Transient suppressor for 48 V rails — what the ratings mean
The STMicroelectronics 1.5KE56ARL is a unidirectional Zener transient voltage suppressor from the 1.5KE TRANSIL™ family, designed to clamp overvoltage events on general-purpose DC power and signal lines. Its 47.8 V reverse standoff voltage sits just below the nominal 48 V telecom and industrial bus levels, so it stays out of conduction during normal operation. Breakdown is guaranteed at 53.2 V minimum, and the clamping voltage is held to 100 V at the peak pulse current of 100 A (8/20 µs waveform). With a peak pulse power rating of 1500 W, this part handles substantial surge energy in a through-hole DO-201 axial package — a common footprint for board-level protection in power supplies, motor drives, and base stations.
Obsolete — sourcing the 1.5KE56ARL today
STMicroelectronics no longer manufactures this exact suffix variant. For a BOM line that still specifies this order code, the supply channel is independent distribution — stock is sourced from excess inventory, last-time-buy remnants, and verified broker inventory.
Design-in note: capacitance and unidirectional use
The 1.5KE56ARL is a single unidirectional channel — it clamps positive transients only; for bidirectional protection on AC or bipolar rails, two devices or a bidirectional variant is needed. Capacitance is 1800 pF at 1 MHz.