The **FRT-5B-R** is an electronic component primarily classified as a **Precision Thermal Fuse** (Thermal Cutoff) manufactured by **Uchihashi Estec**. It is designed to protect electronic devices from overheating by permanently breaking the circuit when a specific temperature threshold is reached. --- ### 1. Key Technical Specifications The "FRT" series is known for its lead-type configuration and high reliability. Below are the typical parameters for the FRT-5B-R: | Parameter | Specification | | :--- | :--- | | **Functioning Temperature ($T_f$)** | $130^{\circ}\text{C}$ (Standard for the 5B-R variant) | | **Holding Temperature ($T_h$)** | Approx. $100^{\circ}\text{C}$ to $105^{\circ}\text{C}$ | | **Rated Current ($I_r$)** | 2A | | **Rated Voltage ($V_r$)** | 250V AC | | **Resistance** | Very low (miliohms) until triggered | | **Compliance** | RoHS, REACH, UL, VDE | --- ### 2. Physical Construction The FRT-5B-R is built using several critical layers to ensure safety and precision: 1. **Thermal Element:** A low-melting-point alloy (fusible alloy) that melts at the designated $T_f$. 2. **Ceramic Case/Encapsulation:** Provides electrical insulation and high heat resistance. 3. **Flux:** A special resin coating the alloy to prevent oxidation and ensure a clean "break" when melting. 4. **Lead Wires:** Tin-plated copper wires for soldering onto a PCB or crimping into a wire harness. --- ### 3. How It Works (The Operating Principle) The device acts like a "one-shot" safety switch: * **Normal State:** The fusible alloy is solid, allowing current to flow through the leads. * **Fault State:** If the ambient temperature exceeds $130^{\circ}\text{C}$, the alloy melts. * **Surface Tension Effect:** Once melted, the internal flux causes the liquid alloy to pull away from the leads and form small drops, creating a physical gap that current cannot cross. --- ### 4. Typical Applications The FRT-5B-R is commonly found in household appliances and power electronics where thermal runaway is a risk: * **Small Appliances:** Coffee makers, irons, and hair dryers. * **Power Supplies:** Inside AC/DC adapters or chargers. * **Battery Packs:** Protecting against overheating during rapid charging or discharging. * **Motors:** Integrated into fan motors or small actuators. ### 5. Installation Precautions * **Soldering:** Because it is a heat-sensitive device, excessive heat during soldering can trigger the fuse. Heat sinks (like pliers) should be used on the leads during assembly. * **Non-resettable:** Once the FRT-5B-R has "blown," it must be replaced; it cannot be reset like a circuit breaker.