A heat dissipater that operates as a result of the temperature difference and thermal resistances between the heat source (semiconductor) and the ambient air. The Heatsink increases the surface area available for heat transfer from the semiconductor thus increasing the amount of heat that can be dissipated. The amount of heat that can be removed is most often characterised by thermal resistance i.e. the lower the thermal resistance the better the performance. The only way thermal resistance can be reduced is by either increasing the physical size of the heat sink i.e. changing the surface area or by moving more air across the sink (changing from natural to forced convection coefficients, typically a fan or blower).
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