BD679 Pinout, Equivalent, Applications, Datasheet

The BD679 is a high-gain NPN Darlington transistor in a TO-126 package, used for medium-power switching and amplification. This article explains BD679 pinout, datasheet details, working principle, and key applications.

Introduction to BD679 NPN Transistor

The BD679 is a medium-power NPN Darlington transistor designed for high-gain amplification and efficient switching. It is widely used in audio amplifiers, relay drivers, and voltage regulator circuits that demand high current gain and minimal base drive.

Encapsulated in a TO-126 package, the BD679 offers excellent heat dissipation and mechanical durability, making it suitable for both linear and switching applications.

Its Darlington configuration integrates two NPN transistors in one package, producing a significantly high DC gain (hFE) and allowing control of large output currents with small base inputs. As a result, BD679 is a preferred component in industrial control, automation, and signal amplification circuits.

BD679 NPN Transistor

Pinout of BD679

Understanding the BD679 Pinout Configuration

The BD679 pinout follows a standard layout typical to most TO-126 NPN Darlington transistors. Knowing the correct pin orientation ensures safe and efficient installation in any circuit design.

Pin Configuration of BD679 Pinout

Key Features of BD679 Transistor

• NPN Darlington configuration for high amplification gain
• Low base drive current for high collector current output
• High switching efficiency and fast response
• Suitable for linear and switching operations
• Compact and durable TO-126 package
• Complementary to BD680 (PNP) transistor
• High thermal stability and low leakage current

BD679 Transistor Datasheet and Specifications

• Collector-Emitter Voltage (Vceo): 80 V
• Collector-Base Voltage (Vcbo): 80 V
• Emitter-Base Voltage (Vebo): 5 V
• Collector Current (Ic): 4 A
• Power Dissipation (Ptot): 40 W
• DC Current Gain (hFE): 750 minimum
• Transition Frequency (fT): 3 MHz typical
• Junction Temperature (Tj max): 150 °C
• Polarity: NPN
• Package: TO-126

According to the BD679 transistor datasheet, the device is ideal for medium-power control and amplification applications that require high gain and stable performance. Its higher voltage rating compared to BD677 provides more flexibility for higher power circuits.

Working Principle of BD679 NPN Transistor

The BD679 NPN transistor operates as a Darlington pair, where two NPN transistors are connected internally to achieve a very high gain. The emitter of the first transistor drives the base of the second, resulting in amplified collector current.

When a small base current flows into the transistor, it allows a large current to pass from collector to emitter, making it an efficient amplifier or switch.

This characteristic makes BD679 suitable for signal amplification, relay driving, and motor control circuits, where high output current and efficiency are required with minimal input power.

More Circuit Layouts

Typical Applications of BD679

• Audio amplifier driver stages
• Voltage regulator and control circuits
• Relay and solenoid switching
• Motor driver and control modules
• Power control and automation systems
• Complementary push-pull configurations with BD680
• Industrial and consumer electronic equipment

PNP Complementary Transistor

The PNP complementary transistor of BD679 is BD680.
Both transistors are designed to work together in push-pull amplifier configurations, where BD679 handles the positive half-cycle and BD680 handles the negative half-cycle of the signal. This pairing ensures linear amplification and high efficiency in both AC and DC circuits.

Equivalent Transistors and Alternatives

If BD679 is not available, several equivalent NPN Darlington transistors can be used with similar or improved characteristics. These include:

Equivalent or Alternative Transistors:

• BD677 (lower voltage version)
• TIP122 (NPN Darlington, TO-220 package)
• MJE800 (NPN Darlington, medium power)
• 2N6038 (NPN Darlington transistor)

Always verify the maximum voltage, current, and power dissipation ratings from datasheets before replacement to ensure circuit compatibility.

Comparison BD679 vs BD680 Complementary Transistors

The BD679 (NPN) and BD680 (PNP) are complementary Darlington transistors, designed for symmetrical use in amplifier and switching circuits.

BD679 conducts when the base is positive relative to the emitter, while BD680 conducts when the base is negative. Together, they form efficient push-pull stages, ensuring complete signal reproduction and minimal crossover distortion.

Both share similar ratings, 80 V collector-emitter voltage, 4 A collector current, 40 W power dissipation, and high DC gain, making them ideal for balanced power amplifier and control designs.

Frequently Asked Questions (FAQ)

What is the BD679 transistor used for?

BD679 is used for medium-power amplification, switching, and control in audio, relay, and voltage regulation circuits.

What type of transistor is BD679?

It is an NPN Darlington transistor with a high current gain and medium power capability.

What is the BD679 pin configuration?

From left to right (flat side facing you): Emitter, Collector, Base.

What is the complementary transistor for BD679?

The complementary transistor is BD680 (PNP).

Can I use TIP122 instead of BD679?

Yes, TIP122 can be used as an alternative with higher power handling (TO-220 package), but circuit adjustments may be necessary.

Conclusion

The BD679 NPN Darlington transistor provides excellent performance for medium-power switching and amplification applications. With a high DC gain, low base current requirement, and robust 80 V voltage rating, it is ideal for audio amplifiers, regulators, and motor controllers.

When paired with its PNP complement BD680, it becomes part of a highly efficient and linear push-pull pair, ensuring balanced performance in industrial and consumer electronics.

Datasheet of BD679 NPN Transistor

Click the following Button to download the datasheet of BD679 Transistor :

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