This post explains for the semiconductor K3878.
The Part Number is K3878.
The function of this semiconductor is 900V, Field Effect Transistor.
Manufacturers : Toshiba, Pinout : 1. Gate 2. Dreain ( Heatsink ) 3. Source
Preview images :
2SK3878 TOSHIBA Field Effect Transistor Silicon N-Channel MOS Type (π- MOSIV)
Switching Regulator Applications
• Low drain-source ON-resistance: RDS (ON) = 1.0 Ω (typ.)
• High forward transfer admittance: ⎪Yfs⎪ = 7.0 S (typ.)
• Low leakage current: IDSS = 100 μA (max) (VDS = 720 V)
• Enhancement model: Vth = 2.0 to 4.0 V (VDS = 10 V, ID = 1 mA)