVS diode in the 1.5KE series from Littelfuse — a Zener-type unidirectional transient suppressor designed to clamp voltage spikes on a DC rail. The 1500W rating is the device's ability to absorb a single 10/1000µs pulse without failing — not continuous power. For repetitive surges, derate per the datasheet's pulse derating curve. The unidirectional channel (1) means it clamps only one polarity; for AC lines or bidirectional protection you need the bidirectional variant in the same family.
Through-hole DO-201AA (DO-27 axial) package — the body is 9.1 mm long with 0.96 mm diameter leads, standard for 1.5 kW TVS diodes. The bulk packaging means loose tubes or bag, not tape-and-reel. Lead forming for PCB insertion is straightforward; the axial leads suit point-to-point wiring or through-hole boards with 0.100-inch pitch spacing. The junction temp rating is the absolute limit; derate power above 25°C per the manufacturer's curve.
Lifecycle reality — obsolete, sourced through surplus
For a BOM line that calls out the 1.5KE43-B, the functional replacement is another 1500W unidirectional TVS with 36.8V standoff in DO-201 — but the exact clamping voltage and breakdown tolerance may shift. Pin-compatible alternatives exist within the 1.5KE series (e.g., 1.5KE43A for tighter tolerance), but no direct cross-reference is published. Confirm the protection window against the original design's transient requirements before substituting.