TO-220, TO-39, TO-46: Which TO Package Fits Your Application Best?

When it comes to selecting the right transistor outline (TO) package for your electronic components, the decision can be crucial to the efficiency and reliability of your system. TO packages are a standard form factor used for encapsulating electronic components such as transistors, diodes, and other semiconductors.

The three most widely used TO packages, TO-220, TO-39, and TO-46, serve a variety of applications, from power electronics to small-signal devices.

What is a TO Package?

A TO package refers to a metal or plastic casing used for protecting electronic components such as transistors, diodes, and integrated circuits. The package provides not only mechanical protection but also ensures electrical connections are made with ease. TO packages come in various sizes and forms, with the most common being the TO-220, TO-39, and TO-46 packages.

These packages are designed to handle the varying thermal and electrical requirements of electronic components. The size, thermal resistance, and current-handling capability of each package differ, making it essential to choose the right one for a specific application. While the TO-220 is primarily used in power devices, the TO-39 and TO-46 are more suited for smaller, low-power applications.

TO-220 Package

The TO-220 is one of the most widely used TO packages, especially in power electronics. It is characterized by a relatively large form factor compared to other TO packages, making it suitable for devices requiring high power dissipation. For effective thermal control, the packaging usually has a metal tab for heat sinking.

Applications

Power Transistors: The TO-220 is widely used in high-power transistors for power supplies and amplifiers.

Voltage Regulators: This package is used in voltage regulators where high power dissipation and thermal management are critical.

Power Amplifiers: Audio and RF power amplifiers also use TO-220 packages for effective thermal management.

TO-39 Package

The TO-39 package is a small, cylindrical metal-can package designed primarily for low-power applications. It is commonly used in small signal devices, including photodiodes, phototransistors, and small transistors. The metal-can design helps protect the components from physical damage while providing a reliable electrical connection.

Applications

Small-Signal Transistors: The TO-39 package is typically used for small-signal transistors in low-power applications.

Photodiodes and Sensors: Photodiodes and small sensors often come in TO-39 packages due to their compact size.

Low-Power Devices: This package is commonly found in devices like audio equipment, signal processors, and other low-power components.

TO-46 Package

The TO-46 package is similar to the TO-39 in terms of size, but it offers enhanced performance for applications that require even more compact designs. It is mainly used in sensor applications, particularly photodiodes, and other small-signal devices.

Applications

Sensors: The TO-46 is widely used for sensor applications, particularly in photodetectors, where its small size is advantageous.

Medical Devices: It is present in medical devices that need to be small and precise.

Communication Devices: The package is used in communication systems, including those involving photonics and optoelectronics.

Comparison of TO-220, TO-39, and TO-46

Key Factors in Selecting a TO Package

When choosing the most suitable TO package for your application, there are several important aspects to take into account:

Power Requirements: For high-power applications, the TO-220 package is ideal due to its superior heat dissipation capabilities. For low-power applications, the TO-39 or TO-46 packages are more suitable.

Size Constraints: If space is limited, the smaller TO-39 and TO-46 packages are the best choices. However, if the device requires substantial heat management, the TO-220’s larger size becomes more practical.

Heat Management: Maintaining the longevity and functionality of your components depends on effective heat dissipation. The TO-220 offers the best thermal management, while the TO-39 and TO-46 packages are more suitable for devices that do not generate excessive heat.

Cost: If cost is a primary consideration, the TO-39 package offers the most cost-effective solution. However, for high-performance applications, the TO-220 package, while more expensive, provides superior reliability and thermal management.

Application Type: The application’s power requirements, size constraints, and heat dissipation needs will determine the best TO package. For high-power applications like amplifiers and voltage regulators, the TO-220 is ideal, while the TO-39 and TO-46 are better suited for sensors, small-signal components, and low-power devices.