Definition of an industrial heatsink

One of the steps in determining the various components making up a power converter is the choice of heatsink, in order to preserve the thermal integrity of the power semiconductors. This is achieved by keeping the junction temperature of the component below its critical value during the operating cycle.

The cost of the heatsink, or more generally of the cooling function, is closely linked to the heatsink-component pairing.

For example, to maintain the temperature of one or two TO3 cases, the cost of the "heatsink + fan" pair is often greater than the sum of the costs of the components to be cooled. As a general rule, the higher the power level of the application, the more the "semiconductor + control stage" pairing dominates, compared with the heatsink. This is partly due to the cost of power semiconductors.

The choice of heatsink can only be made with knowledge of the following elements:

• number and type of components to be cooled, and therefore knowledge of the housing used for each component (discrete component, module, presspack, etc.) ;

• losses generated by each component (depending on operating cycle and assembly topology), possible overloads ;

• desired cooling mode (natural convection, forced ventilation, water chambers, etc.) ;

• mechanical constraints and integration of the system in its final environment (dielectric constraints, mounting fixtures, boxing).

The aim of this dossier is to develop the industrial approach to choosing a heat sink, a compromise between academic calculation and sometimes laborious simulation.