The **MF-R700** is a specific model of a **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by **Bourns**. These components are widely used for overcurrent protection in electronic circuits. --- ## 1. Technical Specifications The MF-R700 belongs to the MF-R series, which are radial-leaded through-hole devices. | Parameter | Specification | | :--- | :--- | | **Hold Current ($I_{hold}$)** | 7.0 Amperes | | **Trip Current ($I_{trip}$)** | 14.0 Amperes | | **Maximum Voltage ($V_{max}$)** | 30 Volts (DC/AC) | | **Maximum Current ($I_{max}$)** | 100 Amperes | | **Power Dissipation ($P_d$)** | 3.8 Watts (typical) | | **Resistance ($R_{min} / R1_{max}$)** | 0.005 $\Omega$ / 0.02 $\Omega$ | --- ## 2. Operating Principle Unlike a standard one-time fuse that melts and breaks the circuit permanently, the MF-R700 is **resettable**. 1. **Normal State:** The device has a very low resistance, allowing current to flow to the load. 2. **Fault State (Overcurrent):** When current exceeds the trip threshold, the internal polymer heats up and expands. Its resistance increases exponentially. 3. **Protection:** This high resistance limits the current to a safe, low level (trickle), protecting downstream components. 4. **Reset:** Once the fault is removed and the power is cycled or the device cools down, the polymer contracts, and the resistance returns to a low state. --- ## 3. Physical Characteristics * **Package Type:** Radial Leaded (Through-hole). * **Material:** Conductive polymer mixed with carbon black. * **Coating:** Flame retardant epoxy polymer (meets UL 94V-0). * **Marking:** Usually marked with "B" (Bourns logo), "R700", and a date code. --- ## 4. Common Applications Due to its high hold current (7.0A), the MF-R700 is typically found in: * **Power Supplies:** Protecting against short circuits in industrial or desktop units. * **Motor Control:** Protecting motors from stalling or overheating. * **Battery Packs:** Preventing excessive discharge or charging currents. * **Computer Peripherals:** High-power USB hubs or internal power rails.