85V standoff — what it protects
The SMBJ85A-TR is a unidirectional TRANSIL™ TVS diode from STMicroelectronics, designed to clamp transients on 85V nominal DC rails. Its 94V minimum breakdown voltage and 137V maximum clamping ensure the protected circuit sees no more than 137V during a 10/1000µs surge event.
600W pulse — sizing the protection
Rated for 600W peak pulse power (10/1000µs waveform), this part handles 4.6A peak pulse current at the clamping voltage. That power rating is standard for the DO-214AA SMB package — enough for secondary protection on 24V industrial buses or 48V telecom rails where the primary suppressor takes the main hit.
STMicroelectronics lists the SMBJ85A-TR as obsolete. No official successor part is published. For new designs, look at the current SMBJ series (same base product number SMBJ) with the same DO-214AA footprint — the voltage rating must match the rail.
DO-214AA footprint — board fit
Surface-mount in a DO-214AA (SMB) package, the same footprint used across the SMBJ family.