## Overview of FSMD025-1206-R The **FSMD025-1206-R** is a Surface Mount Device (SMD) Resettable Fuse, specifically a **Polymeric Positive Temperature Coefficient (PPTC)** device. It is manufactured by companies like Littelfuse or Fuse-Tech and is designed to protect electrical circuits from overcurrent and short-circuit conditions. --- ### Technical Specifications | Parameter | Value / Description | | :--- | :--- | | **Part Number** | FSMD025-1206-R | | **Hold Current ($I_{hold}$)** | 0.25 Amps (250mA) | | **Trip Current ($I_{trip}$)** | 0.50 Amps (500mA) | | **Maximum Voltage ($V_{max}$)** | 16V - 30V (Depending on specific series/brand) | | **Maximum Current ($I_{max}$)** | 40A - 100A | | **Package Size** | 1206 (3.2mm x 1.6mm) | | **Operating Temperature** | -40°C to +85°C | --- ### Key Features & Components 1. **Material Construction**: The device is made of a non-conductive polymer mixed with conductive carbon black particles. Under normal conditions, these particles form a conductive chain, allowing current to flow with low resistance. 2. **Resettable Mechanism**: * **Normal Operation**: The device remains in a low-resistance state. * **Fault State**: When excess current flows, internal heating causes the polymer to expand. This breaks the carbon chains, increasing resistance drastically and limiting the current to a safe level. * **Reset**: Once the power is removed and the device cools down, the polymer contracts, the carbon chains reconnect, and the fuse resets to a low-resistance state. 3. **1206 Form Factor**: The "1206" refers to the physical dimensions in inches (0.12" x 0.06"), making it suitable for automated SMT (Surface Mount Technology) assembly on dense Printed Circuit Boards (PCBs). --- ### Typical Applications * **USB Port Protection**: Safeguards against overcurrent in peripherals. * **Battery Packs**: Protects Li-ion or NiMH cells from discharging too quickly. * **Consumer Electronics**: Used in smartphones, tablets, and gaming consoles. * **Industrial Controls**: Protects sensors and low-voltage communication lines. --- ### How to read the Part Number ```text F S M D 025 - 1206 - R | | | | | | | | | | | | | +-- RoHs Compliant / Tape & Reel | | | | | +--------- Package Size (1206) | | | | +------------------ Hold Current (0.25A) +--+--+--+---------------------- Fuse Surface Mount Device ```