2SC2879: Everything you Need to Know and More!

Introduction to the 2SC2879 Transistor

The 2SC2879 is a high-frequency, high-power NPN bipolar junction transistor commonly used in RF power amplifier applications. This transistor is designed for operation in the VHF and UHF frequency ranges, making it suitable for use in radio transmitters, cellular base stations, and other wireless communication systems.

Key Features of the 2SC2879

High power output: The 2SC2879 is capable of delivering up to 150 watts of power under optimal conditions.
Wide frequency range: This transistor can operate effectively in frequencies ranging from 30 MHz to 500 MHz.
High gain: The 2SC2879 offers a high gain, typically around 10 dB, which allows for efficient power amplification.
Rugged construction: Designed to withstand high temperatures and harsh operating conditions, the 2SC2879 is built to last.

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Electrical Characteristics

Understanding the electrical characteristics of the 2SC2879 is crucial for proper circuit design and implementation. Here are some of the key parameters to consider:

Maximum Ratings

Parameter	Symbol	Value	Unit
Collector-Base Voltage	VCBO	200	V
Collector-Emitter Voltage	VCEO	140	V
Emitter-Base Voltage	VEBO	4	V
Collector Current	IC	20	A
Total Power Dissipation	Ptot	250	W
Junction Temperature	Tj	200	°C
Storage Temperature Range	Tstg	-65~200	°C

DC Characteristics

Parameter	Symbol	Min	Typ	Max	Unit
Collector Cutoff Current (VCB=140V)	ICBO	–	–	1	mA
Emitter Cutoff Current (VEB=4V)	IEBO	–	–	1	mA
DC Current Gain (IC=10A, VCE=10V)	hFE	20	60	140	–
Collector-Emitter Saturation Voltage	VCE(sat)	–	0.5	1.5	V
Base-Emitter On Voltage (IC=10A, VCE=10V)	VBE(on)	–	1.2	1.6	V

AC Characteristics

Parameter	Symbol	Min	Typ	Max	Unit
Transition Frequency (IC=2A, VCE=10V)	fT	–	150	–	MHz
Collector Capacitance (VCB=10V, f=1MHz)	Cob	–	280	420	pF
Collector-Emitter Capacitance (VCE=10V, f=1MHz)	Ccs	–	120	–	pF
Turn-On Time (IC=10A, VCC=50V, IB1=1A)	ton	–	0.2	1.0	μs
Turn-Off Time (IC=10A, VCC=50V, IB1=IB2=1A)	toff	–	1.2	2.5	μs

Applications

The 2SC2879 transistor finds use in a variety of high-power, high-frequency applications, such as:

1. RF Power Amplifiers

The primary application of the 2SC2879 is in RF power amplifier circuits. Its high gain, high power output, and wide frequency range make it an excellent choice for designing power amplifiers for radio transmitters, cellular base stations, and other wireless communication systems.

Common RF Power Amplifier Configurations

Class A: Class A amplifiers offer the highest linearity but lowest efficiency. The 2SC2879 can be used in Class A mode for applications requiring extremely low distortion.
Class AB: Class AB amplifiers provide a balance between linearity and efficiency. The 2SC2879 is commonly used in Class AB mode for applications that demand both good signal quality and reasonable power efficiency.
Class C: Class C amplifiers prioritize efficiency over linearity. The 2SC2879 can be used in Class C mode for applications where power efficiency is the primary concern, such as in high-power pulsed radar systems.

2. Wireless Communication Systems

The 2SC2879’s high-frequency capabilities make it suitable for use in various wireless communication systems, including:

Cellular base stations
Two-way radios
Wireless data links
Satellite communication systems

In these applications, the 2SC2879 is typically used as the final power amplifier stage, providing the necessary power to drive the antenna and ensure reliable communication over long distances.

3. Industrial and Scientific Equipment

The 2SC2879 can also be found in high-power industrial and scientific equipment, such as:

RF heating systems
Plasma generators
Particle accelerators
Medical imaging devices

In these applications, the 2SC2879’s high power output and rugged construction make it well-suited for demanding operating conditions and high-reliability requirements.

Designing with the 2SC2879

When designing circuits using the 2SC2879 transistor, there are several key considerations to keep in mind:

1. Biasing

Proper biasing is essential for optimal performance and longevity of the 2SC2879. The transistor should be biased according to the desired operating mode (Class A, AB, or C) and the specific requirements of the application. Key biasing parameters include:

Quiescent collector current (ICQ)
Base-emitter voltage (VBE)
Collector-emitter voltage (VCE)

Example Biasing Circuit

Here is a simple example of a biasing circuit for the 2SC2879 in Class AB mode:

           +Vcc
            |
            |
           +-+
           | |
           | |  R1
           | |
           +-+
            |
            +-----+------+
                  |      |
                  |     +-+
                  |     | |
                  |     | |  R2
                  |     | |
                  |     +-+
                  |      |
                  +------+
                         |
                        +-+
                        |B|
                  +-----|>|-----+
                  |     |E|     |
                  |     +-+     |
                  |      |      |
                  |      |      |
                  |     +-+     |
                  |     |C|     |
                  +-----|>|-----+
                        +-+
                         |
                         |
                        +-+
                        | |
                        | |  RL
                        | |
                        +-+
                         |
                         |
                        ===
                         -

In this circuit, R1 and R2 form a voltage divider that sets the base voltage and determines the quiescent collector current. The values of R1 and R2 should be chosen based on the desired ICQ and the supply voltage (Vcc). RL represents the load impedance, which is typically a resonant tank circuit in RF applications.

2. Impedance Matching

Proper impedance matching is critical for maximizing power transfer and minimizing signal reflections in RF circuits. The input and output impedances of the 2SC2879 must be matched to the source and load impedances, respectively, using appropriate matching networks.

Common Impedance Matching Techniques

L-network: A simple matching network consisting of a series inductor and a shunt capacitor. L-networks are easy to design and implement but have limited bandwidth.
Pi-network: A more complex matching network consisting of two shunt capacitors and a series inductor. Pi-networks offer wider bandwidth than L-networks but are more difficult to design.
Transformer matching: Uses a transformer to match impedances. Transformer matching is useful for achieving wide bandwidth and isolating DC voltages but can be bulky and expensive.

3. Heat Dissipation

Given the high power dissipation of the 2SC2879, proper heat management is essential for reliable operation and long-term reliability. The transistor should be mounted on a suitable heatsink, and adequate airflow should be provided to ensure efficient heat dissipation.

Thermal Resistance

The thermal resistance of the 2SC2879 is a key parameter that determines the temperature rise of the transistor for a given power dissipation. The thermal resistance from junction to case (Rth(j-c)) is typically around 0.5 °C/W. The thermal resistance from case to heatsink (Rth(c-h)) depends on the Mounting Method and the quality of the thermal interface material used.

To calculate the required heatsink thermal resistance (Rth(h-a)), use the following formula:

Rth(h-a) = (Tj(max) - Ta) / Pd - Rth(j-c) - Rth(c-h)

Where:
– Tj(max) is the maximum allowed junction temperature (200 °C for the 2SC2879)
– Ta is the ambient temperature
– Pd is the power dissipation of the transistor
– Rth(j-c) is the junction-to-case thermal resistance
– Rth(c-h) is the case-to-heatsink thermal resistance

Handling and Safety Precautions

When working with the 2SC2879 transistor, it is important to follow proper handling and safety precautions to avoid damage to the device and ensure personal safety:

ESD Protection: The 2SC2879 is sensitive to electrostatic discharge (ESD). Always handle the transistor using appropriate ESD protection measures, such as wearing a grounded wrist strap and working on an ESD-safe mat.
Lead Forming: If lead forming is required, use a proper lead forming tool and avoid applying excessive stress to the leads. Improper lead forming can cause damage to the transistor package and affect device performance.
Soldering: When soldering the 2SC2879, use a temperature-controlled soldering iron and avoid applying excessive heat. Follow the recommended soldering temperature and time profiles to prevent damage to the device.
High Voltages: The 2SC2879 is designed to handle high voltages. Always exercise caution when working with high-voltage circuits, and ensure proper insulation and safety measures are in place to prevent electrical shock.
RF Energy: High-power RF circuits can generate significant levels of electromagnetic radiation. Follow proper RF safety guidelines, such as using shielded enclosures and avoiding exposure to high-intensity RF fields.

2SC2879 vs. Other RF Power Transistors

When selecting an RF power transistor for a specific application, it is important to compare the performance and characteristics of the 2SC2879 with other available options. Some common alternatives to the 2SC2879 include:

2SC2782: A lower-power version of the 2SC2879, with a maximum power dissipation of 150 W.
MRF454: A popular RF power transistor from Microsemi, with similar power and frequency capabilities to the 2SC2879.
BLF188XR: A high-power LDMOS transistor from Ampleon, offering higher efficiency and gain compared to bipolar transistors like the 2SC2879.

When comparing RF power transistors, consider factors such as:

Power output and gain
Frequency range
Efficiency
Linearity
Cost and availability
Package type and thermal characteristics

FAQ

1. What is the maximum power output of the 2SC2879?

The 2SC2879 is capable of delivering up to 150 watts of power under optimal conditions.

2. What is the frequency range of the 2SC2879?

The 2SC2879 can operate effectively in frequencies ranging from 30 MHz to 500 MHz.

3. What is the typical gain of the 2SC2879?

The 2SC2879 offers a high gain, typically around 10 dB.

4. How do I properly bias the 2SC2879 for Class AB operation?

To bias the 2SC2879 for Class AB operation, use a voltage divider network to set the base voltage and quiescent collector current. The specific values of the Biasing Resistors depend on the desired operating point and supply voltage.

5. What safety precautions should I take when working with the 2SC2879?

When working with the 2SC2879, always use proper ESD protection measures, handle the device with care to avoid mechanical damage, and follow proper high-voltage and RF safety guidelines to ensure personal safety and prevent damage to the transistor.

Conclusion

The 2SC2879 is a high-performance RF power transistor that offers an excellent combination of high power output, wide frequency range, and high gain. Its rugged construction and reliable performance make it a popular choice for a variety of high-power, high-frequency applications, including RF power amplifiers, wireless communication systems, and industrial and scientific equipment.

When designing with the 2SC2879, careful consideration must be given to biasing, impedance matching, and thermal management to ensure optimal performance and long-term reliability. Additionally, proper handling and safety precautions are essential to prevent damage to the device and ensure personal safety.

By understanding the characteristics, applications, and design considerations of the 2SC2879, engineers can effectively leverage this powerful transistor to create high-performance RF systems that meet the demands of today’s wireless world.