How to Use PTC: Examples, Pinouts, and Specs

A Positive Temperature Coefficient (PTC) thermistor is an electronic component that exhibits an increase in electrical resistance as its temperature rises. This characteristic makes it an ideal choice for applications requiring temperature sensing, overcurrent protection, and self-regulating heating elements. PTC thermistors are commonly found in automotive, consumer electronics, and industrial systems.

• Overcurrent protection in power supplies and circuits
• Self-regulating heaters for automotive mirrors or battery packs
• Temperature sensors in rechargeable batteries
• Motor protection to prevent overheating

• Resistance at 25°C (R25): Specified in ohms (Ω), typical values range from a few ohms to several kilo-ohms.
• Operating Temperature Range: The temperature range over which the PTC operates effectively.
• Maximum Voltage Rating: The maximum voltage the PTC can withstand without damage.
• Current Rating: The maximum current the PTC can handle before it starts to limit the current.

Note: PTC thermistors are typically two-terminal devices.

1. Current Limiting: Connect the PTC in series with the load to protect against overcurrent conditions. When the current exceeds a certain threshold, the PTC heats up and its resistance increases, limiting the current flow.

2. Temperature Sensing: Place the PTC in the location where temperature monitoring is required. Connect it to a measurement circuit that can detect changes in resistance.

3. Self-Regulating Heating: Wire the PTC in parallel with a power source. As the PTC heats up, its resistance increases, which limits the current and prevents overheating.

• Precautions: Avoid mechanical stress and ensure proper handling to prevent damage to the PTC.
• Thermal Response: Consider the thermal mass and response time of the PTC in your application.
• Mounting: Ensure good thermal contact if the PTC is used for temperature sensing or heating.
• Circuit Design: Account for the initial resistance and the resistance at the operating temperature when designing your circuit.

• PTC Not Limiting Current: Check if the PTC has reached its switching temperature. Ensure that the current is high enough to cause the PTC to heat up.
• Inaccurate Temperature Sensing: Verify that the PTC is properly mounted and that there is no significant thermal lag.

• Testing PTC: Measure the resistance at room temperature and compare it with the specified R25 value.
• Circuit Analysis: If the PTC is not functioning as expected, review the circuit design for any errors or omissions.

Q: Can a PTC be used for both overcurrent protection and temperature sensing in the same circuit?

A: Yes, but careful circuit design is required to ensure that the PTC's change in resistance due to temperature does not interfere with its current-limiting function, or vice versa.

Q: How do I choose the right PTC for my application?

A: Consider the operating temperature range, the desired resistance at room temperature (R25), the maximum voltage, and the current rating based on your application's requirements.

Q: What happens if a PTC is subjected to a voltage higher than its rating?

A: Exceeding the maximum voltage rating can damage the PTC, potentially causing it to fail in an unsafe manner.

// Example code for interfacing a PTC thermistor with an Arduino UNO for temperature sensing

const int analogPin = A0; // Analog pin where the PTC is connected
const float referenceResistor = 10000; // Reference resistor value in ohms

void setup() {
  Serial.begin(9600);
}

void loop() {
  int sensorValue = analogRead(analogPin); // Read the analog value from the PTC
  float voltage = sensorValue * (5.0 / 1023.0); // Convert to voltage
  float resistance = (5.0 * referenceResistor / voltage) - referenceResistor; // Calculate PTC resistance
  
  // TODO: Convert the resistance to temperature (requires calibration or a datasheet)
  
  Serial.print("PTC Resistance: ");
  Serial.println(resistance);
  
  delay(1000); // Wait for a second before reading again
}

Note: The code above is a simple example of how to read the resistance of a PTC thermistor. To convert the resistance to temperature, you will need to refer to the PTC's datasheet and perform a calibration or use a conversion formula specific to the PTC's characteristics.