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PTC Resettable Fuses: TRF250-110UT application field and working principle

PTC Resettable Fuses (aka polymeric positive temperature coefficient or PTC fuses ) are used in a variety of applications, such as consumer electronics, power supplies, telecommunications, medical devices and more. The TRF250-110UT is a thermistor-based resettable fuse that is designed for use in applications that require a self-resetting, time delay fuse.

Application Field

TRF250-110UT resettable fuse offers overcurrent protection for devices and circuits requiring small current interruption ratings. These fuses can also protect power converters, such as power supplies, batteries, and AC/DC adapters. They provide internal temperature-based current limiting and self-resetting protection with a fast response time. With increasing current levels, the self-heating of the fuse element causes the fuse to open, cutting off the circuit.

The fuse is ideal for protecting LCDs, television sets, car audio systems, and other consumer electronics from overcurrent events. It can also be used to protect small power supplies, such as uninterruptible power supplies, laptop adapters, and consumer power tools. It is also suitable for protecting powered components in electronic toys, robots, and home automation devices.

Working Principle

When an overcurrent sits in the circuit, the internal fuse element of the TRF250-110UT heats up, which causes a resistance change. This results in a rapid internal heating of the fuse elements, combined with a gradual external heating of the ceramic casing. The leverage of the heat delivers a rapid response, reducing the cycle time of the fuse, and thus the dissipated energy is much lower than traditional overcurrent devices.

As the temperature rises, the internal resistance of the fuse element increases. The increased resistance limits the flow of current, thus preventing the device from overheating. This temperature-dependent protection is known as the positive temperature coefficient (PTC). As the fuse element is cooled, the internal resistance drops.

Once the temperature of the device drops, the built-in bimetallic plungers move to their original positions, allowing the circuit to resume normal operation. This resetting process reduces the number of current interruptions, protects downstream components and, ultimately, increases the lifetime of the device. The product also has a built-in alarm that will sound when the fuse is in a tripped state.

Conclusion

The TRF250-110UT is a PTC resettable fuse offering time-delay protection with current-limiting characteristics. It is suitable for protecting power converters, such as power supplies, batteries, and AC/DC adapters. It provides rapid overcurrent protection for a variety of consumer electronics, from LCDs and televisions, to power tools and other powered components in various home automation devices. The device’s self-resetting and temperature-dependent protection make it one of the most reliable overcurrent protection solutions available.

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