What the 1500W rating means for the protection threshold
The 1.5KE550C-B: The 495V minimum breakdown voltage and 798V maximum clamping define the transient it can absorb — a 2A peak pulse current at that waveform. For a 480VAC line or a 400VDC bus, this part clamps before the downstream silicon sees destructive overvoltage, but the 495V standoff means it does not conduct during normal rail ripple. The bidirectional channel handles both positive and negative transients in a single DO-201AA axial package, saving board space over two unidirectional devices.
Obsolete — sourcing through surplus and last-time-buy channels
Littelfuse has marked the 1.5KE550C-B as obsolete. For a BOM that already carries this part number, the procurement decision is whether the remaining stock in the channel covers the production run or whether a board spin to a current TVS family is more cost-effective. The DO-201 footprint is still common, but the 495V breakdown point is specific — a parametric substitute would need matching standoff and clamping within the same axial package.
Through-hole DO-201AA axial package, also listed as DO-27. The leads are tin-plated copper, sized for solder or socket insertion into a 1.0 mm to 1.3 mm plated-through hole. The body length is about 9.1 mm, and the lead diameter is 1.3 mm — standard for this power class. Bulk packaging means the parts ship loose in a bag, not taped and reeled.