PFRA.040.3

Resistance - Initial (Ri) (Min):	520 mOhms
Approvals:	CSA, TUV, UL
Lead Spacing:	0.201" (5.10mm)
Thickness (Max):	--
Size / Dimension:	0.291" Dia x 0.122" W (7.40mm x 3.10mm)
Package / Case:	Radial, Disc
Mounting Type:	Through Hole
Ratings:	--
Operating Temperature:	-40°C ~ 85°C
Resistance - Post Trip (R1) (Max):	1.29 Ohms
Series:	PFRA
Time to Trip:	3.8s
Current - Trip (It):	800mA
Current - Hold (Ih) (Max):	400mA
Current - Max:	40A
Voltage - Max:	60V
Type:	Polymeric
Part Status:	Obsolete
Lead Free Status / RoHS Status:	--
Packaging:	Tape & Box (TB)

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Introduction to PTC Resettable Fuses

A resettable fuse, also known as a polymeric positive temperature coefficient (PPTC) device, is an electronic component that is designed to protect other components, circuits, and wiring from over-current failures. It works by permanently increasing its resistance when an excessive current is applied. The resistance change causes a raising temperature that drastically reduces the current flow and dissipates it, preventing damage. This type of fuse contains a special thermally-sensitive polymer whose resistance increases when it is heated above a predetermined temperature, which is why it is known as a "positive temperature coefficient" device. It is often used as an alternative to a conventional fuse, which must be replaced after use.

Construction and Working Principle of PTC Resettable Fuses

PTC resettable fuses typically have two terminals and are constructed with a polymer film which has been treated to produce a positive temperature coefficient; when the temperature exceeds a predetermined point, the polymer film begins to resist current flow, thus reducing the current passing through the device and dissipating it as heat. As the temperature continues to increase, the resistance increases, further reducing the current flow. Once the temperature reaches its maximum threshold, the current is cut off, and the device is considered to be "tripped." The device can then be reset by reducing the temperature, allowing the polymer film to relax, at which point the current-limiting protection is restored.

PFRA.040.3 Application Field and Working Principle

The PFRA.040.3 Resettable Fuse from Phoenix Contact is a resettable fuse with a typical hold current of 40 mA and a hold time of 12.5 ms. The fuse has a gold-plated, silver-terminal housing, and is UL recognized for a wide range of products, including power supplies, network cards, printers, and more. The PFRA.040.3 has a fast, self-resetting circuit protection that automatically resets after current interruption, providing a higher level of safety and protecting against shorts and overloads.The working principle of the PFRA.040.3 is simple, yet effective; when the current flowing through the device exceeds its selected trip-point value, the device will automatically suspend the current until the root cause has been resolved. This automatic action is made possible by the integrated thermally-sensitive polymer, which rapidly alters its own resistance when the temperature rises above its pre-determined point, causing a rapid increase in the amount of heat dissipated and a corresponding decrease in the flow of current. Once the temperature has been reduced, the device can be reset and the protection will restore its normal current-limiting operation.

Conclusion

In conclusion, PTC resettable fuses are an invaluable asset for protecting electronic products, as they are designed to regulate the amount of current flowing through a circuit and provide automatic protection without requiring any external intervention. The PFRA.040.3 resettable fuse is a reliable example of this technology, offering a wide range of applications with a UL approved design and a fast self-resetting circuit protection. Its unique working principle enables the device to interfere with the current flow when the temperature exceeds a predetermined point, thus protecting the circuit against excessive or prolonged current flow.

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