BC107 Transistor: Which Project You Need It For and How to Use It?

Table of Contents

• Introduction to the BC107 Transistor
• Characteristics and Specifications
• BC107 Transistor Pinout
• Common Applications
• Amplifier Circuits
• Switching Circuits
• Oscillator Circuits
• How to Use the BC107 Transistor
• Biasing the Transistor
• Calculating Resistor Values
• Example Circuit: Common Emitter Amplifier
• Tips and Precautions
• Frequently Asked Questions (FAQ)
• Conclusion

Introduction to the BC107 Transistor

The BC107 is a small-signal NPN bipolar junction transistor designed for low-power applications. It is part of the BC107 series, which includes BC107A, BC107B, and BC107C, each with slightly different specifications. The transistor is housed in a TO-18 metal can package and is known for its reliability and good performance in various circuit designs.

Characteristics and Specifications

To effectively use the BC107 transistor in your projects, it is essential to understand its key characteristics and specifications. The following table summarizes the main parameters of the BC107:

Parameter	Value
Collector-Base Voltage (VCBO)	50 V
Collector-Emitter Voltage (VCEO)	45 V
Emitter-Base Voltage (VEBO)	5 V
Collector Current (IC)	100 mA
Power Dissipation (Ptot)	300 mW
Transition Frequency (fT)	300 MHz
Current Gain (hFE)	110-450

These specifications indicate that the BC107 is suitable for low-voltage and low-current applications, with a maximum collector current of 100 mA and a power dissipation of 300 mW. The high transition frequency of 300 MHz makes it useful for high-frequency applications, while the current gain range allows for flexibility in circuit design.

BC107 Transistor Pinout

Understanding the pinout of the BC107 is crucial for proper circuit connections. The transistor has three pins: collector (C), base (B), and emitter (E). The following diagram shows the BC107 pinout:

     _____
    /     \
   /       \
  |   C     |
  |         |
  |  B   E  |
   \_______/

When viewing the transistor from the bottom with the pins facing towards you, the pinout is as follows:
– Left pin: Collector (C)
– Middle pin: Base (B)
– Right pin: Emitter (E)

Common Applications

The BC107 transistor is used in a wide range of electronic projects due to its versatility and reliability. Some common applications include:

Amplifier Circuits

The BC107 is often used in small-signal amplifier circuits, such as:
– Audio amplifiers
– Preamplifiers
– Instrument amplifiers

In these applications, the transistor is used to amplify weak signals to a higher level suitable for further processing or output.

Switching Circuits

The BC107 can also be employed in switching circuits, where it is used to control the flow of current through a load. Examples include:
– Relay drivers
– LED drivers
– Logic gates

In switching applications, the transistor is operated in either saturation or cut-off mode, acting as an electronic switch.

Oscillator Circuits

The high transition frequency of the BC107 makes it suitable for use in oscillator circuits, such as:
– RC oscillators
– LC oscillators
– Crystal oscillators

In these circuits, the transistor is used to generate a periodic signal at a specific frequency determined by the circuit components.

How to Use the BC107 Transistor

To properly use the BC107 transistor in your projects, you need to understand how to bias the transistor and calculate the appropriate resistor values for your specific application.

Biasing the Transistor

Biasing the transistor involves setting the DC operating point to ensure proper operation in the desired region (active, saturation, or cut-off). The most common biasing configuration for the BC107 is the common emitter configuration, where the emitter is connected to ground, and the base and collector voltages are set using resistors.

Calculating Resistor Values

To calculate the resistor values for biasing the BC107, you need to consider the desired collector current (IC), the base current (IB), and the supply voltage (VCC). The following steps outline the process:

1. Determine the required collector current (IC) based on your application.
2. Calculate the base current (IB) using the transistor’s current gain (hFE): IB = IC / hFE.
3. Choose a suitable value for the collector resistor (RC) based on the supply voltage (VCC) and the collector current (IC): RC = (VCC – VCE) / IC, where VCE is the collector-emitter voltage.
4. Calculate the base resistor (RB) value using the base current (IB) and the desired base voltage (VB): RB = (VCC – VB) / IB.

Example Circuit: Common Emitter Amplifier

To illustrate the use of the BC107 transistor, let’s design a simple common emitter amplifier circuit. The circuit will amplify a small input signal using a 9V supply and a gain of approximately 100.

              +9V
               |
              +-+
              | |
              | |  Collector
              | |  Resistor (RC)
              | |
              +-+
               |
               |
               |   BC107
               |   ___
Input ----|--+-|--|___|--+--|   
Signal    |  |   |       |  |
          |  +-+ |_______|  | 
          |    |            |
          |    | Emitter    |
          |    | Resistor   |
          |    | (RE)       |
          |    |            |
          +--||+------------+
             ||      |
            -__-    === Ground
             ||      |
             ||      |
            Ground   |
                     |
                    +-+
                    | | Base
                    | | Resistor (RB)
                    | |
                    +-+
                     |
                    +9V

Let’s choose the following values for our design:
– Collector current (IC): 1 mA
– Collector-emitter voltage (VCE): 5 V
– Current gain (hFE): 200

Step 1: Calculate the base current (IB).
IB = IC / hFE = 1 mA / 200 = 5 µA

Step 2: Calculate the collector resistor (RC) value.
RC = (VCC – VCE) / IC = (9 V – 5 V) / 1 mA = 4 kΩ

Step 3: Choose a suitable base voltage (VB) and calculate the base resistor (RB) value. Let’s set VB to 1 V.
RB = (VCC – VB) / IB = (9 V – 1 V) / 5 µA = 1.6 MΩ

Step 4: Select an emitter resistor (RE) to provide stability and improve linearity. A typical value is 10% of the collector resistor value.
RE = 0.1 × RC = 0.1 × 4 kΩ = 400 Ω

With these component values, the common emitter amplifier using the BC107 transistor will provide a voltage gain of approximately 100, amplifying the input signal accordingly.

Tips and Precautions

When working with the BC107 transistor, keep the following tips and precautions in mind:

1. Always ensure the transistor is properly biased to operate in the desired region (active, saturation, or cut-off).
2. Do not exceed the maximum ratings specified in the transistor’s datasheet to avoid damage.
3. Use appropriate heat sinking when the transistor is required to dissipate significant power.
4. Be mindful of the transistor’s polarity when connecting it in a circuit. Incorrect connections can lead to malfunction or damage.
5. Use coupling capacitors when dealing with AC signals to prevent DC biasing issues.
6. Consider the transistor’s high-frequency limitations when designing high-frequency circuits.

Frequently Asked Questions (FAQ)

1. What is the difference between BC107A, BC107B, and BC107C?

2. The main difference between these variants is their current gain (hFE) range. BC107A has an hFE range of 110-220, BC107B has a range of 200-450, and BC107C has a range of 420-800. Choose the appropriate variant based on your circuit requirements.

3. Can I replace a BC107 with another transistor?

4. In many cases, yes. However, ensure that the replacement transistor has similar or better specifications, such as voltage and current ratings, power dissipation, and pin configuration. Some suitable alternatives include BC108, BC547, and 2N3904.

5. How do I test a BC107 transistor?

6. To test a BC107 transistor, you can use a multimeter to check the continuity between the pins. A functional transistor should show continuity between the base and emitter pins and between the base and collector pins, but no continuity between the collector and emitter pins. You can also perform a gain test using a transistor tester or by setting up a simple test circuit.

7. What is the maximum power dissipation of the BC107 transistor?

8. The maximum power dissipation of the BC107 is 300 mW. This means that the transistor can safely dissipate up to 300 mW of power without damage. However, it’s essential to use proper heat sinking when the transistor is required to dissipate power close to its maximum rating.

9. Can I use a BC107 for high-power applications?

10. No, the BC107 is a small-signal transistor designed for low-power applications. Its maximum collector current is limited to 100 mA, and its power dissipation is only 300 mW. For high-power applications, you should consider using power transistors such as the 2N3055 or TIP31.

Conclusion

The BC107 transistor is a versatile and reliable NPN bipolar junction transistor that finds use in a wide range of electronic projects, including amplifiers, switches, and oscillators. By understanding its characteristics, pinout, and biasing requirements, you can effectively incorporate the BC107 into your circuits and achieve the desired performance. Remember to consider the transistor’s limitations and always adhere to its maximum ratings to ensure reliable operation and prevent damage. With its versatility and ease of use, the BC107 transistor is an excellent choice for hobbyists and professionals alike.