The **5ST 125-R** is a specific type of electronic component known as a **Subminiature Time-Delay Fuse**. It is part of the 5ST series manufactured by companies like Bel Fuse, designed for primary circuit protection in various electronic devices. --- ### ## Technical Specifications Below are the primary electrical and physical characteristics of the 5ST 125-R: | Feature | Specification | | :--- | :--- | | **Fuse Type** | Glass Body / Cartridge | | **Current Rating** | 125mA (0.125A) | | **Voltage Rating (AC)** | 250V | | **Characteristic** | Time-Delay (Slow Blow) | | **Size / Dimension** | 5mm x 20mm | | **Breaking Capacity** | 35A @ 250V AC | | **Termination Style** | Cartridge (Ferrule) | | **RoHS Status** | Compliant (indicated by the "-R" suffix) | --- ### ## Key Features & Components 1. **Time-Delay (Slow Blow):** Unlike "Fast-Acting" fuses, the 5ST 125-R is designed to withstand temporary surges in current (inrush currents) without blowing. This is essential for circuits with inductive loads like small motors or transformers. 2. **Glass Tube Body:** The transparent housing allows for easy visual inspection to determine if the internal filament has melted (blown). 3. **Nickel-Plated Brass Caps:** The end caps provide high conductivity and corrosion resistance for secure contact in a fuse holder or clip. 4. **The "-R" Suffix:** In the Bel Fuse nomenclature, the "R" signifies **RoHS compliance**, meaning the part is lead-free and meets environmental safety standards. --- ### ## Common Applications Because of its low amperage and time-delay nature, this fuse is typically found in: * **Power Supplies:** Protecting the input stage of AC/DC adapters. * **Consumer Electronics:** Televisions, audio equipment, and chargers. * **Industrial Equipment:** Small control panels and instrumentation where startup spikes occur. --- ### ## Replacement Safety When replacing a 5ST 125-R, ensure the replacement matches these three critical parameters: 1. **Amperage:** Must be exactly **125mA**. 2. **Voltage:** Must be **250V** or higher (never lower). 3. **Speed:** Must be **Time-Delay (T)**; using a Fast-Acting (F) fuse will cause the fuse to blow immediately upon device startup.