The **SD25-221-R** is a specific model of power inductor manufactured by **Eaton (formerly Bussmann)**. It belongs to the SD25 series of low-profile, shielded drum core inductors designed for high power density applications. --- ### 1. Key Specifications The technical identity of the SD25-221-R can be broken down into the following parameters: | Parameter | Value / Detail | | :--- | :--- | | **Inductance** | 220 µH (Microhenries) | | **Tolerance** | ±20% | | **Current Rating (Irms)** | ~0.45 Amps (Current causing 40°C rise) | | **Saturation Current (Isat)** | ~0.49 Amps (Current causing 30% drop in L) | | **DC Resistance (DCR)** | ~1.11 Ohms (Maximum) | | **Package / Case** | Surface Mount (SMD) | | **Dimensions** | 5.2mm x 5.2mm x 2.5mm | | **Shielding** | Ferrite Drum Core (Shielded) | --- ### 2. Functional Characteristics #### A. Shielded Construction The "SD" in the part number stands for **Shielded Drum**. The inductor is encased in a ferrite material that contains the magnetic flux. This is critical for: * **Low EMI:** Reducing electromagnetic interference with neighboring components. * **High Density:** Allowing components to be placed closer together on a PCB. #### B. The "-R" Suffix The suffix "-R" indicates that the part is **RoHS Compliant**. This means it is manufactured without hazardous substances like lead, making it suitable for modern environmental standards and global manufacturing. --- ### 3. Common Applications The SD25-221-R is typically found in power management circuits where space is limited and efficiency is required: 1. **DC-DC Converters:** Used in Buck, Boost, and SEPIC topologies. 2. **Portable Electronics:** Smartphones, tablets, and handheld devices due to its low 2.5mm profile. 3. **LED Drivers:** Providing stable current for lighting applications. 4. **Computer Peripherals:** Hard drives and solid-state drives. --- ### 4. Part Number Breakdown `SD` `25` - `221` - `R` * **SD:** Series (Shielded Drum Inductor). * **25:** Size code (refers to the physical height/footprint). * **221:** Inductance code. The first two digits (22) are the value, and the third (1) is the number of zeros. $22 \times 10^1 = 220$ µH. * **R:** RoHS compliant. ---