MOSFET Junction Temperature

Compute MOSFET junction temperature from drain current, RDS(on), thermal resistance, ambient temperature and duty cycle. Flags marginal and danger conditions against the configured Tj-max.

DomainElectronicsVersionv1.0.0Added2026-05-16

Inputs

Drain CurrentA

RDS(on)mΩ

From the datasheet at the gate-drive voltage you use.

θ-JA°C/W

Junction-to-ambient thermal resistance — depends heavily on copper area.

Ambient Temp°C

Duty Cycle

1.0 = continuous on. Use the actual on-time fraction for switched applications.

Max Junction Temp°C

Datasheet Tj-max. 150 °C is typical for silicon, 175 °C for SiC.

Result

version1.0.0

POST /v1/electronics/mosfet-thermal-junction

curl -X POST https://api.toolsamurai.com/v1/electronics/mosfet-thermal-junction \
  -H "Authorization: Bearer sk_live_•••••••••••••••" \
  -H "Content-Type: application/json" \
  -d '{
     "drain_current_a": 5,
     "rds_on_mohm": 20,
     "theta_ja_c_per_w": 62,
     "ambient_temp_c": 25,
     "duty_cycle": 1,
     "max_junction_temp_c": 150
  }'

mosfetthermaljunction-temperaturepower-dissipationelectronics