The TO-220 is a style of electronic component package, commonly used for transistors, silicon-controlled rectifiers, and integrated circuits. The "TO" designation stands for "transistor outline". [1] 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.
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The TO-220 package is an example of a through-hole design rather than a surface-mount technology type of package. TO-220 packages are heatsinkable, and thus can be used for applications where large amounts of power are dissipated as heat. The top of the package has a metal tab with a hole used in mounting the component to a heatsink. 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 not heatsinked typically dissipates around 1 watt (W), at a temperature 62.5C higher than the ambient temperature.
The standard TO220 outline is defined by the JEDEC organization. There are a number of variations on this outline [2], such as:
Sometimes the designation is followed by the number of leads, as in TO-220AB-5L for five leads, etc.