## Overview: FSMD010-1206-R The **FSMD010-1206-R** is a Surface Mount Technology (SMT) **Resettable PTC (Positive Temperature Coefficient) Fuse**, also known as a **PolySwitch**. It is manufactured by companies like Formosa MS and is designed to protect electrical circuits from overcurrent and short-circuit conditions. --- ### 1. Key Technical Specifications The following table summarizes the primary electrical characteristics of the FSMD010-1206-R: | Parameter | Specification | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.10 A (100mA) | The maximum current the device will pass without tripping at 23°C. | | **Trip Current ($I_{trip}$)** | 0.30 A (300mA) | The minimum current that will cause the device to switch to a high-resistance state. | | **Max Voltage ($V_{max}$)** | 30V (or 60V depending on series) | The maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 10A / 40A | The maximum fault current the device can safely interrupt. | | **Package Size** | 1206 (EIA) | Physical dimensions: 3.2mm x 1.6mm (0.12" x 0.06"). | | **Typical Power ($P_d$)** | 0.4 - 0.6 W | Power dissipated when the device is in a tripped state. | --- ### 2. Functional Principles The FSMD010-1206-R operates on the principle of thermal expansion: 1. **Normal Operation:** The device has a low resistance, allowing current to flow to the load. 2. **Overcurrent Event:** Excessive current flows, causing internal heating ($I^2R$). 3. **Tripping:** Once the temperature reaches a critical threshold, the polymer matrix expands, breaking the conductive pathways. Resistance increases sharply, reducing current to a safe leakage level. 4. **Resetting:** Once the fault is removed and the power is cycled or the device cools down, the polymer contracts, restoring the conductive paths and returning the fuse to a low-resistance state. --- ### 3. Physical Dimensions (1206 Package) | Dimension | Minimum (mm) | Maximum (mm) | | :--- | :--- | :--- | | Length (L) | 3.00 | 3.50 | | Width (W) | 1.50 | 1.80 | | Thickness (T) | 0.45 | 0.75 | --- ### 4. Typical Applications * **USB Port Protection:** Protecting ports from shorted peripherals. * **Battery Packs:** Shielding lithium-ion cells from external shorts. * **HDMI/DisplayPort:** Overcurrent protection for signal lines. * **Computer Peripherals:** Protecting motherboards from faulty I/O devices. * **Industrial Controls:** Low-voltage DC power supply protection. --- ### 5. Part Number Breakdown * **FSMD:** Series Name (Formosa Surface Mount Device). * **010:** Hold Current rating (0.10 Amps). * **1206:** Package size (Industry standard 1206). * **R:** Denotes RoHS compliance and Lead-Free.