What Does an Inductor Do to Current?

In electronic circuits, an inductor is a passive component that plays a crucial role in controlling and modifying the flow of current. Its primary function is to oppose changes in current, which in turn generates voltage and stores energy in its magnetic field.

Magnetic Flux and Self-Inductance

When a current flows through an inductor, it generates a magnetic flux. This magnetic flux is directly proportional to the current passing through the inductor. As a result, a self-inductance is established, and the inductor opposes any changes in the current in order to maintain the magnetic field.

Inductor Voltage and Current Relationship

The relationship between the voltage V and the current I in an inductor is described by the fundamental equation:

V L × dI/dt

This equation indicates that the voltage across an inductor is directly proportional to the rate of change of current. If the current is constant, no voltage is induced, but when the current changes, a voltage is generated. This voltage leads the current by 90 degrees.

Inductive and Capacitive Circuits

Compared to a capacitor, an inductor behaves differently in terms of how it interacts with voltage and current:

Inductive Circuit (ELI the ICE man): In an inductive circuit, the voltage E leads the current I. This is a key concept in understanding the behavior of inductors, as it affects the phase shift between voltage and current during alternating current (AC) operation. Capacitive Circuit (ICE): In contrast, in a capacitive circuit, the current I leads the voltage V. This phase relationship is the opposite of that in an inductive circuit, which is useful to distinguish and analyze the two components' behaviors.

Impedance and Phase Shift

The impedance of an inductor depends on its self-inductance L and the frequency of the applied signal. Typically, for AC signals, the voltage across an inductor leads the current, which is a fundamental property of inductive circuits. This phase shift is critical for designing circuits that require specific tuning or filtering.

Energy Storage and Release

An inductor stores energy in its magnetic field, which it opposes when the current is changing. When the inductor is part of a circuit, it resists changes in current by generating a voltage that opposes the change. This phenomenon can be observed in both the charging and discharging processes, with some key differences:

Charging: When a constant voltage is applied across an inductor, the current starts from zero and rises linearly with time. This is similar to charging a capacitor, but the roles of current and voltage are interchanged. Discharging: When the voltage is removed or changed, the inductor attempts to maintain its current, much like a resistor would oppose the change. However, the energy stored in the magnetic field will be released, causing the inductor's voltage to potentially rise to high values, which can be dangerous if not managed carefully.

It's essential to consider the resistive losses in the inductor, which can dissipate energy as heat. These losses can be minimized with superconducting materials, although they are not practical for most applications. For conventional inductors, the losses are always present, but they can be reduced by optimizing the core material and wire conductivity.

Understanding these principles is crucial for engineers and electronics enthusiasts to effectively utilize inductors in a wide range of applications, from electrical motors to power supplies and filtering circuits.