This part is a kind of semiconductor called 3S1265R.

Function of this product has KA3S1265R.

Manufacturers : Fairchild Semiconductor

Image and pinout :

Some of the text within the PDF file :

www.fairchildsemi.com KA3S1265R/KA3S1265RF/ KA3S1265RD Fairchild Power Switch(FPS) Features • • • • • • • • • Wide operatimg frequency range up to (150kHz) Pulse by pulse over current limiting Over load protection Over voltage protecton (Min. 23V) Internal thermal shutdown function Under voltage lockout Internal high voltage sense FET External sync terminal Auto Restart Mode Description The Fairchild Power Switch(FPS) product family is specially designed for an off line SMPS with minimal external components. The Fairchild Power Switch(FPS) consist of high voltage power SenseFET and current mode PWM IC. Included control IC features a trimmed oscillator, under voltage lock-out, leading edge blanking, optimized gate turn-on/turn-off driver, thermal shut down protection, ov [ ... ]

3S1265R PDF Datasheet Download