This part is a kind of semiconductor called STR6707.

Function of this product has OFF-LINE SWITCHING REGULATORS WITH BIPOLAR SWITCHING TRANSISTOR.

Manufacturers : Allegro

Image and pinout :

Some of the text within the PDF file :

STR-S6707 THRU STR-S6709 OFF-LINE SWITCHING REGULATORS – WITH BIPOLAR SWITCHING TRANSISTOR COLLECTOR 1 COMMON 2 FAULT The STR-S6707, STR-S6708, and STR-S6709 are specifically designed to meet the requirement for increased integration and reliability in off-line quasi-resonant flyback converters. These devices incorporate the primary control and proportional drive circuit with a thirdgeneration high-voltage bipolar switching transistor. Crucial system parameters such as maximum ON time and OFF time are fixed during manufacture. Local control circuit decoupling and layout are optimized within each device. Cycle-by-cycle current limiting, under-voltage lock-out with hysteresis, over-voltage protection, and thermal shutdown protect these devices during all normal and overload conditions. [ ... ]

STR6707 PDF Datasheet Download