Description
BD TO-126 Transistor Series – NPN/PNP & Darlington for Amplifiers and Switching (BD136, BD137, BD139, BD140, BD438, BD441, BD681, BD682)
The BD Series Power Transistors (TO-126 package) are versatile through-hole BJTs widely used in audio amplification, switching, and driver circuits. This expanded range includes standard NPN/PNP transistors as well as Darlington pair transistors, offering flexibility for both low- and high-gain applications.
Models like BD139/BD140 are commonly used in audio amplifier stages, while BD681/BD682 Darlington transistors provide high current gain, making them suitable for relay driving, motor control, and high-load switching.
With reliable performance, good thermal characteristics, and easy PCB mounting, these transistors are ideal for makers, students, and professional electronics repair and design work.
Key Features
- Wide Range of Models – Standard & Darlington transistor options
- NPN & PNP Complementary Pairs – Ideal for push-pull designs
- High Current Gain Options – Darlington variants (BD681 / BD682)
- Audio Amplifier Ready – Commonly used in amplifier circuits
- TO-126 Package – Good heat dissipation with heatsink support
- Multipurpose Usage – Switching, amplification, and control
Variants – Available Models
| Model | Type | Polarity | Category | Typical Use |
|---|---|---|---|---|
| BD136 | BJT | PNP | Standard | Complementary to BD135, audio & switching |
| BD137 | BJT | NPN | Standard | Driver & amplifier circuits |
| BD139 | BJT | NPN | Standard | Audio amplifier stages |
| BD140 | BJT | PNP | Standard | Complementary to BD139 |
| BD438 | BJT | PNP | Power | Higher voltage applications |
| BD441 | BJT | NPN | Power | Switching & power circuits |
| BD681 | Darlington | NPN | High Gain | Relay, motor driver |
| BD682 | Darlington | PNP | High Gain | Complementary high current switching |
Specifications (typical – varies by model)
- Package: TO-126
- Type: BJT / Darlington Transistor
- Mounting: Through-hole
- Collector Current: Up to ~1.5A (higher for Darlington variants)
- Voltage Rating: ~45V – 100V (model dependent)
- Power Dissipation: ~8W – 12W
Applications
- Audio amplifier circuits
- Push-pull amplifier designs
- Relay & motor driver circuits
- Power switching applications
- Voltage regulators & power supplies
- DIY electronics & repair work