Looking for this LittelFuse part

Looks to be a type of diode from the board identification of ‘D’

Markings are ‘J51’ and the ‘Lf’ symbol for littelfuse.
below it is MMC which should just be a date code based on the way they do markings. an older version of this product had a TVS diode in this place, but this doesn’t show up in their TVS diode area, also this tests good in one direction and the other TVS diodes were bi-directional so i had no reading in either direction. so this is a regular type of diode or a single direction TVS possibly?

Thanks in advance!

While we are on this topic. Is there any way to identify that blue component next to it? It’s labeled Z1 and appears to be part of the incoming circuit power along with the “TVS” diode and capacitor there.

The Z is a symbol for Impedance, but I would not be able to identify what the part is. Maybe one of the engineers can add to this post.

Another component is a K14 with MMC below it… Is the marking supposed to be MMC and the date code the K14/J51?

MMC marking appears consistent with P/N 1SMB33CAT3G per this datasheet.

“Z” reference designator can be found applied to MOVs in some cases, and would seem a reasonable guess in this instance.


Nice, appreciate the legwork on that. Appears I already have replacement TVS diodes under SMBJ33CA part number. oddly enough the newer part had the older components in it.

How are you able to find these within the datasheets? last time i found something I had to open every single PDF, then search them individually and hope i opened the right set of 20 datasheets to find the number.

By carefully feeding the available clues into a search engine…

In this case the query “+mmc site:littelfuse.com pdf tvs” popped the desired document to the top via my search provider of choice.

+mmc → desired results must contain the string “mmc”

site:littelfuse.com → only show results from the manufacturer’s website, inferred from the logo on the part

pdf ->Interesting documents are almost certainly in PDF format

tvs → we’re pretty certain that it’s a TVS diode

From there, open likely results and CTRL+F for the “mmc” string. Works pretty well for parts like TVS diodes where listing the markings in the datasheet is the norm.


well you’re much better than I at it.

I’ve done a lot of searches like this ‘tvs diode mmc site:littelfuse.com filetype:pdf’

hoping to hit what I wanted and came up short and had to resort to brute force method the last couple of times. I get a lot of littelfuse PDFs and nothing to do with a TVS or diode in a lot of cases. I think part of the problem comes from search engines learning your search history and trying to cater results as well.

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