Table of Contents
Introduction
The BD135 is an NPN medium-power silicon transistor widely used in amplifier and switching applications. Designed for moderate current and voltage handling, this transistor can deliver up to 1.5A of collector current and withstand up to 45V collector-emitter voltage, making it ideal for driving loads such as relays, motors, and lamps.
Manufactured in a TO-126 plastic package, the BD135 provides efficient heat dissipation through its metal mounting tab, which can be easily attached to a heatsink for improved thermal performance. It is part of the BD135–BD139 transistor family, where each variant offers slightly different voltage ratings to suit different circuit needs.
Because of its high reliability, low cost, and availability, BD135 is commonly used in audio amplifier stages, voltage regulator circuits, power control modules, and signal amplification systems. It exhibits excellent linearity, making it suitable for analog designs, while its fast switching speed allows it to be used effectively in digital or pulse-based circuits as well.
Overall, the BD135 transistor is a versatile and durable component that serves as a bridge between low-power signal transistors and high-power output transistors, offering a balance of performance and affordability for a wide range of electronic applications.
BD135 Pinout
| Pin Number | Pin Name | Description |
|---|---|---|
| 1 | Emitter | Current flows out through this terminal. Usually connected to ground in NPN configuration. |
| 2 | Collector | Current enters the transistor through this terminal. Connected to the load. |
| 3 | Base | Controls the transistor’s biasing and switching. A small base current controls a large collector current. |
BD135 Transistor Specifications
| Parameter | Value |
|---|---|
| Transistor Type | NPN |
| Package Type | TO-126 |
| Collector-Emitter Voltage (V<sub>CEO</sub>) | 45V |
| Collector-Base Voltage (V<sub>CBO</sub>) | 45V |
| Emitter-Base Voltage (V<sub>EBO</sub>) | 5V |
| Collector Current (I<sub>C</sub>) | 1.5A |
| Total Power Dissipation (P<sub>tot</sub>) | 12.5W |
| DC Current Gain (h<sub>FE</sub>) | 40 – 250 |
| Transition Frequency (f<sub>T</sub>) | 190 MHz |
| Operating and Storage Temperature | -65°C to +150°C |
Features
- Medium power NPN transistor
- High transition frequency (up to 190 MHz)
- Suitable for high-speed switching
- Good thermal stability
- Can be used in Class AB amplifier stages
- Low collector-emitter saturation voltage
Applications
- Audio amplifier circuits
- DC motor driver circuits
- Relay driver modules
- Voltage regulator circuits
- Switching and signal amplification
- Power supply and control circuits
Equivalent and Alternative Transistors
You can replace BD135 with any of the following transistors, depending on the circuit requirements:
| Equivalent / Alternative | Type | Notes |
|---|---|---|
| BD137 | NPN | Same series, slightly higher voltage handling |
| BD139 | NPN | Higher collector current and power dissipation |
| 2N1711 | NPN | Similar characteristics for low to medium power |
| TIP31 | NPN | Suitable for high current applications |
| 2N3053 | NPN | Lower power but similar gain range |
Conclusion
The BD135 transistor is an excellent choice for medium-power amplification and switching applications. Its robust design, moderate gain, and reliable performance make it suitable for various audio, control, and power circuits. With compatible alternatives like BD137 and BD139, designers can easily select the right transistor based on voltage and current requirements.
