BD135

Product Overview

The STMicroelectronics BD135 is a silicon NPN power transistor designed for medium-power applications, offering a balance between voltage, current handling capability, and gain performance. It is widely used in audio amplification, power regulation, switching circuits, and general-purpose linear applications. The BD135 is part of a well-established family of transistors (BD135/BD137/BD139), recognized for their robustness, availability, and compatibility in a variety of analog and power system designs.

The transistor is packaged in a TO-126 form factor, which provides efficient heat dissipation and a small physical footprint. It supports moderate collector current levels and offers stable gain across a range of operating conditions, making it suitable for both consumer and industrial applications.

Key Features

* NPN bipolar junction transistor (BJT) for linear and switching applications
* Collector-emitter voltage rating up to 45 V
* Collector current rating up to 1.5 A continuous
* High DC current gain, with hFE selection classes (e.g., BD135-6, BD135-10, BD135-16)
* Suitable for audio amplifier stages and general-purpose switching
* TO-126 package for efficient thermal management
* Complementary with BD136 (PNP version) for symmetric design use
* Robust operating characteristics over a wide temperature range

Electrical Specifications

* Transistor Type: NPN
* Collector-Emitter Voltage (V_CEO): 45 V
* Collector-Base Voltage (V_CBO): 60 V
* Emitter-Base Voltage (V_EBO): 5 V
* Collector Current (I_C): 1.5 A continuous
* Peak Collector Current (I_C peak): Up to 3 A (non-repetitive)
* Base Current (I_B): Max 0.5 A
* Total Power Dissipation (P_TOT): 12.5 W at T_C = 25 °C (with proper heatsinking)
* DC Current Gain (h_FE):

* Typically 40–250 depending on selection and test conditions
* BD135-16: hFE ≥ 100
* Tested at I_C = 150 mA, V_CE = 5 V
* Collector-Emitter Saturation Voltage (V_CE(sat)):

* Typically 0.5 V at I_C = 0.5 A, I_B = 50 mA
* Transition Frequency (f_T): Around 190 MHz (typical), measured at V_CE = 10 V, I_C = 50 mA
* Operating and Storage Temperature Range: –55 °C to +150 °C
* Thermal Resistance, Junction-to-Case (R_thJC): ~10 °C/W

Functional Description

The BD135 operates as a standard NPN bipolar transistor, controlled by current flow into the base terminal. When used in the active region, it functions as a linear amplifier, while in saturation and cutoff, it serves as an effective switch. Its 45 V V_CEO rating and 1.5 A collector current capability make it useful in moderate power circuits that require reliable current amplification or switching performance.

The hFE classification (with options such as BD135-6, -10, -16) allows designers to select devices with suitable gain for their application needs. The BD135’s relatively high transition frequency (f_T) also enables operation in circuits up to low MHz ranges, suitable for audio and low-speed digital switching.

The TO-126 package enables good thermal management, and its exposed metal tab can be connected to a heat sink, which is essential for sustained high-current operation.

Typical Applications

* Driver and output stages in audio power amplifiers
* Voltage regulation and series pass elements in linear regulators
* Relay, solenoid, and lamp drivers in control systems
* Switching loads in power supplies or embedded systems
* Class A, B, or AB amplifier circuits
* Push-pull output stages (in combination with BD136)
* Buffer and level-shifting transistors in analog signal paths
* Basic motor driver circuits for small DC motors

Design Considerations

* Thermal Management: Ensure adequate heat sinking to support full power dissipation, especially in applications exceeding 0.5 A of collector current.
* Biasing: Proper base resistor sizing is critical to maintain stable operation and avoid thermal runaway or insufficient saturation.
* Saturation Performance: At moderate collector currents (≤ 1 A), the BD135 exhibits low V_CE(sat), enabling efficient power switching with minimal voltage drop.
* Complementary Pairing: When paired with the BD136 PNP transistor, symmetrical designs such as full-bridge drivers or push-pull amplifiers can be implemented.
* Switching Speed: While the BD135 is not designed for high-speed logic, its MHz-range frequency response is adequate for audio and slow digital control signals.
* SOA Compliance: Ensure operation within the Safe Operating Area (SOA) to prevent secondary breakdown, particularly under inductive loads. Flyback diodes or snubber circuits may be required.

Summary

The STMicroelectronics BD135 is a robust and flexible NPN medium-power transistor that delivers consistent performance in both analog and digital circuits. Its 45 V voltage rating, 1.5 A current capacity, and broad gain range make it a preferred choice in amplifier stages, power switches, and control circuitry. Whether used in consumer electronics, industrial control, or embedded systems, the BD135 offers a proven solution with solid thermal and electrical characteristics for medium-power discrete designs.