How to Select a Heat Sink

Heat sinks are an important element in circuit design because they provide an efficient path for heat to be transferred into the ambient air and away from electronic devices (eg. BJTs, MOSFETs, linear regulators, etc.). The general theory behind a heat sink is to increase the surface area of the heat-producing device, enabling a more efficient transfer of heat into the ambient environment. This improved thermal pathway reduces the temperature rise in the junction of the electronic device. The following post is intended to provide high-level primer on heat sink selection utilizing thermal data from your application and specifications from the heat sink vendor.

Is a Heat Sink Required?

For the remainder of this post, let us assume that an application is being developed using a transistor housed in a TO-220 package, the switching and conduction losses of the transistor equate to a power dissipation of 2.78 W, and the ambient operating temperature of this application is not expected to exceed 50°C. Will a heat sink be required for this transistor?

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