A 5.1 V, 1 W Zener diode in the axial DO-41 package, from the 1N4728-1N4764 family. Reverse-biased past its 5.1 V breakdown it holds that voltage nearly constant while it conducts, which makes it a cheap voltage reference, a rail clamp that protects inputs from overvoltage, and a shunt regulator when paired with a series resistor. The 1 W rating (versus the 500 mW of a small SMD Zener like the BZT52C5V1) lets it absorb more current. The banded end is the cathode (pin 1); in a Zener circuit the cathode goes to the more positive side.

Pinout

Pin	Name	Type	Function
1	K	passive	Cathode. Marked on the package with a polarity band. In normal Zener operation the cathode is the more positive terminal; reverse breakdown clamps the cathode-anode voltage to VZ (nominally 5.1 V for 1N4733A, or the value listed for the selected BZT52C variant in the datasheet's Electrical Characteristics table).
2	A	passive	Anode. Return terminal for Zener reverse-bias regulation and forward-bias conduction (VF = 0.9 V at IF = 10 mA per the Maximum Ratings table).

Key specifications

Parameter	Value
Type	Zener diode
Zener voltage (Vz)	5.1 V (at 49 mA)
Power rating	1 W
Tolerance	±5% (A suffix)
Max Zener current	~178 mA
Test current	49 mA
Marking	band = cathode (pin 1)
Package	DO-41 (axial THT)

Ordering variants

1N4733A-T (DO-41)
1N4733A-B (DO-41, bulk)

CAD (KiCad official)

Symbol: Device:D_Zener
Footprint: Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal
3D model: DO-41 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Diodes Incorporated datasheet (5 pp, sha256 0fbd7d137524820f, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF