# What is this SOT-89 component marked 43B H42?

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.

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

• Might be a transistor, or a voltage regulator. Probably only answerable in the context of a schematic. – Marcus Müller Oct 31 '19 at 9:24
• As you suggested, I've added a sketch of the circuitry surrounding the component I'm asking for. – elena Oct 31 '19 at 9:34
• Could it be a TL431? – winny Oct 31 '19 at 10:09