The **MF-RX300** is a specific model within the Bourns MF-RX series of Resettable Fuses, technically known as **Polymer Positive Temperature Coefficient (PPTC)** devices. These components are used for overcurrent protection in electronic circuits. --- ## 1. Technical Specifications The MF-RX300 is designed to "trip" and limit current when a fault occurs, then reset once the fault is removed and the power is cycled. | Feature | Specification | | :--- | :--- | | **Hold Current ($I_{hold}$)** | 3.00 Amperes | | **Trip Current ($I_{trip}$)** | 6.00 Amperes | | **Max Voltage ($V_{max}$)** | 60 Volts | | **Max Current ($I_{max}$)** | 40 Amperes | | **Typical Power ($P_d$)** | 2.8 Watts | | **Mounting Type** | Radial Leaded (Through-hole) | --- ## 2. How it Works (The PPTC Principle) The MF-RX300 consists of a conductive plastic matrix combined with carbon black particles. 1. **Normal State:** The particles form low-resistance paths, allowing current to flow freely to the load. 2. **Fault State (Overcurrent):** If the current exceeds 6.0A, $I^2R$ heating causes the polymer to expand. 3. **Tripped State:** As the polymer expands, the carbon chains break apart, causing the resistance to increase exponentially. This effectively "opens" the circuit, leaving only a small trickle current. 4. **Reset:** Once the fault is fixed and the device cools down, the polymer contracts, the carbon chains reconnect, and the device returns to a low-resistance state. --- ## 3. Physical Dimensions As a radial-leaded component, it has a distinct "teardrop" or rectangular coated shape. | Dimension | Value (Approx.) | | :--- | :--- | | **Width (A)** | 23.9 mm | | **Height (B)** | 28.6 mm | | **Thickness (C)** | 3.0 mm | | **Lead Spacing** | 10.2 mm | --- ## 4. Common Applications * **Industrial Controls:** Protecting PLCs and motors from surges. * **IEEE 802.3 Ethernet:** Protection for network interface cards. * **Power Supplies:** Used as a secondary protection layer for transformers. * **Security Systems:** Protecting sensors and alarm loops from short circuits. --- ## 5. Typical Part Number Breakdown: `MF-RX300` ```text MF - Multifuse (Bourns Trademark) R - Radial Leaded X - 60V Rated Series 300 - Hold Current Rating (3.00 Amps) ```