The **MF-R015** is a specific model of **Resettable Fuse** (also known as a Polymer Positive Temperature Coefficient device or **PPTC**), manufactured primarily by Bourns. These components are used for overcurrent protection. Unlike traditional fuses that blow and must be replaced, PPTCs "trip" by increasing their resistance significantly when current exceeds a limit and reset once the fault is removed and the power is cycled. --- ### 1. Key Technical Specifications The "015" in the part number typically refers to the **Hold Current ($I_{hold}$)**, which is 0.15 Amperes (150mA). | Parameter | Value | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.15 A | The maximum current the device will carry without tripping. | | **Trip Current ($I_{trip}$)** | 0.30 A | The minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60 V | The maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 40 A | The maximum fault current the device can safely handle. | | **Typical Power ($P_d$)** | 0.3 W | Power dissipated when the device is in the tripped state. | | **Form Factor** | Radial Lead | Through-hole mounting (looks like a small disc capacitor). | --- ### 2. How It Functions The MF-R015 works based on a composite of semi-conductive particles (carbon black) embedded in a non-conductive polymer. 1. **Normal State:** The polymer is in a crystalline state; carbon particles form dense chains, allowing current to flow with low resistance. 2. **Overcurrent State:** If current exceeds the limit ($I_{trip}$), $I^2R$ heating occurs. The polymer expands and becomes amorphous. 3. **Tripped State:** The expansion breaks the carbon chains. Resistance spikes (often by several orders of magnitude), effectively "opening" the circuit. 4. **Resetting:** Once the fault is cleared and the device cools down, the polymer shrinks, the carbon chains reconnect, and the fuse returns to a low-resistance state. --- ### 3. Application Use Cases Because the MF-R015 has a low hold current (150mA), it is commonly found in: * **USB Port Protection:** Protecting peripherals from drawing too much power. * **Sensor Protection:** Safeguarding delicate industrial or automotive sensors. * **Security Systems:** Overload protection for low-voltage alarm circuits. * **Medical Equipment:** Portable devices requiring non-replaceable protection. --- ### 4. Comparison: PTC vs. Standard Fuse | Feature | Standard Glass Fuse | MF-R015 (PTC) | | :--- | :--- | :--- | | **Reusability** | One-time use | Resettable | | **Response Time** | Very Fast | Slower (Thermal based) | | **Resistance** | Negligible | Moderate (increases with heat) | | **Maintenance** | Requires replacement | Maintenance-free |