WOBBLmosfet

How hot does this MOSFET get switching 15 A at 20 kHz in a 50 C box?

Circuit report
2026-10-15 19:19
OK

Junction reaches about 110 C (1.51 W: 1.37 W conduction, 0.144 W switching) with 40 C/W to 50 C air; limit 150 C.

junction
110 C
limit
150 C
loss
1.51 W
theta JA
40 C/W

Confidence high

  • passed hand calculation, thermal loop

Simulation

Bench setup drawn from this run. A 12 V supply drives 15 A through a 0.792 ohm load and a TO-220 MOSFET on a 40 C/W heatsink, switched at 20 kHz, and the junction settles at 110 C. DC POWER SUPPLY 12.00 V 7.53 A CV PULSE GENERATOR 20.00 kHz 50.0 % OUT 792 mΩ JUNCTION 110 °C OK 150 °C limit
Bench setup, drawn from this run
Schematic of MOSFET conduction with a resistive load, drawn from the netlist. SCHEMATIC MOSFET conduction with a resistive load A V1 12 V RL 792 mΩ S1 on 8 mΩ VS 0 V, current sense VG pulse 0 to 10 V 20 kHz, 50% on vbus 12 V d 0.12 V on
Schematic, drawn from the netlist

Checks

statuscheckresult
passhand calculationconduction loss I_rms^2 R = 0.903 W; ngspice average of V x I = 0.903 W (0.00079% apart)
passthermal loopjunction settles at 110 C after the on resistance warms up (12.1 mohm hot)

Assumptions

  1. On resistance 8 mohm at 25 C rising 0.6% per C.
  2. Switching loss from 40 ns edges: 0.5 V I (tr + tf) f.
  3. Junction to air 40 C/W (datasheet, no heatsink unless included).