The **MF-RK** series refers to a specific family of **Radial Leaded Resettable Fuses (PTCs)** manufactured by Bourns. These are widely used in electronic circuits for overcurrent protection. --- ## 1. Core Technology: PPTC The MF-RK series utilizes **Polymeric Positive Temperature Coefficient (PPTC)** technology. * **Normal State:** The device has very low resistance and allows current to flow freely. * **Fault State:** If an overcurrent or short circuit occurs, the internal polymer heats up and expands, causing its resistance to increase exponentially (tripping). * **Reset State:** Once the fault is removed and the device cools down, it returns to a low-resistance state. --- ## 2. Key Specifications The following table highlights the general technical parameters typical for the MF-RK series: | Parameter | Description | Typical Range | | :--- | :--- | :--- | | **$I_{hold}$** | The maximum current the device will not trip at. | 0.7A to 13.0A | | **$I_{trip}$** | The minimum current at which the device will always trip. | 1.4A to 26.0A | | **$V_{max}$** | The maximum voltage the device can withstand. | 60V (Standard for RK) | | **$I_{max}$** | The maximum fault current the device can safely handle. | 40A to 100A | | **$P_d$** | Power dissipated from the device when in tripped state. | 0.8W to 6.9W | --- ## 3. Physical Construction The MF-RK parts are designed for **Through-Hole** mounting on Printed Circuit Boards (PCBs). * **Lead Type:** Radial leads (two wires extending from the bottom). * **Coating:** Cured, flame-retardant epoxy polymer (meeting UL 94V-0 requirements). * **Marking:** Usually marked with the Bourns logo, "RK", and the hold current rating (e.g., `RK300` for 3.0A). --- ## 4. Common Applications Due to their 60V rating and resettable nature, they are commonly found in: * **Industrial Controls:** Protecting sensors and actuators. * **Computer Peripherals:** USB ports and internal power rails. * **Telecommunications:** Protection against power crosses. * **Transformers:** Preventing overheating due to secondary shorts. --- ## 5. Advantages over Standard Fuses 1. **Resettable:** No need to replace the component after a fault. 2. **Solid State:** No moving parts or filaments to break under vibration. 3. **Cost:** Reduces warranty and service costs by eliminating fuse replacement.