This part is a kind of semiconductor called 3S0680RFB.

Function of this product has KA3S0680RF.

Manufacturers : Fairchild Semiconductor

Image and pinout :

Some of the text within the PDF file :

www.fairchildsemi.com KA3S0680RB/KA3S0680RFB 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 controller IC. controller IC features a trimmed oscillator, under voltage lock out, leading edge blanking, optimized gate turn-on/turn-off driver, thermal shut down [ ... ]

3S0680RFB PDF Datasheet Download