TO-259 Package

The TO-259 is a type of "transistor outline" package that features a metallic body with two flat metal tabs (see Figure 1) to enable it to dissipate large amounts of heat. The TO-259 is very similar to the TO-258 in size but they differ in the metal tabs attached to their bodies.

The TO-259 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-259 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 tabs of the TO-259 serve as heat sinks themselves, but they each have a hole so that they can easily be screwed onto a larger heat sink if higher power handling capability is required. The tabs are located on opposite corners of the back of the body as shown in Figure 1.

A typical TO-259 package has 3 leads, although TO-259's with other lead counts may be encountered. The typical lead pitch (distance between leads) of a 3-lead TO-259 package is 5.08 mm.

Table 1. Properties of a Typical TO-259

Body Size (HxW)

Size of Each Tab

(HxW)

Body Thickness

Metal Tab Thickness

Lead Length

13.7 mm x 17.5 mm

6.35 mm x 6.35 mm

6.48 mm

1 mm

15.9 mm

Figure 1. Image of a TO-259 Package

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