How to Use BC547 Transistor: Examples, Pinouts, and Specs

The BC547 is a general-purpose NPN bipolar junction transistor (BJT) widely used in low-power amplification and switching applications. It is a reliable and versatile component, making it a popular choice for hobbyists and professionals alike. With a maximum collector current of 100 mA and a voltage rating of 45 V, the BC547 is suitable for a variety of electronic circuits, including signal amplification, small motor control, and digital switching.

• Signal amplification in audio and RF circuits
• Switching small loads such as LEDs or relays
• Oscillator circuits
• Voltage regulation and current limiting
• General-purpose low-power applications

Below are the key technical details of the BC547 transistor:

The BC547 transistor comes in a TO-92 package with three pins. The pinout is as follows:

The pinout diagram for the BC547 (TO-92 package) is shown below:

   _______
  |       |
  |       |
  |_______|
   | | |
   1 2 3
   C B E

1. Determine the Configuration: The BC547 can be used in three configurations:

   • Common Emitter: For amplification and switching.
   • Common Base: For high-frequency applications.
   • Common Collector: For impedance matching.

2. Biasing the Transistor:

   • To operate the BC547 in the active region (for amplification), apply a small current to the base pin. Ensure the base-emitter voltage (Vbe) is approximately 0.7 V.
   • For switching applications, drive the base pin with sufficient current to saturate the transistor.

3. Connect the Load:

   • For switching, connect the load (e.g., LED, relay) to the collector pin.
   • Use a current-limiting resistor in series with the base pin to prevent damage.

4. Calculate Resistor Values:

   • Base Resistor (Rb): Use Ohm's law to calculate the resistor value based on the input voltage and required base current.
   • Example: If the input voltage is 5 V and the base current is 5 mA, Rb = (5 V - 0.7 V) / 5 mA = 860 Ω.

The BC547 can be used to control an LED with an Arduino UNO. Below is an example circuit and code:

• The base of the BC547 is connected to a digital pin of the Arduino through a 1 kΩ resistor.
• The collector is connected to the positive terminal of the LED.
• The emitter is connected to ground.
• A 220 Ω resistor is connected in series with the LED to limit current.

// Define the pin connected to the BC547 base
const int transistorBasePin = 9; // Digital pin 9

void setup() {
  pinMode(transistorBasePin, OUTPUT); // Set pin as output
}

void loop() {
  digitalWrite(transistorBasePin, HIGH); // Turn on the transistor
  delay(1000); // Keep the LED on for 1 second
  digitalWrite(transistorBasePin, LOW);  // Turn off the transistor
  delay(1000); // Keep the LED off for 1 second
}

• Do not exceed the maximum ratings for voltage, current, or power dissipation.
• Always use a base resistor to limit the base current.
• Ensure proper heat dissipation if the transistor operates near its maximum power rating.

1. Transistor Not Switching Properly:

   • Cause: Insufficient base current.
   • Solution: Check the base resistor value and ensure the base current is adequate.

2. Overheating:

   • Cause: Exceeding the power dissipation limit.
   • Solution: Reduce the load current or use a heat sink.

3. No Output Signal:

   • Cause: Incorrect pin connections.
   • Solution: Verify the pinout and ensure proper wiring.

4. LED Not Lighting Up in Example Circuit:

   • Cause: Incorrect resistor values or damaged components.
   • Solution: Double-check the resistor values and test the LED and transistor.

Q1: Can the BC547 handle high-power loads?
A1: No, the BC547 is designed for low-power applications with a maximum collector current of 100 mA. For high-power loads, consider using a power transistor like the TIP120.

Q2: What is the difference between BC547A, BC547B, and BC547C?
A2: The difference lies in their DC current gain (hFE) range:

• BC547A: 110 to 220
• BC547B: 200 to 450
• BC547C: 420 to 800

Q3: Can I use the BC547 for audio amplification?
A3: Yes, the BC547 is suitable for small-signal audio amplification.

Q4: What is the maximum frequency the BC547 can handle?
A4: The BC547 has a transition frequency (ft) of 150 MHz, making it suitable for high-frequency applications within this range.