The **MF-R005** is a specific model of **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured primarily by Bourns. These components are used for overcurrent protection in electronic circuits. --- ### 1. Key Technical Specifications The following table highlights the critical electrical characteristics of the MF-R005: | Parameter | Value | Description | | :--- | :--- | :--- | | **I-hold** | 0.05 A (50mA) | The maximum current the device will pass without tripping. | | **I-trip** | 0.15 A (150mA) | The minimum current at which the device will switch to high resistance. | | **V-max** | 60 V | The maximum voltage the device can withstand without damage. | | **I-max** | 40 A | The maximum fault current the device can safely handle. | | **Pd (Typ.)** | 0.26 W | Power dissipated from the device when in tripped state. | | **R-min** | 7.30 $\Omega$ | Minimum resistance in the initial (un-tripped) state. | | **R1-max** | 20.00 $\Omega$ | Maximum resistance one hour after reflow or tripping. | --- ### 2. Physical and Material Characteristics * **Package Type:** Radial Leaded (Through-hole). * **Material:** Conductive polymer integrated with carbon black particles. * **Coating:** Flame retardant epoxy polymer (meeting UL 94V-0). * **Lead Material:** Tin-plated copper. --- ### 3. How It Works (The PTC Effect) The MF-R005 operates as a "self-healing" fuse: 1. **Normal State:** Under normal current (below 50mA), the polymer is in a crystalline state, and the carbon particles form conductive paths. Resistance is low. 2. **Overcurrent/Trip State:** If current exceeds the trip point (150mA), internal $I^2R$ heating causes the polymer to expand and turn amorphous. This breaks the carbon chains. 3. **High Resistance:** The resistance jumps significantly, limiting the current to a safe leakage level. 4. **Reset:** Once power is removed and the fault is cleared, the device cools down, the polymer shrinks, and the conductive paths reform. --- ### 4. Typical Applications Because of its very low hold current (50mA), the MF-R005 is ideal for protecting sensitive, low-power electronics: * **Sensors:** Protecting industrial or IoT sensor nodes. * **Communication Ports:** Guarding RS-232 or RS-485 lines. * **Medical Equipment:** Low-power diagnostic tools. * **Security Systems:** Control panels and alarm circuits. --- ### 5. Example Circuit Implementation ```cpp // Schematic representation [Power Source (60V max)] --- [MF-R005 Fuse] --- [Sensitive Load/Sensor] --- [Ground] ``` *If the "Sensitive Load" shorts out, the MF-R005 will heat up and "open" the circuit until the short is removed.*