TO-258 Package

The TO-258 is a type of "transistor outline" package that features a metallic body with a flat metal tab at its back (see Figure 1) to enable it to dissipate large amounts of heat. The TO-258 is very similar to the TO-257.

The TO-258 is hermetically sealed to protect the device from environmental factors such as contaminants and moisture. The leads protrude from the bottom of the package through glass and ceramic feed-throughs that insulate them from the metal body.

The TO-258 is commonly used for housing transistors, thyristors, and integrated circuits with low lead counts such as voltage regulators that are intended for high-reliability and mission-critical circuits.

The metal tab at the back of the TO-258 serves as a heat sink itself, but it has a hole so that it can be screwed onto a larger heat sink if higher power handling capability is required.

A typical TO-258 package has 3 leads, although TO-258's with other lead counts may be encountered. The typical lead pitch (distance between leads) of a 3-lead TO-258 package is 5.08 mm.

Table 1. Properties of a Typical TO-258

Body Size (HxW)

excl. Metal Tab

Body Size (HxW)incl. Metal Tab

Body Thickness

(inc. tab)

Metal Tab Thickness

Lead Length

20.9 mm x 17.5 mm

13.7 mm x 17.5 mm

6.48 mm

1 mm

15.9 mm

Figure 1. Graphical Representation of a TO-258 Package

See more TO Package Types

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