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

A Resettable Fuse PTC (Positive Temperature Coefficient) is a protective electronic component designed to limit the flow of excessive current in a circuit. Unlike traditional fuses, which must be replaced after a single use, a PTC fuse automatically resets after the overcurrent condition has been cleared and the unit cools down. This makes them ideal for a wide range of applications where overcurrent protection is necessary but manual resetting or replacement of fuses is impractical or undesirable.

• Overcurrent protection in consumer electronics (e.g., smartphones, laptops)
• Protection for battery packs and chargers
• Automotive electronics
• Power supplies
• Medical devices

• Voltage Rating: The maximum voltage the PTC can withstand without damage.
• Current Rating: The nominal operating current before the PTC trips.
• Trip Current: The current at which the PTC will trip and increase its resistance.
• Maximum Interrupt Current: The maximum fault current the PTC can withstand without damage.
• Time to Trip: The time it takes for the PTC to trip at a specified multiple of its rated current.
• Resistance: The initial resistance of the PTC before tripping and the resistance after tripping.

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

1. Identify the Correct PTC: Select a PTC with a voltage rating above the maximum circuit voltage and a current rating that matches the normal operating current of the circuit.
2. Circuit Placement: Place the PTC in series with the load that needs protection.
3. Soldering: Solder the PTC to the PCB with care to avoid excessive heat, which could trip the PTC prematurely.

• Selecting PTC: Ensure the trip current of the PTC is above the normal operating current but below the current that could damage the circuit.
• Thermal Considerations: Be aware of the thermal environment as PTCs can trip due to ambient temperature increases.
• Recovery Time: After tripping, allow time for the PTC to cool down and reset before resuming normal operation.
• Testing: Test the PTC in the actual circuit to ensure it trips at the appropriate current levels.

• PTC Does Not Reset: If the PTC does not reset after tripping, check if the overcurrent condition still exists or if the ambient temperature is too high.
• Nuisance Tripping: If the PTC trips during normal operation, it may be incorrectly specified. Check the trip current and ambient temperature conditions.

• Persistent Overcurrent: Investigate the circuit for faults or short circuits that may cause continuous overcurrent conditions.
• Ambient Temperature: Ensure the PTC is operating within its specified temperature range.
• Proper Sizing: Verify that the PTC is correctly sized for both the operating current and the maximum fault current of the circuit.

Q: Can a PTC be used multiple times? A: Yes, a PTC is designed to reset itself after cooling down, allowing for multiple uses.

Q: How quickly does a PTC reset? A: The reset time can vary based on the PTC's design and the severity of the overcurrent condition. It can range from a few seconds to several minutes.

Q: Is a PTC the same as a thermistor? A: While both PTCs and thermistors have temperature-dependent resistance, a PTC is specifically designed to protect against overcurrent, while thermistors are generally used for temperature sensing.

Q: Can I use a PTC with an Arduino UNO? A: Yes, a PTC can be used in circuits involving an Arduino UNO for overcurrent protection.

// Example code to demonstrate the use of a PTC with an Arduino UNO
// This code does not directly interact with the PTC but shows a typical setup.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT); // Set the built-in LED as an output
}

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

// Note: The PTC would be placed in series with the LED or other components
// to protect against overcurrent. The code itself does not control the PTC.

Remember to keep the PTC's specifications in mind when designing circuits with the Arduino UNO to ensure proper protection.