The **MF-R250-2** is a specific electronic component known as a **Resettable Fuse** (also called a PTC Thermistor or PolySwitch), manufactured by Bourns. It is part of the MF-R series, which are radial-leaded through-hole devices used for overcurrent protection. --- ### 1. Key Technical Specifications The "250" in the part number indicates the holding current (2.50 Amps). Below are the primary technical parameters: | Parameter | Specification | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 2.50 A | The maximum current the device will pass without tripping. | | **Trip Current ($I_{trip}$)** | 5.00 A | The minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60 V | The maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 40 A | The maximum fault current the device can safely interrupt. | | **Resistance ($R_{min}/R1_{max}$)** | 0.05 - 0.13 $\Omega$ | The initial resistance range of the component. | | **Packaging** | Tape & Reel (-2) | The "-2" suffix indicates Tape and Reel packaging for automated assembly. | --- ### 2. How it Works Unlike a traditional fuse that "blows" and must be replaced, the MF-R250-2 is **resettable**: 1. **Normal State:** The device has a very low resistance, allowing current to flow to the circuit. 2. **Fault State:** If an overcurrent or short-circuit occurs, the internal polymer heats up and expands, causing the resistance to increase exponentially. 3. **Protection:** This high resistance limits the current to a safe leakage level, protecting downstream components. 4. **Reset:** Once the fault is removed and the power is cycled (or the device cools down), it returns to a low-resistance state. --- ### 3. Physical Characteristics and Materials * **Form Factor:** Radial leaded (through-hole). * **Material:** Carbon-filled polymer. * **Operating Temperature:** Typically -40°C to +85°C. * **Visual Identification:** Usually a yellow or tan circular disk with "MF-R250" printed on the body. --- ### 4. Typical Applications The MF-R250-2 is commonly found in circuits where transient faults are expected and manual fuse replacement is difficult: * **Power Supplies:** Protecting against output shorts. * **Motor Control:** Protecting against stalled motor conditions. * **Industrial Controls:** Protecting I/O ports and PLC circuits. * **Medical Equipment:** General overcurrent protection in sensitive devices.