This part is a kind of semiconductor called SF1533.

Function of this product has PWM Power Switch.

Manufacturers : SiFirst Technology

Image and pinout :

Some of the text within the PDF file :

SF1533 η-BalanceTM PWM Power Switch Fixed 50KHz Fsw FEATURES ◆ Built-in 600V Power MOSFET ◆ Proprietary η-BalanceTM Control to Boost Light Load Efficiency ◆ Proprietary “Zero OCP/OPP Recovery Gap” Control ◆ Fixed 50KHz Switching Frequency ◆ Built-in Soft Start Function ◆ Very Low Startup Current ◆ Frequency Reduction and Burst Mode Control for Energy Saving ◆ Current Mode Control ◆ Built-in Frequency Shuffling ◆ Built-in Synchronous Slope Compensation ◆ Cycle-by-Cycle Current Limiting ◆ Built-in Leading Edge Blanking (LEB) ◆ Constant Power Limiting ◆ Pins Floating Protection ◆ Audio Noise Free Operation ◆ VDD OVP & Clamp ◆ VDD Under Voltage Lockout (UVLO) APPLICATIONS Offline AC/DC Flyback Converter for ◆ AC/DC Adaptors ◆ Open-frame SMPS ◆ Se [ ... ]

SF1533 PDF Datasheet Download