### MF-RX012: Multifuse® Resettable PTC Fuse The **MF-RX012** is a radial-leaded Resettable PTC (Positive Temperature Coefficient) fuse manufactured by Bourns. It is commonly used in electronic circuits to provide overcurrent protection without requiring replacement after a fault occurs. --- ### 1. Key Technical Specifications The following table outlines the electrical and physical characteristics of the MF-RX012: | Parameter | Value / Specification | | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.12 Amps (120 mA) | | **Trip Current ($I_{trip}$)** | 0.24 Amps (240 mA) | | **Max Voltage ($V_{max}$)** | 60 Volts (AC/DC) | | **Max Current ($I_{max}$)** | 40 Amps | | **Typical Power ($P_d$)** | 0.40 Watts | | **Initial Resistance ($R_{min}$)** | 1.50 $\Omega$ | | **Post-Trip Resistance ($R_{1max}$)** | 6.50 $\Omega$ | | **Mounting Type** | Through-hole (Radial Leaded) | --- ### 2. How it Works (Theory of Operation) The MF-RX012 functions as a **thermistor** with a non-linear resistance profile: 1. **Normal State:** In standard operating conditions, the device has a very low resistance, allowing current to pass through with minimal heat generation. 2. **Fault State (Overcurrent):** If the current exceeds the trip threshold ($I_{trip}$), internal heat builds up rapidly. This causes the polymer structure to expand, significantly increasing the resistance. 3. **Protection:** This high resistance limits the current flow to a safe level, protecting the downstream components. 4. **Resetting:** Once the fault is removed and the device cools down, the polymer contracts, and the fuse returns to its low-resistance state. --- ### 3. Application Areas The MF-RX012 is ideal for low-power applications requiring reliable circuit protection: * **Computer Peripherals:** USB ports, keyboards, and mouse interfaces. * **Telecommunications:** Protection for line cards and modems. * **Industrial Controls:** Sensors and low-voltage control circuits. * **General Electronics:** Power supplies and battery chargers. --- ### 4. Circuit Diagram Representation In a schematic, a PTC fuse is often represented by a resistor symbol with a diagonal line or a specific fuse symbol labeled "PTC" or "Polyfuse." ```text Input (+) ---[ PTC (MF-RX012) ]--- Output (+) | [LOAD] | Input (-) ------------------------- Output (-) ``` ---