science

TO-66

TO-66 is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand TO-66 rather than just read about it. In short: TO-66 is a type of semiconductor package for devices with three connections, such as transistors. The shape is similar to the TO-3 package, but the size is smaller.

Key takeaways

TO-66 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-66 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of TO-66 from memory before moving on to harder problems.

Reference excerpt

TO-66 is a type of semiconductor package for devices with three connections, such as transistors. The shape is similar to the TO-3 package, but the size is smaller. The TO-66 package is made entirely of metal and is commonly used by silicon controlled rectifiers and power transistors. In Europe, it was popularly used by the complementary germanium power transistors AD161/AD162. The TO-66 package consists of a diamond-shaped base plate with diagonals of 31.4 mm (1.24 in) and 19.0 mm (0.75 in). The plate has two mounting holes on the long diagonal, with the centers spaced 23 mm (0.91 in) apart. A cap attached to one side of the plate and under which the semiconductor chip is located, brings the total height to up to 8.63 mm (0.340 in). Two pins on the other side of the plate are isolated from the package by individual glass-metal seals. The metal case forms the third connection (in the case of a bipolar junction transistor this is typically the collector).

Variants TO-66 is often used as a synonym for any of the variants that have the same footprint (i.e. position of mounting holes and pins) as TO-66.

TO-123 TO-123 reduces the maximum thickness of the base plate from 1.90 mm (0.075 in) to 1.02 mm (0.040 in).

TO-124 TO-124 increases the maximum thickness of the base plate from 1.90 mm (0.075 in) to 2.59 mm (0.102 in) and the maximum total height from 8.63 mm (0.340 in) to 9.02 mm (0.355 in).

TO-213 TO-213 is intended to replace previous definitions of flange-mounted packages with a 5.08 mm (0.200 in) pin spacing. The different outlines are now defined as variants of TO-213: TO-66 is renamed to TO-213-AA, TO-123 to TO-213-AB, TO-124 to TO-213-AC.

National standards

See also TO-126 - a plastic package with power ratings similar to TO-66

References

External links TO-66 Package, EESemi.com

Illustrations

Worked examples

Example 1 — a first encounter with TO-66

Start with the simplest possible case. Write down what TO-66 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-66 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-66 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-66

In research: TO-66 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-66 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-66 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electronics stubs, Semiconductor packages, so understanding it makes those chapters shorter.
In everyday life: Look for TO-66 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.

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How to study TO-66 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what TO-66 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-66 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is TO-66 in simple terms?

TO-66 is a type of semiconductor package for devices with three connections, such as transistors. The shape is similar to the TO-3 package, but the size is smaller.

Why does TO-66 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-66?

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-66.