What is a PCB Inductor?

A PCB (Printed Circuit Board) inductor is a passive electronic component that stores energy in the form of a magnetic field when an electric current flows through it. Inductors are widely used in various electronic circuits, such as power supplies, filters, and oscillators, to provide frequency-dependent impedance and to control the flow of alternating current (AC).

PCB inductors are specifically designed to be mounted on printed circuit boards, making them suitable for use in compact electronic devices. They come in various shapes and sizes, including surface-mount devices (SMD) and through-hole components.

Types of PCB Inductors

There are several types of PCB inductors, each with its own characteristics and applications:

1. Air Core Inductors: These inductors have no core material and consist of a coil of wire or a conductive trace on a PCB. Air core inductors have low inductance values and are suitable for high-frequency applications.

2. Ferrite Core Inductors: These inductors have a core made of ferrite material, which is a ceramic compound containing iron oxide. Ferrite core inductors have higher inductance values and better temperature stability compared to air core inductors. They are commonly used in power supply circuits and EMI (Electromagnetic Interference) filters.

3. Iron Powder Core Inductors: These inductors have a core made of compressed iron powder. They offer higher inductance values than air core inductors and better high-frequency performance than ferrite core inductors. Iron powder core inductors are often used in switching power supplies and RF (Radio Frequency) circuits.

4. Multilayer Inductors: These inductors are constructed using multiple layers of conductive material, such as copper, separated by insulating layers. Multilayer inductors have a compact size and high inductance values, making them suitable for use in high-density PCB designs.

Methods of Computing Inductance Value

The inductance value of a PCB inductor is a crucial parameter that determines its performance in a circuit. There are several methods to compute the inductance value, depending on the type of inductor and the available information.

1. Inductance Formula for a Single-Layer Air Core Inductor

For a single-layer air core inductor, the inductance value can be calculated using the following formula:

L = (μ0 × N^2 × A) / l

Where:
– L is the inductance in henries (H)
– μ0 is the permeability of free space (4π × 10^-7 H/m)
– N is the number of turns in the coil
– A is the cross-sectional area of the coil in square meters (m^2)
– l is the length of the coil in meters (m)

2. Inductance Formula for a Multilayer Inductor

For a multilayer inductor, the inductance value can be calculated using the following formula:

L = (μ0 × μr × N^2 × A) / l

Where:
– L is the inductance in henries (H)
– μ0 is the permeability of free space (4π × 10^-7 H/m)
– μr is the relative permeability of the core material
– N is the number of turns in the coil
– A is the cross-sectional area of the coil in square meters (m^2)
– l is the length of the coil in meters (m)

The relative permeability (μr) depends on the core material used in the inductor. Some common values for μr are:

Core Material	Relative Permeability (μr)
Air	1
Ferrite	50-10,000
Iron Powder	5-100

3. Inductance Calculation Using Inductance Factor (AL)

Some PCB inductor manufacturers provide an inductance factor (AL) in their datasheets, which simplifies the inductance calculation. The inductance factor represents the inductance per turn squared and is expressed in nanohenries per turn squared (nH/N^2).

To calculate the inductance value using the inductance factor, use the following formula:

L = AL × N^2

Where:
– L is the inductance in nanohenries (nH)
– AL is the inductance factor in nanohenries per turn squared (nH/N^2)
– N is the number of turns in the coil

4. Inductance Measurement Using an LCR Meter

An LCR meter is an electronic instrument that measures the inductance (L), capacitance (C), and resistance (R) of a component. To measure the inductance value of a PCB inductor using an LCR meter:

1. Set the LCR meter to the inductance measurement mode.
2. Connect the inductor to the LCR meter’s test leads, ensuring proper contact.
3. Set the appropriate test frequency, if applicable.
4. Read the inductance value displayed on the LCR meter’s screen.

Factors Affecting Inductance Value

Several factors can affect the inductance value of a PCB inductor:

1. Number of Turns: The inductance value is proportional to the square of the number of turns in the coil. Increasing the number of turns will result in a higher inductance value.

2. Core Material: The core material’s relative permeability (μr) directly affects the inductance value. Materials with higher relative permeability will result in higher inductance values for the same number of turns and coil dimensions.

3. Coil Dimensions: The cross-sectional area and length of the coil influence the inductance value. Increasing the cross-sectional area or decreasing the length of the coil will result in a higher inductance value.

4. Frequency: The inductance value of a PCB inductor can vary with frequency due to the skin effect and proximity effect. At higher frequencies, the effective cross-sectional area of the conductor decreases, leading to a reduction in inductance value.

5. Temperature: The inductance value of a PCB inductor can change with temperature, primarily due to the temperature dependence of the core material’s permeability. Ferrite core inductors, for example, exhibit a decrease in inductance value as the temperature increases.

Selecting the Right PCB Inductor

When choosing a PCB inductor for a specific application, consider the following factors:

1. Inductance Value: Select an inductor with the appropriate inductance value for your circuit’s requirements. Consider the frequency range, current rating, and desired performance characteristics.

2. Current Rating: Ensure that the inductor can handle the expected current in your circuit without saturating or overheating. Check the inductor’s datasheet for the rated current and saturation current specifications.

3. Frequency Range: Choose an inductor that is suitable for the operating frequency range of your circuit. High-frequency applications may require air core or iron powder core inductors, while lower-frequency applications can use ferrite core inductors.

4. Size and Packaging: Consider the available space on your PCB and select an inductor with a suitable package size. Surface-mount inductors are commonly used in high-density PCB designs, while through-hole inductors are suitable for larger components or higher power applications.

5. Temperature Range: Ensure that the inductor can operate reliably over the expected temperature range of your application. Consider the temperature coefficients of the inductance value and the core material’s properties.

6. Quality Factor (Q): The quality factor is a measure of an inductor’s efficiency in storing energy. A higher Q value indicates lower losses and better performance. Select an inductor with an appropriate Q value for your application’s requirements.

Frequently Asked Questions (FAQ)

1. What is the difference between an inductor and a transformer?

2. An inductor is a passive component that stores energy in a magnetic field, while a transformer is a device that transfers energy between two or more circuits through electromagnetic induction. Inductors have a single winding, while transformers have multiple windings that are magnetically coupled.

3. Can I use an inductor with a different inductance value than the one specified in my circuit design?

4. It is generally not recommended to use an inductor with a significantly different inductance value than the one specified in your circuit design. Changing the inductance value can alter the circuit’s performance, such as the resonant frequency, filtering characteristics, or power efficiency. If you need to make changes, it is advisable to consult with an experienced electronic engineer or refer to the circuit’s design guidelines.

5. How do I determine the current rating of a PCB inductor?

6. The current rating of a PCB inductor is usually specified in the component’s datasheet. There are two important current ratings to consider: the rated current and the saturation current. The rated current is the maximum continuous current the inductor can handle without overheating or damaging the component. The saturation current is the current at which the inductor’s core material begins to saturate, leading to a decrease in inductance value. Ensure that your circuit’s expected current is within the inductor’s rated current and below the saturation current.

7. What is the self-resonant frequency (SRF) of an inductor, and why is it important?

8. The self-resonant frequency (SRF) is the frequency at which an inductor’s parasitic capacitance resonates with its inductance, causing the inductor to behave like a capacitor above this frequency. At the SRF, the inductor’s impedance is at its maximum, and its Q factor drops significantly. It is important to choose an inductor with an SRF well above the operating frequency of your circuit to ensure proper inductive behavior and avoid unwanted resonances.

9. Can I use a PCB inductor in a high-temperature environment?

10. The suitability of a PCB inductor for a high-temperature environment depends on the inductor’s construction and materials. Some inductors are specifically designed for high-temperature applications, using materials with higher thermal stability and insulation ratings. When selecting an inductor for a high-temperature environment, review the component’s datasheet for the maximum operating temperature and any derating curves. Ensure that the inductor can reliably operate at the expected ambient temperature and consider any necessary derating of the current rating or inductance value.