The **MF-R135** is a specific model of **PTC (Positive Temperature Coefficient) Resettable Fuse**, manufactured by Bourns. It is widely used in electronic circuits to protect against overcurrent conditions. --- ### 1. Key Technical Specifications The following table highlights the primary electrical characteristics of the MF-R135: | Parameter | Specification | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 1.35 A | The maximum current the device will pass without tripping. | | **Trip Current ($I_{trip}$)** | 2.70 A | The minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60 V | Maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 40 A | Maximum fault current the device can safely handle. | | **Resistance ($R_{min}$)** | 0.12 $\Omega$ | Initial resistance at 23°C. | | **Resistance ($R1_{max}$)** | 0.30 $\Omega$ | Max resistance one hour after tripping/reflow. | --- ### 2. How It Works The MF-R135 is a **Multifuse®**. Unlike a standard one-time fuse that blows and must be replaced, this part "resets" itself once the fault is cleared and the temperature drops. 1. **Normal Operation:** The device has low resistance, allowing current to flow normally. 2. **Overcurrent Event:** Excessive current causes internal heating (Joule heating). 3. **Tripping:** Once the temperature reaches a critical point, the polymer structure expands, causing the resistance to spike significantly. This "chokes" the current to a safe leakage level. 4. **Resetting:** Once power is removed and the device cools down, the polymer contracts, and the fuse returns to a low-resistance state. --- ### 3. Physical Attributes & Applications * **Package Type:** Radial Leaded (Through-hole). It looks like a small, circular/rectangular "dipped" disc, usually yellow or orange. * **Material:** Conductive polymer. * **Common Applications:** * Power supplies and transformers. * Industrial controls. * Computer peripherals (USB ports, etc.). * Security systems. --- ### 4. Comparison: PTC vs. Standard Fuse | Feature | MF-R135 (PTC) | Standard Fuse | | :--- | :--- | :--- | | **Life Cycle** | Reusable many times | One-time use (Blows) | | **Resistance** | Higher | Very Low | | **Action Speed** | Relatively slow (thermal-based) | Can be very fast (Fast-blow) | | **Maintenance** | Low (Self-resetting) | High (Manual replacement) |