MF-RX018/250-2 Bourns Inc., MF-RX018/250-2 Datasheet - Page 3

• Manufacturer Part Number: MF-RX018/250-2
• Description: FUSE PTC RESETTABLE
• Manufacturer: Bourns Inc.
• Series: MF-RX/250r

Specifications of MF-RX018/250-2

• Voltage - Max: 250V
• Current - Max: 10A
• Current - Hold (ih) (max): 180mA
• R Min/max: 0.800 ~ 2.000 Ohm
• Package / Case: Radial
• Holding Current: 180mA
• Initial Resistance Max: 2ohm
• Operating Voltage: 60V
• Ptc Fuse Case: Radial Lead
• Initial Resistance Min: 0.8ohm
• Lead Spacing: 5.1mm
• Length: 13.6mm
• External Depth: 4.6mm
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Trip (it): -
• Time To Trip: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Resettable fuses are manufactured in the form of a conductive plastic, which is comprised of a non-
conductive crystalline polymer with highly conductive carbon black particles impregnated throughout
the crystal lattice. Because of the close proximity of the carbon black particles within the crystal lattice,
under normal conditions current is allowed to flow easily through the conductive plastic. However
under a fault condition, when there is an increase in current, the conductive plastic heats at the rate of
I 2 R. As the material continues to heat, it eventually reaches the phase transformation temperature, which
changes the crystal structure into an amorphous structure. Once the material has transformed into this
amorphous structure, the conductive particles become isolated and are unable to conduct current hence
the drastic change in material resistance. It is only when the current is removed that the material is
allowed to cool and return to its original crystal structure.
It is the materials used in resettable fuses that allow
them to reset after a fault condition has been
removed. Resettable fuses exhibit a positive
temperature coefficient effect when heated. While
many materials exhibit a PTC effect when heated
(an increase in resistance in response to a positive
change in temperature), what makes the material
used in resettable fuses unique is the fact that the
increase in resistance changes exponentially rather
than in a linear manner.
Multifuse® Products – How They Work
Multifuse® Products – How They Are Used
PTC Response Characteristic
I=V/R L
Temperature
PTC Response Characteristic
I=V/R MF
I=V/R L
Temperature
I=V/R MF
Crystalline
Polymer
V S
c o l d
It is because of this transformation from a low
resistance state to a high resistance state that allows
the resettable fuse to protect loads. It is this
transition from the low resistance state to high
resistance state that is referred to as tripping. The
time it takes for a resettable fuse to trip is relatively
quick, depending on how high the fault current is
and it can be as quick as a fraction of a second.
Hence they are an excellent form of protection for
most applications where sensitive devices need
extra protection.
3
Typical Circuit Application
I
Carbon Chains
V S
Conducting
Typical Circuit Application
+t°
I
Amorphous
R MF
Polymer
+t°
h o t
R L
R MF
Non-conducting
Carbon Chains
R L