TO-3

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Template:Short description

File:Transistorer (cropped).jpg
Size comparison of BJT transistor packages, from left to right: SOT-23, TO-92, TO-126, TO-3
File:TO-3 transistor package.stl
3D model of TO-3 package

In electronics, TO-3 is a designation for a standardized metal semiconductor package used for power semiconductors, including transistors, silicon controlled rectifiers, and, integrated circuits. TO stands for "Transistor Outline" and relates to a series of technical drawings produced by JEDEC.[1]

The TO-3 case has a flat surface which can be attached to a heatsink, normally via a thermally conductive but electrically insulating washer. The design originated at Motorola around 1955 from a group headed by Dr. Virgil E. Bottom.[2] who was director of research of the Motorola Semiconductor Division. The first use of this design was for the germanium alloy-junction power transistor 2N176 – the first power transistor to be put into quantity production.[2][3] The lead spacing was originally intended to allow plugging the device into a then-common tube socket.[4]

Typical applications

File:TO-3 mounting.png
Typical TO-3 mounting profile, with insulator from chassis

The metal package can be attached to a heat sink, making it suitable for devices dissipating several watts of heat. Thermal compound is used to improve heat transfer between the device case and the heat sink. Since the device case is one of the electrical connections, an insulator may be required to electrically isolate the component from the heatsink. Insulating washers may be made of mica or other materials with good thermal conductivity.

The case is used with high-power and high-current devices, on the order of a few tens of amperes current and up to a hundred watts of heat dissipation. The case surfaces are metal for good heat conductivity and durability. The metal-to-metal and metal-to-glass joints provide hermetic seals that protect the semiconductor from liquids and gases.

Compared with equivalent plastic packages, the TO-3 is more costly. The spacing and dimensions of the case leads make it unsuitable for higher frequency (radio frequency) devices.

Construction

File:Darlington transistor MJ1000.jpg
Inside of an MJ1000 Darlington transistor in TO-3 package

The semiconductor die component is mounted on a raised platform on a metal plate, with the metal can welded on top of it; providing high heat conductivity and durability. The metal case is connected to the internal device and the leads are connected to the die with bonding wires.

The TO-3 package consists of a diamond-shaped base plate with diagonals of Script error: No such module "convert". and Script error: No such module "convert".. The plate has two mounting holes on the long diagonal, with the centers spaced Script error: No such module "convert". apart.[5] The cap attached to one side of the plate brings the total height to up to Script error: No such module "convert".. Two pins on the other side of the plate are isolated from the package by individual glass-metal seals. The metal case forms the third connection (in the case of a bipolar junction transistor this is typically the collector).

Dimensions

File:Dimensions TO-3 package in mm.svg
Dimensions TO-3 package in mm[1]

Variants

File:Wzmacniacze.jpg
Power amplifier integrated circuit (CEMI UL1403) in a TO-3 package variant

TO-3 package variants for integrated circuits can have more than two leads. The height of the cap and the thickness of the leads differs between variants of the TO-3 package.

TO-41

File:AD133.jpg
AD133 transistor in a TO-41 package. The third pin connected to the case

The two pins of the TO-41 package end in soldering pads with holes in them to make it easier to solder wires to the pins for point-to-point construction (as opposed to soldering a TO-3 package on a printed circuit board). Otherwise the TO-41 package has the same dimensions as the TO-3 package.[6] Some variants of the TO-41 package have a third pin with a soldering pad connected to the case (e.g. AD133,[7]Template:Rp AUY21[7]Template:Rp). This 3-pin package was standardized by IEC as C14B/B28.[7]Template:Rp

TO-204

TO-204 is intended to replace previous definitions of flange-mounted packages with a Script error: No such module "convert". pin spacing.[8][9] The different outlines are now defined as variants of TO-204: TO-3 is renamed to TO-204-AA, TO-41 to TO-204-AB. A new package with a reduced maximum height of Script error: No such module "convert". is added as TO-204-AC. Two additional variants specify pins thicker than the original Script error: No such module "convert". to allow higher currents: Script error: No such module "convert". for TO-204-AD and Script error: No such module "convert". for TO-204-AE.

National standards

Standards organization Standard Designation for
TO-3 TO-41 – –
JEDEC JEP95[9] TO-204-AA TO-204-AB TO-204-AC TO-204-AD
IEC IEC 60191Template:Efn[7]Template:Rp C14A/B18 C14B/B18
DIN DIN 41872[10][11] 3A2 3B2Template:Efn
EIAJ / JEITA ED-7500ATemplate:Efn[12] TC-3/TB-3 – TC-3A/TB-3Template:Efn –
British Standards BS 3934Template:Efn[13][14] SO-5A/SB2-2 SO-5B/SB2-2Template:Efn
Gosstandart GOST 18472—88[15] KT-9Template:Efn – – KT-9B
Rosstandart GOST R 57439[16] KT-9C
Kombinat Mikroelektronik Erfurt TGL 11811[17] Eeb – Eea –
TGL 26713/11[17] L2A2 – L2A1 –

Template:Notelist

Common components in a TO-3 package

Common voltage regulator integrated circuits:

  • LM317, voltage regulator
  • LM78xx, voltage regulator
  • LM340, voltage regulator

Common transistors:

  • 2N3055, NPN power transistor
  • MJ2955, PNP power transistor (not to be confused with a 2N2955 which is a small signal PNP transistor [18])
  • KD503, NPN power transistor

See also

  • TO-66, smaller package of similar shape
  • TO-220 plastic case used for power semiconductors with similar ratings to TO-3 cases

References

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External links

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