The **SDQ25-221-R** is a specific surface-mount (SMD) power inductor from the **SDQ series**, manufactured by Eaton (formerly Bussmann/Coiltronics). These components are known as "Dual Winding" or "Coupled" inductors, meaning they contain two separate coils inside a single package. --- ### 1. Key Technical Specifications The part number follows a specific nomenclature that defines its electrical characteristics: | Parameter | Specification | | :--- | :--- | | **Inductance** | 220 µH (indicated by "221") | | **Tolerance** | ±20% | | **Configuration** | Dual Winding (Coupled Inductor) | | **DCR (Direct Current Resistance)** | High (typically used for low-current applications) | | **Operating Temperature** | -40°C to +125°C | | **Package Size** | 5.2mm x 5.2mm x 2.5mm | --- ### 2. Physical Structure and Pinout The SDQ25 series features a shielded construction to minimize Electromagnetic Interference (EMI). * **Four-Terminal Design:** Because it has two windings, it has four pads on the bottom. * **Winding Ratio:** It has a **1:1 turns ratio**, meaning both coils are identical. * **Shielding:** The ferrite drum and sleeve construction provides magnetic shielding, which is critical for high-density PCB layouts. --- ### 3. Functional Use Cases Because this part contains two windings, it is highly versatile and can be used in several ways: 1. **SEPIC Converters:** The primary use for coupled inductors is in Single-Ended Primary-Inductor Converters (SEPIC), where two inductors are needed to allow the output voltage to be higher or lower than the input. 2. **Flyback Transformers:** It can act as a miniature 1:1 transformer for isolated power supplies. 3. **Common Mode Choke:** It can be used to filter out noise in data or power lines by passing signals through both windings. 4. **Parallel/Series Inductor:** * **Series:** Connecting the coils in series quadruples the inductance ($L_{total} = 4 \times 220\mu H$). * **Parallel:** Connecting them in parallel keeps the inductance at $220\mu H$ but increases the current carrying capacity. --- ### 4. Circuit Symbol Representation ```text 1 o---( Coil 1 )---o 2 4 o---( Coil 2 )---o 3 ``` *Note: Dots on the schematic usually indicate the polarity/phase of the windings.*