Inductors are components that can generate inductance and are commonly referred to as inductors. They are electromagnetic induction elements made by winding insulated wires, such as enameled wire or silk-wrapped wire. Inductors are widely used in electronic circuits. Their main function is to block AC signals while allowing DC to pass through, and they can also be used for filtering, combining with capacitors and resistors to form resonant circuits, or for tuning, frequency selection, and decoupling. Inductors work based on the principle of electromagnetic induction. In an AC circuit, inductors impede the flow of AC but have no effect on DC (except for the coil's own DC resistance). Therefore, inductors can be used for blocking, step-down, cross-linking, and load management in AC circuits. When paired with capacitors, they can be used for tuning, filtering, and frequency selection. As a fundamental component, inductors play a crucial role in circuit design.
The unit of inductance is named after the scientist Joseph Henry, and it is called "Henry" (H). The symbol for inductance is L, and common units include Hen (H), millihenry (mH), and microhenry (μH). The conversion between these units is 1 H = 1000 mH = 1,000,000 μH.
Inductor models typically consist of four parts: the first part indicates the main name, where L represents an inductor and ZL denotes a choke. The second part describes the characteristics, such as G for high-frequency applications. The third part refers to the type, like X for small size, and the fourth part is the difference code, which may be numbers or letters. For example, LGX stands for a small high-frequency inductor. However, it should be noted that different manufacturers may use varying naming conventions, so there is no universal standard.
Structurally, inductors are composed of a skeleton, windings, shield, packaging material, core, or magnetic rod. The skeleton supports the coil, and some large fixed or adjustable inductors are wrapped around cores such as iron or copper to increase their inductance. The skeleton is usually made of plastic, bakelite, or ceramic. Windings can be single-layer or multi-layer, including flat, chaotic, or honeycomb types. Cores and magnetic rods are often made from materials like nickel-zinc or manganese-zinc ferrite, available in various shapes such as E-shaped, column-shaped, or can-shaped. Shields are used to prevent interference from magnetic fields, although they can increase losses and reduce the Q factor. Packaging materials like plastic or epoxy resin are used to protect the coil and core.
Small fixed inductors are often wound directly on cores using enameled wires and are used for filtering, oscillation, and delay functions. They come in both sealed and non-sealed packages, with vertical and horizontal structures. Vertical sealed inductors, such as LG and LG2 series, have inductance ranges from 0.1 to 2200 μH and rated currents up to 1.6 A. Horizontal sealed inductors, like LG1, LGA, and LGX series, offer similar specifications. These inductors are used in various applications, including color-coded and color-ring inductors.
Inductance markings can be done using the straight standard method, where parameters are marked directly on the casing, or the color standard method, similar to resistor color coding. The inductance symbol is often represented in diagrams or schematics.
Key characteristic parameters of inductors include nominal inductance, allowable error, inductive reactance (XL), quality factor (Q), rated current, nominal voltage, distributed capacitance, and self-resonant frequency. The inductive reactance XL is calculated as XL = 2Ï€fL, where f is the frequency and L is the inductance. The quality factor Q reflects the efficiency of the coil, with higher values indicating lower losses. Distributed capacitance affects the stability and Q value of the inductor, and reducing it through segmented winding improves performance. Self-resonant frequency is the point at which the inductor transitions from inductive to capacitive behavior, affecting its performance at high frequencies.
Inductors can be classified based on shape, application, and package type. Hollow inductors (air-core) are used in high-frequency circuits, while solid inductors are used in general signal and power applications. Fixed inductors have a set inductance value, while tunable inductors allow adjustment. Common types include chip inductors, color ring inductors, and axial inductors.
When selecting inductors, factors such as operating frequency, required inductance, DC resistance, and rated current must be considered. High-frequency inductors are designed to operate above their self-resonant frequency, while general signal inductors are used for high-speed signals. Power supply inductors are optimized for filtering and handling higher currents.
Inductor packages include surface-mount (SMD) and through-hole types. SMD inductors are available in sizes like 0603, 0805, and 1206, while through-hole inductors are labeled with wattage ratings such as 1/8W, 1/4W, etc. Color ring inductors use color bands to indicate inductance values, similar to resistors. Vertical and axial inductors have specific dimensions and ratings, while magnetic ring inductors are used for compact designs.
Inductors serve multiple roles in circuits, including filtering, oscillation, delay, and notch functions. They are known for "passing DC and blocking AC." In combination with capacitors, they form LC filter circuits, which help eliminate noise and improve signal quality. The energy stored in an inductor is given by WL = ½Li², showing that larger inductance values store more energy.
Derating of magnetic components involves reducing their operational parameters to ensure reliability under stress conditions. For example, inductors should be derated by 90% in terms of DC and surge currents, and 90% in terms of surge voltage.
When choosing inductors, factors such as environmental conditions, frequency characteristics, maximum current rating, and material properties must be considered. Ferrite materials are commonly used for high-frequency applications due to their low loss and high permeability. Proper selection ensures optimal performance and longevity in electronic circuits.
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