The **5ST400-R** is a specific electronic component primarily categorized as a **Surface Mount (SMD) Fuse**, specifically a Time-Lag (Slow Blow) fuse. It is part of the 5ST series manufactured by Bel Fuse Inc. Below is a detailed breakdown of its specifications, physical properties, and typical applications. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Part Number** | 5ST400-R | | **Current Rating** | 400 mA (0.4A) | | **Voltage Rating (AC)** | 250 V | | **Fuse Type** | Time-Lag / Slow Blow (T) | | **Breaking Capacity** | 35A @ 250V AC | | **Mounting Type** | Through-Hole (Cartridge Style) | | **Size/Dimension** | 5mm x 20mm (Standard Miniature size) | | **Material** | Glass Body / Nickel Plated Brass Caps | --- ### 2. Operational Characteristics The "R" suffix in the part number indicates compliance with **RoHS (Restriction of Hazardous Substances)**, meaning it is lead-free and environmentally friendly. * **Time-Lag (Slow Blow):** Unlike "Fast Acting" fuses, the 5ST400-R is designed to withstand temporary surges in current (inrush currents) without blowing. This is essential for circuits with motors or capacitors that pull high current for a fraction of a second upon startup. * **Interrupting Rating:** It can safely interrupt a short circuit of up to 35 Amperes at its rated voltage of 250V AC. * **Operating Temperature:** Typically rated to function between **-55°C to +125°C**, making it suitable for industrial environments. --- ### 3. Physical Construction The fuse consists of three main parts: 1. **Glass Tube:** Transparent body allowing for easy visual inspection to see if the internal filament has melted. 2. **End Caps:** Nickel-plated brass caps for high conductivity and corrosion resistance. 3. **Filament:** A specifically calibrated wire or spiral element that melts when the current exceeds 400mA for a sustained period. --- ### 4. Common Applications Due to its 400mA rating and slow-blow nature, this part is commonly used in: * **Power Supplies:** Protecting the primary side of low-wattage AC/DC adapters. * **Consumer Electronics:** Televisions, audio equipment, and chargers. * **Industrial Equipment:** Control boards where small motors or solenoids might cause brief current spikes. * **LED Lighting:** Drivers that experience inrush current during power-on. --- ### 5. Part Number Breakdown ```text 5ST - Series Name (5x20mm Time-Lag Glass Fuse) 400 - Amperage Rating (400 Milliamperes) -R - RoHS Compliant ```