The **MF-R300** is a high-performance **PTC (Positive Temperature Coefficient) Resettable Fuse**, manufactured primarily by Bourns. It is part of the Multifuse® line and is designed to protect electronic circuits from overcurrent and short-circuit conditions. --- ### 1. Technical Specifications The following table highlights the core electrical characteristics of the MF-R300: | Parameter | Specification | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 3.0 Amps | The maximum current the device will carry without tripping. | | **$I_{trip}$** | 6.0 Amps | The minimum current at which the device will switch to high resistance. | | **$V_{max}$** | 30 Volts | Maximum voltage the device can withstand without damage. | | **$I_{max}$** | 40 Amps | Maximum fault current the device can safely interrupt. | | **$P_{d}$** | 2.3 Watts | Typical power dissipated when in the tripped state. | | **Termination** | Radial Leaded | Through-hole mounting style. | --- ### 2. How It Functions The MF-R300 operates based on the physical properties of a conductive polymer. 1. **Normal Operation:** At rated current, the conductive particles inside the polymer form a low-resistance path, allowing electricity to flow freely. 2. **Overcurrent Event:** If the current exceeds the trip point (6.0A), the polymer heats up rapidly. 3. **Tripping:** The heat causes the polymer to expand, breaking the conductive chains. The resistance increases dramatically, reducing the current flow to a trickle. 4. **Resetting:** Once the fault is removed and the device cools down, the polymer contracts, the conductive paths reconnect, and the fuse "resets" to its low-resistance state. --- ### 3. Key Features and Applications #### Features * **Resettable:** Unlike traditional glass fuses, it does not need to be replaced after a fault. * **Safety Standards:** Typically UL, CSA, and TUV recognized. * **Form Factor:** Circular or rectangular "teardrop" shape with a yellow or tan coating. #### Common Applications * **Power Supplies:** Protection against output short circuits. * **Industrial Controls:** Protecting PLCs and sensor loops. * **Computer Peripherals:** Protecting USB ports or internal drive circuits. * **Motors:** Protection against stall/locked rotor conditions. --- ### 4. Typical Marking Code On the physical component, you will usually see: `B 300` or `MF-R 300` * **B**: Manufacturer Logo (Bourns). * **300**: Denotes the 3.0A hold current.