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

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