This part is a kind of semiconductor called AP431.

Function of this product has ADJUSTABLE PRECISION SHUNT REGULATOR.

Manufacturers : Diodes Incorporated

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Some of the text within the PDF file :

AP431/AP431A ADJUSTABLE PRECISION SHUNT REGULATOR Features • Precision reference voltage AP431 : 2.495V ± 1% AP431A : 2.495V ± 0.5% Sink current capability: 200mA Minimum cathode current for regulation: 300µA o Equivalent full-range temp coefficient: 30 ppm/ C Fast turn-on response Low dynamic output impedance: 0.2Ω Programmable output voltage to 36V Low output noise Packages: SOT23, SOT23R, SOT25, SC59 (W package code), SC59 (R package code), SOP-8L and TO92-3L SOT23, SOT23R, SOP-8L and SC59: Available in “Green” Molding Compound (No Br, Sb) (Note 1) Lead Free Finish/RoHS Compliant for Lead Free and “Green” Products (Note 2) General Description The AP431 and AP431A are 3-terminal adjustable precision shunt regulators with guaranteed temperature stability over the applicab [ ... ]

AP431 PDF Datasheet Download