The **MF-RX250/72** (specifically the **MF-RX250/72-0** or variants like **MF-RX250/72-2**) is a Radial Leaded **PTC (Positive Temperature Coefficient) Resettable Fuse**, part of the Multifuse® line manufactured by **Bourns**. It is primarily used for overcurrent protection, acting as a "resettable" alternative to traditional one-time fuses. --- ### 1. Key Technical Specifications The part number follows a specific nomenclature where "250" refers to the hold current and "72" refers to the maximum voltage. | Parameter | Specification | Description | | :--- | :--- | :--- | | **I-hold (Hold Current)** | 2.50 Amps | The maximum current the device will pass without tripping at 23°C. | | **I-trip (Trip Current)** | 5.00 Amps | The minimum current at which the device will switch to a high-resistance state. | | **V-max (Max Voltage)** | 72 Volts | The maximum voltage the device can withstand without damage. | | **I-max (Max Current)** | 40 Amps | The maximum fault current the device can safely interrupt. | | **R-min / R-max** | 0.05 / 0.08 $\Omega$ | Initial resistance range of the component before tripping. | | **Power Dissipation** | 2.5 Watts | Power dissipated when the device is in its tripped state. | --- ### 2. Physical Characteristics * **Package Type:** Radial Leaded (Through-hole). * **Material:** Cured, flame-retardant epoxy polymer (meets UL 94V-0). * **Lead Material:** Tin-plated copper. * **Operating Temperature:** -40°C to +85°C. --- ### 3. How it Functions The MF-RX250/72 utilizes a conductive polymer compound. 1. **Normal State:** The polymer is in a crystalline state with carbon particles forming conductive paths, allowing current to flow with low resistance. 2. **Overcurrent State:** If the current exceeds the trip point, $I^2R$ heating causes the polymer to expand and become amorphous. 3. **Tripped State:** The expansion breaks the carbon chains, causing the resistance to spike exponentially, effectively "shutting off" the circuit. 4. **Resetting:** Once the fault is removed and the power is cycled, the device cools down, the polymer shrinks, and the conductive paths are restored. --- ### 4. Common Applications * **Industrial Controls:** Protection for transformers and motors. * **Power Supplies:** Secondary side protection for DC power ports. * **Security Systems:** Overcurrent protection for sensors and alarms. * **Automotive Electronics:** Protection for small motors and wire harnesses.