The SMCJ170A-13-F is a 1500W (1.5kW) peak pulse power Zener TVS diode from Diodes Incorporated, housed in a DO-214AB (SMC) package. That 1500W rating is the peak power it can absorb in a 10/1000µs surge waveform — the standard telecom surge shape — so it clamps a transient before the downstream IC sees the full spike.
Clamping voltage and current — the numbers that decide fit
Reverse standoff voltage is 170V, meaning the line can sit at 170V DC or AC peak without the diode conducting. For a 170V rail, the 275V clamp gives about 60% headroom above the operating voltage — enough margin to protect downstream silicon rated for 250-300V without the TVS itself failing short.
DO-214AB (SMC) is a standard surface-mount package with a large copper tab for heat sinking.