This post explains for the MOSFET.
The Part Number is K3934, 2SK3934.
The function of this semiconductor is 500V, 15A, N-Channel MOSFET.
The package is TO-220 Type
Manufacturer: Toshiba Semiconductor
Preview images :
This is Silicon N Channel MOS Type Field Effect Transistor.
1. Low drain-source ON resistance: RDS (ON) = 0.23Ω (typ.)
2. High forward transfer admittance: |Yfs| =8.2 S (typ.)
3. Low leakage current: IDSS = 100 μA (VDS = 500 V)
4. Enhancement-mode: V th = 2.0~4.0 V (V DS = 10 V, ID = 1 mA)
Absolute Maximum Ratings (Ta = 25°C)
1. Drain to source voltage: VDSS = 500 V
2. Gate to source voltage: VGSS = ± 30 V
3. Drain current: ID = 15 A
4. Drain Power Dissipation: Pd = 50 W
5. Channel temperature: Tch = 150 °C
6. Storage temperature: Tstg = -55 to +150 °C
1. Switching Regulator