Planar Transformer

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planar transformer construction

Planar transformer: The planar transformer, or inductor, is a low profile device that covers a large area, whereas, the conventional transformer would be more cubical in volume.

Planar Transformer

Planar Magnetics is the new “buzz” word in the field of power magnetics. It can be a way to increase the power density, while at the same time increasing the overall performance, and also, making it cost effective.

Read: Best Books for Transformer Design and Electrical Machine Design

A whole new learning curve can be seen on low profile ferrite cores and printed circuit boards if one is going to do any planar transformer designs.

It is an all-new technology for the transformer engineer. The two basic items that made this technology feasible were the power, MOSFETs that increased the switching frequency and enabled the designer to reduce the turns, and the ferrite core, which can be molded and machined into almost any shape.

Planar Transformer Basic Construction


Here, shown in Figure 1 through Figure 4 are four views of a typical EE core, planar construction method.

The assembled planar transformers have very unique characteristics in their finished construction.


In the assembled planar transformer, every primary turn is at a precise location, governed by the PC board.


The primary is always the same distance from the secondary.

This provides a tight control over the primary to secondary leakage inductance. Using the same insulating material will always provide the same capacitance between primary and secondary; in this way, all parasitics will be the same from unit to unit.


With this type of planar construction, the engineer will have a tight control over leakage inductance, the
resonant frequency, and the common-mode rejection. A tight control is necessary on all materials used.

planar transformer construction
planar transformer construction
top view planar transformer construction

end view planar transformer construction
perspective view planar transformer construction

Planar Integrated PC Board Magnetics


Planar transformers and inductors are now being integrated right on the main PC board. Design engineers
are pushing the operating frequency higher and higher to where it is commonplace to operate at frequency
range between 250-500kHz. As the frequency increases the power supplies are getting smaller and smaller.
To reduce the size of the power supply even further engineers are going to planar magnetics that are
integrated into the main PC board. An exploded view to show the multi-layers PC board of a planar
transformer that has been integrated into the main PC board is shown in Figure 20-5. The final assembly of
the same planar transformer is shown in Figure

Planar Integrated PC Board Magnetics

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