BT138 Triac Technical Summary

Overview

The BT138 is a glass passivated triac designed for general-purpose AC switching and control applications. Housed in a robust plastic package, this component is optimized for high reliability and performance in a variety of industrial and consumer electronics. The BT138 is part of a family of triacs that provide efficient switching for AC loads, making it suitable for applications such as dimmers, motor controllers, and heating controls.

With its glass passivation, the BT138 offers enhanced stability and protection against environmental factors, ensuring long-term operational integrity. The device is designed to handle moderate to high current loads, making it a versatile choice for engineers requiring dependable AC switching solutions.

Features

• Glass Passivation: Provides improved reliability and protection against moisture and contaminants.
• High Current Capability: Suitable for switching moderate to high AC loads.
• Low Holding Current: Ensures stable operation in low-power applications.
• Plastic Package: Offers mechanical durability and ease of mounting.
• Symmetrical Triggering: Ensures consistent performance in both positive and negative half-cycles of AC waveforms.
• High Noise Immunity: Reduces susceptibility to false triggering from electrical noise.
• Isolated Tab: Simplifies heat sink mounting without requiring additional insulation.

Applications

The BT138 triac is widely used in AC switching and control circuits across various industries. Below are some common applications:

• Lighting Control: Used in dimmer circuits for incandescent and LED lighting systems.
• Motor Speed Control: Ideal for small to medium-sized AC motor controllers in appliances and industrial equipment.
• Heating Systems: Employed in thermostats and heating element controls for precise temperature regulation.
• Power Tools: Provides switching functionality in drills, saws, and other power tools.
• Home Automation: Used in smart switches and relays for home automation systems.
• Industrial Automation: Suitable for controlling solenoids, actuators, and other AC loads in automated systems.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the BT138 triac under standard operating conditions:

Absolute Maximum Ratings

• Repetitive Peak Off-State Voltage (V_DRM): Up to 600V
• RMS On-State Current (I_T(RMS)): 12A
• Non-Repetitive Peak On-State Current (I_TSM): 120A (for 10ms half-sine wave)
• Gate Trigger Current (I_GT): 5mA to 50mA (depending on variant)
• Gate Trigger Voltage (V_GT): 1.5V max
• Operating Temperature Range: -40°C to +125°C

Dynamic Characteristics

• Critical Rate of Rise of Off-State Voltage (dv/dt): 50V/µs min
• Critical Rate of Rise of On-State Current (di/dt): 20A/µs min
• Turn-On Time (t_gt): 2µs max
• Turn-Off Time (t_q): 10µs max

Package Information

The BT138 is available in a TO-220AB package, which is widely used for power semiconductor devices due to its excellent thermal and mechanical properties. Below are the key details of the package:

TO-220AB Package Dimensions

• Package Type: Through-hole, isolated tab
• Mounting Style: Vertical or horizontal
• Lead Material: Copper alloy
• Weight: Approximately 2.0 grams
• Thermal Resistance (Junction-to-Case, R_thJC): 3.0°C/W
• Thermal Resistance (Junction-to-Ambient, R_thJA): 62.5°C/W (without heat sink)

Mechanical Drawing

The TO-220AB package features three leads with standard pin spacing:

• Pin 1 (Main Terminal 2 - MT2): Connects to the load or AC supply.
• Pin 2 (Gate - G): Control terminal for triggering the triac.
• Pin 3 (Main Terminal 1 - MT1): Common return path for the load current.

The isolated tab allows direct mounting to a heat sink without electrical insulation, simplifying thermal management in high-current applications.

Conclusion

The BT138 triac is a reliable and versatile component for AC switching applications, offering a balance of performance, durability, and ease of use. Its glass passivation and robust TO-220AB package make it suitable for demanding environments, while its electrical characteristics ensure efficient operation across a wide range of loads. Whether used in lighting, motor control, or industrial automation, the BT138 provides engineers with a dependable solution for AC power control.