The 1.5SMC300A-E3/9AT: The 1.5SMC300A-/9AT is marked Obsolete by Vishay General Semiconductor - Diodes Division, meaning the manufacturer no longer produces this part.
Clamping performance and fit
Reverse standoff voltage is 256 V, so it sits across a 240 VAC or 300 VDC rail without conducting in normal operation. Breakdown starts at 285 V minimum, giving a 29 V margin before clamping engages. Single unidirectional channel — use one per rail polarity.
Temperature range and board integration
The wide range suits outdoor telecom, industrial drives, and automotive under-hood environments where ambient heat plus self-heating must stay within the TJ limit. Surface-mount DO-214AB (SMC) — the copper pad area under the cathode tab sets the thermal resistance. A generous ground-plane pour on the PCB pulls heat from the die; a small pad raises the junction temperature at the same pulse power.