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PTC Resettable Fuses: RUEF400K-AP application field and working principle

PTC resettable fuses, also known as polymeric positive temperature coefficient (PPTC), are variable resistance devices which are self-resetting, overcurrent protection components. The RUEF400K-AP is a bi-directional PPTC device produced by Raychem that can be used in applications that include consumer electronics, computers and peripherals, telecommunications and many others. It is designed to reset after the overcurrent is removed, thus providing an easy, and safe alternative to a traditional fuse or circuit breaker.

Application Field

In many applications, the advantages of the RUEF400K-AP are highly desirable, as the device can provide reliable component and system protection with a simple and economical solution. It is often used in portable and consumer electronics applications, which require protection from over current, damage caused by short circuits or over voltage. Some typical applications of the RUEF400K-AP include: consumer electronics, computers and peripherals, telecommunications, home appliance, automotive electronics, lighting, etc.

Working Principle

Essentially, the working principle of the RUEF400K-AP is based on the combination of two physical effects: temperature increase due to current flow, and non-linearity resisitivity of a polymeric film. When current passes through the PTC material, it increases the temperature of the material, which increases its resistance. If the current flow is high enough, then a condition known as thermal runaway is achieved. The resistance increases exponentially, and the heating effect further increases the device’s resistance. As the temperature exceeds the PTC’s Curie point, it then results in the device switching its state of operation from conductive to resistive. This causes a rapid decrease in the current flow, thus protecting the circuit and its components from any potential damage due to overcurrent or short circuit.

The reaction time of the RUEF400K-AP is quick enough to protect system components from potential failure, yet slow enough to accommodate the inrush currents often associated with start-up surge, thus providing effective protection when it is needed most. The device can then reset itself after the overcurrent event has passed, and the temperature of the material has decreased.

Benefits

There are many benefits associated with the use of the RUEF400K-AP in applications such as consumer electronics and telecommunications. One of these is the ability to reset the device after an over current or short circuit event. This eliminates the need to replace the component or fuse after a fault, reducing maintenance and repair costs. Additionally, the device has a broad operational temperature range allowing for flexibility in design.

In comparison to traditional fuse or circuit breaker designs, the RUEF400K-AP provides a cheaper, simpler solution. This reduces space and complexity. The device also requires no additional components as can be the case with fuse or relay designs. Finally, the fact that the device requires no operating voltage or current makes it a more reliable choice over alternatives such as a relay, as it is not affected by any voltage or current fluctuations.

Conclusion

The RUEF400K-AP is a bi-directional PPTC device manufactured by Raychem, which can be used in many applications that require protection from high current or electrical faults. It has a broad operational temperature range, which makes it a suitable choice for many applications. Additionally, it is known to have a fast reaction time and is able to provide reliable protection from over current or short-circuits. Furthermore, the device offers a cheap, simple and reliable solution compared to traditional fuse or circuit breaker designs. This makes it an attractive option for manufacturers who are looking for a simple and economical solution to their protection needs.

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