BD647 Pinout, Equivalent, Applications, Datasheet

The BD647 NPN transistor is a high-power Darlington transistor designed for audio output stages, motor control, and power regulation circuits. Known for its high current gain and robust TO-220 package, the BD647 delivers strong performance in both linear and switching applications.
In this detailed guide, we’ll explore the BD647 pinout, datasheet specifications, applications, working principle, and its PNP complementary transistor BD648.

Introduction to BD647 NPN Transistor

The BD647 is a high-gain NPN Darlington power transistor capable of handling large collector currents up to 8A and voltages up to 100V. It integrates two NPN transistors internally, providing an exceptionally high DC gain ideal for applications requiring large amplification from small base currents.

Engineered for audio amplifiers, DC motor drivers, and power supplies, the BD647 is a preferred choice for projects needing a balance of power efficiency and ruggedness. The transistor’s TO-220 package ensures excellent heat dissipation, making it suitable for long-duration, high-load operations.

Its complementary PNP transistor, the BD648, makes it perfect for push-pull amplifier configurations and symmetrical output stages.

BD647 NPN Transistor

Pinout of BD647

Understanding the BD647 Pinout Configuration

The BD647 transistor pin configuration follows the standard TO-220 layout, making it easy to integrate into most existing circuit boards. When viewed from the front (label facing you, metal tab behind), the pins are arranged as Base, Collector, and Emitter respectively.

Pin Configuration of BD647 Pinout

The metal tab at the back is internally connected to the collector, so it must be insulated if mounted on a shared heatsink.

Key Features of BD647 Transistor

• High current handling capacity (up to 8A continuous)
• High gain due to internal Darlington configuration
• Low saturation voltage and high switching efficiency
• TO-220 package for effective heat dissipation
• Complementary to BD648 (PNP version)
• Ideal for audio amplifiers and regulated power supplies
• Suitable for high-current relay and motor driver circuits

BD647 Transistor Datasheet and Specifications

Below are verified BD647 transistor datasheet parameters, summarized for accurate circuit design:

• Collector-Emitter Voltage (Vceo) = 100 V
• Collector-Base Voltage (Vcbo) = 120 V
• Emitter-Base Voltage (Vebo) = 5 V
• Continuous Collector Current (Ic) = 8 A
• Peak Collector Current (Icm) = 12 A
• Power Dissipation (Pc) = 62.5 W (at Tc = 25°C)
• DC Current Gain (hFE) = 750 (min at Ic = 3 A)
• Collector-Emitter Saturation Voltage (Vce(sat)) = 2.0 V max
• Base-Emitter Voltage (Vbe(on)) = 2.5 V max
• Thermal Resistance (Junction to Case) = 2°C/W
• Operating Junction Temperature Range = –65°C to +150°C

These parameters highlight the BD647’s strength in power-demanding environments and its ability to amplify large signals efficiently.

Working Principle of BD647 NPN Transistor

The BD647 transistor functions as a Darlington pair, where two NPN transistors are connected internally for exponential current gain. A small base current is amplified by the first transistor, which drives the second, resulting in a very high total current gain.

When used in amplifier circuits, the BD647 conducts during the positive half-cycle of the input signal, providing smooth linear output when paired with its complementary BD648 (which handles the negative cycle).

In switching applications, BD647 acts as a current-controlled switch, turning on when a small base current is applied and allowing high current to flow through the collector to the emitter.

More Circuit Layouts

Typical Applications of BD647

• Audio amplifier output and driver stages
• DC motor control and relay drivers
• Power switching circuits
• Voltage and current regulator designs
• Inverter and UPS output stages
• LED driver and power interface circuits

PNP Complementary Transistor

The BD648 is the PNP complementary transistor to the BD647 NPN transistor.
Together, they form a complementary Darlington pair used in push-pull amplifier designs, motor control circuits, and voltage regulators.

Both share nearly identical electrical specifications, ensuring consistent performance in dual-phase circuits where balanced signal amplification is required.

Equivalent Transistors and Alternatives

If the BD647 transistor is unavailable, the following equivalents or alternatives can be used depending on the required voltage and current specifications:

• BD649 (higher voltage variant)
• BD651 (similar Darlington with higher gain)
• TIP122 / TIP120 (general-purpose Darlington NPN alternatives)
• MJ11015 (industrial-grade power equivalent)

Always cross-check Vce, Ic, and hFE before substitution to ensure compatibility.

Comparison BD647 vs BD648 Complementary Transistors

The BD647 (NPN) and BD648 (PNP) are complementary Darlington power transistors used in paired configurations for balanced amplification.

The BD647 conducts current from collector to emitter when a small base current is applied (NPN operation), while the BD648 conducts in the reverse polarity (PNP operation).
Both transistors offer the same voltage and current ratings, making them perfect for push-pull amplifiers, power control circuits, and audio driver systems.

Frequently Asked Questions (FAQ)

What is the BD647 transistor used for?

The BD647 transistor is used in audio amplifiers, inverters, motor drivers, and power regulator circuits that require high current gain and efficiency.

What type of transistor is BD647?

It is an NPN Darlington power transistor, consisting of two NPN transistors internally connected for high current amplification.

What is the BD647 pin configuration?

Pin 1 = Base, Pin 2 = Collector, Pin 3 = Emitter. The metal tab is internally connected to the collector.

What is the complementary transistor for BD647?

The BD648 is the PNP complementary transistor to BD647.

Can I use TIP122 instead of BD647?

Yes, TIP122 can be used as a substitute in lower-voltage or general-purpose circuits, but verify power and voltage ratings before replacement.

Conclusion

The BD647 NPN Darlington transistor is a high-performance power device ideal for audio, motor, and power regulation circuits. Its high current gain, strong thermal capacity, and rugged design make it perfect for demanding industrial and audio applications.

When paired with its PNP counterpart BD648, it forms an efficient and balanced transistor pair suitable for push-pull amplifiers and symmetric driver designs. For engineers and hobbyists, the BD647 transistor remains a reliable component for both switching and amplification purposes.

Datasheet of BD647 NPN Transistor

Click the following Button to download the datasheet of BD647 Transistor :

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