TO-220

The TO-220 is a style of electronic component package, commonly used for discrete semiconductors as transistors and silicon-controlled rectifiers, as well as integrated circuits. The "TO" designation stands for "transistor outline". TO-220 packages have three leads. Similar packages with two, four, five or seven leads are also manufactured. A notable characteristic is a metal tab with a hole, used in mounting the case to a heatsink. Components made in TO-220 packages can dissipate more heat than those constructed in TO-92 cases.

The TO-220 package is a "power package" intended for power semiconductors and an example of a through-hole design rather than a surface-mount technology type of package. TO-220 packages can be mounted to a heat sink to dissipate several watts of waste heat. On a so-called "infinite heat sink", this can be 50W or more. The top of the package has a metal tab with a hole used in mounting the component to a heat sink. Thermal compound is often applied to further improve heat transfer from the package to the heatsink.

The metal tab is often connected electrically to the internal circuitry. This does not normally pose a problem when using isolated heatsinks, but an electrically-insulating pad or sheet may be required to electrically isolate the component from the heatsink if the heatsink is electrically conductive, grounded or otherwise non-isolated. Many materials may be used to electrically isolate the TO-220 package, some of which have the added benefit of high thermal conductivity.

In applications that require a heatsink, damage or destruction of the TO-220 device due to overheating may occur if the heatsink is dislodged during operation.

A TO-220 package that is heatsinked, dissipating 1W of heat, will have an internal (junction) temperature typically 2 to 5 °C higher than the package's temperature (due to the thermal resistance between the junction and the metal tab) and the metal tab of the TO-220 package will typically have a temperature of 1 to 60 °C higher than the ambient temperature, depending on the type of heatsink (if any) used.

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