The 1.5KE12ARL is a unidirectional Zener TVS diode from the 1.5KE TRANSIL series, rated for 1500W peak pulse power over a 10/1000µs waveform. That 1500W rating means it can absorb a hefty surge — think industrial power-line transients, inductive load dumps, or lightning-induced spikes on outdoor cabling — without the junction giving way. The 10.2V reverse standoff voltage lets it sit on a 12V rail without conducting during normal operation, and it clamps at 21.7V to keep the protected circuitry from seeing a destructive overvoltage.
461A peak pulse current — surge handling in practice
Peak pulse current is 461A when tested with an 8/20µs waveform — that's the kind of short, high-energy pulse you get from a nearby lightning strike or a capacitor bank discharge. The DO-201 axial package (also known as DO-27) is a through-hole format that handles the thermal mass needed for that energy; the leads solder into a board or can be crimped into a terminal block for panel-mount transient suppression.
Breakdown and clamping window
Minimum breakdown voltage is 11.4V, so the diode starts conducting at that threshold. The clamping voltage caps at 21.7V at the full peak pulse current — that's the maximum voltage the protected circuit ever sees across the diode. For a 12V nominal rail, that leaves about 9.5V of headroom above the rail before the clamp fires, which is typical for a TVS in this voltage class. Capacitance is 6000pF at 1 MHz — high enough that you wouldn't put this on a high-speed data line (think Ethernet or USB), but fine for power inputs, relay coils, or slow GPIO.
For BOM lines that still call out this exact code, the supply route is the independent distribution channel — surplus stock, NOS (new old stock), or broker-sourced inventory. If you're qualifying a new design, look at current-production TVS diodes in the same 1500W, 12V class — the 1.5KE series has many siblings still active, but the 'ARL' suffix variant specifically is end-of-life.