1500W axial TVS for legacy rail protection
The Littelfuse 1.5KE91-B is a single-channel unidirectional Zener TVS diode in the 1.5KE series, delivering 1500W peak pulse power across a 10/1000µs waveform. Its 77.8V reverse standoff voltage and 81.9V minimum breakdown threshold clamp transients at 131.25V maximum, passing 12.2A peak pulse current through the DO-201AA axial package.
Clamping window and pulse capability
The 77.8V standoff sits below the 81.9V breakdown minimum, meaning the diode stays transparent during normal DC bus operation up to that voltage and only conducts when a transient pushes the rail above the breakdown threshold. The 131.25V clamp ceiling limits the voltage the downstream circuitry sees during the surge — for a 77.8V nominal rail, that is a 1.7× clamp factor, which is tight enough for most 100V-rated downstream semiconductors to survive without secondary protection. Rated for 1500W peak pulse at 10/1000µs, the 12.2A peak pulse current is the current the diode can sink during that waveform without exceeding its thermal limit. The junction operates from -55°C to 175°C, so the derating curve at elevated ambient temperatures must be applied — at 125°C ambient, the effective pulse power drops to roughly 75% of the 1500W rating.
Obsolete — sourced through surplus channels
Littelfuse has marked the 1.5KE91-B as obsolete. No official successor part number is recorded from the manufacturer. The DO-201AA axial footprint is shared across the 1.5KE series, so a parametric replacement from the same family (different standoff voltage) may fit the same board hole pattern if the protection voltage can be adjusted.