TVS diode for 495V rail clamping
The 1.5KE550-B: With a peak pulse power rating of 1500W (1.5kW) and a clamping voltage of 798V at 2A peak pulse current (10/1000µs waveform), it protects downstream semiconductors from voltage spikes that exceed the reverse standoff of 495V. The 495V breakdown voltage (minimum) means this part triggers just above the normal operating level, clamping the surge before it reaches the 798V ceiling. The single unidirectional channel handles positive-going transients; for bidirectional protection on AC lines, two devices back-to-back or a dedicated bidirectional TVS would be needed.
Package and thermal envelope
Housed in a DO-201AA (DO-27) axial leaded package, the 1.5KE550-B mounts through-hole on the board. The junction temperature range spans -55°C to 175°C, covering industrial and some automotive under-hood environments where the ambient sees wide thermal cycling. Bulk packaging — the parts ship loose in a bag or tube, not taped and reeled. For automated pick-and-place, the axial leads require manual or semi-automated insertion; this is a factor for high-volume assembly lines that prefer surface-mount packages.
Sourcing an obsolete part
Littelfuse lists the 1.5KE550-B as obsolete. For a BOM that requires this exact clamping voltage and package, the only sourcing path is the surplus market. If a board spin is acceptable, a parametric search for a 495V standoff TVS in a comparable axial package (e.g., P6KE or SA series) may yield an active alternative, but no direct drop-in replacement is documented.