The **MF-R040** is a specific model of **Polymer Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured primarily by Bourns. These components are used for overcurrent protection in electronic circuits. --- ## 1. Technical Specifications The following table outlines the key electrical characteristics of the MF-R040: | Parameter | Value | Description | | :--- | :--- | :--- | | **Ihold** | 0.40 Amps | Maximum current the device will pass without tripping. | | **Itrip** | 0.80 Amps | Minimum current at which the device will always trip. | | **Vmax** | 60 Volts | Maximum voltage the device can withstand without damage. | | **Imax** | 40 Amps | Maximum fault current the device can safely handle. | | **Pd (Typ.)** | 0.55 Watts | Power dissipated from the device while in a tripped state. | | **Rmin / Rmax** | 0.55 / 1.29 $\Omega$ | Resistance range of the component before tripping. | --- ## 2. How It Works The MF-R040 operates based on the thermal properties of its conductive polymer: 1. **Normal State:** In standard operation, the carbon particles in the polymer form low-resistance paths, allowing current to flow. 2. **Fault State (Overcurrent):** When current exceeds the threshold ($I_{trip}$), the polymer heats up and expands. This breaks the conductive paths, causing resistance to spike sharply. 3. **Reset State:** Once the power is disconnected and the fault is removed, the component cools down, the polymer contracts, and the device returns to a low-resistance state. --- ## 3. Physical Attributes and Mounting * **Package Type:** Through-hole (Radial Leaded). * **Material:** Cured, flame-retardant epoxy polymer meeting UL 94V-0 requirements. * **Lead Wire:** Tin-plated copper. ### Visual Dimensions (Typical) * **Width:** ~7.4 mm * **Height:** ~12.7 mm * **Thickness:** ~3.1 mm --- ## 4. Common Applications * **Power Supplies:** Protection against short circuits in DC power lines. * **Industrial Controls:** Safeguarding PLC I/O ports. * **Computer Peripherals:** USB port protection and motherboard circuitry. * **Consumer Electronics:** Protecting motors or batteries from overheating.