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

A Resettable Fuse PTC (Positive Temperature Coefficient) is a protective device designed to safeguard electronic circuits from overcurrent conditions. Unlike traditional fuses, which need to be replaced after tripping, a Resettable Fuse PTC automatically resets itself once the fault condition is removed and the device cools down. This makes it a cost-effective and reusable solution for circuit protection.

• Overcurrent protection in power supplies and battery packs
• Short-circuit protection in consumer electronics
• Automotive electronics to protect wiring and components
• Industrial control systems
• USB ports and peripheral devices

• Operating Voltage Range: Typically 6V to 60V (varies by model)
• Hold Current (I_HOLD): 0.1A to 14A (depending on the specific fuse)
• Trip Current (I_TRIP): 2x to 3x the hold current
• Maximum Voltage: 60V DC (common for most models)
• Resistance (R_MIN to R_MAX): 0.01Ω to 10Ω
• Operating Temperature: -40°C to +85°C
• Reset Time: Varies depending on the fault duration and ambient temperature

Resettable fuses are typically two-terminal devices. Below is a general description of the pins:

1. Placement in the Circuit:

   • Place the Resettable Fuse PTC in series with the load you want to protect.
   • Ensure the fuse is positioned as close as possible to the power source for optimal protection.

2. Selecting the Right Fuse:

   • Choose a fuse with a hold current (I_HOLD) slightly higher than the normal operating current of your circuit.
   • Ensure the trip current (I_TRIP) is below the maximum current rating of your components.

3. Connection:

   • Connect one terminal of the fuse to the power source.
   • Connect the other terminal to the load or circuit you want to protect.

4. Testing:

   • Power on the circuit and verify that the fuse does not trip under normal operating conditions.
   • Simulate an overcurrent condition to ensure the fuse trips and resets as expected.

• Ambient Temperature: The hold and trip currents are affected by the ambient temperature. Higher temperatures may reduce the hold current.
• Voltage Rating: Ensure the operating voltage of your circuit does not exceed the maximum voltage rating of the fuse.
• Reset Time: Allow sufficient time for the fuse to cool down and reset after a fault condition.
• Parallel Connections: Avoid connecting multiple PTC fuses in parallel, as this can lead to uneven current distribution.

Below is an example of how to use a Resettable Fuse PTC to protect an Arduino UNO from overcurrent conditions:

• Connect the PTC fuse in series with the 5V power supply line to the Arduino UNO.

The following code demonstrates how to monitor the Arduino's power status after a fault condition:

// Example code to monitor Arduino power status after a fault condition
// This code assumes an LED is connected to pin 13 to indicate power status.

const int ledPin = 13; // Pin connected to the status LED

void setup() {
  pinMode(ledPin, OUTPUT); // Set the LED pin as an output
  digitalWrite(ledPin, HIGH); // Turn on the LED to indicate normal operation
}

void loop() {
  // Simulate normal operation
  delay(1000); // Wait for 1 second

  // If a fault occurs (e.g., overcurrent), the PTC fuse will trip
  // After the fault is removed, the fuse will reset automatically
  // No additional code is required to handle the reset process
}

1. Fuse Does Not Reset:

   • Cause: The ambient temperature is too high, or the fault condition persists.
   • Solution: Allow the fuse to cool down completely and ensure the fault condition is resolved.

2. Fuse Trips Under Normal Load:

   • Cause: The hold current (I_HOLD) of the fuse is too low for the circuit's operating current.
   • Solution: Replace the fuse with one that has a higher hold current rating.

3. Fuse Does Not Trip During Overcurrent:

   • Cause: The trip current (I_TRIP) is too high for the fault condition.
   • Solution: Use a fuse with a lower trip current rating.

4. Excessive Heat Generation:

   • Cause: The fuse is operating near its maximum current rating for extended periods.
   • Solution: Ensure the circuit's operating current is well below the fuse's hold current.

Q1: Can a Resettable Fuse PTC be used in AC circuits?
A1: Yes, but ensure the fuse is rated for AC operation and the voltage does not exceed its maximum rating.

Q2: How many times can a Resettable Fuse PTC reset?
A2: Resettable fuses can reset hundreds or even thousands of times, depending on the operating conditions and the severity of the faults.

Q3: Can I use a Resettable Fuse PTC to protect a motor?
A3: Yes, but ensure the fuse's hold current is higher than the motor's startup current to avoid nuisance tripping.

Q4: What happens if I connect the fuse backward?
A4: Resettable fuses are non-polarized, so they can be connected in either direction without affecting functionality.