TO-92

Four views of the TO-92 package

Front views of the TO-92 package. Pin 1 is on the left.

Back views of the TO-92 package

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.

History and origin

The JEDEC TO-92 descriptor is derived from the original full name for the package: Transistor Outline Package, Case Style 92.

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 for 2N series (JEDEC) transistors, however, other configurations are possible, such as emitter, collector, and base commonly used for 2S series (Japanese) transistors.

The leads coming out of the case are spaced 0.05" (1.27 mm) apart. It is often convenient to bend them outward to a 0.10" (2.54 mm) spacing to make more room for wiring. 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.

Advantages

• Transistors of this type can be made very inexpensively and take up very little board space. Most models 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

The main disadvantage of this style of case is the lack of heat sinking.

• Transistors and ICs of these types cannot handle as much power as higher-power equivalents, such as the TO-220.
• This type of transistor or IC is easily susceptible to heat damage, and can burn out quickly if they dissipate excessive power.

More often than not, however, the disadvantages concerning accidental destruction are greatly outweighed by the small size and 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-e Effect transistor|FET]]
  • Leads are 1 SOURCE, 2 GATE, 3 DRAIN
• BS170, N-Channel FET, similar to SN7000
  • Leads are 1 DRAIN, 2 GATE, 3 SOURCE
• PN2222A, 2N2222 NPN
  • Leads are 1 EMITTER, 2 BASE, 3 COLLECTOR
• 2SC945, NPN
  • Leads are 1 EMITTER, 2 COLLECTOR, 3 BASE

Additional uses of the TO-92 case

• MK484, AM radio IC
• 78L05, 79L05, 78L12, 79L12 voltage regulators
• TCR1AM, Triac
• DS18S20, Temperature sensor
• DS2501-UNW/DS2502, Add-only memory

See also

• Chip carrier Chip packaging and package types list