### Overview of the MF-RX135 The **MF-RX135** is a specific model of a **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse, manufactured by Bourns. It is commonly referred to as a "multifuse" or "polyfuse." Unlike traditional fuses that blow and must be replaced, these components "trip" into a high-resistance state during an overcurrent event and reset once the fault is cleared and power is cycled. --- ### Technical Specifications The following table outlines the primary electrical characteristics of the MF-RX135: | Parameter | Specification | Description | | :--- | :--- | :--- | | **$I_{hold}$** | 1.35 A | Maximum current the device will hold without tripping at 23°C. | | **$I_{trip}$** | 2.70 A | Minimum current at which the device will always trip at 23°C. | | **$V_{max}$** | 60 V | Maximum voltage the device can withstand without damage. | | **$I_{max}$** | 40 A | Maximum fault current the device can safely interrupt. | | **$P_d$ (typ.)** | 1.7 W | Power dissipated when the device is in its tripped state. | | **$R_{min}$** | 0.12 $\Omega$ | Minimum initial resistance (before tripping). | | **$R1_{max}$** | 0.30 $\Omega$ | Maximum resistance measured one hour after tripping. | --- ### Key Features and Behavior #### 1. Resettable Protection The MF-RX135 acts as a solid-state switch. When an overcurrent occurs, the internal polymer heats up, expands, and becomes non-conductive. Once the power is removed and the device cools down, the polymer contracts, restoring the conductive path. #### 2. Radial Leaded Package The "RX" series typically denotes a **Radial Leaded** form factor, meaning it has two wires extending from the bottom of a circular or rectangular "disk" body, intended for through-hole mounting on PCBs. #### 3. Safety Agency Recognition These parts are typically certified by: * **UL:** Underwriters Laboratories * **TUV:** Technischer Überwachungsverein * **RoHS:** Compliant with lead-free standards. --- ### Common Applications * **Industrial Controls:** Protecting sensors and PLC I/O ports. * **Power Supplies:** Secondary protection for transformers and DC-DC converters. * **Computer Peripherals:** Protecting USB ports or IEEE 1394 connections. * **Security Systems:** Overload protection for alarm panels and sirens. --- ### Typical Circuit Implementation ```mermaid graph LR A[Power Source] --> B[MF-RX135 Fuse] B --> C[Protected Load] C --> D[Ground] ```