How to get from BAT54A to BAT54C?

There is a diode for BAT54A. But its supply current do not suit into my application. BAT54C is what I want. Schema symbol and PCB footprints are same, only name changes. What are all the places I need to go to make the replacement?

If there already is a BAT54C part somewhere, then where is it?

Both are 3 bit level shifters if you want to know.

1 Like

Be careful! In real components, BAT54 numbering may be tricky and depend upon vendor. I think that BAT54 is a single diode in SOT23 while BAT54C is a dual common cathode in SOT23. But there are variants (I hate that word) in SOD123 and SOT323 and other packages, so beware of vendor and full part number. See https://www.vishay.com/docs/85508/bat54.pdf as one example.

How much current do you want? Use a completely different device if you want current > 100 mA or so.
BAT54 series are all schottky diodes and forward voltage will be significantly less than that for a small PN junction diode at similar current.

I just made a quick search.

Be Careful” is very good advice.

BAT54A is common anode and BAT54C is common cathode!
https://www.vishay.com/docs/85508/bat54.pdf

EDIT:

Ha!!! Your edit covered (took care of) the link @BobZ :slightly_smiling_face:

Not sure what you mean? My link appears to be fully malfunctional and invisible as intended? :slight_smile:

Nahh,
You originally posted while I was searching for BAT52 (should be BAT54) so I could understand what the OP was writing about.
I then read your reply and decided to contribute with a comment and link.
Meantime you posted the same link as an edit

Great minds thinking alike? :crazy_face:

1 Like

From the fist page of the linked Vishay datasheet (In case it disappears in the future):

image

  • No suffix = Single.
  • A = Common Anode.
  • C = Common Cathode.
  • S = Series connection.

BAT52 != BAT54 but I have not compared datasheets.

And you always have to be extremely careful with any part in a SOT-23 package. The trouble here is that manufacturers do not agree where pin number 1 is on this package. The numbering shown above is the most common, but you can’t rely on that.


[Edit]
I did a picture search, but could not quickly find one of the alternative pin numberings. Some of the datasheets do omit pin numbering at all and show pictures like in the Vishay datasheet, but without pin numbers.
https://duckduckgo.com/?q=sot23+pin+numbering&t=hx&va=g&iax=images&ia=images

But you can find texts like these:

You can put both diodes in parallel to push a bit more current through a SOT-23, but it’s a small package and limited by dissipation, so a diode in that package is never going to conduct much current for long. some MOSfets in SOT-23 do 3A or even 5A, but those have a very low Rds-on and therefore low dissipation.

Woops, Typo.
Thanks for picking it up.

First: For me there are no such term as diode supply current.
Second: Forward current for BAT54A and BAT54C are the same.

Pin numbering is not important. Important is that all BAT54(A/B/C) from all manufacturers have the same configuration - you can replace one with another (however manufacturer numbered pins in his datasheet).

That’s fine if you only have fully specified parts, but when you use a generic diode as a schematic symbol and assign a SOT23 footprint for the BAT54xx, then things can get mixed up.

For example, this is a generic footprint in KiCad For SOT-23:

But due to historical *&^%$#@! somewhere in the '80-ies (probably a single bad FAX I imagine) KiCad also has:

and:

But for this part it is apparently indeed relatively safe. All the BAT54xx variants appear to be default KiCad symbols with Footprints already assigned. I have not verified them, but KiCad’s default libraries tend to be pretty reliable.

So it should be clear now that this is not true:

They are both present in KiCad’s default libraries, and they’re not the same.
image

but if current handling capabilities are too low, then Deion_Adel needs another part altogether anyway.

I have a simple answer to this conundrum (inconsistent pin numbering of SOT23)! Replace pin numbers with:

“The pin that is on the lower left when the view is rotated so that the single pin side appears on top” etc. Then put this into a small font so that it can fit nicely onto the diode symbol. :grinning:

Don’t forget to specify top-down or bottom-up view point. :wink:

A very old PCB program I used long ago (Ultiboard in the DOS age) had no SOT-23 packages with pin numbers. It only had SOT-23 packages with pin names such as “E”, “B”, “C” for BJT’s and or “G”, “S”, “D” for Fet’s.

It was a creative solution that was both simple and usable.
Just have a look at some of KiCad’s default symbols:

The numbers here don’t mean much to me, and neither does a:

Q_DUAL_NMOS_S1G1D2S2G2D1
… unless you stare real hard at it.

Ah, well, there will always be something to complain about.

Staring at it does not help me…still it does not tell me much.

Well now my complaint is that the originator of this thread (the original poster) seems to have gone absent after stirring up this um…this um…

Does it matter?

The long string is “Gate”, “Source”, “Drain” for a dual fet in probably a SOT-23-6 package. and the "GSD for the two transistors are in order of pin numbering, just as the “GDS” and “BCE” suffixes for the other two transistors.

No. I am like most other people and like to complain.

Thanks for the added explanation.