Content

• Introduction
• How Does a PTC Resettable Fuse Work?
• Applications of PTC Resettable Fuses
• Types of PTC Resettable Fuses

Introduction

In modern electronics, circuit protection is crucial to prevent damage from overcurrent conditions. One of the most reliable solutions is the PTC (Positive Temperature Coefficient) resettable fuse, which provides self-resetting overcurrent protection. Unlike traditional fuses that need replacement after tripping, PTC fuses automatically reset when the fault is removed.

This blog explores the working principle, applications, types, and best practices for using PTC resettable fuses in electronic circuits.

1. How Does a PTC Resettable Fuse Work?

A PTC resettable fuse is a thermistor (temperature-sensitive resistor) made from a conductive polymer. Its resistance increases dramatically when exposed to excessive current or high temperatures.

Working Principle:

• Normal Operation:

  • Under normal conditions, the PTC fuse has a low resistance, allowing current to flow freely.

• Overcurrent or Overheat Condition:

  • When excessive current passes through, the fuse heats up due to I²R heating.

  • As temperature rises, the polymer expands, disrupting conductive pathways and increasing resistance (known as “tripping”).

  • This high-resistance state limits current flow, protecting the circuit.

• Reset Mechanism:

  • Once the fault is removed and power is cycled, the PTC cools down and returns to low resistance, allowing normal operation again.

2. Applications of PTC Resettable Fuses

PTC fuses are widely used in consumer electronics, automotive systems, industrial controls, and power supplies where self-resetting protection is needed. Common applications include:

• USB Ports & Chargers – Protects against short circuits and overloads.

• Battery Packs (Li-ion, NiMH, etc.) – Prevents overcurrent damage.

• PCBs & Motherboards – Safeguards sensitive ICs and components.

• Automotive Electronics – Used in ECUs, infotainment systems, and lighting circuits.

• Power Supplies & Converters – Prevents damage from inrush currents.

3. Types of PTC Resettable Fuses

PTC fuses come in different forms based on voltage rating, current rating, and package type:

High-Voltage PTCs

Battery Strap PTCs

Surface-Mount (SMD)

Radial-Lead (Through-Hole)

4. How to Use a PTC Resettable Fuse?

Selection Criteria:

1. Hold Current (IH) – The maximum current the fuse can handle without tripping.

2. Trip Current (IT) – The current at which the PTC will trip (usually 2x IH).

3. Voltage Rating – Must exceed the circuit’s maximum voltage.

4. Operating Temperature – Ensures reliability in different environments.

Installation Tips:

• Place the PTC fuse in series with the load.

• Avoid placing near heat-sensitive components (since PTCs heat up when tripped).

• Ensure proper PCB trace width to handle tripped-state resistance.

Testing & Troubleshooting:

• If a circuit stops working, check if the PTC has tripped (measure resistance).

• If the PTC does not reset, it may be damaged and require replacement.

Conclusion

PTC resettable fuses provide reliable, self-recovering overcurrent protection, making them ideal for modern electronics. By understanding their working principle, types, and correct usage, engineers and hobbyists can enhance circuit safety without frequent fuse replacements.

For your next project, consider integrating a PTC fuse to protect your circuits intelligently!

Have you used PTC fuses in your designs? Share your experience in the comments! 🚀