What is this component? When I search on internet, I get a lot of thermal protection components, but they do not look like this.

I got it as a batch from someone, so I don't know the usage.

The dimensions are 7.5 mm x 5.7mm, it has two legs (one on the other side), which extend to the bottom (thus it must be an SMD component).

enter image description here

(sorry for the white spots, the camera lens was dirty).

  • \$\begingroup\$ I think it's a LDO (Low Drop Out) voltage regulator. \$\endgroup\$
    – Joost
    Jun 28, 2019 at 13:48
  • 6
    \$\begingroup\$ The LF logo belongs to Littelfuse. \$\endgroup\$ Jun 28, 2019 at 13:50
  • 1
    \$\begingroup\$ @joost on what do you base that? \$\endgroup\$
    – user16222
    Jun 28, 2019 at 13:50
  • \$\begingroup\$ Sorry, I thought there where 3 pins. As Andrew said, it's a littelfuse. \$\endgroup\$
    – Joost
    Jun 28, 2019 at 13:54

1 Answer 1


The "LF" means a Littelfuse Part. The casing is SMC, meaning it is likely a Transient Voltage Suppressor (TVS). They make an SMC part with the number SMCJ120CA, which seems like a safe bet as to what this is. The 120C is a bidirectional 120V part.

The job of this part is to limit the voltage on the line it is connected to. In normal operation, it does not conduct, but above a certain threshold, it turns on, effectively clamping the voltage between the terminals like a diode. In this case, it is meant to connect to a line that is nominally between +/- 120V, starts conducting at +/- 133, and will limit its voltage to +/- 193V. Usually the other terminal is ground, but you can also find them providing differential protection, like between cells of a battery charger.

These are typically found near connectors to prevent electrical nastiness from going inside your board and burning something sensitive.

  • \$\begingroup\$ Thank you very much for your comment (accepted and upvoted). I already knew what a TVS is, I plan to use them for my (future) DMX PCB. Too bad I need a different value (for protecting my ICs). But good to know ... maybe I can use them to learn soldering better ;-) \$\endgroup\$ Jun 28, 2019 at 14:10
  • \$\begingroup\$ @Michel Another reason this is a great answer is the explanation of TVS operation. Remember, the site helps future visitors through searches, too. \$\endgroup\$
    – JYelton
    Jun 28, 2019 at 17:07
  • \$\begingroup\$ @JYelton I never said it is not a good answer (in case it's a great answer, I upvoted/accepted it), so I also think it's a great answer. I just wanted to mention I know what a TVS is (but indeed, it's not relevant for the answer). It was in no means to say it should not belong to the answer. \$\endgroup\$ Jun 29, 2019 at 12:55

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