Planar Magnetics in Power Electronics

Key Takeaways

• The higher the switching frequency, the smaller the magnetics. 

• Compared to conventional magnetics, the core of planar magnetics have a low profile or low vertical height.

• Planar windings implemented using PCB technology make the construction of planar magnetics repeatable and manufacturable.

The windings of planar inductors and transformers enable more compact power electronic circuit designs

Power electronics is a branch of study that deals with the conversion of energy. Magnetics (primarily inductors and transformers) play a significant role in power electronics. The size of the magnet is a limitation affecting the design of power electronic PCBs. Using planar magnetics in power electronics reduces the size of the magnetics without compromising the purpose. 

Planar Magnetics in Power Electronics

For the cost of a greater footprint, a planar inductor allows for lower profile assemblies.

Planar magnetics are different from conventional magnetics. Compared to conventional magnetics, the core of planar magnetics have a low profile or low vertical height. Instead of the helical windings in traditional magnetics, the windings of planar magnetics are designed on flat surfaces. In normal magnetics, the windings extend from the center leg.

If the winding build-up in conventional magnetics is in the x, y direction, then in planar magnetics, the windings are stacked in the z-direction. Different technologies are employed to implement planar windings such as PCBs, flex circuits, stamped copper, etc.

Advantages of Planar Magnetics in Power Electronics

• Reduced height
• An improved magnetic cross-sectional area
• Interleaved windings possible
• Improved heat transfer due to greater surface area
• The winding area is small
• Low AC winding resistance
• Low breakage inductance
• Repeatability in manufacturing
• High power density
•  Robust design

Planar Magnetic Applications

Using planar magnetics in power electronics is a new way to achieve products with high power density, high efficiency, and compactness. The applications of planar magnetics are broad and not limited to:

• Industrial equipment such as welding or test equipment
• DC-DC converters such as flyback converters, forward converters, etc.
• Aerospace and military applications
• Automotive systems
• Battery chargers
• Renewable energy-based systems
• Switched-mode power suppliers

Alternative Ways to Achieve Higher Efficiency Within a Smaller Package

Besides using planar magnetics in power electronics, there are a few other techniques employed in power electronics to achieve higher efficiency within a smaller package.

Innovative Components

Innovative components packed compactly can help achieve high power density and smaller power electronics. Designing high-power density PCBs provides compactness without jeopardizing the thermal management system of the power electronics board.

Higher Switching Frequency

Various power electronic devices such as MOSFET, IGBT, TRIAC, etc. are employed in power electronics circuits. The ‘on’ and ‘off’ control of the power electronic switches are implemented at higher switching frequencies. The higher the switching frequency, the smaller the magnetics. 

Wide Band Gap Devices

To achieve even higher frequency with lower losses, there is a new class of devices called Wide Band Gap (WBG) devices. WBG devices use semiconductor materials such as SiC, GaAs, GaN, etc. for fabricating devices by replacing traditional silicon semiconductor materials. WBG devices are at the forefront of fulfilling the demand for higher efficiency, lower losses, smaller sizing, etc.

PCB-Based Planar Windings

Planar windings implemented using PCB technology make the construction of planar magnetics repeatable and manufacturable. Planar windings using PCBs completely eliminate the terminations.

Flex Circuit-Based Planar Windings

In flex circuit-based planar winding, copper is laid on a thin, flexible polymer substrate, which overcomes the low window utilization factor of PCB-based planar magnetic technology. The utilization factor of flex circuit-based planar magnetics is improved due to low dielectric thickness. It is possible to build a rigid planar magnetic structure using flex circuit technology, as it allows many layers to be laminated together without compromising the utilization factor.

Stamped Copper Windings

Stamped copper windings are a low-cost method to implement single, thin windings of high current density. The stamped copper windings require separate insulation layers.

Develop Planar Inductors With Cadence Software

Cadence’s OrCAD PCB design and analysis tools are excellent for developing planar inductors and transformers for any given application. With Cadence, it is possible to design highly-efficient planar transformers and low-leakage planar inductors. 

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