3-Pin Transistor Outline (TO-3) Package
8-Pin Transistor Outline (TO-8) Package
8-Pint Transistor Outline (TO-8B/LP) Package
3-Pin Transistor Outline (TO-92) Package
3-Pin Transistor Outline (TO-202) Package
3-Pin Transistor Outline (TO-220) Package
3-Pin Transistor Outline (TO-226) Package
Transistor Outline (TO) Package
The term "TO" in transistor outline
package (TO package) refers to a type of metal can package used for housing discrete
electronic components, including transistors. The TO (Transistor Outline) series
of metal can and encapsulated plastic packages has been around since the 1950s,
when the first commercial transistors became available. Over time, plastic was substituted
for some applications, and the applications expanded to include circuits like voltage
regulators, photosensors. TO packages are known for their distinctive metal can
shape, which provides thermal and mechanical benefits. Here are some key features
and common variations of TO transistor outline packages:
- Metal Can Shape: TO packages are typically cylindrical metal cans. They are
often made of materials like aluminum or steel, which provide good thermal conductivity
and protection for the enclosed semiconductor device.
- Pin Configuration: TO packages have two or more pins that protrude from the
bottom of the can. The number and arrangement of pins depend on the specific TO
- Variants: There are several variants of TO packages, and the numbering scheme
typically indicates the package's physical dimensions and pin configuration. Common
TO package variants include TO-92, TO-220, TO-247, TO-3, and TO-18, among others.
Each variant has its own size, pin arrangement, and power handling capabilities.
- TO-92: A small, three-pin package commonly used for small-signal transistors.
TO-220: Larger package suitable for medium-power transistors and voltage regulators.
- TO-247: Larger and more robust package often used for high-power transistors
and power semiconductors.
- TO-3: A larger metal can package primarily used for high-power and high-voltage
- TO-18: A smaller metal can package used for various discrete components, including
transistors and photodiodes.
- Heat Dissipation: TO packages are known for their good thermal properties. The
metal can acts as a heat sink, helping to dissipate heat generated by the enclosed
transistor. This makes them suitable for applications where heat management is crucial.
- Mounting: TO packages are designed to be mounted directly onto a printed circuit
board (PCB) or a heat sink using screws or clips. The metal body provides mechanical
stability and can enhance thermal performance when mounted to a heat sink.
- Sealing: TO packages are typically hermetically sealed, which means they are
air-tight to protect the enclosed semiconductor component from moisture and environmental
factors. This sealing enhances the long-term reliability of the component.
- Applications: TO packages are commonly used for a wide range of discrete semiconductor
devices, including bipolar junction transistors (BJTs), power transistors, voltage
regulators, and other components requiring good thermal performance and mechanical
- Obsolete in Some Applications: While TO packages are still used in various applications,
they have been partially replaced by surface-mount packages (SMT) in modern electronics,
especially for smaller and more compact devices where space is a critical consideration.
3-Pin Transistor Outline (TO-237) Package
3-Pin Transistor Outline (TO-263) Package