TO92

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TO-92 is a widely-used style of transistor enclosure construction. The case is often made of epoxy or plastic, and offers compact size at a very low cost. Shown is a common transistor, which uses the TO-92 case.

Contents

1 Construction and Orientation
2 Advantages
3 Disadvantages
4 Common Transistors that use this case
5 Additional uses of the TO-92 case

Construction and Orientation

The case is molded around the transistor elements in two parts; the face is flat, bearing the part number. The part number is printed on by machine.

The back is semi-circularly-shaped. By looking closely from the top, one can observe the seam where the two halves are molded together.

The leads protrude from the bottom of the case. When looking at the face of the transistor, the leads are commonly configured from left-to-right as the emitter, base, and collector, however, other configurations are possible.

Depending on the application, units with their leads pre-bent may be ordered to fit specific board layouts, depending on the purpose at hand. Otherwise, the leads may be bent manually however, care must be taken as they can break easily.

Advantages

Transistors of this type can be made very inexpensively and take up very little board space. Most models cost under 10 cents each, and are readily available in large quantities from wholesale distributors.

They are easy to find in small electronics stores because of their wide usefulness, making them a popular choice for hobby work and prototyping.

Disadvantages

This type of transistor is easily susceptible to heat damage, and can burn out quickly if too much power is sent through them.

Many models are easily vulnerable to electrostatic discharge (ESD).

Transistors of these types cannot handle as much power as higher-power equivalents, such as the TO-220.

More often than not however, the disadvantages concerning accidental destruction are greatly outweighed by the low cost of producing these units.

Common Transistors that use this case

BC548, NPN
BC558, PNP
2N3904, General purpose NPN
2N3905, PNP
2N3906, General purpose PNP
2N7000, N-Channel FET
PN2222A, NPN

Additional uses of the TO-92 case

MK484, AM radio IC
78L05, 79L05, 78L12, 79L12 voltage regulators
1381, voltage trigger IC by Panasonic

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