RL4508-25-110-50-PTF

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PTC Resettable Fuses, such as the RL4508-25-110-50-PTF, have the capability to both protect circuits from over-currents and be reset after overload has been removed. A PTC fuse required no manual resetting - after it trips, current will not resume until the excess heat has dissipated. PTC Resettable Fuses simulate the behavior of a circuit breaker in that a short circuit or overload will cause a current interruption that does not require manual resetting.

The RL4508-25-110-50-PFT, like most PTC Resettable Fuses, have a simple three-part design. The first part is a molded thermoplastic housing. This housing contains the other two internal components, a positive temperature coefficient (PTC) thermistor and a resistor. The thermistor and resistor are wired in parallel, and the overall operation determined by the temperature of the PTC thermistor.

The PTC thermistor will only allow current to flow through the fuse at temperatures below its rated value. This means that as the current passes through the PTC in-line fuse, heat is generated, which in-turn raises the temperature of the PTC device resulting in an increase in its resistance. This further reduces the current passing through it until it attains the system and hold current.

While the PTC thermistor’s resistance is increasing, the resistor also has an effect which further limits the current passing through the fuse. When the current passing the fuse meets the fault level or ‘hold current’ point, the PTC thermistor’s resistance becomes greater than the resistor and the overall circuit resistance of the fuse can exceed several hundred Ohms. At this point the PTC thermistor ‘cuts off’ the current flow to the system.

Once the overload has been removed, by disconnecting the load, the PTC thermistor cools down quickly as the heat energy is dissipated. As it cools, the PTC thermistor’s resistance decreases and the current flow between the fuse terminals resumes.

This application of the RL4508-25-110-50-PF provides protection against damaging over-currents and shorts for higher power applications. The advantage of the PTC Resettable Fuses are that it is unaffected by current ripple and over-temperature conditions, meaning that resetting does not occur even if the current is constantly cycling above and below the hold current.

Overall, the RL4508-25-110-50-PF is an effective PTC Resettable Fuse that provides a cost-efficient and robust way of protecting circuits and can be easily incorporated into the design of higher power systems.

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