This part is a kind of semiconductor called C3148.

Function of this product has 2SC3148.

Manufacturers : Toshiba Semiconductor

Image and pinout :

Some of the text within the PDF file :

Switching regulator and high voltage switching applications.

High speed DC-DC converter applications.

1. Excellent switching times ( Ic = 0.8A )
2. High collector-emitter Breakdown voltage : Vceo=800 V

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C3148 PDF Datasheet Download