This part is a kind of semiconductor called BD157.

Function of this product has Low Power Fast Switching Output Stages.

Manufacturers : Fairchild Semiconductor

Image and pinout :

Some of the text within the PDF file :

BD157/158/159 BD157/158/159 Low Power Fast Switching Output Stages • For T.V Radio Audio Output Amplifiers 1 TO-126 2.Collector 3.Base 1. Emitter NPN Epitxial Silicon Transistor Absolute Maximum Ratings TC=25°C unless otherwise noted Symbol VCBO Parameter Collector-Base Voltage : BD157 : BD158 : BD159 : BD157 : BD158 : BD159 Value 275 325 375 250 300 350 5 0.5 1.0 0.25 20 50 - 65 ~ 150 Units V V V V V V V A A A W °C °C VCEO Collector-Emitter Voltage VEBO IC ICP IB PC TJ TSTG Emitter-Base Voltage Collector Current (DC) *Collector Current (Pulse) Base Current Collector Dissipation (TC=25°C) Junction Temperature Storage Temperature Electrical Characteristics TC=25°C unless otherwise noted Symbol BVCEO Parameter *Collector-Emitter Breakdown Voltage : BD157 : BD158 : BD159 Coll [ ... ]

BD157 PDF Datasheet Download