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