This part is a kind of semiconductor called STR-W6750.

Function of this product has Off-Line Quasi-Resonant Switching Regulators.

Manufacturers : Allegro MicroSystems

Image and pinout :

Some of the text within the PDF file :

g n i h tors c t i a Sw egul R Application Note 28103.30 PRODUCT DESCRIPTION www.net Series STR-W6750 Off-Line Quasi-Resonant Switching Regulators INTRODUCTION TERMINAL FUNCTIONS VCC (Pin 4) Start-up circuit The start-up circuit detects the VCC pin voltage (pin 4), and makes the control IC start and stop operation. The power supply of the control IC (VCC pin input) employs a circuit as shown in Figure 1. At start-up, C3 is charged through a startup resistor R2. The R2 value needs to be set for more than the hold current of the latch circuit (140 µA max.) and to operate at the minimum ac input. The Series STR-W6750 devices are hybrid integrated circuits (HICs) with a built-in power MOSFET and a control IC designed for quasi-resonant type switch-mode power supplies (SMPS). [ ... ]

STR-W6750 PDF Datasheet Download