TO-39 vs. TO-46: A Guide to Choosing the Suitable TO Package

In the world of electronics, choosing the right package for your components is crucial to ensuring optimal performance and reliability. Transistors, diodes, and other electronic components are examples of semiconductor devices that frequently use Transistor Outline (TO) packaging.

Among the various TO packages, the TO-39 and TO-46 are two of the most commonly used, but choosing between them can be a challenge.

What Are TO Packages?

TO packages, or Transistor Outline packages, are standardized casing formats used for mounting semiconductors in electronic devices. These packages are designed to protect the internal components while providing heat dissipation, mechanical strength, and electrical connectivity. TO packages come in various shapes and sizes, with the most common being TO-92, TO-220, TO-39, and TO-46.

TO packages are particularly favored for their compact size, ease of use in surface-mount and through-hole applications, and their versatility in handling a wide range of electronic components. They are utilized in consumer electronics, communication systems, power supply, and more.

What is the TO-39 Package?

The TO-39 package is a small, cylindrical casing typically made from metal. It is often used for transistors and small diodes, especially those in high-frequency and small-signal applications. The TO-39 package is broken down in detail below.

Features of the TO-39 Package

Shape: Cylindrical, with a metal casing that is hermetically sealed for protection.

Size: Typically 8.4mm in diameter and 9.5mm in height.

Pins: Three pins are commonly available for the lead connection.

Material: Often made from metal for better heat dissipation, but some variants may use plastic for less demanding applications.

Mounting: Commonly used in through-hole mounting.

Typical Applications

Small-Signal Transistors: Especially in high-frequency applications like RF circuits and audio amplifiers.

Photodiodes and Light Sensors: Frequently used in optical communication devices and sensors.

Current Sensors: Employed in low-power applications where dissipation of heat is not crucial.

What is the TO-46 Package?

The TO-46 package, like the TO-39, is used primarily for small electronic components but has a slightly different design. It is also a cylindrical package but features a smaller, more compact design with slightly different electrical and mechanical characteristics.

Features of the TO-46 Package

Shape: Similar to the TO-39, but slightly smaller and more compact.

Size: Typically 6.8mm in diameter and 5.8mm in height.

Pins: Also typically three leads, but the size and positioning of the pins may differ slightly from the TO-39.

Material: Mostly metal, with plastic options available for some lower-power versions.

Mounting: Primarily through-hole, though some configurations may allow for surface-mount applications.

Typical Applications

Photodiodes: Widely used in optical systems where small, precise sensing is needed.

Low-Power Transistors: Common in signal amplification and radio-frequency (RF) applications.

Temperature sensors: Because of their compact form factor, they are utilized in low-temperature sensing applications.

Key Differences Between TO-39 and TO-46

Although both the TO-39 and TO-46 are small cylindrical packages used in low-power applications, they differ in several key areas. The following table compares the TO-39 and TO-46 packages based on important factors:

Explanation of the Key Differences:

Size and Dimensions: The TO-46 is slightly smaller in both diameter and height compared to the TO-39. This makes it a better fit for applications with strict space constraints.

Power Handling: The TO-39 can handle slightly higher power than the TO-46, though both packages are still considered low-power solutions.

Cost: Due to its compactness and specific use cases, the TO-46 tends to be slightly more expensive than the TO-39.

Key Considerations When Deciding Between TO-39 and TO-46

Choosing between the TO-39 and TO-46 packages depends on several factors that need to be aligned with the specific requirements of your project. The following are important factors to think about when making your decision:

Power Handling:

If your application requires higher power handling, the TO-39 might be more suitable.

If you're working with low-power signals or small components, the TO-46 could be ideal due to its smaller form factor.

Space Constraints:

For applications where space is a premium, such as compact electronics or handheld devices, the TO-46's smaller size offers a clear advantage.

Thermal Performance:

Both packages are made of metal, which helps with heat dissipation. However, the TO-39 may offer slightly better performance for heat management due to its larger surface area.

Cost Considerations:

The TO-39 can be the more cost-effective option if you're working on a project with limited funds. The TO-46, being more specialized, may carry a slight premium.

Which TO Package is Right for Your Project?

Best Use Cases for TO-39:

Ideal for small-signal applications where heat dissipation is not a major concern.

Suitable for power transistors, RF circuits, and photodiodes where size is important but not overly constrained.

Best Use Cases for TO-46:

Best for compact designs where minimizing space is crucial.

Preferred for low-power transistors, photodiodes, and sensors where small form factor and precise performance are required.

Decision-Making Tips:

For small-volume, low-power applications in space-constrained devices, the TO-46 may be the better option.

For slightly higher power applications where size is not as critical, the TO-39 may provide a better balance of cost and performance.