Applications and Types of Inductance Coils

The applications of inductance coils are divided into three categories: choking, filtering, and oscillating.

1. Choking

In low-frequency circuits, it is used to block low-frequency alternating current (AC) and convert pulsating direct current (DC) into pure DC. It is commonly placed between two filter capacitors at the output of a rectifier circuit. In high-frequency circuits, inductance coils prevent high-frequency currents from flowing to the low-frequency side.

2. Filtering

It blocks the pulsating DC current after rectification from flowing into the pureDC circuit. By utilizing the charging/discharging effect of capacitors and the characteristics of chokes (conducting DC while blocking AC), it smooths the pulsating DC to obtain pure DC.

3. Oscillating

Rectification converts AC to DC, while oscillation is the reverse process of converting DC to AC. The circuit that accomplishes this is called an oscillator.

Waveforms of oscillators: Include sinusoidal waves, sawtooth waves, trapezoidal waves, square waves, rectangular waves, and spike waves. Frequencies range from several hertz (Hz) to tens of gigahertz (GHz), with wide applications in wired and wireless communication fields.

In a circuit, when current flows through a conductor, an electromagnetic field is generated. The inductance is defined as the ratio of the electromagnetic field's magnitude to the current magnitude. Inductance is a physical quantity that measures a coil's ability to generate electromagnetic induction. When current is passed through a coil, a magnetic field is generated around it, and magnetic flux passes through the coil. The greater the current through the coil, the stronger the magnetic field and the larger the magnetic flux through the coil. Experiments show that the magnetic flux through a coil is proportional to the current, and their ratio is called the self-inductance coefficient, or inductance.

The mechanism of inductance lies in the generation of a changing magnetic field by non-steady currents, which in turn affects the current. Therefore, any conductor carrying non-steady current will generate a changing magnetic field and exhibit self-inductance, meaning self-inductance occurs in all conductors under non-steady current conditions.

On circuit boards, many copper wire-wound coils can be seen, which are called inductors. Inductors are mainly divided into two types: core inductors and air-core inductors (hollow inductors):

Core inductors: Have large inductance values and are commonly used in filtering circuits.

Air-core inductors: Have small inductance values and are commonly used in high-frequency circuits.

Inductors exhibit characteristics opposite to capacitors: they allow DC to pass through while blocking AC. The higher the frequency, the greater the impedance of the coil. Inductors often work with capacitors in circuits to form LC filters, LC oscillators, etc. Additionally, based on the characteristics of inductance, components such as choke coils, transformers, and relays have been developed.