TO3
Encyclopedia
TO-3 is one of a number of standardised packages used by transistor manufacturers inside which the transistor chip is sealed. The TO element stands for "transistor outline" and refers to a series of technical drawings produced by the semiconductor industry standardisation body, JEDEC
.
TO-3, or "metal can", is a package type commonly used for very large transistors, silicon-controlled rectifier
s, and, occasionally, integrated circuits. The component is mounted on a metal plate with a metal can crimped on top of it, providing good heat conduction and durability. TO-3 packages usually have three leads, though devices with four leads exist and more leads are possible. The leads pass through the metal plate and a glass seal, except for one lead which is usually attached to the case itself. They have two tabs with holes for mounting to a heatsink. The TO-3 design originated at Motorola
around 1955, the lead spacing was originally intended to allow plugging the device into a then-common tube socket
.
The case is usually connected electrically to the internal circuitry. An insulator may be required to electrically isolate the component from the heatsink if the heatsink is grounded or is mounted to multiple devices. Mica insulators were once popular because they have good thermal conductivity
while acting as an electrical insulator, but they have been superseded by ceramic.
Common Transistors:
JEDEC
The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
.
TO-3, or "metal can", is a package type commonly used for very large transistors, silicon-controlled rectifier
Silicon-controlled rectifier
A silicon-controlled rectifier is a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W...
s, and, occasionally, integrated circuits. The component is mounted on a metal plate with a metal can crimped on top of it, providing good heat conduction and durability. TO-3 packages usually have three leads, though devices with four leads exist and more leads are possible. The leads pass through the metal plate and a glass seal, except for one lead which is usually attached to the case itself. They have two tabs with holes for mounting to a heatsink. The TO-3 design originated at Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
around 1955, the lead spacing was originally intended to allow plugging the device into a then-common tube socket
Tube socket
Tube sockets are electrical sockets into which vacuum tubes can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins. Sockets are designed to allow tubes to be plugged in in only one orientation...
.
Typical applications
TO-3 packages are heatsinkable, and thus can be used in projects where a large amount of power is being drawn. The sides of the package are metal tabs with holes used in mounting the component to a heatsink. Thermal compound is also used to provide greater heat transfer.The case is usually connected electrically to the internal circuitry. An insulator may be required to electrically isolate the component from the heatsink if the heatsink is grounded or is mounted to multiple devices. Mica insulators were once popular because they have good thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
while acting as an electrical insulator, but they have been superseded by ceramic.
Advantages
- Can be used in high-power and high-current applications where equivalent components of other cases may be susceptible to damage.
- Almost all surfaces are metal for better heat conduction and durability.
- Mounting with the tabs ensures the component to be held firmly in place.
- Metal-glass seal is hermeticHermetic sealA hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
to protect the semiconductor from liquids and gases
Disadvantages
- More costly than equivalent components of other cases.
- Component size and lead placement makes soldering to a circuit board difficult—off-board space must be dedicated to the components and/or their heatsinks, thereby increasing production costs.
- Large lead spacing puts a limit on operating frequency
Common components that use the TO-3 package
Common Voltage Regulators:- LM317LM317The LM317 is a popular variable voltage regulator. It was invented by Robert C. Dobkin and Robert J. Widlar in 1970 while they worked at National Semiconductor.-Specifications:-See also:...
, voltage regulator - LM340, voltage regulator
Common Transistors:
- 2N30552N3055The 2N3055 is a silicon NPN power transistor intended for general purpose applications.It was introduced in the early 1960s by RCA using a hometaxial power transistor process, transitioned to an epitaxial base in the mid 1970s. Its numbering follows the JEDEC standard...
, NPN power transistor
See also
- Chip carrierChip carrierA chip carrier, also known as a chip container or chip package, is a container for a transistor or an integrated circuit. The carrier usually provides metal leads, or "pins", which are sturdy enough to electrically and mechanically connect the fragile chip to a circuit board. This connection may be...
Chip packaging and package types list - TO-18TO-18In electronics, TO-18 is a designation for a style of transistor metal case. The case is made of metal and is therefore more expensive than the similarly sized plastic TO-92 package used for other transistors. The name is from JEDEC, signifying Transistor Outline Package, Case Style...
, a small metal package for low-power semiconductors