How to Use 2N7002 SOT23: Examples, Pinouts, and Specs

The 2N7002 is an N-channel MOSFET housed in a compact SOT-23 package. It is widely used in low-power switching applications due to its low on-resistance, fast switching speeds, and ease of integration into circuits. This component is ideal for driving small loads, interfacing with microcontrollers, and general-purpose switching in low-voltage systems.

• Low-power switching circuits
• Signal-level MOSFET for microcontroller interfacing
• DC-DC converters
• Load switching in battery-powered devices
• Logic-level signal amplification

The 2N7002 has three pins, as shown below:

1. Basic Circuit Setup:

   • Connect the Source pin to ground (for low-side switching).
   • Connect the Drain pin to the load, with the other side of the load connected to the positive supply voltage.
   • Apply a voltage to the Gate pin to control the MOSFET. A voltage of 2.5V or higher (logic-level) is typically sufficient to fully turn on the MOSFET.

2. Gate Resistor:

   • Use a resistor (e.g., 10kΩ) between the Gate and ground to ensure the MOSFET remains off when no signal is applied.
   • Optionally, use a small resistor (e.g., 100Ω) in series with the Gate to limit inrush current during switching.

3. Load Considerations:

   • Ensure the load current does not exceed the maximum continuous drain current (200mA).
   • Verify that the voltage across the MOSFET does not exceed the maximum drain-source voltage (60V).

4. Driving with a Microcontroller:

   • The 2N7002 can be directly driven by a 3.3V or 5V logic signal from a microcontroller like an Arduino UNO.

Below is an example of using the 2N7002 to control an LED with an Arduino UNO:

• Source: Connect to GND.
• Drain: Connect to the cathode of the LED. The anode of the LED connects to a current-limiting resistor, which is then connected to +5V.
• Gate: Connect to a digital output pin of the Arduino (e.g., pin 9).

// Define the pin connected to the MOSFET Gate
const int mosfetGatePin = 9;

void setup() {
  pinMode(mosfetGatePin, OUTPUT); // Set the Gate pin as an output
}

void loop() {
  digitalWrite(mosfetGatePin, HIGH); // Turn on the MOSFET (LED ON)
  delay(1000);                       // Wait for 1 second
  digitalWrite(mosfetGatePin, LOW);  // Turn off the MOSFET (LED OFF)
  delay(1000);                       // Wait for 1 second
}

• Thermal Management: Ensure the MOSFET does not overheat by staying within the power dissipation limits.
• Voltage Spikes: Use a flyback diode across inductive loads (e.g., motors) to protect the MOSFET from voltage spikes.
• Gate Drive Voltage: Ensure the Gate voltage is sufficient to fully turn on the MOSFET (logic-level compatible).

1. MOSFET Not Turning On:

   • Verify that the Gate voltage is at least 2.5V (logic-level threshold).
   • Check for a proper connection between the Source pin and ground.

2. Excessive Heat:

   • Ensure the load current does not exceed 200mA.
   • Check for proper heat dissipation and avoid exceeding the power dissipation rating.

3. Load Not Switching Properly:

   • Confirm that the Gate resistor is correctly connected to ground.
   • Verify the polarity and connections of the load.

4. MOSFET Always On:

   • Check for a short circuit between the Gate and Source pins.
   • Ensure the Gate voltage is not floating; use a pull-down resistor.

Q: Can the 2N7002 handle high-power loads?
A: No, the 2N7002 is designed for low-power applications with a maximum continuous current of 200mA. For higher power, consider using a MOSFET with a higher current rating.

Q: Is the 2N7002 compatible with 3.3V logic?
A: Yes, the 2N7002 can be driven by 3.3V logic signals, as its Gate threshold voltage is as low as 1V.

Q: Do I need a heatsink for the 2N7002?
A: In most low-power applications, a heatsink is not required. However, ensure the power dissipation remains within the specified limits.

Q: Can I use the 2N7002 for PWM control?
A: Yes, the 2N7002 is suitable for PWM applications due to its fast switching speed.