TransZorb Zener TVS — 1500 W peak pulse, 73.7 V standoff
The 1.5KE91-E3/54: The 1.5KE91-/54 is a Vishay TransZorb® Zener TVS diode in the 1.5KE series, designed to clamp transients on general-purpose DC power and signal lines. The reverse standoff voltage of 73.7 V sets the DC operating ceiling: the line voltage must stay below this level during normal operation, or the diode leaks and eventually fails short. The breakdown window starts at 81.9 V minimum, giving about 8 V of headroom before the device begins conducting.
Package and board-fit — DO-201AA axial
Housed in a DO-201AA (DO-27) axial-lead through-hole package, the 1.5KE91-/54 mounts into a 1.1 mm diameter hole on the PCB with a lead spacing of about 8.9 mm. The axial body stands off the board; the leads are typically formed or bent to fit the pad layout. This package is common across the 1.5KE family, so a replacement from the same series shares the same footprint.
Sourcing reality — obsolete, sourced on request
Vishay has marked the 1.5KE91-/54 as obsolete. No official successor order code is recorded for this specific breakdown voltage and package variant. For a design still using this TVS, the closest functional match is another 1.5KE-series Zener at the same 73.7 V standoff — but the exact breakdown window and clamping voltage should be cross-checked against the application's transient requirements before committing a replacement.