Planar Inductor Design
Key Takeaways
- The low-profile planar inductors and transformers showcase excellent performance with high efficiency and compact physical sizing.
- The planar magnetic technology utilizing rigid techniques has the limitation of a low window utilization factor.
- The inductance value of a planar inductor fabricated using PCB technology depends on geometrical parameters such as the number of turns, trace width, trace separation, and inner and outer winding diameter.
Planar inductor designs can be circular, rectangular, square, hexagonal, octagonal, etc.
Planar magnetics refers to planar inductors and transformers in power magnetics. Planar technology can convert conventional, more cubical volume magnetics into low-profile magnetics. Planar transformers or planar inductor designs aim to economically increase power density and performance. In this article, let's read more about planar magnetics, especially planar inductors.
The Need for Planar Inductors
Modern power electronics operate at higher frequencies to address load demands. For example, in switched mode power supplies (SMPS), it is common to use high-frequency switching and high-density circuit design for high efficiency and compact sizing. The high-frequency switching benefits the size reduction of the power magnetics. However, losses due to the skin and proximity effects are consequences of increasing the switching frequency.
A novel technology is developed in power magnetics to overcome the difficulties put forward by conventional high-frequency inductors and capacitors. Planar technology offsets the disadvantages of traditional magnetics. The upcoming section gives more details about planar magnetics.
The Merits of Planar Inductors and Transformers
Planar magnetics is a boon to the electronic field of engineering. Low-profile planar inductors and transformers showcase excellent performance with high efficiency and compact physical sizing. Planar inductors and transformers are made of low-profile windings with low leakage and AC winding resistance, reducing losses. The larger surface area brings improved temperature characteristics to the planar magnetic technology.
Planar Magnetic Disadvantages
Planar magnetics are only sometimes beneficial, as there are some disadvantages to planar magnetic technology. Their weaknesses are listed below.
|
Disadvantages |
Description |
|
The number of turns is limited |
A larger number of turns can be achieved in conventional magnetic structures. However, in planar magnetics, the number of turns is limited. |
|
Larger surface area or footprint |
Planar magnetics with a large footprint has both advantages and disadvantages. Even though it improves the thermal characteristics, a larger footprint can limit applications if there are any area constraints. |
|
Low window utilization |
The planar magnetic technology utilizing rigid techniques has the limitation of a low window utilization factor. |
Still, the advantages outweigh the disadvantages. The market demand for compact electronic gadgets encourages the incorporation of planar inductors and transformers in circuit boards.
Planar Magnetic Technologies
There are various technologies available for constructing planar magnetics. Some of the methods are:
- Printed circuit board (PCB) technology
- Flex circuit technology
- Stamped copper-based planar magnetics
- Low-temperature C-fired ceramic (LTCC) based technology
Among the technologies mentioned above, the most economically variable method of planar magnetic construction is the PCB-based method. PCB fabrication technology is so mature that the cost of manufacturing turns out to be low and the predictability is excellent, so the same inductor or transformer replicas with exactly the same parasitic elements can be built.
Planar Inductor Design vs. Planar Transformer Design
Planar inductors are constructed in a similar way as conventional inductors. There are magnetic cores and windings. However, compared with traditional inductors, the difference is that the cores are planar. The windings are in the Z-direction in a PCB, opposite to the helical windings laid in the x-y direction in conventional inductors.
Planar transformers and planar inductors can be constructed as stand-alone or integrated elements in the main circuit board. The stand-alone inductors are like discrete elements and can be electrically connected to the other circuit boards. When integrated into a main PCB board, the planar inductors and other sub-circuits are a part of the board.
Compared to planar transformers, planar inductors introduce gaps in their construction to prevent premature DC saturation of the core.
Shapes of Planar Inductor Design
The planar inductors can be elliptical, circular, rectangular, square, hexagonal, octagonal, etc. The simple layout of the square-shaped spiral inductors has made them popular for various applications such as wearables, communication systems, electronic gadgets, etc.
Planar Inductor Design and Geometrical Parameter
The inductance value of a planar inductor fabricated using PCB technology depends on the following geometrical parameters:
- Number of turns
- Trace width
- Trace separation
- Inner and outer winding diameter
The planar inductor design starts with planar core selection. The cores usually used are ferrite cores. The wires selection is also made at this stage. Considering the inductance value and shape of the windings, the copper traces of calculated width and separation are routed to as many turns as predetermined. The coil windings can be routed into different layers of a PCB.
Cadence OrCAD PCB design and analysis tools can be utilized for calculating the losses in planar inductor design. In light of the analysis results, the gap in planar inductors can be optimized to reduce the losses.
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