This is one of the semiconductor types. This part name is K3911.
This product has Field Effect Transistor functions.
Manufacturers of product is Toshiba.
Image and pinout :
2. Drain ( Heatsink )
K3911 PDF Datasheet
Some of the text files within the PDF file
2SK3911 TOSHIBA Field Effect Transistor Silicon N-Channel MOS Type (MACHII π-MOSVI)
Switching Regulator Applications
• Small gate charge: Qg = 60 nC (typ.)
• Low drain-source ON resistance: RDS (ON) = 0.22Ω (typ.)
• High forward transfer admittance: |Yfs| = 11 S (typ.)
• Low leakage current: IDSS = 500 μA (VDS = 600 V)
• Enhancement model: Vth = 2.0~4.0 V (VDS = 10 V, ID = 1 mA)
[ … ]
Please refer to the file for details.