How to Use BD135 NPN: Examples, Pinouts, and Specs

The BD135 is a general-purpose NPN bipolar junction transistor (BJT) designed for amplification and switching applications. It is widely used in audio amplifiers, motor drivers, and other medium-power electronic circuits. With a maximum collector current of 1.5A and a maximum collector-emitter voltage of 45V, the BD135 is a versatile and reliable component for various applications.

• Audio signal amplification
• Motor control circuits
• Switching low to medium power loads
• Voltage regulation circuits
• General-purpose amplification in analog circuits

Below are the key technical details of the BD135 transistor:

The BD135 transistor comes in a TO-126 package with three pins. The pin configuration is as follows:

Below is the pinout diagram for the BD135 (front view of the TO-126 package):

   _______
  |       |
  |       |
  |   C   |  Pin 2: Collector
  |   B   |  Pin 3: Base
  |   E   |  Pin 1: Emitter
  |_______|

1. Biasing the Transistor:

   • To use the BD135 as a switch, apply a small current to the base pin (B) to control a larger current between the collector (C) and emitter (E).
   • For amplification, ensure the transistor is properly biased in the active region.

2. Base Resistor:

   • Always use a base resistor to limit the current flowing into the base pin. The value of the resistor can be calculated using Ohm's law: [ R_b = \frac{V_{in} - V_{be}}{I_b} ] where ( V_{in} ) is the input voltage, ( V_{be} ) is the base-emitter voltage (typically 0.7V for the BD135), and ( I_b ) is the desired base current.

3. Heat Dissipation:

   • The BD135 can dissipate up to 12.5W of power. If operating near this limit, attach a heatsink to prevent overheating.

4. Connection Example:

   • Below is an example of using the BD135 to drive a motor:

+12V ---- Motor ---- Collector (C)
                  |
                  |
                 Emitter (E) ---- GND
                  |
                  |
                 Base (B) ---- Resistor ---- Microcontroller Pin

The following code demonstrates how to use the BD135 to control a motor with an Arduino UNO:

// Define the pin connected to the BD135 base
const int transistorBasePin = 9;

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

void loop() {
  // Turn the motor ON by sending a HIGH signal to the transistor base
  digitalWrite(transistorBasePin, HIGH);
  delay(2000); // Keep the motor ON for 2 seconds

  // Turn the motor OFF by sending a LOW signal to the transistor base
  digitalWrite(transistorBasePin, LOW);
  delay(2000); // Keep the motor OFF for 2 seconds
}

Note: Ensure the base resistor is properly calculated to limit the current from the Arduino pin to the BD135 base.

• Voltage and Current Limits: Do not exceed the maximum voltage (45V) or current (1.5A) ratings to avoid damaging the transistor.
• Heat Management: Use a heatsink if the transistor operates at high power levels.
• Base Resistor: Always include a base resistor to prevent excessive current from damaging the transistor or the control circuit.

1. Transistor Overheating:

   • Cause: Operating near the maximum power dissipation without a heatsink.
   • Solution: Attach a heatsink to the BD135 to improve heat dissipation.

2. No Output Current:

   • Cause: Insufficient base current or missing base resistor.
   • Solution: Verify the base resistor value and ensure the base current is sufficient to drive the load.

3. Low Amplification:

   • Cause: Incorrect biasing or low DC current gain (hFE).
   • Solution: Check the biasing circuit and ensure the transistor is operating in the active region.

4. Transistor Not Switching Properly:

   • Cause: Base current too low or incorrect connections.
   • Solution: Verify the circuit connections and increase the base current if necessary.

Q1: Can the BD135 be used for high-frequency applications?
A1: Yes, the BD135 has a transition frequency (( f_T )) of 190 MHz, making it suitable for some high-frequency applications.

Q2: What is the difference between the BD135 and BD139?
A2: The BD139 is a higher-power variant of the BD135, with similar characteristics but a higher maximum collector-emitter voltage (80V).

Q3: Can I use the BD135 without a heatsink?
A3: Yes, but only if the power dissipation is well below 12.5W. For higher power levels, a heatsink is recommended.

Q4: What is the typical base-emitter voltage (( V_{be} )) of the BD135?
A4: The typical ( V_{be} ) is around 0.7V when the transistor is conducting.