Essential Parameters for Inductor Design

I. An inductor is a component capable of converting electrical energy into magnetic energy and storing it. The structure of an inductor is similar to that of a transformer but with only one winding. An inductor possesses a certain inductance, which impedes changes in current. If the inductor is in a state with no current flow when the circuit is connected, it will attempt to阻止 the flow of current through it. If the inductor is in a state with current flow when the circuit is disconnected, it will attempt to maintain the current unchanged. Inductors are also known as chokes, reactors, or dynamic reactors.

II. Traditionally, inductors generally consist of a bobbin, winding, shielding cover, packaging material, magnetic core, or iron core.

1. Bobbin: The bobbin generally refers to the bracket used for winding the coil. Larger fixed inductors or adjustable inductors (such as oscillation coils and choke coils) are typically made by winding enameled wire (or yarn-covered wire) around a bobbin, and then inserting a magnetic core, copper core, or iron core into the inner cavity of the bobbin to increase the inductance. The bobbin is usually made of plastic, bakelite, or ceramic and can be shaped as needed. Small inductors (e.g., color-code inductors) generally do not use a bobbin and instead directly wind the enameled wire around the magnetic core. Air-core inductors (also known as air-core coils, often used in high-frequency circuits) do not use a magnetic core, bobbin, or shielding cover. Instead, they are wound on a mold and then removed from the mold, with the coils spaced a certain distance apart.
   
2. Winding: The winding refers to a set of coils with specified functions and is the basic component of an inductor. Windings can be single-layer or multi-layer. Single-layer windings can be closely wound (with wires wound side by side) or spaced wound (with a certain distance between each turn of wire). Multi-layer windings include layered parallel winding, random winding, and honeycomb winding, among others.
   
3. Magnetic Core and Magnetic Rod: Magnetic cores and rods are generally made of materials such as nickel-zinc ferrite (NX series) or manganese-zinc ferrite (MX series). They come in various shapes, including 'I'-shaped, cylindrical, cap-shaped, 'E'-shaped, and pot-shaped.
   
4. Iron Core: Iron core materials mainly include silicon steel sheets and permalloy, with 'E'-shaped being the most common form.
   
5. Shielding Cover: To prevent the magnetic field generated by some inductors during operation from affecting other circuits and components, a metal shielding cover is added (e.g., the oscillation coil in a semiconductor radio). The use of a shielding cover increases the loss of the coil and reduces the Q value.
   
6. Packaging Material: Some inductors (e.g., color-code inductors and color-ring inductors) are sealed with packaging materials after winding. Packaging materials typically include plastic or epoxy resin.
   
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III. Inductor Classification
Based on the function of inductors in circuits, commonly used inductors can be categorized as follows:

1. Input/Output Common-Mode Inductor: Used for common-mode suppression and filtering high-frequency interference harmonics. The core is made of high-permeability material.
   
2. Input/Output Differential-Mode Inductor: Used for differential-mode suppression and filtering high-frequency interference harmonics. The core is made of power-type material.
   
3. PFC (Power Factor Correction) Inductor: Used for power factor adjustment. It is a power device, and the core is selected from power core types.
   
4. Resonant Inductor: Used in LLC resonant circuits. It is a power device, and the core is selected from power core types.
   
5. Input/Output Buck and Smoothing Filter Inductor: Used for step-up/step-down and smoothing filtering functions. It is a power device, and the core is selected from power core types.
   
6. Filter Inductor in High-Frequency Circuits: Used for filtering high-frequency noise in various control boards. It is a power device, and the core is selected from power core types.
   
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