This part is a kind of semiconductor called SF10A400HD.

Function of this product has ULTRA FAST RECOVERY POWER RECTIFIER.

Manufacturers : AUK

Image and pinout :

Some of the text within the PDF file :

ULTRA FAST RECOVERY POWER RECTIFIER SF10A400HD Ultrafast Recovery Rectifier Features  High voltage and high reliability  Ultrafast reverse recovery time  High speed switching  Low power loss and High efficiency  Halogen-free component and RoHS compliant device Pin Configuration Pin 1, 3: Anode Pin 2, 4: Cathode Applications  General purpose  Switching mode power supply  Free-wheeling diode for motor application  Power switching circuits  DC-DC converter systems TTOO-2-25522 Product Characteristics IF(AV) VRRM VFM @ Tj=125℃ 10A 400V 1.2V Description trr 30ns The SF10A400HD is ideally as boost diode in discontinuous or critical mode power factor corrections. The device is also intended for use as a freewheeling diode in power supplies and other pow [ ... ]

SF10A400HD PDF Datasheet Download