TO-220

Key takeaways

TO-220 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect TO-220 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TO-220 from memory before moving on to harder problems.

Reference excerpt

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". 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 to mount the case to a heatsink, 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.

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 to mount the component to a heat sink. Thermal compound is often applied between package and heatsink to further improve heat transfer. 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 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. 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) or 1.5 °C/W and 4 °C/W (according to another). The junction-to-case thermal resistance of the LM317 voltage regulator (National Semiconductors, page 5, TO200 version) is 4 °C/W. 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. Further increase of heat dissipation capability is possible with power modules. 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. The junction-to-air thermal resistance of the LM317 voltage regulator (National Semiconductors, page 5, TO200 version) is 50 °C/W.

Variations

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

TO-220F, TO-220FP a 3 lead JEDEC outline which plastic encapsulates the entire body and mounting tab metal that are normally exposed providing electrical insulation which inevitably increases the package thermal resistance relative to the uninsulated metal tab version. TO-220AB a 3 lead JEDEC outline TO-220AC a 2 lead JEDEC outline 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.

Common components that use the TO-220 package The TO-220 case is found on semiconductor devices handling less than 100 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.

National Standards

Related packages TO-257 is a hermetically sealed metal package that is otherwise considered equivalent to TO-220. TO-220F also known as the SOT186 and SC67 is TO-220 like package, where the heatsink mounting tab has been encased in the plastic.

See also TO-3, a metal package with similar power ratings TO-126, a plastic package with lower power ratings TO-263, the surface-mount equivalent of the TO-220

References

External links

TO-220 standard - JEDEC TO-220 outline drawing - ON Semiconductor TO-220AB outline drawing - Vishay Intertechnology TO-220FP (Full Pack) - Amkor Technology

Illustrations

Worked examples

Example 1 — a first encounter with TO-220

Start with the simplest possible case. Write down what TO-220 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to TO-220 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about TO-220 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of TO-220

In research: TO-220 appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses TO-220 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: TO-220 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Semiconductor packages, so understanding it makes those chapters shorter.
In everyday life: Look for TO-220 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study TO-220 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TO-220 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain TO-220 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TO-220 in simple terms?

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".

Why does TO-220 matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study TO-220?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on TO-220.