BD138 PNP Power Transistor Technical Summary

Overview

The BD138 is a PNP power transistor designed for medium-power amplification and switching applications. Encased in a TO-126 (SOT32) plastic package, this transistor is well-suited for applications requiring high current handling and low voltage operation. Its robust construction and reliable performance make it a popular choice among engineers for a variety of electronic circuits.

The BD138 is part of a complementary pair with the BD139 NPN transistor, allowing for symmetrical circuit designs in push-pull configurations. Its high current gain and low saturation voltage ensure efficient operation in both linear and switching applications.

Features

• High Current Capability: Maximum collector current of 1.5 A, making it suitable for driving loads in power applications.
• Low Voltage Operation: Maximum collector-emitter voltage (V_CEO) of 80 V, enabling use in low-voltage circuits.
• Complementary Pair: Designed to work alongside the BD139 NPN transistor for symmetrical circuit designs.
• High Current Gain (h_FE): Typical current gain ranges from 40 to 160, ensuring efficient signal amplification.
• Low Saturation Voltage: Ensures minimal power loss during switching operations.
• TO-126 Package: Robust plastic package with good thermal performance, suitable for through-hole mounting.
• Wide Operating Temperature Range: Can operate in environments ranging from -55°C to +150°C.

Applications

The BD138 PNP transistor is widely used in various electronic circuits due to its versatile characteristics. Below are some common applications:

• Audio Amplification: Used in audio output stages, particularly in push-pull configurations with its complementary NPN counterpart, the BD139.
• Power Switching: Suitable for low-frequency switching applications such as relay drivers and motor control circuits.
• Voltage Regulation: Employed in linear voltage regulators and power supply circuits due to its high current handling capability.
• Signal Amplification: Used in general-purpose amplification stages where medium power output is required.
• LED Drivers: Can be used to drive high-power LEDs in lighting applications.
• Consumer Electronics: Found in devices like televisions, radios, and other household electronics requiring power amplification.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the BD138 PNP transistor under typical operating conditions (unless otherwise specified):

Absolute Maximum Ratings

• Collector-Emitter Voltage (V_CEO): 80 V
• Collector-Base Voltage (V_CBO): 80 V
• Emitter-Base Voltage (V_EBO): 5 V
• Collector Current (I_C): 1.5 A
• Base Current (I_B): 0.5 A
• Total Power Dissipation (P_tot): 12.5 W (at T_amb ≤ 25°C)
• Operating Junction Temperature (T_j): -55°C to +150°C
• Storage Temperature Range (T_stg): -55°C to +150°C

Thermal Characteristics

• Thermal Resistance, Junction-to-Ambient (R_thJA): 83.3 °C/W
• Thermal Resistance, Junction-to-Case (R_thJC): 10 °C/W

Dynamic Characteristics

• Current Gain (h_FE): 40 to 160 (at I_C = 0.5 A, V_CE = -2 V)
• Collector-Emitter Saturation Voltage (V_CE(sat)): -0.5 V (max) at I_C = -1 A, I_B = -0.1 A
• Transition Frequency (f_T): 50 MHz (typical)

Package Information

The BD138 is available in a TO-126 (SOT32) plastic package, which is a through-hole mounting style with three leads. Below are the key dimensions and mechanical details:

Package Dimensions

• Total Height: 9.65 mm (max)
• Lead Length: 3.3 mm (min) to 3.7 mm (max)
• Lead Diameter: 0.45 mm to 0.6 mm
• Body Width: 5.2 mm (max)
• Body Length: 10.4 mm (max)

Pin Configuration

The TO-126 package has three pins arranged in a single row. When viewing the transistor with the flat side facing you and leads pointing downward, the pinout is as follows:

• Pin 1 (Left): Emitter (E)
• Pin 2 (Center): Collector (C)
• Pin 3 (Right): Base (B)

Mounting Considerations

The TO-126 package is designed for through-hole PCB mounting. For optimal thermal performance, it is recommended to use a heatsink when operating near maximum power dissipation limits. The package is compliant with industry-standard soldering processes, including wave and reflow soldering.

Conclusion

The BD138 PNP power transistor is a versatile and reliable component for medium-power amplification and switching applications. Its high current capability, low saturation voltage, and complementary pairing with the BD139 make it a valuable part of many electronic designs. Whether used in audio amplifiers, power supplies, or general switching circuits, the BD138 delivers consistent performance in a compact and robust package.