Heat flow in electronics - maximum power dissipate

Description

The heat flow can be modelled by analogy to an electrical circuit where heat flow is represented by current, temperatures are represented by voltages, heat sources are represented by constant current sources, absolute thermal resistances are represented by resistors and thermal capacitances by capacitors.

The diagram shows an equivalent thermal circuit for a semiconductor device with a heat sink

The formula says how much power can be put into the transistor before it overheats.

Related formulas

Variables

QMAXpower dissipated (W)
TJMAXjunction temperature (K)
TAMBambient air temperature (K)
ΔTHSchange in temperature (K) (K)
RJCdevice's absolute thermal resistance from junction to case (K/W)
RBabsolute thermal resistance of the bond between the transistor's case and the metalwork (K/W)
RHAabsolute thermal resistance of the heat sink (K/W)