TL431 not working due to incorrect pinouts !

[TheDefpom]

Hi All,
I just designed a small project and was stumped for a while as it just wouldn't work, despite it being a very simple circuit and checking multiple times that everything was correctly connected!

As it was a simple circuit I hadn't even chucked it in a breadboard to mock up and had just gone straight to PCB, which would have been fine, only after a lot of messing around trying to figure out why it didn't work I did chuck it on a breadboard and use that to figure out what was going on... well it didn't work there either, great, so I went about trying some stuff and tried putting the TL431 in backwards to swap its Reference and Cathode around... and it started working !

I replicated this on my PCB and yep, problem was solved, so it seems that the TL431 (in TO-92 package) I got from Aliexpress (yes I know!) has the pinout flipped by 180 degrees !

So I thought I would just share this here as there will be plenty more of these units floating around I expect and others may come across this problem too.

[David_AVD]

Not just a case of misreading the pinout (top view vs pin view) ?

[TheDefpom]

Nope, I verified it in the data sheet and from the footprint markings in eagle, that was my first thought too.

[magic]

 

There are SMD versions with different pinout, but most vendors call them TL432 after TI, and they are SMD.
TO92 should be RAC.

[eugene]

Yes, and if the TL432 were offered in TO-92 package, then it would have the pinout the OP describes.

No law that a manufacturer can't make a TL432 in TO-92, but they need to call it a TL432 not a TL431.

[Niklas]

Nexperia makes a TL431 available in both normal and mirrored pinout. The only difference is an additional letter M in the part number.

https://www.nexperia.com/products/bipolar-transistors/3-terminal-adjustable-shunt-regulators/series/TL431-FAMILY.html

[Leeroy]

Just lost several days to this too.. Sure I'm not the last one.

Had to buy 431 from two different Asian manufacturers via legitimate distributors: HTC Korea (TAEJIN Tech) and UMW (Youtai Semi), last one is huge btw.
Both have proper datasheets and use uniform pinout for all 3-pin packages (ref, anode, cathode) as if it was agreed upon.

What's not helping is that sot-23-3 parts are clearly marked "431" on both and some distributors make it worse buy "improving" their SEO by reusing TI's suffixes like "DBZ" (although there is nothing like that in mfg specs) or even loosely attaching TI's datasheets on product page.