This part is a kind of semiconductor called STRW6051S.
Function of this product has Current Mode Control PWM Regulator IC.
Manufacturers : Sanken
Image and pinout :
Some of the text within the PDF file :
STR-W605xS Current Mode Control PWM Regulator IC For Switching Power Supplies Features and Benefits ▪ TO-220F power package with 30 to 90 W power output ▪ Current Mode PWM control ▪ Built-in Random Switching function, reducing EMI noise, and simplifying EMI filters, and therefore reducing cost ▪ Built-in Slope Compensation function, avoiding subharmonic oscillation ▪ Built-in Auto Standby function (Input Power, PIN < 30 mW at no load) ▫ Normal operation: PWM mode ▫ Light load operation: Standby mode (burst oscillation) ▪ Built-in Audible Noise Suppression function during Standby mode ▪ Built-in Startup Circuit, reducing power consumption in standby operation, and eliminating external components. ▪ Bias-Assist function, improving startup operation, suppressing VCC voltag [ ... ]