The power dissipation of an IGBT is specified as collector power dissipation (PC) in its datasheet.
Collector power dissipation (PC) is defined as the maximum permissible power dissipation that the IGBT can consume continuously and expressed as:
Collector power dissipation (PC) = permissible_rise_in_temperature (Tj(max) – 25°C) / thermal_resistance (Rth)
Collector power dissipation and thermal resistance are shown in the datasheet. The conditions under which they are guaranteed are specified for individual IGBTs. Heat dissipation conditions are specified for collector power dissipation whereas two positions with a temperature difference are specified for thermal resistance.
In Table (a), a PC of 2 W is specified under free-air cooling conditions without any thermal fin whereas a PC of 40 W is specified under cooling conditions with infinite thermal conductivity. In Table (b), an Rth(j-a) of 62.5°C/W is junction-to-ambient thermal resistance under free-air cooling conditions whereas Rth(j-c) is junction-to-case thermal resistance. To calculate thermal resistance under actual usage conditions, it is necessary to take insulation materials, thermal fins, and the contact thermal resistance of each component into consideration. The thermal resistance thus calculated should be used to calculate collector power dissipation using the equation shown above.