This part is a kind of semiconductor called K3911.

Function of this product has Field Effect Transistor.

Manufacturers : Toshiba

Image and pinout :

Some of the text within the PDF file :

2SK3911 TOSHIBA Field Effect Transistor Silicon N-Channel MOS Type (MACHII π-MOSVI) 2SK3911 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) Unit: mm Absolute Maximum Ratings (Ta = 25°C) Characteristic Drain-source voltage Drain-gate voltage (RGS = 20 kΩ) Gate-source voltage Drain current DC Pulse (Note 1) (Note 1) Symbol VDSS VDGR VGSS ID IDP PD EAS IAR EAR Tch Tstg Rating 600 600 ±30 20 80 150 792 20 15 150 -55~150 Unit V V V A W mJ A mJ °C °C 1. Gate 2. Drain (heatsink) 3. Source Drain power dissipation (Tc = 25°C) Singl [ ... ]

K3911 PDF Datasheet Download