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
• Protection of USB ports and peripheral devices
• Safeguarding motor drives and industrial equipment
• Use in telecommunications and networking devices
• Circuit protection in consumer electronics, such as laptops and chargers

• Operating Voltage Range: Typically 6V to 60V (varies by model)
• Hold Current (I_H): 0.1A to 14A (depending on the specific fuse)
• Trip Current (I_T): 2x to 3x the hold current
• Maximum Voltage (V_MAX): 60V (varies by model)
• Resistance (R_MIN to R_MAX): 0.01Ω to 10Ω
• Trip Time: Milliseconds to seconds, depending on the overcurrent level
• Reset Time: Typically a few seconds to minutes after fault removal
• Operating Temperature: -40°C to +85°C

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 or circuit you want to protect.
   • Ensure that the fuse is positioned between the power source and the load.

2. Selecting the Right Fuse:

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

3. Soldering and Mounting:

   • For through-hole fuses, solder the terminals to the PCB pads.
   • For surface-mount fuses, use appropriate reflow soldering techniques.

4. Testing the Circuit:

   • 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.

• Thermal Management: Avoid placing the fuse near heat-generating components, as excessive ambient heat can affect its performance.
• Voltage Rating: Ensure the operating voltage of your circuit does not exceed the fuse's maximum voltage rating.
• 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 uneven current sharing can lead to improper operation.

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

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

// Example code to demonstrate normal operation of an Arduino UNO
// protected by a Resettable Fuse PTC in the power supply line.

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

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

// If an overcurrent condition occurs, the Resettable Fuse PTC will trip,
// cutting off power to the Arduino. Once the fault is cleared, the fuse
// will reset, and the Arduino will resume normal operation.

1. Fuse Trips Under Normal Load:

   • Cause: The hold current (I_H) 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.

2. Fuse Does Not Trip During Overcurrent:

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

3. Fuse Does Not Reset After Fault Removal:

   • Cause: The fuse has not cooled down sufficiently or is damaged.
   • Solution: Allow more time for the fuse to cool. If the issue persists, replace the fuse.

4. Excessive Heat Around the Fuse:

   • Cause: Poor thermal management or high ambient temperature.
   • Solution: Improve ventilation or relocate the fuse away from heat sources.

• Q: Can a Resettable Fuse PTC be used in AC circuits?
  A: Yes, but ensure the fuse's voltage and current ratings are suitable for AC operation.

• Q: How many times can a Resettable Fuse PTC trip and reset?
  A: Most PTC fuses can reset hundreds to thousands of times, depending on the operating conditions.

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

• Q: What happens if I exceed the fuse's maximum voltage rating?
  A: Exceeding the voltage rating can cause the fuse to fail permanently or result in unsafe operation.

By following this documentation, you can effectively integrate a Resettable Fuse PTC into your electronic designs for reliable overcurrent protection.