The **MF-R Series** refers to a popular line of **Radial Leaded Resettable Fuses**, commonly known as **PTCs** (Positive Temperature Coefficient) or **Polyswitches**. These components are manufactured by companies like Bourns and are used for overcurrent protection. --- ### 1. Key Characteristics The MF-R series is designed to protect circuits from damage caused by overcurrent or short-circuit conditions. Unlike traditional fuses, these are **resettable**. | Feature | Description | | :--- | :--- | | **Technology** | Polymeric Positive Temperature Coefficient (PPTC) | | **Form Factor** | Radial Leaded (Through-hole mounting) | | **Material** | Flame retardant epoxy polymer (UL 94V-0) | | **Function** | Limits current flow when a fault occurs, then resets after power is cycled | --- ### 2. How it Works 1. **Normal State:** The device has a very low resistance, allowing current to pass through to the load. 2. **Fault State (Trip):** If the current exceeds the "Trip Current," the internal polymer heats up rapidly, causing its resistance to increase by several orders of magnitude. This restricts the current to a safe leakage level. 3. **Reset State:** Once the fault is removed and the power is disconnected/cooled down, the material returns to its low-resistance state. --- ### 3. Technical Specifications When selecting an MF-R part (e.g., MF-R050), you must look at these parameters: | Parameter | Meaning | | :--- | :--- | | **$I_{hold}$** | The maximum current the device can carry without tripping. | | **$I_{trip}$** | The minimum current that will cause the device to "blow" (trip). | | **$V_{max}$** | The maximum voltage the device can withstand in the tripped state. | | **$R_{min} / R_{max}$** | The initial resistance range of the device before it trips. | --- ### 4. Common Applications * **Power Supplies:** Protection against short circuits in AC/DC adapters. * **Industrial Controls:** Protecting PLCs and sensor inputs. * **Consumer Electronics:** Used in toys, game consoles, and peripherals. * **Automotive:** Protection for motors, door locks, and window lifters. --- ### 5. Identification Example An **MF-R050** indicates: * **MF-R:** The series (Radial PPTC). * **050:** The Hold Current ($I_{hold}$), which in this case is **0.50 Amps**.