The **MF-RX012/250** is a specific model of **PTC (Positive Temperature Coefficient) Resettable Fuse**, manufactured by Bourns. These components are used for overcurrent protection in electronic circuits. Unlike traditional fuses that blow and must be replaced, a resettable fuse "trips" (increases resistance) during a fault and resets once the power is removed and the device cools down. --- ### 1. Key Technical Specifications Below are the primary electrical characteristics for the MF-RX012/250: | Parameter | Specification | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.12 A (120 mA) | The maximum current the device can carry without tripping. | | **Trip Current ($I_{trip}$)** | 0.24 A (240 mA) | The minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60V / 250V | Rated for 60V continuous; can withstand 250V power line surges. | | **Max Current ($I_{max}$)** | 3.0 A | The maximum fault current the device can safely withstand. | | **Resistance ($R_{min}$ / $R_{max}$)** | 6.0 $\Omega$ / 12.0 $\Omega$ | The resistance range of the device in its initial "on" state. | | **Packaging Style** | Radial Leaded | Through-hole component with two wire leads. | --- ### 2. How it Works The MF-RX012/250 is made from a conductive polymer composite. 1. **Normal Operation:** Under normal current levels, the polymer is in a crystalline state, allowing carbon particles to form a low-resistance path. 2. **Fault Condition:** When an overcurrent occurs, the $I^2R$ heating causes the polymer to expand and turn into an amorphous state. 3. **Protection:** This expansion breaks the carbon chains, causing the resistance to spike dramatically, effectively "opening" the circuit. 4. **Reset:** Once the fault is cleared and power is cycled, the polymer cools and returns to its low-resistance state. --- ### 3. Applications The "/250" designation often implies this part is designed for **telecommunications** or AC power line applications where high-voltage surges (like lightning or power cross) might occur. * **Customer Premise Equipment (CPE):** Modems, routers, and set-top boxes. * **POTS (Plain Old Telephone Service):** Protecting line cards from surges. * **Industrial Controls:** Low-current sensor protection. * **Power Supplies:** Secondary protection against short circuits. --- ### 4. Part Number Breakdown `MF-RX` `012` / `250` * **MF-RX:** Multifuse Resettable Fuse, Radial Leaded Series. * **012:** Hold current of 0.12 Amps. * **250:** Rated for 250V intermittent/surge capability.