Clamping voltage and the protection window
The 1.5SMC51CA V6G: Its 43.6 V reverse standoff voltage defines the normal operating rail — below this the diode is effectively invisible to the circuit.
1500 W peak pulse power at 10/1000 µs is the standard telecom surge rating — it covers the secondary-side protection needed after the primary protector on a 48 V DC-feed line. Bidirectional construction (one channel) means the same device clamps both positive and negative transients symmetrically — no need to orient the part on the board, and no risk of reverse-biasing a unidirectional part on an AC signal or a floating return.
DO-214AB footprint and board integration
The cathode band is marked on the body; for a bidirectional part the marking is typically the same both ways, but the pad layout is the same as the unidirectional variant.
The 1.5SMC51CA V6G is listed as Active by Taiwan Semiconductor Corporation. The 1.5SMC series is a mature, widely second-sourced TVS family — multiple manufacturers offer pin-compatible parts with the same DO-214AB footprint and similar clamping specs. Sourced to order against the BOM; availability and current pricing confirmed at RFQ.