The **MF-RX Series** consists of radial-leaded **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuses, manufactured primarily by **Bourns**. These components are essential for protecting electronic circuits from overcurrent and short-circuit conditions. --- ### 1. How the MF-RX Series Works The MF-RX series acts as a "resettable fuse." Unlike traditional glass or ceramic fuses that blow and must be replaced, PPTC devices "trip" to a high-resistance state and reset once the fault is cleared and the power is cycled. | State | Resistance | Current Flow | Behavior | | :--- | :--- | :--- | :--- | | **Normal** | Very Low | Full | The polymer contains conductive carbon chains that allow current to pass. | | **Tripped** | Very High | Negligible | Excessive current causes Joule heating; the polymer expands, breaking the carbon chains. | | **Reset** | Low | Full | Once the fault is removed and the device cools, the chains reconnect. | --- ### 2. Technical Specifications The MF-RX series is specifically known for its **high voltage rating** (typically up to 60V) compared to standard surface-mount versions. | Parameter | Description | | :--- | :--- | | **$I_{hold}$ (Hold Current)** | The maximum current the device can carry without tripping. | | **$I_{trip}$ (Trip Current)** | The minimum current at which the device is guaranteed to trip. | | **$V_{max}$** | Maximum voltage the device can withstand without damage (often 60V). | | **$I_{max}$** | The maximum fault current the device can safely handle. | | **$P_{d}$** | Power dissipated by the device when in a tripped state. | --- ### 3. Key Features and Applications #### Features: * **Radial Leaded:** Through-hole packaging for easy PCB mounting. * **Cured Flame Retardant:** Coated with epoxy polymer meeting UL 94V-0 requirements. * **Agency Recognition:** Generally UL, CSA, and TUV approved. #### Common Applications: 1. **Industrial Controls:** Protecting motors and PLC I/O ports. 2. **IEEE 802.3 Ethernet:** Protection for network interface cards. 3. **Power Supplies:** Secondary side protection for transformers. 4. **Security Systems:** Overcurrent protection for sensors and alarms. --- ### 4. Part Numbering Example If you see a part labeled **MF-RX110/72**: * **MF:** Multifuse (Bourns Brand). * **RX:** Series Name (Radial Leaded, 60V-72V high voltage). * **110:** Hold Current (e.g., 1.10 Amps). * **/72:** Maximum Voltage Rating (72 Volts).