The **LD1-3R9-R** is a high-current, surface-mount (SMD) power inductor typically manufactured by Eaton (formerly Cooper Bussmann/Coiltronics). It is part of the LD series, designed for high-density power applications. ### 1. Technical Specifications Below are the primary electrical and physical characteristics of the LD1-3R9-R: | Parameter | Value | | :--- | :--- | | **Inductance** | 3.9 µH (Microhenries) | | **Tolerance** | ±20% | | **Current Rating (Irms)** | ~2.55 A (Amperes) | | **Saturation Current (Isat)** | ~3.15 A (Amperes) | | **DC Resistance (DCR)** | 0.053 Ω (Max) | | **Package / Case** | SMD (approx. 6.1mm x 5.6mm) | | **Operating Temperature** | -40°C to +125°C | --- ### 2. Core Components and Materials The "Electronic Parts" or internal structure of this component consist of: * **Ferrite Drum Core:** The central "bone" of the component made of ferrite material, which provides high magnetic permeability while minimizing eddy current losses. * **Copper Wire (Winding):** An insulated copper wire is wound around the ferrite core. The thickness and number of turns determine the 3.9 µH inductance and the current handling capability. * **Solder Pads:** Lead-free (RoHS compliant) terminations used to mount the part onto a Printed Circuit Board (PCB). * **Protective Coating:** Often features a resin or lacquer coating to protect the copper windings from environmental moisture and vibration. --- ### 3. Part Number Breakdown Understanding the nomenclature helps identify its specific properties: | Segment | Meaning | | :--- | :--- | | **LD** | Series Name (Low Profile, High Current Inductor) | | **1** | Size Code (Physical dimensions of the footprint) | | **3R9** | Inductance Value (3.9 µH; R acts as the decimal point) | | **-R** | RoHS Compliant / Lead-Free | --- ### 4. Common Applications This specific inductor is generally used in power management circuits where space is limited but efficiency is required: 1. **DC-DC Converters:** Used in buck, boost, or buck-boost regulators. 2. **Voltage Regulator Modules (VRMs):** Common in laptops and desktop motherboards. 3. **Battery Powered Devices:** Used in handheld electronics to filter noise and manage power. 4. **LED Drivers:** Provides steady current for high-brightness lighting. ---