Product Overview
LM431ACZ Programmable Shunt Voltage Reference, Marked with National's Script N and an 02AB Code
Condition
Unused, new old stock, which is how this listing has always described it. The photographed piece is a small three-lead plastic package with one flat marked face. The marking reads in three lines: National's script N logo followed by 02AB on the top line, LM431 on the second, and A C Z on the third, all legible in the closeups without magnification. The leads are straight, uncut and unbent, with no solder on them and no cut kink of the kind a board removal leaves. Lead plating photographs bright silver in three of the four frames and duller grey in one of the two in-hand closeups, which reads as a difference in lighting between shots rather than a difference in the plating. The reverse face is plain black with a small round mould mark and carries no printing. No packaging appears in any frame, so nothing here is said about how the part was stored.
Thirteen pieces are in stock and one is shown. The photographed piece is representative; the marking, including the 02AB code, is the spec for that piece only and codes can differ across the group.
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Product Overview
The LM431ACZ is a programmable shunt voltage reference, the part that sits in a feedback loop and decides where the rail settles. Two external resistors set the reference point and the device sinks whatever current the loop asks of it, which is why it turns up in the secondary side of switching supplies, in linear regulator feedback, and anywhere a designer needs a stable threshold without building one out of discretes. National's published data for the LM431 family gives an adjustable output to 36 V, a dynamic impedance of 0.2 ohms, and a sink current range of 1.0 mA to 100 mA. This one is the through-hole ACZ version, marked LM431 with the ACZ suffix split across two lines on the body, and it carries the National script N rather than a second-source logo.
Key Features
- Manufacturer: National Semiconductor, script N logo on the case
- Part number: LM431ACZ, marked LM431 with the A C Z suffix on the body
- Type: programmable shunt voltage reference and regulator
- Package: three-lead plastic through-hole, one flat marked face
- Adjustable output: up to 36 V per National's published family data
- Dynamic impedance: 0.2 ohms per National's published family data
- Sink current range: 1.0 mA to 100 mA per National's published family data
- Top-line marking on the photographed piece: 02AB, a factory date and lot marking
- Pin function lettering: not printed on the body, so verify pin assignment against the datasheet before wiring
- Sold each, from stock of thirteen
Applications
- Power supply technician replacing the secondary-side reference in a legacy switching supply's feedback loop
- Bench engineer setting an adjustable rail with a two-resistor divider on a prototype board
- Instrument restorer matching an original National part on an analog board rather than dropping in a modern substitute
- Hobbyist building an opto-isolated feedback loop and needing one reference, not a bag of fifty
Frequently Asked Questions
What do the three lines of marking on the body mean?
Top line is National's script N logo followed by 02AB, which is a factory date and lot marking. The second and third lines are the part number itself, LM431 over A C Z, split by the width of the case.
The bottom line reads A C Z - is that pin lettering for anode, cathode and reference?
No. It is the ACZ suffix of the part number LM431ACZ, not a pin legend, and this package carries no pin function markings at all. Identify the pins against National's datasheet for the LM431 in the three-lead plastic package before you wire it in.
How is the output voltage set?
By an external resistor divider from the cathode to the reference pin, in the usual shunt reference arrangement. National's published family data covers adjustment up to 36 V; confirm the divider values and the minimum operating current against the datasheet for your target voltage before committing the design.
Will the piece I receive carry the same 02AB code as the photos?
Not guaranteed. Thirteen are in stock and one was photographed. The part number marking is what we are selling on; the date and lot code can vary within the group, so if your build needs a matched code, ask us before ordering.
What am I actually getting here, and what am I taking on?
One LM431ACZ, sold each, in the physical state the photos show: markings legible, leads straight and untouched by solder. We have not put this device on a bench and we publish no test result for it, so treat it as untested and check the reference against your datasheet before it holds up a supply rail. On a part in this price class that honesty is the whole deal, and the trade is that you buy the one or two you need instead of a reel. Shipping is $8 flat rate and free once the order passes $28, and orders leave the Idaho warehouse the same or next business day.
National's script N ended up on a lot of small black three-leggers, and this is the one whose whole job was telling a switching supply when to stop. Set the divider, and it goes back to quietly holding the line in whatever you are building next.
