The **3JS2.5-R** is a specific model of subminiature, fast-acting surface mount fuse (SMD) manufactured by **Bel Fuse Inc.** This part is widely used in power supplies, consumer electronics, and industrial controllers to provide overcurrent protection. Below is a detailed breakdown of its electronic specifications and characteristics. --- ### 1. Key Technical Specifications The model number "3JS2.5-R" follows a specific nomenclature that defines its electrical limits. | Feature | Specification | | :--- | :--- | | **Current Rating** | 2.5 Amps | | **Voltage Rating (AC)** | 350V | | **Voltage Rating (DC)** | 140V | | **Fuse Type** | Glass Body / Cartridge (Subminiature) | | **Response Characteristic** | Fast-Acting (F) | | **Interrupting Rating** | 100A @ 350V AC / 100A @ 140V DC | | **Termination Style** | Axial Leaded (Standard for through-hole or custom bending) | | **RoHS Compliant** | Yes (indicated by the "-R" suffix) | --- ### 2. Physical Construction The 3JS series is known for its **subminiature form factor**, which allows for high-density board placement where a traditional 5x20mm fuse would be too large. * **Body Material:** High-quality glass. * **Dimensions:** Approximately 2.8mm x 7mm (excluding leads). * **Lead Material:** Tin-plated copper, optimized for wave soldering or manual soldering. --- ### 3. Electronic Performance Characteristics #### A. Fast-Acting Response Unlike "Slow-Blow" (Time-Delay) fuses, the 3JS2.5-R is designed to open almost instantly when a short circuit or significant overcurrent occurs. This is critical for protecting sensitive semiconductor components like ICs and transistors. #### B. Nominal Resistance The cold resistance for this specific 2.5A model is typically very low (around **0.038 Ohms**), ensuring minimal voltage drop across the fuse during normal operation. #### C. Melting Integral ($I^2t$) The $I^2t$ value (thermal energy required to melt the fuse element) for the 2.5A version is approximately **3.1 $A^2sec$**. This value is used by engineers to ensure the fuse doesn't blow during brief, normal inrush currents. --- ### 4. Typical Applications * **AC/DC Adapters:** Protecting the primary side of small power bricks. * **LED Lighting:** Ensuring safety in driver circuits. * **Battery Chargers:** Preventing fire hazards during cell failure. * **Monitors/TVs:** Providing localized protection on logic boards. ---