Can anyone help me identify the SOT-89 component in the picture below? It is marked \$\text{43B H42}\$. I have searched to find anything resembling a match, and I found that it could be both a programmable shunt regulator and a NPN power transistor.

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Here following a sketch of the circuit surrounding the component of interest.

enter image description here

  • \$\begingroup\$ Might be a transistor, or a voltage regulator. Probably only answerable in the context of a schematic. \$\endgroup\$ Commented Oct 31, 2019 at 9:24
  • \$\begingroup\$ As you suggested, I've added a sketch of the circuitry surrounding the component I'm asking for. \$\endgroup\$
    – elena
    Commented Oct 31, 2019 at 9:34
  • \$\begingroup\$ Could it be a TL431? \$\endgroup\$
    – winny
    Commented Oct 31, 2019 at 10:09

1 Answer 1


It's LM431SB. Check the datasheet and you can find its package marking.


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