2N3771 Transistor Pinout

The 2N3771 transistor has a TO-3 metal package with 2 leads:

Pin	Symbol	Description
1	B	Base
2	E	Emitter
Case	C	Collector

The case/tab of the TO-3 package is connected internally to the collector. Proper heatsinking of the case is essential for managing the thermal dissipation in high power applications.

Key Features of the 2N3771

Some of the notable features and maximum ratings of the 2N3771 power transistor include:

• NPN polarity
• High DC current gain (hFE): 15-60 at 15A
• Maximum collector current (IC): 30A
• Maximum collector-emitter voltage (VCEO): 40V
• Maximum collector-base voltage (VCBO): 80V
• Maximum emitter-base voltage (VEBO): 7V
• Maximum power dissipation (PD): 150W
• Transition frequency (fT): 2.5 MHz
• Operating junction temperature range (Tj): -65°C to +200°C

These specs make the 2N3771 suitable for demanding applications that require high current handling capability, moderate voltage blocking capacity, and excellent power dissipation. The high current gain allows the transistor to be driven into saturation with a relatively small base current.

Typical Applications

Audio Power Amplifiers

One of the most common applications of the 2N3771 is in the output stages of high power audio amplifiers. It can deliver tens of amps of current to drive low impedance speaker loads. Usually, multiple 2N3771 transistors are used in a push-pull Class AB configuration with complementary PNP power transistors like the 2N3772. Proper biasing, driver staging, and protection circuitry are essential.

Linear Power Supplies

The 2N3771 is also popularly used as a pass transistor in linear voltage regulator and power supply circuits. It can handle the high currents and power dissipation required to maintain a constant output voltage under varying load conditions. The transistor is driven by an op-amp or dedicated regulator IC that monitors the output voltage and adjusts the base current accordingly.

Motor Drivers

With its high current capability, the 2N3771 can also serve as a switching transistor in motor driver circuits. It can rapidly switch on and off to control the current flow through DC motors, stepper motors, solenoids, etc. Flyback diodes are necessary to suppress the voltage spikes during switching transients. PWM techniques are used to regulate speed or torque.

Other Applications

There are many other potential uses for the 2N3771 transistor, such as:

• Battery chargers
• Power inverters
• Welding equipment
• Laser/LED drivers
• Relay/valve controllers
• etc.

Essentially, any application that demands controlling high load currents at moderate voltages can utilize the 2N3771, with proper circuit design and thermal management.

2N3771 Alternatives

While the 2N3771 is a popular and versatile power transistor, there are some alternatives available that may be better suited for certain applications or design constraints. Here are a few examples:

TIP35C

The TIP35C is another NPN power transistor that comes in the TO-247 package. It has a higher maximum collector current rating of 25A and a higher maximum collector-emitter voltage rating of 100V compared to the 2N3771. However, its current gain and power dissipation ratings are lower.

MJL21194

The MJL21194 is a high-performance audio power transistor in the TO-264 package. It is specifically optimized for better linearity, noise, and SOA compared to general-purpose types like the 2N3771. It has a maximum collector current of 16A, a maximum collector-emitter voltage of 250V, and a power dissipation of 250W.

TIP3055

For lower power applications, the TIP3055 is a popular choice in the TO-218 package. It has a maximum collector current of 15A and a maximum collector-emitter voltage of 60V. The TIP3055 is widely used in low-cost audio amplifiers, power supplies, and general-purpose switching circuits.

MJW21194

The MJW21194 is the complementary PNP transistor to the MJL21194, suitable for audio push-pull output stages. It has similar power and frequency characteristics optimized for low distortion.

The choice of transistor depends on the specific requirements of voltage, current, power, linearity, frequency, cost, and availability for the target application. Verify the datasheets for accurate specifications.

Frequently Asked Questions (FAQ)

1. What is the maximum power dissipation of the 2N3771 transistor?

The 2N3771 has a maximum power dissipation rating of 150W. However, this is only achievable with proper heatsinking to maintain the junction temperature within the safe operating area (SOA). The actual power handling in a given application depends on factors like ambient temperature, thermal resistance, and duty cycle.

2. Can the 2N3771 be used for high-frequency applications?

The 2N3771 has a relatively low transition frequency (fT) of 2.5 MHz, which limits its usefulness in high-frequency applications like RF power amplifiers or switch-mode power supplies. For those applications, transistors with higher fT and better switching characteristics, like RF MOSFETs or IGBTs, are more suitable.

3. How do you properly heatsink a 2N3771 transistor?

Proper heatsinking is crucial for maintaining the 2N3771 within its safe operating temperature range and preventing thermal runaway. The transistor should be securely mounted to a heatsink using thermal grease or a thermally conductive pad to minimize the thermal resistance at the interface. The heatsink size and type depend on the specific power dissipation and ambient conditions in the application. Forced air cooling or other thermal management techniques may be necessary for very high power levels.

4. What are the typical causes of failure for the 2N3771?

Some common causes of failure for the 2N3771 include:

• Exceeding the maximum voltage, current, or power ratings
• Inadequate heatsinking or thermal runaway
• Reverse biasing the base-emitter junction
• Overdriving the base current and entering deep saturation
• Rapid switching transients that cause avalanche breakdown
• Mechanical stress or damage to the package

Following good design practices, using proper drive circuitry, and providing adequate protection and thermal management can help mitigate these failure modes.

5. Can the 2N3771 be replaced with a MOSFET for better performance?

In some applications, replacing the 2N3771 bipolar transistor with a suitable power MOSFET may offer benefits such as:

• Lower drive current requirements
• Faster switching speeds
• Higher efficiency
• Simpler drive circuitry
• No thermal runaway

However, MOSFETs also have some drawbacks like higher cost, susceptibility to ESD and gate oxide breakdown, and nonlinear transfer characteristics. The best choice depends on the specific performance, cost, and reliability targets for the end application.

In summary, the 2N3771 is a popular and versatile power transistor for high current, low to moderate voltage applications. Understanding its characteristics, proper usage, and potential alternatives can help designers make the optimal choice for their specific needs.