The **MJS 3.5-R** is a specific model of a **Miniature Surface Mount (SMT) Fuse**, manufactured by Bel Fuse Inc. It belongs to the MJS series, which is characterized by its small footprint and **time-delay (slow-blow)** characteristics. --- ## 1. Technical Specifications The "3.5" in the part number indicates the current rating, and the "R" typically signifies RoHS compliance. | Feature | Specification | | :--- | :--- | | **Current Rating** | 3.5 Amperes | | **Voltage Rating (AC)** | 125 VAC | | **Fuse Type** | Time-Delay / Slow-Blow | | **Mounting Type** | Surface Mount (SMT) / Square Pipe | | **Body Material** | Ceramic Tube with Gold/Silver plated brass caps | | **Interrupting Rating** | 50A @ 125V AC | | **Operating Temp** | -55°C to +125°C | --- ## 2. Key Electronic Characteristics ### Time-Delay (Slow-Blow) Function Unlike "Fast-Acting" fuses, the MJS 3.5-R is designed to withstand temporary **inrush currents** or power surges. * **Purpose:** It prevents "nuisance blowing" caused by the initial startup current of motors, capacitors, or transformers. * **Mechanism:** The internal filament has a higher thermal mass, requiring a sustained overcurrent to melt the element. ### Physical Design The MJS series uses a **square ceramic body** design. This is advantageous for automated PCB assembly because: * It provides a flat surface for vacuum pick-and-place nozzles. * The ceramic body provides excellent insulation and heat resistance compared to glass. ### Standards & Compliance * **RoHS 2:** Fully compliant with lead-free requirements. * **Agency Approvals:** Usually UL Recognized (UL 248-14) and CSA Certified. --- ## 3. Typical Applications The MJS 3.5-R is commonly found in compact electronic devices where space is limited but protection against surges is necessary: 1. **Power Supplies:** Protecting the input stage of AC/DC converters. 2. **LCD Monitors:** Guarding backlight inverters. 3. **Industrial Equipment:** Board-level protection for controllers. 4. **Telecom:** Line cards and network interface units. --- ## 4. Part Number Breakdown ```text MJS 3.5 - R | | | Series | RoHS Compliant Amps (3.5A) ```