600W TVS for 170V rails — what the ratings mean
The STMicroelectronics SMBJ170A-TR is a unidirectional transient voltage suppressor from the TRANSIL™ SMBJ series, designed to clamp overvoltage transients on DC power rails up to 170V. Despite the 'Zener' type classification, this is a TVS diode — its job is surge clamping, not voltage regulation. The 189V minimum breakdown voltage ensures the device stays out of conduction during normal 170V operation, while the 275V maximum clamp at 2.2A limits the let-through voltage during a 10/1000µs surge event. The single unidirectional channel makes it a fit for positive-rail protection where reverse polarity is handled separately.
Housed in the DO-214AA (SMB) surface-mount package, the SMBJ170A-TR fits standard pick-and-place assembly. No power line protection feature — this is a standalone TVS, not a filtered or integrated protector.