September.09,2025
A power inductor, sometimes referred to as an inductor coil or choke inductor, is a passive electronic component made of wire wound around a ferrite core with an air gap. It is primarily used to smooth or filter the output of high-frequency switching power supplies.
Choosing a suitable inductor involves more than simply selecting an inductance value. To ensure reliable performance within a circuit, several key specifications must be evaluated. Power inductors are generally classified based on factors such as:
DC resistance
Tolerance
Package dimensions
Nominal inductance
Packaging type
Shielding method
Maximum rated current
An inductor is defined by its structure and the materials used. It is created by winding insulated copper wire into a coil around a core material, often ferrite, resulting in a two-terminal passive component. When current passes through the coil, a magnetic field forms, and an electromotive force (EMF) is induced based on the rate at which the magnetic flux changes. By storing energy within this magnetic field, inductors provide low magnetic radiation, making them suitable for low-noise applications.
Within a circuit, a power inductor functions as an energy storage element. During the on-time of the circuit, it accumulates energy in its magnetic field, and during the off-time, it releases that stored energy to the load.
To understand how AC and DC behave in a power inductor, it is essential to consider Lenz’s Law. This law explains that when a changing magnetic field induces a current in a conductor, the resulting magnetic field will oppose the change that created it.
When alternating current (AC) passes through an inductor, the changing current is resisted by the inductor, which increases its reactance. In line with Lenz’s Law, this generates a magnetic field whose strength depends on the AC frequency. The higher the frequency, the greater the rate of current change and the stronger the inductor’s blocking effect.
In contrast, when direct current (DC) flows steadily through an inductor, it produces a stable magnetic field with constant magnetic flux. Because there is no change in current, no self-induction or induced voltage occurs, and the inductor offers no opposition to the DC flow.
Inductance refers to the electromotive force generated in an electrical circuit as a result of a changing current. A power inductor resists variations in current flow, which allows it to block or “choke” high-frequency signals while permitting lower-frequency signals to pass through—hence the common nickname “choke.”
This reactance provides opposition to alternating current (AC) while allowing direct current (DC) to pass. However, in practical applications, an inductor may still encounter ripple voltage, which is the residual AC component that remains on a DC output after AC has been converted to DC.
When a power inductor is used to smooth ripple current in the output of a DC/DC converter, it is often specified with an inductance tolerance of around ±20%. Tolerance represents the difference between the actual inductance of the component and the value listed in the datasheet, typically measured at room temperature. Because inductance can change significantly with temperature, it is essential to evaluate performance over the full operating range.
The temperature coefficient of inductance varies by design and material. Standard wire-wound and ceramic inductors typically have a coefficient of about +25 to +125 ppm/°C, while ferrite-core inductors can exhibit much broader coefficients, reaching 700 ppm/°C or more.
Yes, the inductance of an inductor changes as the frequency of the applied voltage increases.
In a standard inductor, the nominal inductance rises to a peak as frequency increases, but parasitic capacitance eventually comes into play and reduces the effective inductance to zero at the component’s self-resonant frequency. Below this resonance point, the inductor behaves with its normal inductive characteristics, while beyond it, the parasitic effects dominate the response.
Inductors function based on two fundamental principles of electromagnetism: Ampere’s Law and Faraday’s Law.
Ampere’s Law
Ampere’s Law defines the relationship between the current flowing through a wire wound around a core and the resulting magnetic field within the inductor’s core. It states that, for any closed loop, the sum of the magnetic field along the path multiplied by the path length equals the permeability of the core multiplied by the electric current in the loop.
From the datasheet specifications of an inductor, the magnetic field strength can be determined using:
Where:
B is the magnetic field
µ is the permeability of the core
I is the current
n is the number of coil turns
Faraday’s Law
Faraday’s Law explains how a changing magnetic environment around a coil induces a voltage (EMF) in the coil. The induced voltage is equal to the negative rate of change of magnetic flux multiplied by the number of turns in the coil. This voltage can be produced by variations in magnetic field strength, moving a magnet relative to the coil, moving the coil within a magnetic field, or rotating the coil in relation to a magnet. EMF is measured in volts.
Where:
N is the number of turns in the coil
Φ is the magnetic flux
B is the external magnetic field
A is the coil area
t is time
Together, these laws show that ferrite cores, commonly used in inductors, provide high permeability, creating low magnetic reluctance. This allows the magnetic flux to be efficiently contained within the core, enabling inductors to achieve high inductance values in a compact size.
One common challenge in modern electronics is the quality of the power source. Voltage instability, phase noise, and fluctuating current can all disrupt device performance or even cause failure. Inductors help address these issues by filtering out voltage spikes, unwanted noise, and current variations, ensuring a clean and stable DC power supply.
Typical applications for low DC resistance, shielded inductors include:
DC/DC line conditioning
AC/DC power supplies
Digital switch-mode power supplies
Differential mode filtering
Signal line chokes
Other common uses of inductors include:
RF tuning circuits
RFI suppression
Energy storage
Inductive sensors
Filters
These applications highlight the critical role of inductors in maintaining reliable performance and efficiency in electronic systems.
Power inductors play a vital role in ensuring clean, stable, and efficient operation of electronic systems. For reliable performance and high-quality solutions, trust YET to provide advanced inductors designed to meet your demanding applications.
