Protection window — breakdown, clamping, and standoff voltages
The 1.5KE91C-B: The 77.8 V standoff means the protected line can ride at that DC or peak AC voltage without the TVS conducting leakage current — the clamping triggers only when the transient exceeds the breakdown threshold.
Bidirectional configuration and application fit
A single bidirectional channel protects signal lines that swing both positive and negative relative to ground — common in AC-coupled data interfaces, RS-485 transceivers, and audio paths where polarity is not fixed. The DO-201AA (DO-27) axial leaded package mounts through-hole on a PCB or terminal block, suited for bulkhead or panel-mounted protection modules where surface-mount reflow is not available. Power line protection is not listed — this device is intended for data, signal, or general-purpose secondary surge suppression, not for direct AC mains clamping.