20 V rail clamp at 1.3 W — what that means on the board
The 1N4747A-TAP is a 20 V zener diode rated for 1.3 W continuous dissipation in the DO-204AL (DO-41) axial package. That 20 V nominal is the voltage where it starts conducting in reverse breakdown — useful for clamping a 15 V or 18 V supply rail, or as a reference in a shunt regulator. The ±5% tolerance means the actual breakdown lands between 19 V and 21 V, tight enough for most protection and reference circuits without trimming.
Automotive-grade — AEC-Q101 and 175°C junction
This part carries the Automotive, AEC-Q101 qualification, which means it has passed the stress tests for under-hood and chassis-domain electronics — thermal cycling, high-temperature reverse bias, and humidity. The 175°C maximum junction temperature gives headroom over the 150°C common on standard zeners; useful if the diode sits near an exhaust manifold or inside a sealed ECU enclosure where ambient heat builds.
Active production — no obsolescence headache
No last-time-buy clock is running, no forced redesign waiting.
Through-hole axial — field-swappable with a soldering iron
DO-204AL (DO-41) is the classic axial-lead package. The banded cathode end is moulded into the body — no orientation guesswork. On a site repair, you can pull the old one and solder this in with a standard iron; no hot-air station needed. The Tape & Box (TB) or Cut Tape (CT) packaging options let you order the quantity that matches the job.