Product Overview
National Semiconductor LM340T-12 Fixed 12V Positive Regulator, 1A, TO-220 Three-Terminal Package
Condition
Used. The photographed piece is a standard three-lead TO-220 with a black epoxy body and a bare metal mounting tab with the usual single fixing hole. The body marking is fully legible and reads, top line down, the National Semiconductor script N logo followed by -29FT, then LM340T12, then 7812 P+. The three leads are straight, full length, and uncut, with a dull grey finish and light handling marks. The tab face shown from the reverse is plain, with the surface scuffing you expect on stamped metal. No cracks, no chips, no bent pins, no corrosion. Stock is deep and the photographs are representative of what is on the shelf: markings and date codes on other pieces may differ from the one shown here.
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Product Overview
The LM340T-12 is National Semiconductor's three-terminal positive fixed voltage regulator in the TO-220 power package, the 12V member of the LM340 family and the part most benches simply call a 7812 - a designation printed right on the body of the piece photographed here, directly under the LM340T12 line. Three terminals, no external programming network, no adjustment pot: unregulated positive DC in, a fixed positive rail out, ground in the middle, with the metal tab available for heatsinking. The listing's own published spec line covers complete specifications at 1A load, internal thermal overload protection, internal short-circuit current limit, and output transistor safe area protection, and the P+ suffix on the body matches the P Product Enhancement tested note carried in the original specification. Dropout voltage, maximum input voltage, line and load regulation figures and thermal resistance are not confirmed here - verify against the LM340 datasheet before use.
Key Features
- Part marking on the photographed piece: National script N logo, -29FT, LM340T12, 7812 P+
- Fixed positive 12V output, three-terminal regulator, no external set resistors required
- Complete specifications at 1A load, per the original published specification
- Internal thermal overload protection
- Internal short-circuit current limit
- Output transistor safe area protection
- P Product Enhancement tested, matching the P+ marking on the body
- TO-220 package with bare metal mounting tab and single fixing hole for heatsinking
- Three straight uncut leads on the photographed piece, through-hole ready
Applications
- A repair technician rebuilding the linear supply section of a 1980s instrument that expects a 12V rail from a 78xx-style three-terminal part
- An audio hobbyist who wants a quiet linear 12V rail for a preamp or phono stage instead of a switching module
- A control-panel maintainer replacing a failed 12V regulator on a legacy relay or sensor board without redesigning the supply
- A bench builder stocking a drawer with TO-220 regulators so the next power supply project starts with the rail already solved
Frequently Asked Questions
Is this the 12V version, and how do I know?
Yes. The T-12 suffix in LM340T-12 is the 12V output member of the family, and the body of the photographed piece carries both LM340T12 and 7812 on separate lines, 7812 being the industry designation for a 1A fixed 12V positive regulator.
What is the P+ on the body?
It corresponds to the P Product Enhancement tested note that has always been carried in this listing's specifications. What that program covered in detail is not confirmed here - check National Semiconductor or Texas Instruments documentation for the LM340 series if the screening level matters to your application.
Do I need a heatsink?
That depends entirely on your input voltage and load current, and we cannot answer it for your circuit. The package gives you what you need to decide: a TO-220 with a bare metal tab and a mounting hole. Thermal resistance and maximum dissipation figures are not confirmed here - work them out against the datasheet for your operating point.
Will the piece I receive look exactly like the photographs?
It will be the same part in the same TO-220 package, but stock runs deep and pieces came in over time. Date codes and small marking variations between individual pieces are normal. The photographs are the spec for the piece photographed, not a guarantee of identical markings across every unit on the shelf.
What am I actually taking on with a used regulator, and what does shipping cost?
Plainly: these are sold used, on the strength of the photographs and the markings on the body. We publish no test results for this part, so nobody here is telling you it has been powered up and measured - what you are buying is a used LM340T-12 in a TO-220 package, pulled from deep stock and represented by the photographed piece rather than shown individually, with the understanding that you will drop it in and check the rail on your own bench. If that trade suits you, it is a good one; if you need a tested part with a certificate, this is not that. Shipping is $8 flat rate, free once your order passes $28, and orders leave our Idaho warehouse the same or next business day, so pulling a few of these in with the rest of your basket usually costs nothing to ship.
The script N logo on this body belonged to a company that no longer exists, but the 7812 printed under it is a number every technician still reads at a glance. Solder it in, put a meter on the output, and let a forty-year-old convention keep your 12V rail honest one more time.
