PTC resettable fuse, also known as self-restoring fuse, self-restoring fuse or PPTC fuse, is an electronic protection device. It uses the positive temperature coefficient effect of the material, that is, the property that the resistance value increases significantly with the increase of temperature, to achieve circuit protection.

When the circuit is working normally, the PTC fuse presents a low resistance state, allowing the current to pass through smoothly. If there is an overcurrent situation in the circuit, the PTC component will rapidly heat up due to the heat generated by the current, resulting in a sharp increase in its resistance value of several orders of magnitude and entering a high resistance state, which is equivalent to the "open circuit" in the circuit, thus limiting the current and protecting other sensitive components in the circuit from current damage. When the fault is removed and the current in the circuit returns to normal, the PTC fuse will gradually dissipate heat, the resistance value will be reduced, and the circuit will be returned to the low resistance state, and the circuit will be switched on again, realizing the function of self-recovery without manual replacement.

PTC fuses are usually made of polymer materials containing special conductive fillers, which are structurally designed so that they can quickly change form when overheated, thus changing the resistance value. Because of this self-healing property, PTC fuses are widely used in circuits that require frequent protection or are difficult to maintain, such as power supplies, battery packs, communications equipment, automotive electronic systems, and home appliances.

PTC resettable fuse working principle

PTC resets fuses, which play an important role in circuit protection due to their unique positive temperature coefficient characteristics. In normal operation, PTC fuses present low resistance, allowing current to flow smoothly. Once overcurrent or overtemperature occurs in the circuit, the PTC material heats rapidly, and its resistance increases sharply to a high resistance state, effectively limiting the current and preventing circuit damage. After troubleshooting, as the temperature drops, the PTC material gradually cools and returns to a low resistance state without manual replacement, enabling automatic reset.

PTC resettable Fuse selection Guide

Choosing the right PTC fuse requires a combination of factors. First, determine the holding current (IH), which is the maximum current for long-term stable operation of the fuse. Second, the trip current (IT) must be below the maximum non-fault current that can occur in the circuit to ensure a timely response. The maximum operating voltage is an indicator to ensure the safe operation of the fuse at the specified voltage. In addition, response time is also key, with a fast response helping to provide immediate protection in the event of a momentary overcurrent. Using thermal derating curves, designers can assess and compensate for the impact of different ambient temperatures on fuse performance, resulting in more accurate choices.

Application areas where PTC can reset fuses

PTC resettable fuses play an important role in many fields due to their flexibility and reliability.

In terms of battery protection, it can effectively prevent overcharge and overdischarge, and ensure the safe operation of mobile devices and electric vehicles. In power supply systems, PTC fuses protect circuits from transient current shocks. In automotive electronics, from lighting systems to complex ECU protection, PTC is an indispensable safety component. In household appliances, such as washing machines, air conditioners, etc., PTC ensures the stability of the electrical system and user safety.

The difference between PTC resettable fuses and traditional fuses

The main difference between PTC resettable fuses and conventional fuses (also known as disposable fuses) is their response to overcurrent events and recoverability:

Recoverability: The most significant difference is that PTC fuses have self-recovery characteristics. When overcurrent occurs in the circuit, the PTC fuse will increase resistance due to rising temperature, thus limiting the current and playing a protective role. Once the overload condition is lifted, the PTC fuse automatically cools and returns to a low resistance state, allowing current to flow again without manual replacement. Once the traditional fuse is blown, the internal wire or fragment is opened, the circuit is disconnected, and a new fuse needs to be manually replaced in order to restore the circuit to normal work.

How it works: PTC fuses respond to overcurrent events by taking advantage of the material's temperature coefficient property, which means that the resistance value increases significantly with temperature. Traditional fuses rely on the heat generated by the current passing through the fuse to fuse the internal conductor to achieve the purpose of cutting off the current.

Response speed: PTC fuses are generally slower to respond than conventional fuses because they take time to heat up and change the resistance state. Traditional fuses, on the other hand, respond almost instantly and blow quickly once the current exceeds the rated value.

Cost and Application: Traditional fuses are low cost and suitable for cost-sensitive applications that do not require frequent replacement. Although the initial cost of PTC fuses is higher, due to its resetting characteristics, it reduces maintenance costs and downtime, and is more suitable for those systems that require high reliability and continuous operation, such as communications equipment, medical equipment, automotive electronics, and so on.

Installation and maintenance: The installation of PTC fuses may require consideration of heat dissipation conditions to ensure their effective operation and recovery. Traditional fuses are simpler and the replacement process is direct and fast.

Summary of differences: PTC resettable fuses significantly reduce maintenance costs and downtime compared to disposable fuses. No need for frequent replacement, reducing labor and material costs. In terms of maintenance convenience, the self-resetting capability of the PTC fuse reduces the maintenance effort. Although the initial investment may be high, its long life and low maintenance characteristics make it a more cost-effective option in the long run.

PTC resettable fuse installation and use precautions

Proper installation is the prerequisite for PTC fuses to function. Follow the instructions provided by the manufacturer to ensure that the fuse is in good contact with the circuit board to avoid mechanical stress damage caused by too tight mounting. When designing the circuit, consider the thermal management of the fuse to ensure that there is enough heat dissipation space around. In order to prevent false triggering, reasonable layout to avoid placing PTC fuses near components that are prone to high temperature or electromagnetic interference.

PTC reset fuse troubleshooting and repair

If you encounter a suspected PTC fuse fault, you can follow the following steps to troubleshoot and deal with it:

1. Identify the fault phenomenon: First confirm whether the circuit has overcurrent protection behavior, such as the device suddenly stops working, but there is no obvious burn trace, and automatically returns to normal after a period of time, which may be PTC fuse into a high resistance state.

2. Measure the resistance value: Use the resistance gear of the multimeter to measure the resistance value of the PTC fuse when the circuit is off. Under normal conditions, the resistance value of the PTC fuse should be relatively low. If the resistance value is significantly higher than its nominal resistance to maintain current, this may indicate that the fuse has previously experienced overload and is in a protected state.

3. Check the circuit: Even if the PTC fuse appears to return to normal, it is necessary to check the circuit for persistent overcurrent sources, such as short circuits or component failures. Monitor the current in the circuit with an appropriate tool, such as an ammeter, to ensure that the PTC fuse rating is not exceeded.

4. Environmental factors: Consider whether the ambient temperature is within the working range of the PTC fuse. Extreme temperatures may cause misoperation or performance degradation of the fuse.

5. Heat dissipation: Ensure that the heat dissipation conditions around the PTC fuse are good; overheating may cause it to fail to reset properly.

6. Wait and watch: If the PTC fuse does enter a high resistance state due to overload, disconnect the circuit power supply, give it enough time to cool naturally and attempt an automatic reset. Check the reset time and conditions in the product manual.

7. Replacement considerations: Although PTC fuses are designed to be resetable, their performance can degrade under certain circumstances, such as excessive aging, physical damage, or multiple overloads, at which point a new PTC fuse may need to be considered.

8. Consult specifications and data sheets: For specific PTC fuses, consult their specifications and data sheets for normal operating conditions, maximum current, reset time, and troubleshooting guidelines.

Troubleshooting of PTC returnable fuses is more focused on the overall health of the circuit and external factors, while direct repair of PTC fuses is less focused on identifying and resolving the root cause of its trigger protection.

PTC can reset fuse important performance parameter interpretation

The following is INFINITECH's summary of the key parameters of PTC resettable fuses and their interpretation:

1. Maximum voltage: This refers to the maximum DC or AC voltage that the PTC fuse can withstand without being broken down. Beyond this voltage, the thermistor inside the fuse may be damaged, causing the fuse to lose its self-restoring ability. Therefore, when selecting a PTC fuse, ensure that its maximum voltage is greater than or equal to the highest operating voltage in the circuit.

2. Maximum current: This is the maximum current that the fuse can carry continuously without entering a high resistance state. If the current flowing through the fuse exceeds this value for a long period of time, the fuse will heat up and enter the protected state. When selecting, ensure that the Imax is greater than the normal operating current of the circuit, but lower than the current that may cause overload.

3. Holding current: At this current value, the PTC fuse can work stably for a long time without action, which is the current that the fuse can continue to pass without overheating.

4. Trigger current: also known as break current, refers to the fuse from a low resistance state to a high resistance state, beginning to limit the current of the minimum current value. In general, this value is slightly higher than the maximum operating current, ensuring that the fuse will not misoperate when the normal current fluctuates.

5. Time-current characteristics: describes the relationship between the current and the time required for the fuse to change from a low resistance state to a high resistance state. Different PTC fuses have different response curves, which are related to the sensitivity and reaction speed of the protection.

6. Reset time: refers to the time required for the fuse to return from a high resistance state to a low resistance state and allow the current to pass through again. This depends on the heat capacity of the fuse, the heat dissipation conditions, and the size of the overload current.

7. Resistance value: Rmin is the minimum resistance value in the cold state (not activated); Rmax is the maximum resistance at or after triggering the current; Rtrip is the typical resistance of the fuse at the transition point under triggering current.

8. Temperature range: refers to the temperature range at which the fuse can work without affecting its performance, including operating temperature and storage temperature.

9. Cycle life: refers to the number of times the fuse repeats from low resistance state to high resistance state and back to low resistance state under normal operating conditions. High quality PTC fuses have a cycle life of thousands of times or more.

Market trends and brand choices for PTC resetable fuses

The PTC resetable fuse industry is constantly advancing technological innovations such as wider operating temperature ranges, faster response times and higher pressure levels. Mainstream brands such as Littelfuse, Bourns, Raychem, etc., not only offer a diversified product line, but also continuously develop new materials and designs to meet the new needs of the market. The price trend is affected by technological advances and raw material costs, but the overall trend is steady. For investors, paying attention to technological innovation and market demand dynamics is the key to seize investment opportunities.

PTC can reset fuse common problems and solutions

Frequent fuse trips:

Cause: There is a persistent overcurrent in the circuit, which may be due to a short circuit, component failure, or excessive load.

Solution: Check the circuit, locate and resolve the root cause of the overcurrent, such as repairing the short circuit, replacing the damaged component, or adjusting the load.

Fuse out of place:

Cause: The overload is serious, causing the fuse to be in a high resistance state for a long time, and it cannot be cooled and reset within a reasonable time; Or the fuse reaches the end of its service life.

Solution: Check whether there is still abnormal current in the circuit, ensure that there are good heat dissipation conditions around the fuse, and replace the fuse as needed.

Abnormal resistance value:

Cause: The fuse resistance may deviate from the normal range due to overheating, aging, or physical damage.

Solution: Measure the resistance value of the fuse and compare it with the specification, if not, replace the fuse.

Mismatched rated current:

Reason: The rated current of the fuse does not match the actual circuit requirements, too high or too low will affect the protection effect.

Solution: Recalculate and select the appropriate fuse specifications according to the circuit design to ensure that the rated current is suitable for the application requirements.

Ambient temperature impact:

Cause: The extreme ambient temperature exceeds the working range of the fuse and affects its performance.

Solution: Improve the temperature control of the fuse working environment, or choose a fuse model with a wider temperature range.

Improper installation:

Cause: Improper installation position or poor contact of the fuse, affecting its heat dissipation or electrical performance.

Solution: Install correctly as recommended by the manufacturer to ensure good electrical contact and heat dissipation conditions.

Incorrect model selection:

Reason: The type of fuse that is not suitable for the specific application is selected, such as insufficient pressure rating or inappropriate shape and size.

Solution: According to the specific needs of the circuit, including voltage, current, packaging form, etc., re-select the appropriate fuse model.

When addressing these issues, always refer to the PTC fuse data manual and the manufacturer's guidance recommendations to ensure safe and effective use of the fuse protection circuit.