What Is a Variable Inductor?
An inductor (coil) is an electronic component made by wrapping copper wire around an iron core. When an electric current is applied to the copper wire in the inductor and the amount of the current is varied, it generates an induced electromotive force. This is called inductance and is expressed in units of Henleys (H).
A variable inductor is a device whose inductance can be varied by placing a small driver or adjusting the rod on top of the device and rotating a knob to slide the internal iron core up and down.
Applications of Variable Inductors
In general, inductors are used in many electrical products. A familiar example is an AC transformer.
Since it transmits high frequencies, it is also used in various wireless devices (WiFi and non-contact IC chips) and microwave ovens. They are also used in fluorescent light ballasts and various electrical products and are indispensable components for rectifying electronic circuits.
Variable inductors are used in a limited number of applications, such as tuning circuits for car tuners, but are now used less frequently due to the digitization of circuits.
Principles of Variable Inductors
The basic principle of operation of variable inductors is the same as that of fixed inductors.
When a DC current is applied to the coil, a magnetic field is generated in the iron core, and the core becomes an electromagnet.
When a voltage is initially applied or when the voltage is lowered, an induced current flows instantaneously in the moving wires. This causes electrical energy to be stored in the form of a magnetic field.
After a magnetic field of a certain strength is generated, a direct current flows, just like an ordinary copper wire. In contrast, when an alternating current flows through an inductor coil, a magnetic field of varying magnitude is generated in the iron core.
As the magnetic field changes, induced electromotive force in the opposite direction of the current is generated, resulting in resistance (inductance). If an alternating current continues to flow, an induced electromotive force in the opposite direction is always generated, so the current continues to have difficulty flowing.
In the case of an inductor coil, DC current can pass through smoothly, but AC current is challenging to flow because of the resistance generated. Therefore, it is an electronic component with the opposite characteristics of a capacitor, allowing AC current to pass through but not allowing DC current to pass through.