What this Zener is and what it protects
The STMicroelectronics 1.5KE18CARL is a 1500W bidirectional Zener diode from the TRANSIL™ series, housed in a DO-201 axial-lead package. It is designed for general-purpose transient overvoltage suppression where a symmetric clamping characteristic is needed — the single bidirectional channel clamps both polarities of a surge without needing two diodes back-to-back.
The reverse standoff voltage is 15.3V, meaning the device does not conduct appreciably below that level — it stays off the rail during normal operation. Breakdown starts at a minimum of 17.1V, and the clamping voltage is held to a maximum of 32.5V at the peak pulse current of 308A (8/20µs waveform). For a 15V nominal DC bus, this device provides a protection window that triggers before most downstream silicon ratings are exceeded, while the 1500W pulse capability handles heavy surge events from inductive loads or lightning-coupled transients.
Capacitance — a constraint for signal-line use
The capacitance is specified at 2150pF at 1MHz. This part is best suited for power-supply rails, relay coils, or DC bus protection where signal integrity is not a concern.
STMicroelectronics no longer manufactures this specific order code in volume.