In electronics, TO-18 is a designation for a style of transistor metal case. The case is more expensive than the similarly sized plastic TO-92 package. The name is from JEDEC, signifying Transistor Outline Package, Case Style 18.
Construction and orientation The typical TO-18 metal can package has a base diameter of , a cap diameter of , a cap height of . The tab is located 45° from pin 1, which is typically the emitter. The lead diameter is nominally . The leads are arranged in a circle with a diameter of . The minimum length of the leads is .
Different manufacturers have different tolerances, and the actual form factor may vary slightly, depending on function.
Uses and variants
The 3-lead TO-18 is used for transistors and other devices using no more than three leads. Variants for diodes, photodiodes and LEDs may have only two leads. Light-sensitive or light-emitting devices have a transparent window, lens, or parabolic reflectors in the top of the case rather than a sealed, flat top. For example, diode lasers such as those found in CD players may be packaged in TO-18 cases with a lens.
There are variants with between 2 and 8 leads.
TO-46 / TO-52 The TO-46 and TO-52 packages have 3 leads. These packages differ from all other variants in the height of the cap. Instead of the cap height is only for TO-52 and for TO-46.
TO-72 The package with 4 leads but otherwise with dimensions identical to TO-18, is standardized as TO-72. The fourth wire is typically connected to the metal case as a means of electromagnetic shielding for radio frequency applications.
TO-71 The TO-71 package has 8 leads (up to three of those may be omitted). The minimum angle between two adjacent leads is 45°.
TO-206 TO-206 is intended to replace previous definitions of packages with leads arranged in a circle with a diameter of . The different outlines are now defined as variants of TO-206: TO-18 is renamed to TO-206-AA, TO-46 to TO-206-AB, TO-52 to TO-206-AC, TO-72 to TO-206-AF. A new package with 3 leads and a cap height of (i.e. smaller than TO-46) is added as TO-206-AD. TO-206-AE does not require a minimum diameter of the leads but is otherwise identical to TO-18. The somewhat unrelated TO-58 package is included as TO-206-AG.
National standards
Standards organizationStandardDesignation forTO-18TO-46TO-71TO-72JEDECJEP95TO-206-AATO-206-AB —TO-206-AFIECIEC 60191C7/B11C10/B11C7/B12DINDIN 4187618A318A4EIAJ / JEITAED-7500ATC-7/TB-8C, TC-7/TB-16C — —TC-7/TB-9CBritish StandardsBS 3934SO-12A/SB3-6ASO-12C/SB3-6ASO-12A/SB8-1BSO-12A/SB4-3GosstandartGOST 18472—88KT-1-7KT-35-7 —KT-1-12RosstandartGOST R 57439Kombinat Mikroelektronik ErfurtTGL 11811A3/15-3a — —A4/15-4aTGL 26713/07F1BA3 — —F1CA3
See also Common transistors in a TO-18 package: 2N2222, BC108 family Common integrated circuits in a TO-18 package: ZN414
References
External links
TO-18 Package, EESemi.com