The **GMA-3-R** is a specific type of high-performance, sub-miniature **fast-acting fuse** commonly used in electronic circuits to protect sensitive components from overcurrent conditions. It belongs to the GMA series, typically manufactured by brands like Eaton (Bussmann) or Littelfuse. Below is a detailed breakdown of its electronic specifications and characteristics. --- ### 1. Technical Specifications The "GMA-3-R" designation follows a standardized naming convention where the "3" represents the amperage and the "R" signifies RoHS compliance. | Feature | Specification | | :--- | :--- | | **Current Rating** | 3 Amperes (3A) | | **Voltage Rating** | 250V AC (Standard) | | **Response Speed** | Fast-Acting (F) | | **Body Material** | Glass Tube | | **Dimensions** | 5mm x 20mm | | **Interrupt Rating** | 100A at 250Vac / 10kA at 125Vac | | **Termination Style** | Cartridge (Ferrule) | --- ### 2. Core Electronic Components While a fuse appears simple, the GMA-3-R is engineered with specific materials to ensure precise failure points: * **The Element:** A thin wire or metallic strip (usually silver-plated copper or alloy) designed to melt when the current exceeds 3A. Because it is "Fast-Acting," it lacks the thermal mass found in "Slow-Blow" fuses, allowing it to pop almost instantly. * **The Housing:** A clear glass cylinder. This allows for visual inspection to see if the internal element has burned out. * **End Caps:** Nickel-plated brass caps that provide high conductivity and corrosion resistance for the electrical contact points. --- ### 3. Operating Principle The GMA-3-R operates on the principle of **Joule Heating** ($P = I^2R$). 1. **Normal State:** The element has very low resistance, allowing current to pass with minimal heat generation. 2. **Overload State:** If the current rises significantly above 3A, the heat generated exceeds the element's melting point. 3. **Circuit Break:** The wire melts and creates an air gap (arc), stopping the flow of electricity to protect downstream components like ICs, transformers, or transistors. --- ### 4. Common Applications Due to its small form factor ($5 \times 20$mm) and fast response time, the GMA-3-R is found in: * **Power Supplies:** Protecting the input stage of AC/DC adapters. * **Consumer Electronics:** Televisions, audio amplifiers, and chargers. * **Test Equipment:** Multimeters and oscilloscopes. * **Industrial Controls:** Small control circuits where instant disconnection is required during a short circuit. --- ### 5. Identification Code Breakdown `GMA` - `3` - `R` * **GMA:** Series prefix (5x20mm Glass, Fast-acting). * **3:** Rated current in Amperes. * **R:** RoHS Compliant (Lead-free construction).