## Overview: FSMD016-1206-R The **FSMD016-1206-R** is a surface-mount (SMD) **Resettable PTC (Positive Temperature Coefficient) Fuse**, also known as a **PolySwitch** or **PPTC**. 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 part number itself contains information about its package size and current rating. | Property | Specification | | :--- | :--- | | **Package / Case** | 1206 (3216 Metric) | | **Hold Current ($I_{hold}$)** | 0.16 A (160 mA) | | **Trip Current ($I_{trip}$)** | 0.37 A (370 mA) | | **Maximum Voltage ($V_{max}$)** | 30V - 60V (Varies by series) | | **Maximum Current ($I_{max}$)** | 40 A | | **Power Dissipation ($P_d$ typ.)** | 0.6 W | | **Mounting Type** | Surface Mount (SMD/SMT) | --- ### 2. How it Works Unlike a standard one-time fuse that blows and must be replaced, this PTC device acts like a **smart resistor**: 1. **Normal State:** Under normal current ($I_{hold}$), the device has very low resistance. 2. **Fault State:** If the current exceeds the trip threshold ($I_{trip}$), the internal polymer heats up, causing its resistance to increase exponentially. This "trips" the fuse, limiting the current to a safe leakage level. 3. **Reset State:** Once the power is removed or the fault is cleared, the device cools down and returns to a low-resistance state, "resetting" itself for further use. --- ### 3. Physical Dimensions The **1206** designation refers to the physical size of the component in inches: * **Length:** 3.20 mm (0.126") * **Width:** 1.60 mm (0.063") * **Height:** Generally thin, approximately 0.50 mm to 1.00 mm. --- ### 4. Common Applications Due to its small size and resettable nature, it is commonly used in: * **USB Port Protection:** Protecting against shorts in peripherals. * **Battery Packs:** Preventing excessive discharge or charging currents. * **Consumer Electronics:** Power supplies for tablets, smartphones, and IoT devices. * **Industrial Controls:** Protecting sensors and low-voltage signal lines. --- ### 5. Part Number Breakdown * **FSMD:** Formosa SMD series. * **016:** Represents the Hold Current (0.16 Amps). * **1206:** The EIA package size (1.2 x 0.6 inches). * **R:** Usually indicates RoHS compliance or Tape & Reel packaging.