The STMicroelectronics 1.5KE22ARL is a Zener-based transient voltage suppressor in the 1.5KE / TRANSIL series. It is a unidirectional device rated for 1500 W peak pulse power (10/1000 µs waveform), with a reverse standoff voltage of 18.8 V, a minimum breakdown voltage of 20.9 V, and a maximum clamping voltage of 39.3 V at the peak pulse current of 254 A (8/20 µs). The 1500 W rating is the headline number for surge protection — it tells you the device can absorb a single 1 ms surge up to that power without failing. For a 24 V bus or a 18 V rail with a bit of margin, the 18.8 V standoff keeps the part out of conduction during normal operation, while the 20.9 V breakdown guarantees it starts clamping before the downstream circuitry sees damaging overvoltage. The 39.3 V clamp is the worst-case voltage the load sees during a surge — that figure drives the voltage rating of the protected components. If your downstream silicon is rated for 40 V absolute maximum, this part leaves only 0.7 V of headroom, which is thin. For a 30 V-rated rail, it is comfortable.
Through-hole axial package — board-level fit
The 1.5KE22ARL comes in a DO-201AA / DO-27 axial-lead package, through-hole mount. That means it is hand-solderable and rework-friendly, but it takes up board area on both sides — the body sits above the board and the leads go through to the opposite side. For high-reliability or field-repairable assemblies, that is an advantage; for dense SMT boards, it is a compromise. The device is unidirectional, so it protects one polarity only. If your application needs bidirectional clamping (e.g., AC signal lines), you would need two devices back-to-back or a different part number. Capacitance is 3700 pF at 1 MHz — typical for a 1500 W TVS in this voltage class. That is high enough to distort high-speed data lines above a few MHz, so this part is best suited for power-supply rails, relay coils, or low-frequency I/O, not for Ethernet or USB.
The 1.5KE series is broad, and a pin-compatible drop-in replacement would need to match the 18.8 V standoff, 20.9 V breakdown, 39.3 V clamp, and 1500 W rating in the same DO-201 package. Parts like the 1.5KE22A (without the 'RL' suffix) or the 1.5KE22CA (bidirectional) are in the same family but differ in packaging or polarity — verify the exact voltage and package before substituting. The smart move is to qualify a second-source TVS with identical electrical specs and the same DO-201 footprint, then use the 1.5KE22ARL for bridge-buy or repair stock only.