How to Use Resettable Fuse PTC: Examples, Pinouts, and Specs

A Resettable Fuse PTC (Positive Temperature Coefficient) is an electronic component designed to provide overcurrent protection in a circuit. Unlike traditional fuses, which must be replaced after a single use, a resettable fuse 'trips' by significantly increasing its resistance when excessive current flows through it, thus limiting further current to a safe level. Once the overcurrent condition ceases, the PTC cools down, its resistance decreases, and it allows normal current flow again. This self-resetting feature makes PTCs ideal for a wide range of applications, including consumer electronics, automotive circuits, and battery packs.

• Voltage Rating: The maximum voltage the PTC can withstand without damage.
• Current Rating: The nominal operating current before the PTC trips.
• Trip Current: The minimum current at which the PTC will trip.
• Time to Trip: The time it takes for the PTC to trip at a specified current.
• Resistance: The typical resistance value during normal operation and post-trip.

Note: The PTC is a two-terminal device, with the current flowing from pin 1 to pin 2.

1. Identify the Correct PTC: Choose a PTC with a voltage rating above the maximum operating voltage and a current rating that matches the typical operating current of your circuit.
2. Circuit Placement: Connect the PTC in series with the load that needs protection.
3. Orientation: PTCs are non-polarized, so they can be connected in either direction.
4. Testing: After installation, test the circuit to ensure the PTC trips at the appropriate current level.

• Selecting PTC Rating: Ensure the trip current of the PTC is slightly above the maximum expected normal current to avoid nuisance tripping.
• Thermal Considerations: Provide adequate space around the PTC for heat dissipation during and after tripping.
• Recovery Time: Allow time for the PTC to cool down and reset after an overcurrent event.
• Multiple PTCs: Do not parallel PTCs to increase the current rating, as they may not trip simultaneously.

• PTC Does Not Reset: Ensure the overcurrent condition has been removed and sufficient time has passed for the PTC to cool.
• Nuisance Tripping: If the PTC trips during normal operation, verify that the selected PTC's current rating matches the circuit's requirements.

• Ensure Proper Ratings: Double-check the PTC's voltage and current ratings according to the application's needs.
• Check Circuit Design: Review the circuit design for any potential sources of unexpected current spikes.

Q: Can a PTC be used multiple times? A: Yes, PTCs are designed to reset themselves after an overcurrent condition is resolved.

Q: How quickly does a PTC reset? A: The reset time can vary based on the severity of the overcurrent condition and the ambient temperature. It typically takes a few seconds to minutes.

Q: Is there any polarity to be considered when installing a PTC? A: No, PTCs are non-polarized and can be installed in either direction.

// Example code to demonstrate the use of a PTC with an Arduino UNO
// The PTC is assumed to be in series with a load connected to a digital pin

const int loadPin = 2; // Digital pin connected to the load

void setup() {
  pinMode(loadPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(loadPin, HIGH); // Turn on the load
  delay(1000); // Keep the load on for 1 second

  // Simulate an overcurrent condition by keeping the load on for too long
  // In a real-world scenario, the PTC would trip and protect the circuit
  delay(5000); // Keep the load on for an additional 5 seconds

  digitalWrite(loadPin, LOW); // Turn off the load
  Serial.println("Load turned off. Waiting for PTC to reset if tripped.");

  // Wait for the PTC to reset before turning the load back on
  delay(10000); // Wait for 10 seconds

  // The load can now safely be turned back on
  Serial.println("Resuming normal operation.");
}

Note: The above code is for demonstration purposes only and does not directly interface with the PTC. The PTC's behavior is simulated through software delays.