Electronic circuits must be designed to withstand the maximum temperature the components of the circuit will encounter. Many factors impact the temperature of the components including the ambient temperature of air around the circuit, whether the circuit is exposed to additional heat (e.g., whether the circuit is in direct sunlight or positioned near a heat generating element such as an automobile engine), whether the circuit is in an enclosed space, cooling elements (e.g., air flow around the circuit, either natural or fan-driven), and heat generated by the circuit itself. For example, the greater the number of operations being performed by a component (such as a transistor), and the more often the component operates (or is switched on) the more heat the component generates. Further, the more current a component or circuit uses, the more heat it generates (at least in general). It is even possible for components to generate heat as a result of switching losses when they transition from an on state to an off state.
Circuits having components that will experience temperatures in excess of 125° C. are often designed using expensive military grade or other “heavy duty” components. These components are more costly than industrial (−40 to 85° C.) or commercial (0-70° C.) grade components, resulting in higher cost for the circuit than if industrial or commercial grade components were used. Circuits are also designed using components that will generate less heat (e.g., FETs having a low drain to source on-resistance (RDS(on)) or using additional components to reduce the current passing through each component, and thus reducing the heat generated by each component (e.g., using two FETs to drive a single motor).
Each of these design techniques result in increased costs for the circuits simply to ensure the components will not fail due to over heating.