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Planar Transformers and Planar Inductors

ConverNova designs and manufactures custom planar magnetics for high frequency power electronics. Based in Madrid, Spain, we aim to return an engineering answer within 24 hours, deliver prototypes in 4 to 8 weeks, and manufacture from a single unit to production series with no minimum order quantity. Windings on your PCB, on a dedicated winding board, or in stamped copper, on ferrite planar core sets, with the leakage inductance fixed by the artwork rather than by how the wire happened to lie.

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When it wins

Planar is a trade, not an upgrade.

It is the right answer often enough to be worth knowing, and the wrong answer often enough that we will tell you when it is.

Where planar wins

High switching frequency, where the copper can be thin and the skin depth stops punishing you. Low profile, where height is the constraint and not footprint. High volume, where identical units matter more than the cheapest possible bill of materials. And resonant converters, where a repeatable leakage inductance is worth real money.

Where wound wins

Below roughly 100 kHz, where the copper has to be thick and a PCB is an expensive way to carry it. High isolation, where the layer to layer spacing a planar needs eats the advantage. Low volume, where the tooling does not amortise. And anywhere interwinding capacitance is already your problem.

Construction

Three ways to make the winding.

The choice drives the cost, the current capability and how much of your board you get back.

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On your PCB
The winding becomes layers of your main board. No separate part to buy or place, at the cost of layer count and of a board that now has to be qualified as a magnetic
Winding board
A dedicated multilayer PCB carrying only the winding, assembled with the core into a discrete component. Keeps your main board simple and the magnetic testable on its own
Stamped copper
Thick formed copper turns instead of etched traces. Where the current is too high for a reasonable copper weight, this is what carries it
Cores
Standard planar E, EI, ER and EQ ferrite sets, and custom machined geometries where the standard window wastes space
Interleaving
Layer order set in the artwork, so the leakage inductance you measure on the prototype is the one you get on unit ten thousand
Isolation
Layer spacing, prepreg choice and creepage designed against the standard you qualify to, with partial discharge testing where it is asked for

Straight answers

Planar magnetics, the usual questions.

When is planar the right choice?
When the switching frequency is high enough that the copper can be thin, typically above about 200 kHz, and when height is constrained or the design has to repeat identically in volume. Below roughly 100 kHz a wound transformer is usually smaller and cheaper for the same loss, and we will say so.
Why is the leakage inductance so repeatable?
Because the winding geometry is fixed by the artwork, not by how the wire lay. Every unit has the same interleaving and the same layer spacing, so the same leakage. That is what makes resonant converters reproducible in volume.
What is the catch?
Interwinding capacitance. Primary and secondary sit close together over a large area, which is good for leakage and bad for common mode noise. Layer order, shielding and the insulation system are how we manage it, and it is a conversation worth having early.
Can you use my own PCB?
Yes. Windings can go into your main board, onto a dedicated winding board, or into stamped copper. We can design the artwork and the stackup, or work to yours.

Construction

Planar construction.

Core halves closed over a stack of printed winding boards, with the leakage inductance fixed by the artwork.

Planar core halves closed over a stack of printed winding boards
An encapsulated planar transformer on stacked printed winding boards, with pin terminations and the core material marked

Start here

Send us your planar spec.

Topology, switching frequency, power, isolation and the height you have. If you are still deciding between planar and wound, send the requirement and we will tell you which one your design wants.

Send us your spec