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TO-220 Front Coloured.svg
TO-220 front view [1]
TO-220 Back Coloured.svg
TO-220 back view [1]

The TO-220 is a style of electronic package used for high-powered, through-hole components with 0.1 inches (2.54 mm) pin spacing. The "TO" designation stands for "transistor outline". [2] 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, [3] allowing the component to dissipate more heat than one constructed in a TO-92 case. Common TO-220-packaged components include discrete semiconductors such as transistors and silicon-controlled rectifiers, as well as integrated circuits.

A semiconductor package is a metal, plastic, glass, or ceramic casing containing one or more discrete semiconductor devices or integrated circuits. Individual components are fabricated on semiconductor wafers before being diced into die, tested, and packaged. The package provides a means for connecting the package to the external environment, such as printed circuit board, via leads such as lands, balls, or pins; and protection against threats such as mechanical impact, chemical contamination, and light exposure. Additionally, it helps dissipate heat produced by the device, with or without the aid of a heat spreader. There are thousands of package types in use. Some are defined by international, national, or industry standards, while others are particular to an individual manufacturer.

A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics. Such a device is also called a power device or, when used in an integrated circuit, a power IC.

Through-hole technology mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in printed circuit boards and soldered to pads on the opposite side manually or by automated insertion mount machines

Through-hole technology, refers to the mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side either by manual assembly or by the use of automated insertion mount machines.


Typical applications

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 50 W 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 between package and heatsink to further improve heat transfer.

Surface-mount technology method for producing electronic circuits

Surface-mount technology (SMT) is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In industry, it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. Both technologies can be used on the same board, with the through-hole technology used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.

Heat sink hardware component

A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature at optimal levels. In computers, heat sinks are used to cool CPUs, GPUs, and some chipsets and RAM modules. Heat sinks are used with high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light emitting diodes (LEDs), where the heat dissipation ability of the component itself is insufficient to moderate its temperature.

Waste heat Waste heat is by necessity produced both by machines that do work and in other processes that use energy, for example in a refrigerator warming the room air or a combustion engine releasing heat into the environment.

Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example, incandescent light bulbs get hot, a refrigerator warms the room air, an internal combustion engine generates high-temperature exhaust gases, and electronic components get warm when in operation.

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.

The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by , , or .

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 heatsinked TO-220 package dissipating 1  W 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 1 to 60 °C higher than the ambient temperature, depending on the type of heatsink (if any) used. [4] [5] [6]

The watt is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer. In dimensional analysis, power is described by .

The junction-to-case thermal resistance of a TO-220 packaged device (which typically matters less than the case-to-ambient thermal resistance), depends on the thickness and the area of the semiconductor die inside the package, typically in a range between 0.5 °C/W and 3 °C/W (according to one textbook) [7] or 1.5 °C/W and 4 °C/W (according to another). [6]

If more heat needs to be dissipated, devices in the also widely used TO-247 (or TO-3P) package can be selected. TO-3P has a typical junction-to-ambient (heatsink) thermal resistance of only about 40 °C/W, and its TO-3PF variant a slightly lower one. [5] Further increase of heat dissipation capability is possible with power modules.

Power module

A power module or power electronic module provides the physical containment for several power components, usually power semiconductor devices. These power semiconductors are typically soldered or sintered on a power electronic substrate that carries the power semiconductors, provides electrical and thermal contact and electrical insulation where needed. Compared to discrete power semiconductors in plastic housings as TO-247 or TO-220, power packages provide a higher power density and are in many cases more reliable.

When a TO-220 package is used without a heatsink, the package acts as its own heatsink, and the heatsink-to-ambient thermal resistance in air for a TO-220 package is approximately 70 °C/W.


TS7805 linear voltage regulator in a TO-220 variant package with electrically isolated tab. TS7805 voltage regulator.JPG
TS7805 linear voltage regulator in a TO-220 variant package with electrically isolated tab.

The TO-220 family of outlines is defined by the JEDEC organization. There are a number of variations on this outline, [1] [8] such as:

Sometimes the designation is followed by the number of leads, as in TO-220AB-5L for five leads, etc.

There also some vendor-specific variations such as International Rectifier's SUPER-220, which dispenses with the hole in favor of clip-mounting, thus claiming TO-247-like thermal performance in a TO-220 footprint. [11]

Common components that use the TO-220 package

The TO-220 case is found on semiconductor devices handling less than 20 amperes and operating at less than a few hundred volts. These devices operate at DC or relatively low (audio) frequencies, since the TO-220 package is not intended for devices operating at radio frequencies. In addition to bipolar, bipolar Darlington, and power MOSFET transistors, the TO-220 case is also used for fixed and variable linear voltage regulator integrated circuits, and for Schottky diode pairs. [12] [13] [14]

See also

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TO-126 is a type of semiconductor package for devices with three pins, such as transistors. The package is rectangular with a hole in the middle to allow for easy mounting to a board or a heat sink.


  1. 1 2 3 "JEDEC TO-220 family package specification" (PDF). JEDEC . March 24, 1987. Archived from the original (PDF) on June 18, 2017.
  2. List of semiconductor cases,
  3. Torque Recommendations for TO-220 Devices,
  4. "MC7800, MC7800A, NCV7805" (PDF). ON Semiconductor. Retrieved 24 May 2014.
  5. 1 2 Yong Liu (2012). Power Electronic Packaging: Design, Assembly Process, Reliability and Modeling. Springer Science & Business Media. p. 188. ISBN   978-1-4614-1053-9.
  6. 1 2 Mike Tooley (2006). Electronic Circuits: Fundamentals and Applications (3rd ed.). Routledge. p. 353. ISBN   978-0-7506-6923-8.
  7. Yong Liu (2012). Power Electronic Packaging: Design, Assembly Process, Reliability and Modeling. Springer Science & Business Media. p. 184. ISBN   978-1-4614-1053-9.
  8. List of package types,
  9. "TO-220F Package Dimensions" (PDF). Fairchild Semiconductor. Retrieved 24 October 2019.
  10. "Outline Dimensions TO-220AB, TO-220AC" (PDF). Vishay Semiconductor. Retrieved 24 October 2019.
  15. "Power MOSFETs and IGBTs", Bill Travis, EDN: "[…] and the TO-257 is a hermetic TO-220."