An inductor is a passive electronic component designed to temporarily store energy in a magnetic field when electric current passes through its coil. Its basic structure includes two terminals and a wire coil, and it is also referred to as a coil, choke, or reactor in some contexts. Inductors are instrumental in managing fluctuations in electrical current within a circuit.
Inductors and Inductance
When current flows steadily, it passes through an inductor just like it would through a standard wire without any interference from the inductor. However, the inductor actively resists changes in the current. This resistance causes the current to lag behind the voltage due to the inductor’s magnetic field. Any alterations in current lead to changes in the magnetic field, which can induce an opposing electromagnetic field (EMF). If the current decreases, the EMF will try to increase it, and vice versa.
This property of an inductor to resist changes in current is quantified as inductance, measured in henries (H). Smaller units like millihenries (mH) and microhenries (µH) are commonly used as henries represent a large quantity. Factors influencing inductance include the number of wire turns, the length of the coil, the core material, and the core’s dimensions and shape.
Air core inductors have the least inductance, while ferromagnetic materials like iron can significantly enhance inductance, sometimes by thousands of times. The geometry of the core, such as toroidal versus cylindrical shapes, also affects inductance levels. Although integrating inductors onto integrated circuit (IC) chips is challenging due to low inductance, it is feasible, and inductance can sometimes be emulated using transistors, resistors, and capacitors.
What are Inductors Used For?
Inductors serve crucial roles in electronic circuitry, primarily as filters that block unwanted high-frequency signals. For instance, they can eliminate higher harmonics or noise in a power supply, allowing a clean line frequency of 50/60 Hz. Inductors are often paired with capacitors to create frequency band-pass or tuned circuits, which specify allowed frequencies by blocking others.
These band-pass circuits find applications in wireless communications, audio systems, and graphic equalizers. For example, simple radios utilize a band-pass filter with a variable capacitor to select specific stations. In modern technology, such circuits are integral to Wi-Fi and 5G radios, effectively reducing interference.
Inductors are also integral to switching power supplies, storing energy as the circuit rapidly turns on and off, which allows control over output voltage. This capability enhances the efficiency of switching power supplies compared to older passive designs.
Differences Between Inductors and Capacitors
Inductors, capacitors, and resistors form the three essential passive components of electronic circuits. While both inductors and capacitors store energy, they do so in distinct ways: inductors store energy as magnetic flux, while capacitors store it as an electric field.
When current first flows to an inductor, it resists the flow until it saturates, after which it allows the current to pass. Conversely, capacitors permit current to flow initially and then resist it once fully charged. This behavior means that inductors effectively block high-frequency signals while allowing low-frequency signals and direct current to pass through. In contrast, capacitors resist low-frequency signals and direct current but allow high-frequency signals to pass.