TO92
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The 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.
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[edit] History and Origin
The TO-92 descriptor is derived from the original full name for the package: Transistor Outline Package, Case Style 92.
[edit] Construction and Orientation
The case is molded around the transistor elements in two parts; the face is flat, bearing a machine-printed part number.
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.
Units with their leads pre-bent may be ordered to fit specific board layouts, depending on the application. Otherwise, the leads may be bent manually; however, care must be taken as they can break easily.
[edit] 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.
[edit] Disadvantages
- This type of transistor is easily susceptible to heat damage, and can burn out quickly if they dissipate excessive power.
- 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.
[edit] 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, 2N2222 NPN
